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Key Unit Competence
Describe the structure and function of cells in an organism.

Learning objectives
By the end of this unit, I should be able to:
–– Identify plant and animal cell structures visible under a light microscope.
–– State functions of cell structures as seen under an electron microscope.
–– Describe the nature of artefacts.
–– State the importance of freeze fracturing for examining membrane structure.
–– Explain how cell organelles can be isolated by cell fractionation.
–– List the functions of cell membranes.
–– Describe the fluid mosaic structure of cell membranes.
–– Explain the role of the different components of a cell membrane.
–– Explain cell specialization as the differentiation of a cell or process to do a particular function.
–– Interpret charts and micrographs to relate the structure of specialized cells to their functions.
–– Prepare, observe and draw diagrams for specimens on temporary slides for:
Wandering Jew, in plants and cheek cells under a light microscope.
–– Distinguish between ultra-structures of plant cells and animal cells.
–– Compare ultra-structures of prokaryotic and eukaryotic cells
–– Show resilience and be aware of artefacts when preparing temporary slides.
–– Appreciate the importance of cell specialization in multicellular organisms.

Introductory Activity
1. Differentiate between prokaryotic and eukaryotic cells.
2. By using charts for the two cells, identify different organelles of eukaryotic cell that may perform functions similar to those of a prokaryotic cell.

Cytology is the study of the structure and function of cells. A Cell is the basic unit of life. All living organisms are made up of cells.
Living organisms are classified into:
–– Unicellular organisms are made of only one cell, such as bacteria,
–– Multicellular organisms are animals and plants composed of many cells. In
multicellular organisms, cells divide and then undergo differentiation or
specialisation for specific functions.

Cell theory.
The cell theory states that all living organisms are made up of cells, and cells are the basic unit of structure function in all living organisms.
The main principles of cell theory are based on the following ideas.
–– All known living organisms are made up of one or more cells,
–– All cells come from pre-existing cells by division
–– Cells contain the hereditary information that is passed from cell to cell during
cell division.
–– Metabolism takes place in cells
–– Given suitable conditions, cells are capable of independent existence

4.1 Ultra-structure of a cell
Activities 4.1
1. Observe the chart given for Ultra structure of a cell and identify parts that are easily recognizable when compared with a photomicrograph form a light microscope.
2. Identify the se mitochondria and ribosomes and state their roles in the life of the cell.
When viewed under light microscope, the most obvious features observed are the very large nucleus and a clear cytoplasm surrounded by a cell membrane. However, under electron microscope, it is possible to identify a range of organelles in plant and animal cells. Ultrastructure is the detailed of cell as revealed by the electron microscope.

4.1.2 Similarities between animal cell and plant cell
–– Both have a cell membrane, a cytoplasm and a nucleus.
–– Both animal and plant cells have mitochondria, Golgi apparatus, Reticulum endoplasmic, lysosome, big ribosomes (80S), peroxisome, microtubules.
Table 4.1: Differencied between animal and plant cell

Self-assessment 4.1
1. What structures do both animal and plant cells have in common?
2. State any five principles of the cell theory.
3. Give the major difference between a plant and animal cell. Which organelles does this difference relate to?

4.2 Prokaryotic cells
Activities 4.2
Under microscope, observe mounted slides of bacteria, and plant cells. Draw and label the parts that are common in both plant and bacterial specimens

A typical bacterial cell has a cell surface membrane enclosing the cytoplasm that contains enzymes, ribosomes and food granules. The membrane is surrounded by the cell wall and this may in turn be enclosed in a capsule. A bacterial cell lacks high level of organization compared to animal or plant cell. It has no Golgi apparatus or endoplasmic reticulum. The genetic material is a single strand of DNA usually
coiled up into the center of the cell to form a nucleoid. This nucleoid has no double membraned nuclear envelope so is often described as an ‘ill-defined nucleus’.
–– Some bacterial cells contain plasmids with additional DNA.
–– Respiration generally takes placein mesosomeswhich is an in-folding of the
cell surface membrane but lack mitochondria
–– Photosynthesizing bacterial cells such as cyanobacteria(blue green algae) have a special form of chlorophyll but it I not enclosed in a double membraned chloroplast

4.4.1. Comparison between prokaryotic and eukaryotic cells
Table 4.2 Comparison between prokaryotic and eukaryotic cells

Self-assessment 4.2
Organisms such as bacteria are known as prokaryotes.
1. Which structure in a bacterial cell resembles a nucleus?
2. How does it differ from the nucleus of eukaryotic cells?

4.3 Cell organelles
Activities 4.3
By using iodine solution, methylene blue, a piece of onion leaf, a scalpel, forceps, light microscope, slides and cover slips, clean cotton wool bud, and onion bulbs. Observe cells from onion epidermis under light microscope. Observation of a plant cell
–– Add a drop of diluted iodine solution on the slide.
–– Remove a transparent layer of onion epidermis from the inner side that you will mount on the slide and add iodine solution.
–– Cover your preparation with a cover-slip and mount it on the stage.
–– Observe the preparation under the low power and thereafter under high magnification.
Why did you use iodine solution in this experiment?
What main parts of a plant cell are easily observed from a light microscope?

Observe animal cells from mouth cheek epithelium
–– By using a clean cotton wool bud, wipe over inside of your cheek.
–– Smear cells over surface of a clean grass microscope slide containing a drop of methylene blue stain
–– Carefully put the cover-slip on the preparation and mount it on the stage to observe.
Draw both plant and animal cell and label the cell wall, nucleus and vacuole.

4.3.1Nucleus

The cell nucleus contains nearly all the cell’s DNA with the coded instructions for making proteins and other important molecules. The nucleus is surrounded by a double nuclear envelope, which allow materials to move into and out of the nucleus through nuclear pores. The granules found in the nucleus are called chromatin whichconsist of DNA bound to protein. When a cell divides, the chromatin condenses into chromosomes containing the genetic information. The nucleus contains a dense spherical structure called nucleolus in which assembly of ribosomes occurs.

4.3.2 Endoplasmic reticulum (ER)

The ER consists of a series of flattened membrane-bound sacs called cisternae. The rough ER is surrounded with ribosomes. The rough ER transports proteins made on attached ribosomes. The smooth ER is made of tubular cavities lacks ribosomes, and it involves in synthesis of lipids that the cell needs. The number and distribution of the ER relates to the functions of the cell; glandular cells are seen to have several RER for synthesis of hormones and enzymes. Examples include liver cells, plasma cells, and pancreatic cells.

4.3.3 Golgi apparatus

The Golgi apparatus is a stack of membrane-bound, flattened sacs, which receives proteins from the ER and modifies them. It may add sugar molecules to them to form glycoproteins or lipids to form glycolipids. The Golgi apparatus then packages the modified substances into vesicles that can be transported to their final destinations throughout the cell or outside of the cell by exocytosis.

4.3.4 Mitochondria

Mitochondrion have two membranes separated by a fluid-filled intermembrane space. The inner membrane is highly folded to form cristae that plays a big role in aerobic respiration.The central part of the mitochondrion is called matrix. The mitochondria are the site where Adenosine triphosphate (ATP) is produced during aerobic respiration.

4.3.5 Chloroplasts

Chloroplasts are the site of photosynthesis in plant cells. These are found in plant cells and in cells of some protoctists. They also have two membranes separated by a fluid-filled space, circular DNA as in mitochondria. The inner membrane is continuous, with thylakoids. A stalk of thylakoids is called a granum (plural: grana). Chlorophyll molecules are present on the thylakoid membranes.

4.3.6 Lysosomes

These are spherical sacs surrounded by a single membrane. They contain powerful digestive enzymes. Their role is to break down materials such as worn out cell organelles, and destroy foreign microorganisms that enter the body. In acrosome, lysosomes help the sperm to penetrate the egg by breaking down the material surrounding the egg. Lysosomes are also involved in autolysis, breakdown of dead tissues or harmful objects inside the cell. Therefore, lysosomes are referred to as ‘suicide bags’

4.3.7 Ribosomes

Ribosomes appear as dark granules in the cytoplasm and are not surrounded by a membrane. They have the same size as those found attached to the rough endoplasmic reticulum- about 20nm in diameter and known 80S. Free ribosomes make proteins that are as enzymes or in other forms in the cytoplasm. Ribosomes are made in a region of the nucleus called the nucleolus.

4.3.8 Centrioles

Centrioles are small tubes of protein fibers called microtubules which have many roles including moving chromosomes during nuclear division. Animal cells have structures called centrioles which consist of two groups of nine triple microtubules. Centrioles form an anchor point for microtubules during cell division.

4.3.9 Vacuole

A vacuole is a saclike structure that stores materials such as water, salts, proteins, and carbohydrates. In many plant cells there is a single and large central vacuole filled with liquid. The pressure in the cells of central vacuole makes it possible for plants to support heavy structures like leaves and flowers. Some animals and unicellular organisms contain contractile vacuoles which contract to pump excess water out
of the cell.

self-assessment 4.3
1. Explain why muscle cells contain several mitochondria compared to fat storage cells
2. What kind of information is contained in chromosomes?
3. Describe the functions of the endoplasmic reticulum, Golgi apparatus, chloroplasts, mitochondria and nucleus in the cell.
4. The diagram below shows the 3D structures which would be visible in ultrastructure of a plant cell.
Identify the parts labeled in this plant cell and:
a. State one function for 1, 2, 3, 7, and 10
b. What are parts 4 and 5 made of?
c. What are two functions of the cytoskeleton?

4.4 Membrane structure
Activity 4.4
Learners mix a portion of cooking vegetable oil with water and shake the mixture vigorously and leave it to settle. Note the way water and oil are distributed within the mixture and suggest a possible explanation for your observation. Cell membranes cover surfaces of every cell. Some organelles in cytoplasm are
enveloped by membranes. The cell membranes ultrastructure is not easily visible under a light microscope but is studied by electron microscopes, freeze structuring and other modern techniques which reveal complex structures A detailed study of a cell membrane reveals that it is 7-8nm wide and is made of a phospholipid bilayer.
–– Lipid component makes up 45% protein and 10% carbohydrate. Most of the lipids are phospholipids
–– Each molecule of phospholipid consists of a hydrophobic tail of two fatty acids and a hydrophilic phosphate head. They arrange themselves in phospholipids bilayer with their tails pointing inward away from the water both inside and outside the cell

In 1972, Jonathan singer and Garth Nicolson proposed the fluid mosaic model of the cell membrane structure. This was done after realizing that membranes must have a complex structure to carry out a variety of activities. In their model;
–– Individual protein molecules shift and move on a fluid bilayer of phospholipids;
some spanning the width of the membrane (intrinsic proteins), others confined to the outer or inner surface (extrinsic protein)
–– Protein molecules are variable in structure and function but they all contribute to the mechanical strength of membranes

The membrane is referred to as;
–– A fluid because it appears to have the properties of a fluid rather than a solid as the major constituent,lipids and proteins move about the structure
–– Mosaic because protein and lipid components form a pattern of parches model

4.4.1 Properties of the cell membrane
–– It is mainly made of lipids, proteins and carbohydrates.
–– It is semi-permeable or partially permeable to allow some substances to pass through but prevents others to cross depending on their size, charges and polarity.
–– It is positively charged outside and negatively charged inside and has a hydrophilic pole and a hydrophobic pole
–– It is a bilayered sensitive and flexible.It has inorganic ions and its proteins and lipids may be mobile and contains different types of enzymes and coenzymes.
–– It is perforated of pores and recognizes chemicals messengers including hormones and neurotransmitters.

4.4.2 Roles of different components of cell membrane
a. Cholesterol
–– Gives the membranes of some eukaryotic cells the mechanical stability.
–– It fits between fatty acid tails and helps make the barrier more complete, so substances like water molecules and ions cannot pass easily and directly through the membrane.

b. Channel proteins
–– Allow the movement of some substances across the membrane.
–– Large molecules like glucose enter and leave the cell using these protein channels.

c. Carrier proteins
–– Actively move some substances across the cell membrane. For example, magnesium and other mineral ions are actively pumped into the roots hair cells from the surrounding soil.
–– Nitrate ions are actively transported into xylem vessels of plants

d. Receptor sites
–– Allow hormones to bind with the cell so that a cell response can be carried out.
–– Glycoproteins and glycolipids may be involved in cells signaling and they allow the immune system to recognize foreign objects to the cells.
–– Some hormone receptors are glycoprotein and some are glycolipid.

e. Enzymes and coenzymes
–– Some reactions including metabolic processes in photosynthesis take place in membranes of chloroplasts.
–– Some stages of respiration take place in membranes of mitochondria, where Enzymes and coenzymes may be bound to these membranes.
–– The more membrane there is, the more enzymes and coenzymes it can hold and this helps to explain why mitochondrial inner membranes are folded to form cristae, and why chloroplasts contain many stacks of membranes called thylakoids.

4.4.4. Functions of a cell surface membrane
–– The cell membrane acts as a selective barrier at the surface of the cell, and controls the exchange between the cell and its environment.

–– Glycoproteins and glycolipids are involved in the cell protection, the process by which cell adhesions are brought about and in the cell recognition.
–– Receptor sites for hormones and neurotransmitters
–– Transmission of nerve impulses
–– Insulation of nerves to improve transmission speeds. Internal membranes:
–– Act as reaction surfaces
–– Act as an intra cellular transport system
–– Providing separate intra cellular compartment, isolating different chemical reactions as in organelles.

Self-assessment 4.4
1. What is meant by the fluid mosaic model of the cell membrane?
2. State at least three properties of the cell membrane.
3. Describe at least 4 types of the proteins in the cell membrane and their roles.
4. What is a partially permeable membrane?

5. What do the words hydrophilic and hydrophobic mean?
6. The diagram below shows the structure of a cell membrane. Study it carefully and answer the following questions.
a. Name parts labelled A, B, C and D and give the function of the part B.
b. What types of molecule are likely to be involved in?
i. Cell signaling and recognition
ii. Allowing small charged molecules to pass through the cell membrane
iii. Site metabolic reactions
7. What is the difference between rough and smooth endoplasmic reticulum?
8. Describe the role of cytoskeleton

9. The photograph in the figure below shows an organelle of the living cell.

a. Name this organelle.
b. What is the function of this organelle?
c. In which ways is this organelle similar to a chloroplast?

4.5 Specialized cells
Activity 4.5
By using the diagrams below, relate the structure of specialized cells to their functions.

Differentiation refers to the changes occurring in cells of a multicellular organism so that each different type of cell becomes specialized to perform a specific function. In animals, the first type of cells in the developing embryo is stem cells. These are unspecialized cells that go on to form all the different types of cells in adult. Cell can differentiate in many ways, with changes to the shape of the cell, the number of particular organelles and the content of the cell.

4.5.1 Specialized animal cells and their functions
4.5.1.1 Red blood cells

All blood cells are produced from undifferentiated stem cells in the bone marrow but the cells destined to become erythrocytes (red blood cells) lose their nucleus, mitochondria, Golgi apparatus and rough endoplasmic reticulum. They are packed full of the protein called haemoglobin. The shape of this cells change so that they become biconcave discs, and they are then able to transport Oxygen in the body.

4.5.1.2 Sperm cell

Sperm cells are specialized to fertilize the egg. Its specialization involves many
changes in shape and organelles content.

By shape: the sperm cells are very small, long and thin to help them to move easily, and they have a flagellum which helps them to move up the uterine tract towards the egg.

By organelles content: sperm cells contain numerous mitochondria which generate much energy for their movement. Their acrosome has specialized lysosomes containingmany enzymes that are released on the outside of the egg. These enzymes lyse the wall of the egg, and facilitate the sperm nucleus to penetrate easily. In content, the sperm cell nucleus contains the half number of chromosomes of the germ cell in order to fulfil its role as a gamete of fertilizing the egg.

Did you know: As a sperm fuses with an ovum to form a zygote which grows into an individual, in the same way: a man maries a woman to form a couple which will produce children and form a family.

4.5.1.3 Nerve cells

Nerve cells also known as neurons are specialized cells to carry nervous impulses in the body. These signals between neurons occur via specialized connections called synapses. Specialized animal cells have different functions. Some of them are summarized in the following table.

Table 4.3: Specialized animal cells and their functions.

4.5.2 Specialized plant cells and their functions
4.5.2.1 Root hair cells

The root hair cells have hair-like projection from their surface out into the soil. This increase the surface area of root available to absorb water and minerals from the soil.

4.5.2.2 Palisade cells

Palisade cells are in leaves, right below the upper epidermis. They are vertically elongated, a different shape from the spongy mesophyll cells beneath them in the leaf. Their large numbers of chloroplasts allow them have several chloroplasts used in photosynthesis.

Parenchyma cells
Parenchyma is composed of relatively simple and undifferentiated parenchyma cells. They function in storage, photosynthesis. In most plants, metabolic activity such as cell division, respiration, and photosynthesis occurs in these cells because they retain their active cytoplasm. .

4.5.2.3 Guard cells

Guard cells are cells surrounding each stoma. Guard cells are specialized cells in the epidermis of leaves, stems and other organs that are used to control gas exchange. They are produced in pairs with a gap between them that forms a stomatapore. Guard cells have the following feature:
–– Un even thick walls
–– Possess chloroplasts; they are the epidermal cell that have chloroplasts an adaptive feature in controlling pore opening.

Self-assessment 4.5
1. Explain why differentiation to produce erythrocytes involves a change in shape.
2. Red blood cells cannot divide as they have no nucleus. State two other
biological processes that red blood cells cannot carry out.
3. Describe how the following are specialized for their roles:
a. Neutrophil
b. Sperm cellRoot hair cell
3. Explain why photosynthesis is carried out in palisade mesophyll more than
in spongy mesophyll.
4. In what kinds of organisms is cell specialization pronounced characteristic?
5. Discuss the advantages of cell specialization in living things

End of unit assessment 4
Section A. Multiple choice questions
1. Which organelle converts the chemical energy in food into a form that cells can use?
a. Chromosome
b. Chloroplast
c. Nucleus
d. Mitochondrion
2. The cell membranes are constructed mainly of:
a. Carbohydrate gates
b. Protein pumps
c. Lipid bilayer
d. Free-moving proteins
3. In many cells, the structure that controls the cell’s activities is the:
a. Nucleus
b. Nucleolus
c. Cell membrane
d. Organelle
4. Despite differences in size and shape, all cells have cytoplasm and a
a. Cell wall
b. Cell membrane
c. Mitochondria
d. Nucleus
5. If a cell of an organism contains a nucleus, the organism is a (an)
a. Plant
b. Eukaryote
c. Animal
d. Prokaryote

6. Match each part of the cell (left column) to corresponding statement (right column):
Nucleus controls movement of substances in and out of the cell Mitochondrion where photosynthesis takes place Chloroplast where aerobic respiration takes place Smooth ER controls the activity of the cell
Ribosomes where lipids including steroids are made

Section B: Questions with short answers
1. How does a cell membrane differ from a cell wall?
2. Name the structures that animal and plant cells have in common, those found in
only plant cells, and those found only in animal cells.
3. List:
a. Three organelles each lacking a boundary membrane
b. Three organelles each bounded by a single membrane
c. Three organelles each bounded by two membranes (an envelope)
4. Identify each cell structure or organelle from its description below.
a. Manufactures lysosomes and ribosomes
b. Site of protein synthesis
c. Can bud off vesicles which form the Golgi body
d. Can transport newly synthesized protein round the cell
e. Manufactures ATP in animal and plant cells
f. Controls the activity of the cell, because it contains the DNA
g. Carries out photosynthesis
h. Can act as a starting point for the growth of spindle microtubules during
cell division
i. Contains chromatin
j. Partially permeable barrier only about 7 nm thick
k. Organelle about 25 nm in diameter
l. Which two organelles other than the nucleus contain their own DNA?

Section C: Essay questions
1. Describe the structure and function of the cell membrane and cell wall.
2. Describe the basic structure of the cell membrane.
3. Explain two common characteristics of chloroplasts and mitochondria.
Consider both function and membrane structure.
4. The diagram below shows the structure of a liver cell as seen using an electron microscope.

a. Name the parts labelled A, B, C and D.
b. The magnification of the diagram above is x12 000. Calculate the actual length of the mitochondrion labelled M, giving your answer in μm. Show your working.
c. Explain the advantage to have a division of labor between different cells in the body.

Key Unit Competence
Describe different specialized plant and animal cells and adaptation of tissues.

Learning objectives
By the end of this unit, I should be able to:
–– Define a tissue as a group of cells with similar structure working together for a function.
–– Name the main types of animal and plant tissues.
–– Define an organ as a structure made up of a group of tissues with related
functions working together to perform bodily functions.
–– Explain how epithelial tissues are adapted to perform a diversity of functions in the body.
–– State the advantages and disadvantages of being unicellular.
–– Observe and draw plant and animal tissues as seen under a light microscope.
–– Interpret photomicrographs of plant and animal tissues
–– Acknowledge the relationship between levels of organization
–– Recognize the efficiency shown by multicellular organisms to explore more modes of life that are not available to single celled organisms that show little or no specialization

Introductory activity
Read the following passage and use it to answer the following questions:

In an anthill, there are different groups of termites such as a queen, workers and soldiers. Each group has a specific role to play in the colony. The structure termites of each group is related to their role for example soldiers that protect the colony have mouth parts shaped like a pair of scissors building and a slightly larger abdomen for storing water. The queen is the largest of all and has a role of laying eggs. Workers have mouth parts for cutting and chewing food or soil particles. Some members of workers are in charge of caring for the young while others find food and defend the colony or remove dead members. Their specialization and division of labor bring about efficiency in the colony.
1. Specify the message addressed by the above paragraph.
2. Explain how is the structure of termites related to their functions?
3. What is the significance of specialized tissues in multicellular organisms like plants and animals?

The study of tissues is known as Histology. A tissue is a group of associated, similarly structured cells that perform specialized functions for the survival of the organism. In histology, differentiation is the process by which structures become modified and specialized to perform specific functions. Differentiation is also known as ‘specialization’. In animals, the first type of cells in the developing embryo is stem cells. These are unspecialized cells that go on to form all the different types of cells in adult.

5.1 Specialized plant tissues
Activity 5.1.1
–– Remove an epidermis layer from the ventral side of an onion leaf.
–– Mount it on the slide containing a drop of iodine solution
–– Observe your preparation under a light microscope
–– Draw, label and describe your findings.
–– From your discussion:
1. What is a tissue?
2. What is the role of epidermis in onion?

5.1.1. Plant tissues
Activity 5.1.2
The following figure represents the flow chart of subdivisions of plant tissues. Use it to answer the following questions.

1. How do meristems differ from permanent tissues?
2. Plant tissues are classified into ground tissues and vascular tissues as shown in the figure above. What is meant by the term vascular tissues?
3. How is the structure of the xylem and phloem vessels related to their function?
4. From the flow diagram above, identify three types of ground tissues.

5. Write down short notes on each of the following types of meristems.
a. Apical meristems.
b. Lateral meristems
c. Intercalary meristems
Plant tissues can be divided into two main groups, Meristematic tissues (apical, lateral, and intercalary meristems) and Permanent tissues (ground tissues and vascular tissues).

5.1.2. Meristem tissues
Meristem tissue is a group of cells which retain the ability to divide by mitosis. Meristematic tissues are specialized to carry out specific functions such as reproduction, growth, photosynthesis and replacement of old or damage tissues. The cells making a meristem tissue are small, have a central large nucleus and dense cytoplasm, thin-walled, with no or small vacuole, and no specialized features. The cells are rectangular and closely packed with no intercellular air spaces.

Types of meristematic tissues
Meristematic tissues are subdivided into apical meristems, lateral meristems (cambium) and intercalary meristems

a. Apical meristems
They are located in the root and shoot apex (at the growing points of roots and stems). They are responsible for primary growth, leading to the increase of primary plant body.

b. Lateral Meristems (cambium)
Lateral meristems are in lateral parts of the plant, where they are responsible for Biology Senior Four Student’s Book 87 secondary growth. The cambium gives rise to secondary vascular tissues (secondary
xylem and secondary phloem) in dicotyledonous plants.

c. Intercalary meristems
These are found in the region of permanent tissues like at nodes of monocotyledonous plants (e.g. sugar cane). It allows growth in length to occur between internodes. Functions of meristematic tissues
–– The main function of meristematic tissue is to produce new cells by mitosis.
The cells elongate and differentiate to form new cells for primary growth of shoot and root.
–– Vascular cambium produces new cells to increase the diameter of stems and roots during secondary growth.
–– Cork cambium called (phellogen) produces the outer cork layer called phellem which consists of suberized cells. The cork layer reduces water evaporation from the plant and protects the plant against the entry of pathogens.
–– The intercalary meristems allow growth and increase in length in regions other than the tips.

5.1.3 Permanent tissues
Permanent tissues consist of two groups of tissues such as: ground and vascular tissues.

5.1.4. Ground tissues
The ground or fundamental tissues are plant tissues which function in storage, metabolism and support. There are three types of ground tissues: parenchyma, collenchyma and sclerenchyma tissues.

5.1.5. Parenchyma tissues
Parenchyma is a soft plant tissue made up of thin-walled cells that forms the greater part of leaves, stem pith, roots, and fruit pulp. They are the main sites for physiological and biochemical processes in the plants including photosynthesis, protein synthesis and storage of starch and mineral ions. Parenchyma tissues can be found in epidermis, mesophyll, endodermis, pericycle, aerenchyma and secretory cells.

Characteristics
–– Parenchyma tissues consist of large living cells, with relatively thin wall containing cellulose, pectin and hemicellulose.
–– Parenchyma tissues consist of cells, usually having a large central vacuole. They are often partially separated from each other.
–– Spongy cells present intercellular spaces that intervene in gaseous exchange and transpiration through stoma. They are usually stuffed with plastids.
–– Parenchyma tissues consist of cells with polygonal and spherical shapes in the leaf. They form the mesophyll, and are located between upper and lower epidermises. They are responsible for photosynthesis.

Functions of parenchyma tissues
–– In the leaves, parenchyma tissues form the mesophyll and are sites for photosynthesis, gaseous exchange and transpiration.
–– They store food substances such as starch, proteins and lipids
–– They can be modified to form specialized cells to carry out other function in epidermis, endodermis, pericycle, parenchyma, and secretory cells.

Adaptations of parenchyma for its function
–– Parenchyma tissues are made of unspecialized cells with variety of functions:
–– Parenchyma can become specialized to carry out specific functions e.g. mesophyll has cells with many chloroplasts, and aerenchyma which has air spaces. All of these adaptations help in photosynthesis and gas exchange.
–– They have isodiametric cells and function as packing tissue and storage tissue.
–– Cells are loosely packed with many large intercellular spaces. This permits diffusion of gases.
–– They have thin cellulose cell wall which is permeable so that it permits passage of materials.
–– The walls are transparent and permit entry of light in photosynthesis cells.
–– Large cells with large vacuoles provides space for storage of substances, where the entry of water causes vacuole to expand and cells become turgid
–– Leucoplasts act as storage of starch while chromoplasts present in some cells
e.g. in petals attract insects for pollination.

5.1.6. Collenchyma tissues
Their cells are elongated with irregularly thickened cell walls that provide structural support, particularly in growing shoots and leaves. Their thick cell walls are composed of cellulose and pectin. These cells are often found under the epidermis, or the outer layer of cells in young stems and in leaf veins.

5.1.7. Sclerenchyma tissues
Sclerenchyma is found in hard parts of the plant body. They are very common in roots, stems, leaves and petioles. They may be present in patches, groups or layers. The cells of the sclerenchyma are dead, they are elongated, narrow, and thick walled and lignified. They are pointed at both ends where it gives strength, rigidity and flexibility to the plant body. They consist of fibres and sclereids. Fibres are long,
narrow, thick and liquefied cells usually tapering at both ends. Sclereids cells are normally short with very thick walls, irregular and not tapering at the ends.

Table 5.1: Comparison between collenchyma and sclerenchyma tissues

5.1.8. Vascular tissues
The vascular tissue system consists of two kinds of conducting tissues: the xylem responsible for conduction of water and dissolved mineral nutrients, and the phloem responsible for conduction of elaborated food.

a. Xylem
The xylem tissues are made of dead cells which have the cell walls removed at the end of the cells, forming tubes through which the water and dissolved mineral ions can flow. Xylem vessels are involved in the movement of water through a plant - from its roots to its leaves via the stem. During this process water is absorbed from the soil through root hair cells, moves by osmosis from root cell to root cell until it
reaches the xylem, and finally it is transported through the xylem vessels up the stem and then to the leaves.
Xylem vessels are hollow tubes or lumen with a thick strengthened cellulose cell wall. The hollow tubes act like pipes allowing water and dissolved minerals to flow through them. They develop from cylindrical cells arranged end to end, in which the cytoplasm dies and the cell walls between adjoining cells breaks down leaving a dead empty tube. The cell walls in xylem vessels contain a substance called lignin
which strengthens the cells and gives structural support.

b. Phloem
Phloem vessels are involved in translocation of elaborated substances. Dissolved sugars, produced during photosynthesis, and other soluble food molecules are moved from the leaves to growing tissues such as the tips of the roots and shoots and storage tissues such as in the roots. In contrast to xylem, phloem consists of columns of living cells. The cell walls of these cells do not completely break down,
but instead form small holes at the ends of the cell. The ends of the cell are referred to as sieve plates. The connection of phloem cells effectively forms a tube which allows dissolved sugars to be transported.

Phloem tubes carry food substances like sugar and amino acids produced in leaves during photosynthesis to every part of the plant. The movement of food substances through the plant is called translocation.

Table 5.2: Comparison between Xylem and Phloem tissues

Self-assessment 5.1
1. State where in a flowering plant you would find:
a. Lateral meristem
b. Intercalary meristem
c. Apical meristem
2. Give characteristics of meristematic cells.
3. What do you understand by the following terms?
a. Differentiation
b. Cambium
c. Wood
d. Meristem
4. Differentiate between Collenchyma and sclerenchyma
5. State the main structures (components) that make up a xylem and phloem tissues.
6. Explain how the structure of Parenchyma and Xylem tissues are suitable to their functions.
7. The diagram below shows a longitudinal section of two cells of phloem tissue in a plant stem.

a. Name the cells labelled A and B on the diagram.
b. State the function of phloem in a plant.

5.2 Animal tissues
Activity 5.2.1
Conduct a research by using different sources of information to find out the structures and the main functions of the following four groups of animal tissues: epithelial, connective, muscular and nervous tissues. There are four basic types of animal tissues such as epithelial tissue, muscle tissue, nervous tissue, and connective tissue.

5.2.1. Epithelial tissue
Epithelial tissue consists of closely packed cells arranged in single or multilayered sheets. It is made up of layers of tightly packed cells that form the external surfaces of the body and cover the outer and the inner surfaces of the organs. Some are specialized to form glandular tissues (glands). The epithelium lining the inside of the heart, blood vessels and lymph vessels is referred to as endothelium. Two criteria for classifying epithelia are: the number of cell layers and the shape of cells on the free surface. The following are the types of epithelium tissues:

a. Simple cuboidal epithelium
This is a tissue with cells that are cubical in shape. Cuboidal cells are specialized for secretion and they make up the epithelia of kidney tubules and many glands including salivary glands, and thyroid gland.

b. Simple squamous epithelium
It is thin,leakyand functions in the exchange of material by diffusion. This type of epithelium lines blood vessels and the air sacs of lungs, where diffusion of nutrients and gases is critical.

c. Simple columnar epithelium
These are columnar in shape with free surface containing extensions of micro villi. It lines the intestines. This epithelium secretes digestive juices for the final stages of digestion and absorbs nutrients to blood stream.


d. Pseudo-stratified ciliated columnar epithelium
It forms a mucous membrane that lines the nasal passages of many vertebrates. The beating cilia move the film of mucus along the surface.

e. Stratified squamous epithelium
Itv regenerates rapidly by cell division near the basal lamina. The new cells are pushed outward to , replacecells that are sloughed off. This epithelium is commonly found on surfaces subject to abrasion, such as the outer skin and lining of the esophagus, anus, and vagina.

Figure 5.11 e) Stratified squamous epithelium.

f. Transitional epithelium
In this type of stratified epithelium, the surface cells change their shape from round to squamous. Transitional epithelium lines urinary bladder. When the bladder is empty, the surface cells are rounded. As the bladder fills urine, these cells become flattened. Transitional epithelium enables the bladder to fill and stretch without tearing the lining.

g. Stratified columnar epithelium
It is a rare type of the epithelial tissue composed of column shaped cells arranged in multiple layers. They are found in the conjunctiva or the eye, in parts of the pharynx, anus, uterus, the male urethra and vas deferens.

h. Stratified cuboidal epithelium
It is a type of epithelial tissue composed of multiple layers of cube-shaped cells. Only the most superficial layer is made up of cuboidal cells and the other layers can be cells of other type. It has several locations in the body including sweat gland ducts, egg-producing vesicles and ovaries.

5.2.2. Main characteristics of epithelial tissues

a. Polarity
All epithelia have a free surface and a lower attached basal surface that differ in structure and function. For this reason, epithelium is described as showing polarity.

b. Supported by connective tissue
All epithelia are supported by connective tissue. For instance, deep to the basal lamina is reticular lamina, anextracellular material containing collagen protein fiber which forms the basement membrane. The basement membrane reinforces the epithelium and helps it to resist stretching and tearing.
c. They are avascular; have no blood vessel in them. Nutrients and gases are supplied by blood through the connective tissue by simple diffusion

c. Regeneration
Epithelium have a high regenerative capacity and can reproduce rapidly as long as they receive adequate nutrition.

Functions of epithelium
–– Epithelium forms a protective layer: The epithelium of the skin protects the body from mechanical damage, entry of pathogens, ultraviolet rays and dehydration. Epithelium lining the respiratory air passages secretes mucus which traps inhaled dust particles and microbes.
–– The ciliated epithelium cells have cilia that propel the mucus and trapped particles to the throat.
–– Glandular tissues secrete the digestive enzymes, hormones, mucus, sweat and sebum.
–– Acts as a barrier and regulates movement of substances across kidney
–– Some epithelial cells can divide mitotically producing new cells to replace damaged or dead cells.
–– Some epithelial cells such as taste buds and retina cells are specialized to form sensory receptors.

5.2.3 Muscular tissues
Muscle tissues consist of elongated cells held together by connective tissue. Muscle cells are highly specialized in that they are able to shorten to a half or even a third of their resting length by the process of contraction. The contraction is caused by two types of fibrous proteins: myosin and actin.

Muscles in the body provide the necessary force for the motion and they convert chemical energy into kinetic or mechanical energy. There are three types of muscle tissue:
–– Smooth muscle which is found in the inner linings of organs;
–– Skeletal or striated muscle, which is attached to bone and helps in movement
of the body;
–– Cardiac muscle which is found only in the heart.
Smooth and cardiac muscles are involuntary muscles whereas skeletal muscles are called voluntary muscles because they are under voluntary (conscious) control.

a. Smooth Muscle
Smooth muscle is also called unstriated, unstriped, involuntary or visceral muscle.
It is found in the walls of the hollow internal organs such as blood vessels, intestinal tract, urinary bladder, and uterus. Smooth muscles have the following features;
–– It is under control of the autonomic nervous system; they cannot be controlled consciously, so they are also called involuntarily muscle.They do not have striations.
–– Smooth muscle cells contract slowly and rhythmically

b. Cardiac tissue
Cardiac tissue (figure 5.10 a) is found in the walls of the heart and it is under control of the autonomic nervous system. Cardiac muscle has the flowing basic features.
–– It contracts and relaxes continuously.
–– It is branched and connected to other cardiac muscle fibers through intercalateddiscs(Figure 5.16 b), which are reinforced membranes that hold the cells together during contractions. These interconnections or intercalated discs between the fibers ensure a rapid and uniform spread of excitation throughout the wall of the heart which in turn ensures a synchronous contraction.
–– They are myogenic (their contraction originate from within the heart itself ).

c. Skeletal Muscle
Skeletal muscle is also called striated, striped, or voluntary. They are attached to bone, and are responsible for body movements and body posture. There are approximately 639 skeletal muscles in the human body.
Characteristics of skeletal muscles:
–– They are under control of voluntary nervous system

–– They are attached to bone and this is the reason why they are called skeletal muscles.
–– They are made of elongated and cylindrical muscle fibres
–– They appear under microscope to have alternate light and dark bonds and this is why they are called striated muscles.
–– Their muscle fibres are multinucleated (many nuclei per cell)
–– These muscle cells also contain light and dark stripes called striations

General functions of muscle
The main function of muscle is its contribution to motion, where body movements such as walking, breathing, and speaking, as well as movements associated with digestion and the flow of fluids take place. Muscles contribute to the heat production, maintenance of posture and body support and communication through facial expression, writing and speech.

5.2.4. Nervous tissue
Nervous tissue is composed principally of densely packed cells called the nerve cells (neurons) that together form the nervous system including the brain and spinal cord. Neurons are specialized for transmitting electrical nerve impulses.

A typical neuron has three main parts: Cell body, dentrites and axon.

a. The cell body or soma
–– It is the main part from which, extensions derive (Axon and Dendron).
–– It is made of a great spherical nucleus, granular cytoplasm and controls
all nerve cell activities.

b. Dendrites (Dendron when single): small branches attached to the cell body and receive nerve impulse from other neurons

c. Axon or cylindrax:
–– It is the thinner nerve fibre that carries messages away from the cell body and can be as long as 1 m. In some neurones, the axons have a fatty myelin sheath formed by Schwann cells which wrap themselves around the axon to increase the speed of impulse transmission.

5.2.5. Connective tissues
Connective tissue is made up of many different types of cells that are all involved in structure and support of the body. Bone, blood, fat, and cartilage are all connective tissues. Connective tissues can be densely packed together, as bone cells are or loosely packed, as adipose tissue (fat cells) are. A connective tissue is made up of a variety of cells embedded in a large amount of intracellular substance called matrix
and fibers which are non-living products of the cells.

a. Common functions of connecting tissues:
–– Connective tissues protect and support the body and internal organs.
–– They act as connecting systems, binding all other tissues together.
–– They also form surrounding sheaths to separate the various organs.

b. Cells of connective tissue
The specialized cells of the various connective tissues produce the extracellular matrix. The names of the cells end with suffixes that identify the cell functions as blasts, cytes, or clasts. Blasts create the matrix, cytes maintain it, and clasts break it down for remodeling. For example: Fibroblasts are cells that form fibrous connective tissue and fibrocytes maintain it, chondroblasts form cartilage and chondrocytes
maintain it, and osteoblasts form bone, osteocytes maintain it, and osteoclasts break it down

Adipose, or fat cells, also called Adipocytes, contain large amounts of lipid. The lipid pushes the rest of the cell contents to the periphery, so that each cell appears to contain a large and centrally located lipid droplet with a thin layer of cytoplasm around it. Adipose cells are rare in some connective tissue types like cartilage but they are abundant in others like loose connective tissue, and they are predominant in adipose tissue.

Mast cells are commonly found beneath membranes in loose connective tissue and along small blood vessels of organs. They contain chemicals such as heparin, histamine and proteolytic enzymes. These substances are released in response to injury such as trauma and infection and play important roles in inflammation.

White blood cells continuously move from blood vessels into connective tissues. The rate of movement increases dramatically in response to injury or infection. In addition, accumulations of lymphocytes, a type of white blood cell, are common in some connective tissues, such as in the connective tissue beneath the epithelial lining of certain parts of the digestive system.

Macrophages are found in some connective tissue types. They are derived from monocytes, a white blood cell type. Macrophages are either fixed and do not move through the connective tissue in which they are found or are wandering macrophages and move by amoeboid movement through the connective tissue. Macrophages phagocyte foreign or injured cells, and they play a major role in providing protection against infections.

Note that there are three structural major components of the extracellular matrix of connective tissue such as fluid, ground substance consisting of non-fibrous protein and other molecules and protein fibers. The structure of the matrix gives connective tissue types most of their functional characteristics, such as the ability of bones and cartilage to bear weight, tendons and ligaments to withstand tension, and dermis of the skin to withstand punctures, abrasions, and other abuses.

c. Fiber connective tissues
Another type of connective tissues consists of fibers. Fibers are of different types including:
–– Connective tissue fibers: which are made of protein and are of three kinds:
collagenous, elastic and reticular fibers.
–– Collagenous fibers: These provide strength combined with flexibility. They are made up of collagen, probably the most abundant protein in the animal kingdom.
–– Elastic fibers: These are easily stretched but are also resilient, snapping back to their original length when tension is released. Shaped as long threads, elastic fibers are made of a protein called elastin.
–– Reticular fibers: These are thin collagen fibers coated with glycoprotein. They are very short, thin fibers that branch to form a network and appear different microscopically from other collagen fibers. Reticular fibers are not as strong as most collagen fibers, but networks of reticular fibers fill space between tissues and organs.

d. Loose connective tissue
This is also called areola connective tissue and is the most widespread connective tissue in all animal tissues. It binds epithelial tissues to underlying tissues and functions as packing material, holding organs in place. Loose Connective tissue has the following main components;

–– Fibers: collagen, elastic and reticular.
–– Cells; fibroblasts and macrophages. Fibroblasts secrete the protein ingredients of the extracellular fibers. Macrophages are cells that roam the maze of fibers, engulfing both foreign particles and the debris of dead cells by phagocytosis.

e. Fibrous connective tissue
Fibrous Connective tissue is dense with collagenous fibers. The fibers form parallel bundles, which maximize non-elastic strength. Fibrous Connective tissue is found in tendons, which attach muscles to bones, and ligaments, which connect bones at joint.

f. Adipose tissue
Adipose tissue is a specialized form of loose connective tissue that stores fats in adipose cells distributed throughout its matrix. Adipose tissue consists of adipocytes, or fat cells, which contain large amounts of lipid. Unlike other connective tissue types, adipose tissue is composed of large cells and a small amount of extracellular matrix that consists of loosely arranged collagen and reticular fibers with some scattered elastic fibers. Blood vessels form a network in the extracellular matrix. The fat cells
are usually arranged in clusters or lobules separated from one another by loose connective tissue. Adipose tissue functions as:

–– An insulator against heat loss
–– A protective tissue to delicate internal organs
–– A site of energy storage in the form of fat.

g. Bone and Cartilage tissue
Cartilage has an abundance of collagenous fibers embedded in a rubbery matrix made of a protein-carbohydrate complex called chondroitin sulfate. Cartilage is composed of specialized cells, called chondrocytes, surrounded by a gelatinous matrix of collagen, a tough protein. The cartilage surface is covered by a membrane known as the perichondrium. There are three types of cartilage (hyaline cartilage, yellow elastic and white fibrous cartilage.)

–– Hyaline cartilage is semi-transparent and is often stained light blue or pink in tissue sections. It is extremely very strong but very flexible and elastic. Hyaline cartilage occurs in the trachea, larynx, tip of the nose, connection between the ribs and the breastbone; and at the ends of bones where they form joints. It also forms much of the fetal skeleton.
–– Elastic cartilage is similar to hyaline cartilage, but in addition to the collagenous fibers.The matrix of the elastic cartilage also contains an abundant network of branched elastic fibers. This type of cartilage is found in the lobe of the ears, the epiglottis and in the parts of the larynx. They provide flexibility and elastic support.
–– Fibro-cartilage(White fibrous cartilage) is an extremely tough tissue. It is found as discs between the vertebrae, bones, anterior joint between the two halves of pelvic girdle and at points where tendons inserted on bones near hyaline cartilage. It resists compression and absorbs shock in some joints.

Bone tissue
This is a firmer and denser material that has the following features:
–– Hard and compact
–– Has many collagen fibres
–– Its matrix has inorganic salts such is calcium carbonate and calcium phosphate
–– Has few cells located in the lacunae in the matrix
–– Has osteoblasts as mature and non-dividing cells
–– Have a harversian canal
–– Consists of irregular cylinder with layer of matrix call lamellae The following are the main functions of bone tissue:
–– Structural support of the body
–– Protection of internal organs, heart and lungs.
–– Attachment of the muscles to effect movement
–– Production of blood cells

h. Blood tissue
Blood is a flowing made up of particles suspended in a fluid composed of fluid called plasma, and several kinds of cells. Within the blood plasma, there are erythrocytes (red blood cells), leukocytes (white blood cells), thrombocytes (platelets) and other substances. Blood performs the following important functions:

Transport
–– Blood transports absorbed substances such as glucose, amino acids, mineral ions and vitamins from the small intestine.
–– Blood transports the respiratory gases (Oxygen and Carbon dioxide).
–– Blood transports the excretory wastes such as urea, uric acid to excretory organs to be removed out of the body.
–– Blood transports hormones e.g. insulin from pancreas to the liver where it is stored.

Homeostasis
Na+ affects the water potential of the blood and regulates the diffusion of water between blood and tissues. Hydrogen carbonates help to maintain the pH of the blood.

Protection
–– Leucocytes such as neutrophils and macrophages engulf pathogens e.g. bacteria
–– B-lymphocytes produce antibodies to destroy pathogens or to neutralize toxins.
–– T-lymphocytes destroy infected cells.
–– Platelets, fibrinogen and prothrombin play an important role in blood clotting to reduce blood loss and the entry of pathogens.

Activity 5.2.3
You are provided with photomicrographs or slides of different plant and animal tissue. Study them carefully and answer questions that follow. Identify the different tissues provided and where they are located. One of the images is a blood smear. Draw a well labeled diagram of this tissue

5.3 Levels of organization: cell, tissue, organ and system
Activity 5.3
Visit a classroom block, administration block or any building in school which is constructed with bricks and use it to answer the following questions.
1. What is the smallest unit or component of the classroom block?
2. How are bricks arranged?
3. Do you think the brick has other smaller particles in it?
4. How many bricks does a classroom block have?
5. How are walls, classrooms, washrooms and other apartments of the block formed?
6. Arrange the following in their ascending order of size (from the smallest to the largest); whole block, wall, a brick, a room, course (a line of bricks).
7. Relate the above arrangement of a building to levels of organization in multicellular organisms, beginning with a cell and ending with an organism The human body is organized into structural and functional levels of increasing complexity. Each higher level incorporates the structures and functions of the previous level. The simplest is the cells, organized into tissues, organs, and organ systems. All of the levels of organization of the human body are represented in the following figure.

5.3.1 Cells
The smallest structural and functional living units of living things are cells. There are many different types of human cells, though they all have certain similarities. Each type of cell is made of chemicals and carries out specific chemical reactions.

5.3.2 Tissues
A tissue is a group of cells with similar structure and function. There are four groups of tissues (Epithelial tissues, Connective tissues, Muscle tissues, Nerve tissue)

5.3.3 Organs
An organ is a group of tissues precisely arranged so as to accomplish specific functions. Examples of organs are the kidneys, individual bones, the liver, lungs, and stomach. The kidneys contain several kinds of epithelial or surface tissues, for their work of absorption. The stomach is lined with epithelial tissue that secretes gastric juice for digestion. Smooth muscle tissue in the wall of the stomach contracts to mix food with gastric juice and propel it to the small intestine. Nerve tissue carries impulses that increase or decrease the contractions of the stomach.

5.3.4 Organ systems
An organ system is a group of organs that all contribute to a particular function. Examples are the urinary system, digestive system, and respiratory system. For example, the urinary system consists of the kidneys, ureters, urinary bladder, and urethra. These organs all contribute to the formation and elimination of urine.
The Human body has 11 organ systems: circulatory, digestive, endocrine, and
excretory (urinary), the lymphatic, integumentary, muscular, nervous, reproductive,
respiratory, and skeletal systems.
Table 5.4: Major organ systems of the human body

Self-assessment 5.3
1. Answer by true or false
a. Organic chemicals are often very complex and always contain the element carbon only.
b. A tissue is a group of cells with similar structure and function.
c. Integumentary organ system plays the role in protection of the human
body from injury and fluid loss.
d. An organ system is a group of organs that all contribute to a particular function.
2. Explain why the cell as level of organization of human body is said to be:
a. Basic unit of human body
b. Structural unit of human body
c. Functional unit of human body

5.4 Advantages and disadvantages of being Unicellular or Multicellular
Activity 5.4
Discuss the advantages and disadvantages of an organism being unicellular or Multicellular

5.4.1 Advantages of unicellular organisms
–– Unicellular organisms need fewer nutrients and can survive in unfavorable conditions.
–– Some of the organisms can generate energy through photosynthesis.
–– Sometimes different bacteria work together to work to their advantages.
–– Unicellular organisms can multiply quickly and have less energy/resource demands.

5.4.2. Disadvantages of unicellular organisms
Unicellular organisms only have one cell that is used to function their entire being. This is a disadvantage compared to multicellular organisms, which have many cells and function more easily and properly.

5.4.3 Advantages of a multicellular state of an organism
–– Multicellular organism usually has a wider range of functions because of the aggregation of different types of cells.
–– Multicellular organisms have many more necessities and can only survive in certain conditions.
–– Multicellular organisms such as animals are unable to make their own food so
they survive by eating living things such as vegetables, fruits, and meat. They can also eat things that are produced by other living things such as eggs, milk, and honey.

Self-assessment 5.4
1. Give the advantages and disadvantages of being Unicellular organisms.
2. Describe how unicellular organisms perform their functions.

End of unit assessment 5
1. Which type of tissue forms glands?
a. Epithelial
b. Connective
c. Nervous
d. Muscles
2. What are the four types of animal tissues?
a. Epithelial, squamous, muscular, connective
b. Epithelial, connective, muscular, cardiac
c. Connective, muscular, epithelial, nervous
d. Cuboidal, ciliated, glandular, columnar
3. Which type of the tissues form glands
a. Epithelial
b. Connective
c. Nervous
d. Muscle
4. Describe how epithelial tissues have adapted to their functions
5. Describe the three main functions of the bloo
6. Complete the following table by filling in the examples of the respective tissues:

Key unit competence
Test for biological molecules in a variety of contexts, such as identifying the contentsof mixtures of molecules and to follow the activity of digestive enzymes

Learning objectives
By the end of this unit, I should be able to:
–– Write out procedures in the identification of biological molecules
–– Explain the importance of the reagents used in the identification of biological molecules.
–– Carry out tests for the identification of biological molecules
–– Compare reducing and non-reducing sugars
–– Appreciate the importance of identification of food values in the food industry and in processing and packaging.
–– Show resilience making observations on color changes during food tests

Introductory activity
You are given solutions containing different food stuffs including maize flour, vegetable cooking oil, and egg white sugar cane liquid and passion fruit. Using prior knowledge of biological molecules to suggest the type of biological molecule in each one of them. Suggest the chemical tests used to identify each
of the molecules.

6.1 Test for carbohydrates
Activity 6.1
Materials required:
Starch powder, Irish potatoes juice, prepared porridge, Iodine solution, beakers, droppers, source of heat and test tubes

a. Test for starch
Procedure
–– Mix 1g of starch powder with 100ml of water
–– Boil the mixture while stirring; then cool the solution
–– Boil the mixture while stirring; then cool the solution
–– Put 2ml of starch solution in a test tube labeled 1, 2ml of Irish potato juice in a test tube labeled 2 and 2ml of prepared porridge in a test tube labeled 3
–– In each test tube put 2 drops of Iodine solution and shake
–– Record your observation and draw a conclusion

b. Test for reducing sugar
Requirements
Glucose powder, beaker and test tube, Benedict solution, Bunsen burner, droppers Procedures
–– In the beaker mix 1cm3 of water and 1g of glucose powder.
–– Pour the prepared solution of glucose in a test tube and
–– Add 2ml of benedict’s solution and heat
–– Record your observation.
Biological molecules are grouped into organic molecules including carbohydrates, proteins, lipids, nucleic acids and vitamins. They also contain inorganic molecules such as minerals and water. The first four organic molecules are called macromolecules because they are required in organism in large quantity. Carbohydrates including starch, reducing and non-reducing sugars appear in this category and are the main energy producers in the organisms. Others, including lipids and proteins are needed for building organisms while vitamins protect the organisms against diseases. We need to ensure that what we take from diet have all required biological molecules.

a. Test for starch.
Carbohydrates such as starch are tested by mixing a sample with 2-4 drops of iodine or Lugol’s solution. If the sample contains starch the solution will turn from a yellowbrown color to a dark purple/dark blue (Figure 6.1). The color change is due to a chemical reaction between the large carbohydrate molecule and the iodine ions. If the sample does not contain starch the solution remains yellow-brown.

b. Testing for reducing and non-reducing sugar
The presence of reducing sugar can be tested by using benedict reagent. Benedict solution has copper ions that have a light blue color. When this solution is heated in the presence of simple reducing sugars such as glucose, the blue color of copper ions changes from a light green color to rusty orange-brown color (Figure 6.2).

If the color of Benedict reagent persists, the sugar tested is not a reducing sugar. Note that there is no special reagent to test for non-reducing sugar, but by the addition of HCl, non-reducing sugars can be hydrolyzed to reducing sugars. To test the presence of reducing sugars, a solution of sodium hydroxide is needed to neutralize the acidity because Benedict reagent works better in neutral solution

Self-assessment 6.1
A student prepared carbohydrate solution labeled C. Perform the following experiment to confirm whether C1 is starch, reducing sugar, or non-reducing sugar.

a. Is this solution a carbohydrate?
b. Specify the role of Hydrochloric acid and sodium hydroxide used at stage 3 in the table above.

6.2 Test for proteins
Activity 6.2
Materials required
Milk, eggs, soybeans, test tubes, beakers, mortar for crushing beans, 1% NaOH or
1% KOH solution, 0.1M of CuSO4 solution and Millon’s reagent.

Procedure
–– Extract the white fluid from an egg

–– Prepare an extra of soya bean and 10ml of fresh milk
–– Put 2ml of albumen solution in a test tube labelled A1 and 2ml in A2
–– Put 2ml of milk solution in a test tube labelled B1 and 2ml in B2
–– Put 2ml of soya bean solution in a test tube labelled C1 and 2ml in C2
–– Put 1ml of KOH or NaOH solution in each of the test tubes A1, B1, and C1. Shake the mixture and add 1ml of CuSO4 solution in each (A1, B1, and C1)
test tube
–– Put 1ml of Millon’s reagent in each of test tubes (A2, B2, and C2). Shake the
mixture and thereafter boil the three test tubes (A2, B2, and C2).
The Biuret reagent is used to test for the presence of proteins. It contains copper ions with blue characteristic color. During the copper ions react with protein molecules and causes the biuret solution to turn from a light blue color to purple if proteins are present.

The test can also be done by using Millon’s reagent, which in the presence of proteins, the Millon reagent changes from colorless to pink.

Self-assessment 6.2
1. You are provided with the sample of the substance M and A. Carry out the following experiments and complete the table below.

2. Carry out the same experiment using the substance A and compare your findings with M.
3. Which of the substance A and M contain proteins?

6.3 Test for lipids
Activity 6.3
Materials required - Olive oil, test tubes, ethanol, water, sudan III solution

Procedure:
Use olive oil to carry out the following experiments Add 2 cm3of olive oil in the test tube:
–– Add 5 cm3 of ethanol followed by 5 drops of water.
–– Shake the mixture and record your observation.
–– To another test tube containing 2 cm3 of olive oil:
–– add 5 drops of Sudan III solution
–– Shake thoroughly and examine the mixture in the test tube after few minute and record your observations The presence of lipids can be determined by using Sudan III indicators, which are fat-loving
molecules that are colored. During the test for a solution containing lipids, two results are likely to be found: there is either the separation of layers indicating the levels of water and lipid, or the dye migrates toward one of the layers. If the mixtureis composed of water, the conclusion is that the lipids are not present. In this case, the Sudan III indicator will form small micelles/droplets and disperse throughout the solution. A positive result indicates the lipid layers sitting on top of the water layer with a red-orange color. When using ethanol for testing lipids the presence of the color changes from colorless to milky (emulsion test).

Self-assessment 6.3
You are provided with a solution X. Use Sudan III indicator to test the presence of lipids in the solution X.

6.4 Test for vitamin C (Ascorbic Acid).
Activity 6.4
Squeeze the orange fruits to extract the juice and carry out the following test.

Which of the two solutions give a positive solution for DCPIP?

Vitamin C is tested by using DCPIP (Dichlophenol Indophenol). Its positive (presence of vitamin C) test decolorizes DCPIP, while the negative (absence of vitamin C) test is indicated by the persistence blue color of DCPIP.

Self-assessment 6.4
In this experiment you are to press a tomato fruit (s) to get juice out of it. Use the juice to carry out the test for vitamin C Draw a table of results that includes the procedure, observation and conclusion.

End of unit assessment 6
1. Biological molecules are divided into:
a. Organic molecules and inorganic molecules
b. Carbohydrates and starch
c. Lipids, carbohydrates and water
d. Carbohydrates, food and potatoes
2. Name the reagents that are used to test for the following food substances
a. Lipids
b. Starch
c. Reducing sugar
3. You are provided with the following specimen:
Specimen A: Sorghum
Specimen B: Irish potatoes
Specimen C: Oranges
Specimen D: Sunflower seeds
a. Carry out chemical tests to determine the composition of the above seed to
tell whether they are composed of proteins, fats, starch or vitamin C.
b. Draw the table of used reagent, procedure and observation in (a)
4. Some drops of fresh pineapple juice are added drop by drop to DCPIP solution.
The deep blue color of the DCPIP quickly fades.
a. Explain why the blue colour disappeared?
b. What is the importance of this food substance to the human body?
5. The result of food tests on unknown sample are shown below. Copy and complete the table to show the conclusions which could be drawn from these tests.

6. This is a practical question to be conducted using provided materials and reagents to determine the food nutrients in each solution: You are provided with the following solutions, A (sucrose 0.5%), B (1%starch), C (dilute hydrochloric acid) and D (sodium hydroxide) and 6 test tubes labeled 1 to 6. Use the reagents provided to determine the chemical nature of the substance present in the solutions. Indicate your observations and conclusions in the table below:

a. Why was it necessary to boil solutions A and B with solution C in test (3) and (6)?
b. Why was solution D added to test tubes 3 and 6?

Key Unit Competences
Explain the important roles of carbohydrates and lipids in the provision and storage of energy and for a variety of other functions.

Learning objectives
By the end of this unit, I should be able to:
–– State the roles of carbohydrates and lipids.
–– Recall the elements that make up carbohydrates and lipids.
–– Explain the proportion of hydrogen in carbohydrates and lipids and relate this to the amount of energy released when oxidized.
–– Define the terms monomer, polymer, macromolecule, monosaccharide, disaccharide and polysaccharide.
–– Describe the ring forms of α-glucose and β-glucose structure.
–– Explain the formation of glycosidic bonds.
–– Describe the structure of phospholipids and relate to their functions in living organisms.
–– Describe the molecular structure and formation of triglycerides and phospholipids, and give their functions in living organisms.
–– Demonstrate that phospholipids have a hydrophilic head and hydrophobic tails using a heterogeneous mixture made up of water and cooking oil.
–– Interpret the charts and illustrations of molecular structure and the formation of maltose and triglycerides.
–– Demonstrate through a process of combustion that sugars and lipids are biological fuel
–– Differentiate between starch and cellulose.
–– Appreciate the importance of carbohydrates and lipids in organisms.
–– Be aware of the other roles of lipids in the formation of soap and with carbohydrates and syrups in medicine

Introductory activity
1. In the previous unit (test for biological molecules), we tested carbohydrates, starch, reducing sugar, lipids, proteins, and vitamins. Where do you classify monosaccharide, disaccharides and polysaccharides in the above tested biochemical compounds?
2. Sometimes people say that fatty persons do not feel cold. What could be the reasons?

7.1 Classes of monomers
Activity 7.1
1. Give the description of the term monomer
2. Where can we find monomers?
3. What is the biological importance of monomers?
A monomer is a molecule that can combine with others of the same kind to form a polymer. A polymer is a large molecule or macromolecule composed of many repeated sub-units (monomers). Because of their broad range of properties, both synthetic and natural polymers play essential and ubiquitous roles in everyday life. Polymers make up many of the materials in living organisms including proteins,
cellulose, and nucleic acids. Glucose molecules for example, are monomers that combine to form the polymer cellulose. The examples of monomers are summarized in the table 7.1.

Table 7.1: Biological molecules and their monomers

Carbohydrates comprise a large group of organic compounds which contain carbon, hydrogen and oxygen. The word carbohydrate suggests that these organic compounds are hydrates of carbon. Their general formula is Cx (H2O) y. In carbohydrates the ration hydrogen-oxygen is usually 2:1. Carbohydrates are divided into three groups including the monosaccharide (single sugars), disaccharides (double sugars) and polysaccharides (many sugars). The most common monosaccharide of carbohydrates is glucose with molecular formula C6H12O6.

Self-assessment 7.1
1. What are some examples of polymers and monomers?
2. How are monomers, polymers and macromolecules related?

7.2 Ring form of α-glucose and β-glucose
Monosaccharides are group of sweet and soluble

Activity7.2
1. Based on the knowledge acquired during the lesson of monomers and further information from books and internet:
a. What are the examples of monosaccharide?
b. Give the molecular formula of each of the monosaccharide stated above
c. Use the books to illustrate the structural formula of each of the monosaccharide stated above

crystalline molecules of relatively low molecular mass. They are named with the suffix –ose. The general formula of a monosaccharide is (CH₂O) n, with n the number of carbon atoms. The simplest monosaccharide has n=3 and it is a triose sugar. When n = 5, this is a pentose sugar, and when n = 6, this is a hexose sugar. The two common pentose sugars are ribose and deoxyribose, while the most known hexose is glucose. Its molecular formula is C6H12O6. It is the most important simple sugar in
human metabolism called simple sugar or monosaccharide because it is one of the smallest units which has the characteristics of this class of carbohydrates.

Monosaccharides can exist as isomers. The isomer is defined as each of two or more compounds with the same formula but a different arrangement of atoms in the molecule and different properties. For example, glucose, fructose and galactose share the same molecular formula which is C₆H₁₂O₆. However, they differ by their structural formulae as follow:

One important aspect of the structure of pentoses and hexoses is that the chain of carbon atoms is long enough to close up on itself and form a more stable ring structure. This can be illustrated using glucose as an example. When glucose forms a ring, carbon atom number 1 joins to the oxygen on carbon atom number 5 (Figure 7.2).

All hexoses sugars can exist as straight-chain structures but they tend to form ring structures. Glucose, fructose, galactose can exist in ring structures (Figure 7.3).

Ring monosaccharides are said to be alpha (α) if the -OH group located on carbon 1 is below the ring and beta (β) when the -OH group is above the ring. The molecule of glucose for example can exist as alpha and beta glucose denoted by α-glucose and β-glucose (Figure 7.4)

Self-assessment 7.2
1. How do we call the monosaccharide with 3, 5 and 6 carbon atoms?
2. Differentiate between α and β glucose
3. What are the properties of glucose?

7.3 Formation and breakdown of glycosidic bonds
Activity 7.3
1. Monomers are joined to form polymers, use a point as a monomer to illustrate how a polymer can be formed
2. How do you call joining structures between atoms?
3. Use books or other sources to show how monosaccharide form a
disaccharide.

7.3.1 Monosaccharides
Monosaccharides may combine together in pairs to give a disaccharide (doublesugar).
The union involves the loss of a single molecule of water and is therefore a condensation reaction. The bond which is formed is called a glycosidic bond. It is usually formed between carbon atom1of one monosaccharide and carbon atom 4 of the other, hence it is called a -1, 4- glycosidic bond. Any two monosaccharides may be linked together to form a disaccharide of which maltose, sucrose and lactose
are the most common.

The addition of water under suitable conditions is necessary if the disaccharide is to be split into its constituent monosaccharide. This is called hydrolysis waterbreakdown or more accurately, breakdown by water.

7.3.2 Disaccharides
These are carbohydrates made of two monosaccharides. They include maltose (glucose + glucose), sucrose or saccharose (glucose +fructose), and lactose (glucose+ galactose). The maltose is the sugar from the germinating seeds, sucrose or saccharose is the common table sugar obtained from sugarcane, while lactose is the sugar from the milk. In addition, sucrose is a non-reducing sugar.
Table 7.2: Types of disaccharides and their monomers

In maltose ring, the two ring of glucose are bonded by the -1, 4-glycosidic bond  while in sucrose the glucose and fructose are bonded by -1, 2-glycosidic bond.

All the disaccharides are non-reducing sugar, except maltose which behaves in the same as a reducing sugar with benedict’s solution. All monosaccharides and disaccharides have the following characteristics: sweet taste, soluble in water and lower molecular mass.
Self-assessment 7.3
1. Write the molecular structure of sucrose
2. How is the glycosidic link is formed
3. Sucrose is formed when two monosaccharide are assembled together:
a. Name those two monosaccharides.
b. Using the ring form of these monosaccharide named above to explain and
show sucrose formation?

7.3.4 Polysaccharides: starch, glycogen and cellulose
Activity 7.4
1. Based on the meaning of monosaccharide, what is a polysaccharide?
2. Classify the following compound into polysaccharide, monosaccharide and disaccharide
a. Glucose, fructose and galactose
b. Lactose, sucrose, and maltose
c. Starch, cellulose and glycogen
3. Use glucose to form any polysaccharide of your choice In the same way that two monosaccharides may combine in pairs to give a disaccharide, many monosaccharides may combine by condensation reactions to form a polysaccharide.

The number of monosaccharides that combine is variable and the chain produced may be branched or unbranched. Polysaccharide are many but the most known are starch, glycogen and cellulose.

a. Starch
Starch is made up of two components: amylose and amylopectin. Amylose is a linearunbranched polymer of 200 to 1500 α-glucose units in a repeated sequence of α-1,4-glucosidic bonds. The amylose chain coils into helix held by hydrogen bonds formed between hydroxyl groups. A more compact shape is formed. The amylose helices are entangled in the branches of amylopectin to form a complex compact
three dimensional starch molecule.

Amylopectin is a branched polymer of 200 to 200,000 α-glucose units per starch molecule. The linear chains of α-glucose units are held together by α-1, 4-glucosidic bonds. Branches occur at intervals of approximately 25 to 30 where α-1, 6-glucosidic bonds occur. Starch grains are found in chloroplast, potato tubers, cereals and legumes. Starch is insoluble in cold water. It is digested by salivary amylase and pancreatic amylase into maltose and the latter is hydrolyzed by maltase enzyme to form glucose. Therefore, diabetic people should avoid tubers since they are rich in starch which in turn gives glucose (Figure 7.8).

b. Glycogen
Glycogen is often called animal starch because it is a major polysaccharide storage material in animals and fungi. The brain and other tissues require constant supply of blood glucose for survival. Some tissues particularly the liver and skeletal muscles store glycogen in the form that can be rapidly mobilized to form glucose. Like starch, glycogen is made up of α-glucose and exists as granules. It is similar to amylopectin in structure but it has shorter chains (10-20 glucose unit) and is more highly branched.

c. Cellulose
Cellulose is the structural polysaccharide in plant cell wall. It is found in vegetables and fruits but it cannot be hydrolyzed by enzymes in the human digestive system. Cellulose is composed of long unbranched chains of up to 10,000 β-glucose units linked by β-1,4-glucosidic bonds. Each β-glucose unit is related to the next by a rotation of 180 ͦ C with OH groups projecting outwards on either side of the chain.

Cellulose chains run parallel to one another. Unlike amylopectin and glycogen molecules, there are no side chains (no branch) in the cellulose. This allows the linear chains to lie close together. Many H-bonds are formed between the OH groups of adjacent chains. The chains group together to form microfibrils arranged in larger bundles of macrofibrils. The fibrils give the plant cell their high tensile strength and rigidity. The layers of fibrils are permeable to water and solutes.

Cellulose is formed from ß - glucose units linked by 1,4 glycosidic bonds. The hydroxyl groups alternate on either side of the molecule forming straight chains giving cellulose a fibrous structure. Cellulose are strengthened further by hydrogen bonds that link adjacent chains.

d. Chitin
Chitin is one of naturally occurring Polymers. It forms a structural component of many animals such as exoskeleton in arthropods. Chitin is a polymer of glucose although in its structure a molecule of amino acid is added to each glucose. The digestion of chitin yields simple sugars and ammonia.

Self-Assessment 7.4
1. What type of reaction is involved in the formation of glucose from starch?
2. Use the type of reaction above to form glucose from sucrose molecule
3. What are the 2 main components of starch? Give the difference between them

7.3.5 Lipids
Activity 7.5
1. List the monomers that are present in lipids
2. Where can we find lipids?
3. Discuss the reasons why animals like pig do not like hot weather.
Lipids are a broad group of naturally occurring molecules which include fats, waxes, sterols, fat soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, Phospholipids and others. Lipids are grouped into fats which are solid at room temperature and oils which are liquid at room temperature. Lipids are made by carbon, hydrogen and oxygen, but the amount of oxygen in lipids is much smaller than in carbohydrates. Lipids are made by two components namely glycerol and fatty acids. The chemical formula for glycerol is C₃H₈O₃ with structural formula as shown in the figure 7.11

In all lipids glycerol do not show any variation while fatty acids vary. Therefore, the nature of lipid depends on the fatty acid it contains. There are two types of fatty acids: unsaturated fatty acid characterized by the chain of hydrocarbon containing one or more double and triple bonds; and saturated fatty acid characterized by the chain of hydrocarbon without any double or triple bond.

Key Unit Competence
Discuss the roles of minerals and vitamins in diet

Learning objectives
At the end of this unit you be able to:
–– State the mineral requirements for bodily functions.
–– Identify the symptoms of mineral and vitamin deficiency.
–– Outline the need for consumption of minerals and vitamins in small amounts.
–– Organize a list of foods that are good sources of vitamins and mineral salts.
–– Recognize the signs and symptoms of scurvy, night blindness, goiter, and anaemia.
–– Differentiate between water soluble and lipid soluble vitamins.
–– Analyze one’s eating habits and suggest improvements
–– Appreciate the importance of a balanced diet in relation to health and economic prosperity.
–– Advocate for healthy feeding methods.

Introductory activity
1. From the different food stuffs in our community, make a list of food stuffs that are good sources of minerals and vitamins.
2. Using text books and other resources, make a list of e vitamins and mineral deficiency diseases

9.1 Mineral nutrients in humans
Activity 9.1
Use textbooks and internet to list mineral nutrients found in human diet Mineral nutrients are sometimes called mineral salts or just minerals. Mineral salts are essential nutrients that our body needs. They are called essential not because they are more important than other substances in our body but because our
bodiescannot produce them. They include the inorganic substances found in daily diet. They are dissolved in body fluids.

They are found in human body as ions (cations and anions). Organic food like proteins, carbohydrates and fats provide the body with carbon, hydrogen, oxygen, nitrogen, sulfur and phosphorus. Butthere are several more elements that the body needs and occur as salts in the food we eat. They constitute about 1% of an organism by weight. Even though they are required in a very small amount, they are nonetheless essential for body processes.

Some mineral nutrients are required by animals, plants, a few by both. Humans require a number of minerals for the good functions of their bodies. Those are: Calcium (Ca²⁺), phosphorus (H₂PO-₄), Nitrogen(NO-₃), Sulfur (SO²- ₄) Potassium (K⁺), Sodium (Na⁺), Iron (Fe²⁺ or Fe³⁺), Magnesium (Mg²⁺), Iodine (I-), Chloride (Cl^-), Manganese (Mn²⁺), Fluoride (F-), zinc (Zn²⁺), Cobalt (Co²⁺), Chromium (Cr²⁺ or Cr³⁺) and molybdenum (MoO^-₄)

Self-assessment 9.1
1. Outline ten mineral nutrients required in human diet.
2. Answer by true or false and justify your answer: “Minerals are called essential nutrients because they are more important than others”.

9.2 Classification of mineral nutrients
Activity 9.2
Iodized table salt is advised to prevent goiter. In 100g of table salt there is 99% of NaCl, and only 1% of iodine. Refer to the notes below to find the reason behind
this ratio.

The classification of minerals is based upon their requirement rather than on their relative importance. Mineral nutrients are needed in a precise small amount. The five major minerals needed in human body include calcium (Ca²⁺),phosphorus (H₂PO-₄), potassium (K⁺), sodium
(Na⁺) and magnesium (Mg²⁺). Mineral nutrients are grouped into two groups: the macronutrients
or major elements and the micronutrients or trace elements.
Macronutrient or major elements are minerals needed by humans in a relative large amount (greater than 200 mg/day). Their examples include nitrogen(NO₃-) , phosphorus (H₂PO^-₄), sulfur(SO²-₄) , calcium (Ca²⁺), sodium (Na⁺), chlorine (Cl^-), magnesium (Mg²⁺), and iron (Fe²⁺ or Fe³⁺).Micronutrients or trace elements are those which are needed in minute amount (a few parts per million). Examples
include manganese (Mn²⁺), iodine (I^-), zinc (Zn²⁺), molybdenum(MoO^- ₄)and fluorine (F-).

Self-assessment 9.2
1. Categorize mineral nutrients according to their amount in human body.
2. Distinguish the two categories of mineral nutrients needed by the human body.
3. From the minerals listed here, identify the five major minerals in the human body: Sulfur (S), Potassium (K), Sodium (Na), Iron (Fe), Magnesium (Mg), Iodine (I), Chloride (Cl), zinc (Zn), Cobalt (Co), chromium, Calcium (Ca), phosphorus (P), Nitrogen (N).

9.3 Sources, functions and deficiency symptoms of mineral nutrients in humans
Activity 9.3
Use your textbook to answer the following questions:
Hereunder is a variety of food stuffs: Banana, cassava, wholegrain, oranges, pumpkin, potato, beans, water melon, green leafy vegetables, poultry, eggs, liver, and milk. Choose the food stuffs which are good sources of minerals. Human body requires mineral nutrients to survive and to carry out daily functions
and processes. Minerals keep humans healthy and have key roles in several body functions. Humans receive minerals by eating plants that absorb minerals from the soil and by eating meat and other products from animals, which graze on plants. The deficiency of mineral nutrients results into body functional disorders and diseases. Most are found in the blood and cytoplasm of cells, where they assist basic functions. For example, calcium and potassium regulate nerve and muscle activity

Self-assessment 9.3
1. Match the mineral nutrients with its function
a. Iodine                              1. make bones hard
b. Fluorine                           2. maintains the immune system stronger
c. Phosphorus                     3. component of hemoglobin
d. Iron                                  4. prevents tooth decay
e. Copper                            5. used in synthesis of thyroid hormone (thyroxin)
2. In a tabular form, identify the major dietary sources, the functions in human bodies and the deficiency diseases of the following minerals: Ca, I, P, zinc, and Cu
3. Choose the best answer.
i. They are the minerals we need a lot in every day diet. How are they called?
a. Macronutrents
b. Micronutrients
c. Giant minerals
d. Monster minerals
ii. This mineral helps to build up strong teeth and bones. How is it called?
a. Calcium
b. Iron
c. Zink
d. potassium
iii. What are foods that are natural good source of iron?
a. Roast Beef
b. Macaroni and cheese
c. Baked beans
d. Water melon
iv. Select 2 that are natural good sources of calcium?
a. Milk and cheese
b. Whole-wheat bread
c. Iceburg lettuce
d. Scanned salmon
v. The mineral that helps in oxygen transport to lungs is?
a. calcium
b. iron
c. zinc
d. potassium
vi. Which foods are good sources of zinc?
a. Milk and cheese
b. Lamb and pork
c. Macaroni and cheese
d. Peanuts and lentils
vii. Bananas are great source of this mineral, which helps our muscles and nervous
system to maintain your right water levels. What is it called?
a. Calcium
b. Iron
c. Zinc
d. Potassium
viii. Which mineral is important and needed by our body to fight off infection?
a. Calcium
b. Iron
c. Zinc
d. Potassium
ix. Which of the following mineral are needed in large amount every day?
a. Zinc
b. Iron
c. Calcium
d. selenium
x. Which is the type of mineral that keep your nervous system health?
a. Calcium
b. Iron
c. Zinc
d. Potassium
4. From the diseases listed below, what are those caused by the deficiency of minerals?
Goiter, malaria, diabetes, rickets, beriberi, scaly skin, night blindness, anemia, impaired immunity, diarrhea

9.4 Vitamins and the classification of vitamins
Activity 9.4
Two students with different complains went to consult a medical doctor. Student A says to the doctor that whenever he/she bleeds whenever she /he brushes teeth. Student B doesn’t see well objects around him/her, The results from the doctor showed that they all have lack some vitamins.
1) What kind of vitamins that each student needs to take?
2) Use your student textbook to explain your answer
Like minerals, vitamins are also essential for the human body. They are required for metabolism, protection health and growth. Vitamins also assist in formation of hormones, blood cells and genetic material. Vitamins are directly absorbed from the small intestine into the blood stream. Water –soluble vitamins are absorbed in the ileum while fat-soluble vitamins are absorbed in jejunum. Features shared by all vitamins:

–– They are not digested or broken down for energy
–– They are not synthesized into the body structures
–– Most are rapidly destroyed by heat.
–– They are essential for good human health and needed in a very small amount
–– They are required for chemical reactions in cells, working in association with enzymes.

There are thirteen vitamins required by human body. They are classified by their solubility, whether they dissolve in water or in fats. Water-soluble vitamins including vitamins C and B complex, and fat-soluble vitamins including vitamins A, D, E and K (Table 9.2). Excess water- soluble vitamins are simply excreted in urine, while fatsoluble vitamins are stored in body fatty tissues to be used later if there is deficient
in diet. Excess intakes of these vitamins are stored in fatty tissues of the body, where they can build up to toxic levels, especially if they are taken improperly in supplements.

Table 9.2 Water-soluble and fat-soluble vitamins

Self-assessment 9.4
1. How many vitamins does the human body needs to function properly?
2. Describe the classification of vitamins.

9.5 Sources, functions and symptoms of vitamin deficiency
Activity 9.5
Here is a number of foodstuffs rich in vitamins.

From the list of provided food stuffs (Banana, cassava, wholegrain, oranges, pumpkin, potato, beans, water melon, green leafy vegetables, and milk). Can you give some foods that are good sources of vitamins?
Some vitamins, including some vitamin B complex and Vitamin K are produced by bacteria that normally live in the intestines, where they help to digest food. Vitamin D is synthesized in the skin when it is exposed to UV radiation in sunlight.

Vitamins and their derivative are coenzymes; note that a coenzyme is an organic molecule that combines temporaly with enzymes making them more efficient. For example, Niacin or vitamin B3 is an essential component of coenzymes NAD and NADP involved in lipid metabolism. It inhibits production of cholesterol and catabolism of triglyceride. Thiamin or vitaminB1 is a coenzyme for many different enzymes that break complex molecules such as carbohydrates to produce ATP.

Thiamin deficiency results into Beriberi anemia and stunted growth in children. Vitamin K is an essential coenzyme for synthesis of several blood clotting factors. Several vitamins, including vitamins C and E, act as antioxidants. An antioxidant is a compound that neutralizes chemicals called free radicals. Free radicals are produced naturally during cellular activities and may cause some types of cancer. Neutralizing free radicals makes them harmless.

The table: 9.3. The major dietary sources, functions and possible symptoms of vitamin deficiency

Many vitamin supplements are available in the market. However, it is always advisable to obtain them from their natural sources by eating food rich in vitamins daily. Possible symptoms of vitamins deficiency are shown by the following pictures:

End of unit assessment 9
1. Choose a mineral which is an electrolyte and is found in almost every food. It helps to lower blood pressure.
a. Zinc
b. Potassium
c. Calcium
d. Iron

2. choose a mineral which helps to make our blood vessels, tendons, and nerves strong.
a. Iron
b. Magnesium
c. Chromium
d. Copper

3. The following vitamins are part of Niacin and Thiamin minerals
a. Vitamins
b. Vitamins
c. Vitamins
d. Vitamins

4. Vitamin C is required for the production and maintenance of:
a. Collagen
b. Hormone
c. Ascorbic Acid
d. Red Blood Cells

5. Vitamin C deficiency is called:
a. Scurvy
b. Cold
c. Cancer
d. Rickets

6. Which of the following is a function of Vitamin A in the body?
a. Vision, bone and body growth
b. Immune defenses, maintenance of body linings and skin
c. Normal cell development and reproduction
d. All of the above

7. Common food sources of Vitamin A are:
a. Milk, eggs, butter, cheese, cream, and liver
b. White sugar, honey, and sugar cane
c. Broccoli, apricots, Cantaloupe, Carrots, Sweet potato, Spinach
d. Both a and c

8. Which of the following is a function of Vitamin B-12?
a. Influences the cells that build bone tissue
b. Is essential to the formation of bone
c. Helps to maintain acid-base balance
d. Maintains the sheaths that surround and protect nerve fibers

9. Vitamin B-12 deficiency caused by lack of intrinsic factor is called:
a. Pernicious anemia
b. Poor circulation of the red blood cells
c. Beriberi
d. None of the above

10. What groups of people need additional Vitamin K?
a. Premature newborns
b. People who do not have enough bile to absorb fat
c. Both A and B
d. None of the above answers

11. A common function of Thiamin, Riboflavin and Niacin is that:
a. They all are used in synthesis of blood clotting proteins
b. They all work as a part of a coenzyme used in energy metabolism
c. They all help to strengthen blood vessel walls
d. They are used to stabilize cell membranes
12. The vitamin Folate works together with ______________ to produce new red blood cells.
a. Vitamin D
b. Vitamin A
c. Vitamin B-12
d. None of the above

13. Which of the following is a function of Vitamin B-12?
a. Red blood cell formation
b. Myelin sheath that protects nerve biers
c. Vision
d. Both A and B

14. Vitamin C helps in maintenance and repair of collagen which:
a. Forms the base for all connective tissue in the body
b. Aids in digestive processes
c. Promotes good eyesight
d. Prevents PMS symptoms

15. Which of the following is not a function of Vitamin D?
a. Acts like a hormone
b. Stimulates maturation of cells
c. Maintains calcium cells
d. Builds tissue

16. Some food sources of Vitamin D are:
a. Fruits and vegetables
b. Salmon and egg yolks
c. Butter and fortified milk
d. Both B and C.

17. Humans obtain vitamins from natural sources such as vegetables, fruits,
meat, fish and dairy products. What are the two vitamins that are not provided
by fruits and vegetables?

18. What would you advise someone starting to have symptoms of?
a. Scurvy
b. Rickets
c. Teeth decay
d. Heart failure
e. Pernicious anemia

Describe the mode of action and factors affecting enzymes and their importance for the existence of life

Learning objectives
At the end of this unit you be able to:
–– Define the term enzyme.
–– Explain the criteria of naming enzymes.
–– State that enzymes function inside cells and outside cells.
–– Explain that enzymes are globular proteins that catalyze metabolic reactions.
–– Describe the mode of action of enzymes in terms of the lock and key and the induced fit hypotheses.
–– Explain factors affecting enzyme activity.
–– Define enzyme technology and its role in industry.
–– Investigate the progress of an enzyme-catalyzed reaction by measuring rates of formation of products.
–– Investigate the effects of temperature, pH, enzyme and substrate concentration, and inhibitors on enzyme activity.
–– Interpret graphs of the effects of reversible and irreversible inhibitors on the rate of enzyme activity.
–– Investigate the effect of immobilizing an enzyme in alginate as compared with
its activity when free in solution.
–– Use a computer to plot graphs of the rate of enzyme controlled reaction.
Calculate Q10 of an enzyme controlled reaction.
–– Acknowledge that enzymes are essential in speeding up reactions that would be too slow to sustain life.
–– Appreciate the importance of planning and carrying out experiments under controlled conditions.
–– Understand the roles of enzymes in industry and medicine.

Introductory activity
Discuss in pair the following questions and share with another pair your findings.
1. What do you understand by the term enzyme?
2. Two individuals want to reach the last floor of Kigali city tower. One climbs up using the ladder but another one uses a lift. What advantage the lift gives over the ladder?
3. Why is it easy to digest hot foods than cold ones?

10.1 Criteria for naming enzymes
Activity 10.1
You are provided with three groups of enzymes:

Make a research to find out:
a. specific role of each of the six enzymes mentioned above
b. criterion followed to name enzymes of group A, B and C respectively
Enzymes are biological catalysts produced by a living organism to control the rate of specific biochemical reactions by lowering the activation energy of reactants

First of all, individual enzymes are named by adding -ase to the name of the substrate with which they react. The enzyme that controls urea decomposition is called urease; those that control protein hydrolyses are known as proteases.

A second way of naming enzymes refers to the enzyme commission number (EC number) which is a numerical classification scheme for enzymes based on the chemical reactions they catalyze. In a system of enzyme nomenclature, every EC number is associated with a recommended name for the respective enzyme catalyzing a specific reaction. They include:

–– Oxidoreductases: catalyze redox reactions by the transfer of hydrogen, oxygen or electrons from one molecule to another. Example: Oxidase catalyzes the addition of oxygen to hydrogen to form water.

–– Hydrolase: catalyzes the hydrolysis of a substrate by the addition of water.
Sucrose + water glucose+ fructose
–– Ligases: catalyze reactions in which new chemical bonds are formed and use ATP as energy source.
Amino acid + tRNA amino acid-tRNA complex.
–– Transferases: catalyze group transfer reactions. The transfer occurs from one molecule that will be the donor to another molecule that will be the acceptor. Most of the time, the donor is a cofactor that is charged with the group about to be transferred. Example: Hexokinase used in glycolysis.
–– Lyases: catalyze reactions where functional groups are added to break double bonds in molecules or the reverse where double bonds are formed by the removal of functional groups. For example: Fructose bisphosphate aldolase used in converting fructose 1, 6-bisphospate to G3P and DHAP by cutting C-C
bond.
–– Isomerases: catalyze reactions that transfer functional groups within a molecule so that isomeric forms are produced. These enzymes allow for structural or geometric changes within a compound. Sometime the interconverstion is carried out by an intramolecular oxidoreduction. In this case, one molecule is both the hydrogen acceptor and donor, so there’s no oxidized product. The lack of an oxidized product is the reason this enzyme falls under this classification. The subclasses are created under this category by the type of isomerism. For example: phosphoglucose isomerase for converting glucose 6-phosphate to fructose 6-phosphate by moving chemical group inside the same substrate.

A third way of naming enzymes is by their specific names e.g. trypsin and pepsin are proteases. Pepsin, trypsin, and some other enzymes possess, in addition, the peculiar property known as autocatalysis, which permits them to cause their own formation from an inert precursor called zymogen.

10.2 Characteristics of enzymes
Activity 10.2
Requirement: Three test tubes, match box, about 1g of liver, 1g of sands, 1% H₂O₂ and MnO₂ powder.
Procedure:
–– Label three test tubes A, B and C respectively.
–– Put about 0.1 g of MnO₂ powder in test tube A and 1g of liver in tube B and 0.1g of sand in tube C.
–– Pour 5 ml of H₂O₂ (hydrogen peroxide) in each tube. What do you observe?
–– Place a glowing splint in the mouth parts of each test tube. What do you observe?

Questions
1. Explain your observations.
2. Write down the chemical equation of the reaction taking place in tube A and B
3. Carry out your further research to find out the characteristics of enzymes

Enzymes speed up the rate of metabolic reactions by allowing the reaction to go through a more stable transition state than would normally be the case. As a result, the rate of reaction is increased. In many chemical reactions, the substrate will not be converted to a product unless it is temporarily given some extra energy referred to as activation energy (the minimum energy required the make a reaction take place).

Enzymes speed up the rate of biochemical reactions in the cell but remain unchanged at the end of the reactions. An enzyme has no effect on the relative energy content of products versus reactant. Chemical reactions catalyzed by enzymes are usually reversible e.g. enzyme carbonic anhydrase catalyses both synthesis and breakdown of carbonic acid.

An enzyme provides a reaction surfaceand a hydrophilic environment for a reaction to take place. This is normally a hollow or cleft in the enzyme which is called the active site, but it is normally hydrophobic in nature rather than hydrophilic.

A very small amount of enzymes is needed to react with a large amount of substrate. The turnover number of an enzyme is the number or reactions an enzyme molecule can catalyse in one second. Enzymes have a high turnover number e.g. the turnover number of catalase is 200,000 i.e. one molecule of enzyme catalase can catalyse the breakdown of about 200,000 molecules of hydrogen peroxide per second into water and oxygen at body temperature.

A cofactor is the best general term to describe the non-protein substances required by an enzyme to function properly. This term covers both organic molecules and metal ions. A co-enzyme is an organic molecule that acts as a cofactor. A prosthetic group is a cofactor that is covalently bound to the enzyme.

Self-Assessment 10.2
1. State any four properties of enzymes.
2. Enzymes have generally high turnover number. What is the significance of the high turnover of enzymes?

10.3 Mode of action of enzymes
Activity 10.3
There are two main hypotheses that explain the mode of action of an enzyme on its substrate: the lock and key hypothesis and the induced-fit hypothesis. Carry out a research to find the relevance of each.

Enzymes do not change but substrates are converted into products. A substrate is a molecule upon which an enzyme acts. In the case of a single substrate, the substrate binds with the enzyme active site to form an enzyme-substrate complex. Thereafter the substrate is transformed into one or more products, which are then released from the active site. This process is summarized as follows:

Whereby: E = enzyme, S = substrate(s), ES = Complex Enzyme-Substrate and P= product (s). There are two main hypotheses explaining the mechanism of enzyme action:

a. The lock and key hypothesis by Emil Fischer
In this hypothesis the substrate is the key and enzyme is the lock. The active site is exactly complementary to the shape of the substrate as shown below.

b. The induced-fit hypothesis by Daniel Koshland
The induced-fit hypothesis is a modified version of the lock and key hypothesis and is more widely accepted hypothesis. In this hypothesis, the active site is flexible and
is not fully complementary with the shape of the substrate. An enzyme collides with the substrate molecule and binds to the active site. This induces a slight change in the shape of the enzyme making the substrate the fit more precisely. This reduces the potential energy of the substrate and allows the reaction to occur. The products formed move away from the active site and regains its original configuration ready for the next reaction to take place.

Self-Assessment 10.3
The key and lock hypothesis is a model that explain the mode of action of an enzyme on the substrate. In the same context, analyse the diagram below and then answer question that follow.

1. What does the lock represent?
2. What does the key represent?
3. Where is the active site?
4. Suggest another diagram that can better represent the induced fit hypothesis. Write short notes to explain its functioning.

10.4 Factors affecting enzyme action
Activity 10.4
You will need
Eight test tubes containing 2 cm3 starch solution, amylase solution, cold water (ice) water bath, iodine solution, HCl solution, and droppers Procedure:
1. Label your test tubes A-D as follows:

2. Add 1 cm3 of starch solution to each test tube
3. Keep tube A and B in cold (ice) and tube C and D in the water bath at 35oC for 5 minutes.
4. Add 1 cm3 of 1M HCl on test tubes B and D, then shake the mixture to stir.
5. Add 1 cm3 of amylase solution on each test tube. Shake and therefore keep A and B in cold and C and D in water bath for 10 minutes.
6. Take a sample from each tube and mix it with one drop of iodine. Use a different tile for each test tube. Record and interpret your observation and then draw a conclusion.
Enzymes activities can be limited by a number of factors such as the temperature, the pH,
the concentration of the substrate or the enzyme itself and the presence of inhibitors.

i. Temperature
At zero temperature, the enzyme cannot work because it is inactivated. At low temperatures, an enzyme-controlled reaction occurs very slowly. The molecules in solution move slowly and take a longer time to bind to active sites. Increasing temperature increases the kinetic energy of the reactants. As the reactant molecules move faster, they increase the number of collisions of molecules to form enzymesubstrate
complex.

At optimum temperature, the rate of reaction is at maximum. The enzyme is in active state. The optimum temperature varies with different enzymes. The optimum temperature for enzymes in the human body is about 37oc. When the temperature exceeds the optimum level, the enzyme is denatured.

The effect is irreversible. However, some species are thermophilic that is they work better at high temperatures; others are thermophobic, that is they work better at low temperatures. For example, some thermophilic algae and bacteria can survive in hot springs of 60oc.

The rate doubles for each 10oC rise in temperature between 0oC and 40oC (figure 10- 5). The temperature coefficient Q₁₀ is the number which indicates the effect of rising the temperature by 10oC on the enzyme-controlled reaction. The Q₁₀ is defined as the increase in the rate of a reaction or a physiological process for a 10°C rise in temperature. It is calculated as the ratio between rate of reaction occurring at (X + l0) oC and the rate of reaction at X oC. The Q₁₀ at a given temperature x can be
calculated from:

Worked out example
The rate of an enzyme-controlled reaction has been recorded at different temperatures as follows:

Solution

This means that the rate of the reaction doubles if the temperature is raised from 30°c to 40°c

Be aware that not all enzymes have an optimum temperature of 40°c. Some bacteria and algae living in hot springs (e.g. Amashyuza in Rusizi) are able to tolerate very high temperatures. Enzymes from such organisms are proving useful in various industrial applications because they do not denature up to 70oc

ii. The pH
Most enzymes are effective only within a narrow pH range. The optimum pH is the pH at which the maximum rate of reaction occurs. Below or above the optimum pH the H+ or OH- ions react with functional groups of amino acids in the enzyme which loses its tertiary structure and become natured.

Different enzymes have different pH optima (look in the table).
Table 10.1. Optimum pH of some digestive enzymes

iii. Enzyme concentration
The rate of an enzyme-catalyzed reaction is directly proportional to the concentration of the enzyme if substrates are present in excess concentration and no other factors are limiting.

iv. Substrate concentration
At low substrate concentration, the rate of an enzyme reaction increases with increasing substrate concentration. The active site of an enzyme molecule can only bind with a certain number of substrate molecules at a given time. At high substrate concentration, there is saturation of active sites and the velocity of the reaction reaches the maximum rate.

b. Inhibitors
The inhibitors are chemicals or substances that prevent the action of an enzyme. An inhibitor binds to an enzyme and then decreases or stops its activity. There are three types of inhibitors:

i. Competitive inhibitors are molecules that have the similar shape as the substrate. At high concentration, they compete with the substrate for the active site of the enzyme e.g. O₂ competes with CO₂ in RuBP-carboxylase.

ii. Non-competitive inhibitors are molecules that can be fixed to the other part of enzyme (not to the active site) so that they change the shape of active site,due to this the substrate cannot bind to the active sit of the enzyme.

iii. End product inhibitor, Allosteric inhibitor or Allostery.
This is a chain enzymatic metabolic pathway where the final end product acts as an allosteric reversible inhibitor for the first, the second or the third step in the metabolic pathway. The shape of an allosteric enzyme is altered by the binding of the end product to an allosteric site. This decreases enzymatic activity. By acting as allosteric inhibitors of enzymes in an earlier metabolic pathway, the metabolites
can help to regulate metabolism according to the needs of organisms. This is an example of negative feedback.

This often happens when few enzymes are working on a large number of substrate e.g. ATP is an end-product inhibitor of the enzyme PFK (Phosphofructokinase) in glycolysis during cell respiration. The end-product inhibitor leads to a negative feedback.

The products of enzyme-catalysed reactions are often involved in the feedback control of those enzymes. Glucose-1-phosphate is the product formed from this enzyme-catalysed reaction. As its concentration increases, it increasingly inhibits the enzyme.

Importance of reversible and irreversible inhibition
The nerve gas DIPF (DiIsopropyl Phospho Fluoridate) is an irreversible inhibitor. It binds permanently with enzyme acetylcholisterase, altering its shape. The enzyme cannot bind with and break down its substrate acetylcholine (neurotransmitter). Acetylcholine molecules accumulate in the synaptic cleft. Nerve impulses cannot be stopped causing continuous muscle contraction. This leads to convulsions, paralysis and eventually death.

Many pesticides such as organophosphate pesticides act as irreversible enzyme inhibitors. Exposure to pesticides can produce harmful effects to the nervous and muscular systems of humans. Heavy metal ions such as Pb²⁺, Hg²⁺, Ag⁺, As⁺ and iodine-containing compounds which combine permanently with sulphydryl groups in the active site or other parts of the enzyme cause inactivation of enzyme. This usually disrupts disulphide bridges and cause denaturation of the enzyme.

Self-Assessment 10.4
1. What is Q₁₀ of an enzyme controlled reaction?
2. You are provided with the table below of the rate of an enzyme controlled reaction.

Calculate the value of Q10 at:
a. 0° c
b. 10° c
c. 50° c
3. Explain why thermophile bacteria and algae are useful in some industrial processes
4. The diagram below represents a metabolic pathway controlled by enzymes.

–– V is a substrate
–– W, X and Y are intermediate compounds
–– Z is a product
–– e1, e2, e3, and e4 are enzymes
a. Name the type of control mechanism which regulates production of compound Z
b. Explain how an excess of compound Z will inhibit its further production.

10.5 Importance of enzymes in living organisms
Activity10.5
Discuss and present your ideas about the need for different enzymes in living organisms.

Without enzymes, most of the biochemical reactions in living cells at body temperature would occur very slowly or not at all. Enzyme can only catalyze reactions in which the substrate shape fits that of its active site

There are thousands of metabolic reactions that place in the body that require enzymes to speed up their rate of reaction, or will never happen. Enzymes are very specific, so nearly each of these chemical reactions has its own enzyme to increase its rate of reaction. In addition, the organism has several areas that differ from one another by the pH. Therefore, the acid medium requires enzymes that work at low
pH while other media are alkaline and require enzymes that work at high pH. In addition to digestion, enzymes are known to catalyze about 4,000 other chemical reactions in your body. For example, enzymes are needed to copy genetic material before your cells divide.

Enzymes are also needed to generate energy molecules called ATP, move fluid and nutrients around the insides of cells and pump waste material out of cells. Most enzymes work best at normal body temperature about at 370 c -- and in an alkaline environment. As such, high feverand over-acidity reduce the effectiveness of most enzymes. Some enzymes need co-factors or co-enzymes to work properly.

Self-Assessment 10.5
1. Fill the blank with appropriate terms:
Enzymes are biological ____________________ produced by
___________________________ cells. Enzymes reduce the amount of
____________________ energy required for reactions to occur. They consist of
globular ____________________ with _______________________ structure.
2. Answer the following questions:
a. What is the main role of enzymes?
b. What would happen if there are no enzymes in the cell?

10.6 Enzymes technology
Learning activity 10.6
Enzymes are needed in everyday life. At school you can use salivary amylase to hydrolyse starch. There is industrial technique used to get large amounts of enzyme amylase.

Read through the notes below and answer the following questions below:
a. State the different processes in which enzyme technology is applied
b. What is the role of thermophilic bacteria in this process?
c. How is the effectiveness of an enzyme improved for used in industry?

The market for enzymes is prosperous. The demand keeps on increasing as new applications of enzymes are discovered. Enzymes have been used in cheese-making, in leather industries, and making washing powders.

Microbial cells are still the most sources of industrial enzymes because microorganisms naturally produce enzymes inside their cells known as intracellular enzymes. When e microorganisms secrete their enzymes for an action outside their cells, the enzymes are called extracellular enzymes. Microorganisms may have specific genes introduced into their DNA by genetic engineering so that they produce enzymes naturally made by other organisms.

Once enzymes are produced by the microorganisms they are isolated by centrifugation in order to remove the large cell fragments. The enzyme is precipitated from solution by a salt such as (NH₄)₂SO₄ or an alcohol such as CH₃-CHOH-CH₃. Thereafter the enzyme can be purified by the process known as electrophoresis or column chromatography. The enzyme stability is a key factor in the industrial use of
enzymes. The stability of an enzyme is its ability to retain its tertiary structure under a wide range of conditions.

As many industrial processes require high temperatures and extreme pH, it is recommended to use bacteria such as Bacillus subtilis which withstand harsh conditions such as high temperature. Those thermophilic bacteria produce thermostable enzymes that do not denature at high temperature because their optimum temperature between 65 - 75⁰c.

Some useful enzymes are not thermostable. Such enzymes should be improved by the technique called immobilization i.e. the enzyme is attached to or located within an unreactive support such as nylon that protects it from denaturation.

Self-Assessment 10.6
1. What is the role of alcohol or ammonium sulphate during the extraction of enzymes?
2. Why is thermostability of enzymes so important for many industrial processes?

End of unit assessment 10
1.
a. What is the meaning of the following terms related to enzyme activity?
           i. Catalyst
           ii. Activation energy
           iii. Lock and key hypothesis
           iv. Q₁₀
b. Why are there hundreds of different enzymes in a cell?
c. How do enzymes reduce the activation energy of a reaction?
2. Enzyme activity is affected by a number of factors.
a. Explain why enzymes work faster at relatively high temperatures
b. Describe what happens to the enzyme structure if the temperature is raised
above the optimum temperature.
c. How are enzymes affected by pH?
d. Why do different enzymes have a different optimum pH?
e. What is the difference between a reversible and irreversible enzyme
inhibitor?
3. Some bacteria and algae can survive in boiling water of hot springs. Enzymes
from those organisms are used in industrial processes. Why are those enzymes useful?
4. The following set of data shows the effect of temperature on the completion time of an enzyme reaction.

a. Plot the data on a graph
b. What is the optimum temperature of this reaction?
c. Describe the shape of the graph between 10 and 40o c
d. Calculate the rate of increase between 20 and 30o c.

5. The table below shows the rate of an enzyme reaction at a range of temperature:

a. Fill that table with the values of the rate of reaction and plot a graph of rate at different temperatures (use x-axis for temperature).
b. Calculate Q₁₀ at 30°c.
c. Explain what happen between 20 and 30°c, and between 40 and 50°c.
6. The graph below shows the activity of a commercial enzyme alcalase at different pH value. Alcalase is a protease enzyme.

a. What are the compounds digested by this enzyme?
b. Describe the change in enzyme activity with pH.
c. How does this curve compare to the pH curve of a human digestive
enzyme such as pepsin?
7. Outline how a specific enzyme can be produced from bacteria.

Key Unit Competence
Explain the principles of gaseous exchange systems

Learning objectives
At the end of this unit learners will be able to:
–– Explain the relationship between size and surface area to volume ratio.
–– Describe how different respiratory surfaces are modified to speed up the diffusion process.
–– State the characteristics of gaseous exchange surfaces.
–– Describe the effects of tar and carcinogens in tobacco smoke on gas exchange
system with reference to lung cancer and Chronic Obstructive Pulmonary
–– Describe the short-term effects of nicotine and carbon monoxide on the cardiovascular system.
–– Observe prepared slides of gaseous exchange surfaces and identify their
characteristics.
–– Dissect fish gills and observe the surface area for gas exchange.
–– Observe mammal’s lungs and state their adaptation for gaseous exchange.
–– Use internet to make research and deduce the findings
–– Appreciate the evolution of gaseous exchange surfaces from simple to complex.

Introductory activity
Kalisa and Uwase wanted to rear tilapia at their home. They bought a nice transparent plastic box. They filled it with 1.5L of clean mineral water, put in some pieces of meat and plant leaves. They finally introduced a living tilapia in the box and covered. After two days they were happy to see their fish swimming. But on the third day, they become sad after finding it dead and yet the food was still in
water. What could have caused the death of the fish?

11.1 Relationship between size and surface area to volume
Actirvaittyi o11.1
1. Use Manila paper, scissors, and graduate ruler to create three cubes: 3cm x 3cm,2cm x 2cm, 1cm x 1cm
a. Calculate the surface area, the volume, and the surface area to volume ratio of each cube. What do you conclude from these ratios?
b. Compare the surface area to the volume of a spherical alveolus having a radius of 0.001m and that of another animal with a radius of 0.000001m.
2. What do you understand by surface area to volume ratio?

The surface area to volume ratio is the relationship between the surface area and the volume of an object. Small or thin objects have a large surface area compared to the volume. For example, the surface area of a sphere is calculated by



As the length or radius of the sphere increases, the increase in the surface area is squared (X²) and the increase in the volume is cubed (X³). The surface area to the volume ratio gets smaller as the cell or animal gets larger. Thus, if the cell grows beyond a certain limit, not enough material will be able to cross the membrane fast enough to accommodate the increased cellular volume.

As a cell grows, its surface area to volume ratio decreases. At some point in its growth its surface area to volume ration becomes so small that its surface area is too small to supply its raw materials to its volume. The cell will reach a size at which substances cannot enter or leave the cell in sufficient time to sustain life. At this point the cell cannot get larger. The volume of the cell will also be so large that the diffusion
rate will be too low to distribute necessary substances throughout the cell within a reasonable time. This brings about the need of having a mechanism of ventilation that speeds up the rate of gaseous exchange.

The rate of oxygen consumption by an animal gives a relatively accurate indication of the rate of its metabolic activity. The need of oxygen varies with the activity, the size of the organism, and their health. In general, small mammals need more oxygen than large mammals because:
–– Small mammals have a big respiratory surface area to the volume ratio
–– Small mammals are too motile than large mammals. Therefore, they need to produce more energy through aerobic respiration
–– Small mammals reproduce more rapidly than large mammals.

A running man needs a double volume of oxygen than a sleeping man and a pregnant woman needs more oxygen than a normal woman.

Self-Assessment 11.1
Determine the surface area to volume ratio of a sphere having a diameter of 4 mm

11.2 Characteristics of gas exchange surfaces
The following are the characteristic features of gaseous exchange surfaces:

Large surface area: they should have a large surface area to allow adequate and fast gaseous exchange in order to provide enough oxygen to cells and to get rid of the carbon dioxide that is released.

Rich supply of blood: in animals with a transport system, the respiratory surface areas found in the lungs and gills have rich supply in blood capillaries to quickly transport gases to and from the cells. Gases diffuse into the blood and are carried to and from the body cells.

Thin surface or thin wall: respiratory surfaces should have thin walls or thin surface area to maximize the diffusion. The alveoli in the lungs have thin squamous epithelium that enables gases to diffuse quickly between the alveoli and blood. According to Fick’s law, the rate of diffusion is proportional to:

Moist surfaces area: to enable gases to dissolve and pass through the solution. High diffusion deficit / concentration gradient: respiratory surface areas should have a high diffusion deficit / concentration gradient to ensure faster diffusion of respiratory gases.
Protection against injury and dry out: lungs and gills are protected by the bones and cartilage and mucus protects them from drying out

Self-Assessment 11.3
State the features common to all respiratory surfaces in living organisms
1. Explain how the following features of a respiratory surface helps gaseous exchange:
2. Short diffusion distance
a. Protection
b. A rich blood supply
c. Protection

11.3 Modifications of gaseous exchange surfaces to speed up the rate of gaseous exchange in different organims

Activity 11.2
Use appropriate laboratory equipment to extract gills in fish to show the gill filaments. Draw and label to show the parts observed.

a. Insects
The spiracles are openings of small tubes running into the insect’s trachea system that terminates into small fluid-filled tracheoles in which the gases are dissolved. The fluid is drawn into the muscle tissue during physical exercise, and this increases the surface area of air in contact with the cells.

Ventilation movements of the body during exercise may help this diffusion. The spiracles can be closed by valves and may be surrounded by tiny hairs. The later help to keep humidity around the opening to ensure that there is a lower concentration gradient of water vapour, and so less is lost from the insect by evaporation.

b. Fish and tadpoles
Fish and young amphibians (tadpoles) use gills for the gaseous exchange.
Gills have numerous folds that give them a very large surface area.
–– The rows of gill filaments have many protrusions called gill lamellae. These filaments help in the exchange of respiratory gases
–– They also have an efficient transport system within the lamellae which maintains the concentration gradient across the lamellae. The arrangement of water flowing passes the gills in the opposite direction to the blood (called counter-current flow) means that they can extract oxygen at 3 times the rate a human can.

c. Amphibians, Reptiles, Birds and Mammals

These have alveoli in their lungs. Air reaches the alveoli via a system of tubes (trachea, splitting into two bronchi - one for each lung - and numerous bronchioles):
–– Numerous alveoli - air sacs, providing a massive surface area over which gases can diffuse
–– Have a short diffusion distance between the alveolus and the blood because the lining of the lung and the capillary as they are only one cell thick.
–– The blood supply is extensive, which means that oxygen is carried away to the cells as soon as it has diffused into the blood.
–– Ventilation movements and out of the lungs due to changes in volume and press

- Ventilation movements also maintain the concentration gradients because a pressure

Activity11.3
You will need: Lungs of a sheep or pig, newspaper, plastic sheets, dissecting board, sharp scalpel, dissecting needles, scissors, dissecting tray, latex gloves, CPR mouth piece, soap to wash hands and surfaces.