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1.Explain the various ways in which a typical cell is adapted to its functions

Has a cell membrane; with pores; that regulates substances entering and leaving the cell;

Cytoplasm; contain sugars and salts; for maintaining its osmotic pressure; also has a liquid medium; for all biochemical reactions;

Nucleus; contain chromosomes having hereditary material; and controls all the activities of the cell;

Ribosomes; are sites for protein synthesis;

Golgi bodies/apparatus; for secretion of hormones and enzymes; formation of lysosomes;

Lysosomes; contain lytic enzymes for breaking down worn-out organelles;

Secretory vesicles; formed from golgi apparatus for secreting substances;

Smooth endoplasmic reticulum; synthesizes and transports lipids;

Rough endoplasmic reticulum; transport proteins;

Nucleolus; controls the activities of the nucleus; produces ribosomes;

Mitochondria; form sites for energy production;

Centrioles; formation of cilia and flagella; forms spindle fibres used in cell division;

Plant sap vacuoles; store salts and other dissolved substances; controls osmotic pressure and turgidity of cells;

Food vacuoles; involved in digestion of engulfed food;

Chloroplasts; form sites for photosynthesis in plant cells.

2.Explain how the various specialized cells are modified to carry out their functions in plants and animals

Animal cells:

Sperm cell;

Has acrosome containing lytic enzymes; that digest the egg membranes for penetration during fertilization;

Has a long tail; containing numerous mitochondria; to generate maximum energy for propulsion/swimming in the vaginal fluid after ejaculation;

Red blood cells;

Are flattened, circular/spherical biconcave in shape; to increase the surface area for packaging of haemoglobin;

Has haemoglobin; that combines with respiratory gases; for transport to and from body tissues;

White blood cells;

Are amoeboid in shape hence able to change shape; to engulf pathogens through phagocytosis;

Lymphocytes produce antibodies to fight pathogens;

Nerve cell;

Has extensions/dentrites; to receive and send information for sensatio ;Ciliated epithelial cells;

Have cilia for propulsion of mucus that traps dust and micro-organisms in the respiratory tract;

Muscle cells;

Elongated, striated and contractile; to bring about movement;

Plant cells:

Guard cells;

Bean-shaped; to regulate the size of the stomata allowing gaseous exchange; and control water loss;

Has chloroplasts with chlorophyll; for photosynthesis;

Root hair cell;

Elongated; thin-walled; with dense cytoplasm for absorption of water and mineral salts;

Epidermal cell;

Thin; for protection of inner tissues from mechanical and micro-organism attack;

Palisade cell;

Contains numerous chloroplasts with chlorophyll; for photosynthesis; elongated; to increase surface area for trapping maximum amounts of light energy;

Meristematic cell;

Thin-walled; with dense cytoplasm; for primary and secondary growth;



3.How are the leaves of higher plants adapted to their functions

Broad and flattened lamina; to increase surface area; for absorption of light;

Thin blade; to reduce distance for diffusion of gases and penetration of light waves;

Transparent epidermis and cuticle; to allow light to penetrate to tissues;

Cuticle layer absent on stomata; to allow for gaseous exchange;

One-cell thick epidermal layer; to reduce the distance over which sunlight penetrates;

Palisade cells have numerous chloroplasts containing chlorophyll; to trap maximum amounts of light energy;

Have stomata on the epidermis; to allow for gaseous exchange; and control of water loss through transpiration;

Palisade layer have elongated cells located at right angles to the leaf surface; for maximum absorption of light energy;

Spongy mesophyll consists of spherical and loosely-packed cells; to create air spaces; which communicate with the atmosphere through stomata; for purposes of gaseous exchange and control of water loss;

Veins have conducting tissues: xylem; for movement of water and dissolved mineral salts; phloem; for translocation of manufactured food;

4.Explain how the various teeth adapt mammals for nutrition

Incisor; sharp; chisel-shaped; for biting; and cutting food; one root for support in the jaw bone;

Canines; long; sharp; pointed; for holding prey; piercing; and tearing flesh from prey; single root; for support in the jaw bone;

Premolars; large/wide; to increase surface area for grinding food; highly cusped; to increase surface area for grinding food; two roots; for firm support/anchorage in the jaw bone;

Molars; large/wide; to increase surface area for grinding food; highly cusped; to increase surface area for grinding food;

5.Describe what happens to a meal of oily beans and maize from the time of ingestion up to the time of absorption

In the mouth;

Starch in maize; is digested by salivary amylase/ptyalin/diastase into maltose;Food is chewed and mixed by teeth and the tongue; rolled into boluses by peristalsis; it enters into the stomach via the cardiac sphincter;

In the stomach,

Gastric juice containing pepsinogen that is activated to pepsin; digests proteins in the beans; into shorter peptides; food is churned and allowed into the duodenum; via the pyloric sphincter muscle;

In the duodenum;

Bile juice secreted by the gall bladder; emulsifies the oils in the beans into tiny oil droplets; pancreatic juice;secreted by the pancrease; contains pancreatic amylase; that digests starch to maltose; pancreatic lipase; that digests the oil in the beans to fatty acids and glycerol; trypsin; digests proteins into shorter peptides; food enters into the ileum; where succus entericus is secreted; it contains maltase enzyme; that digests the maltose into glucose; that is absorbed; peptidase; digests peptides into amino acids; lipase digests the remaining lipids (oil) into fatty acids and glycerol; which is absorbed through the lacteals of the villi;

6.How are the small intestines in mammals adapted to their functions?

-Small intestines consists of the duodenum and the ileum; most digestion of food occurs in the duodenum;

-Bile from the gall bladder of the liver is secreted through the bile ducts; and it is used to emulsify fats/break fat particles into tiny droplets; to increase the surface area for enzyme action;

-The pancrease secretes pancreatic juice to the duodenum; the juice contains pancreatic amylase; that helps to breakdown the remaining starch into maltose; trypsin; (that is secreted in its inactive form, trypsinogen, and activated by enterokinase enzyme); hydrolyses proteins into shorter peptides;

-Pancreatic lipase; converts lipids into fatty acids and glycerol; sodium hydrogen carbonate is also produced; to neutralize the acidic chyme from the stomach; and provide a suitable alkaline medium for pancreatic and other intestinal enzymes;

-The ileum is long; and narrow; to increase the surface area for complete digestion of food; and maximum absorption of digested food; highly-coiled; to reduce speed of food flow; for maximum digestion; and absorption;

-Presence of villi; and microvilli; to increase surface area; for maximum absorption;

-Dense network of capillaries; to transport blood; for efficient transport of absorbed food;

-Presence of lacteals in the villi; for absorption of fatty acids and glycerol molecules;

-Presence of enzymes: Lipase; for digestion of lipids into fatty acids and glycerol; maltase; for digestion of maltose to glucose molecules; peptidase; for breakdown of peptides into amino acids; sucrase; for digestion of sucrose into glucose and fructose; lactase; for digestion of lactose into glucose and galactose;

-Goblet cells; produce mucus; to lubricate the walls of the ileum; for smooth flow of food; coats the walls of ileum to prevent digestion by peptidase enzyme;

7.Explain why the following conditions are necessary for photosynthesis

a. Carbon (IV) Oxide

Required in the dark stage of photosynthesis; it combines with the hydrogen ion from the light stage; to form glucose, proteins and lipids; low concentrations reduces the rate of production of energy and food; while high concentrations leads to an increase in the amount of energy and food formed;

b. Light

It is used to break down water molecules (through photolysis); into hydrogen ions, oxygen and energy;the energy and hydrogen ions formed are used in the dark stage;

c. Chlorophyll

Green pigment that traps light energy from the sun; that is used in photolysis of water molecules;

d. Suitable temperature and pH

Temperature affects the enzymes involved in photosynthesis; suitable/optimum temperatures activate enzymes; for maximum production of food; while extremely low temperatures inactivate enzymes;leading to less or no production of food; high temperatures denature enzymes; stopping the process of photosynthesis; photosynthetic enzymes work well in low pH; so the rate is high; while higher pH reduces enzyme activity; lowering the rate of photosynthesis;

e. Water

Forms a medium for the chemical reactions; it is split to yield hydrogen ions, oxygen and energy for use in the dark stage; solvent for the materials used in photosynthesis;



8(a.)What is digestion?

Digestion is (mechanical and chemical) the process by which large complex food molecules; are broken down into soluble molecules (for absorption across intestinal wall to bloodstream);

b. What is the importance of a balance diet in human nutrition?

A balanced diet consists of all the food types in their right proportions; it includes proteins,carbohydrates, minerals, lipids, water, vitamins and roughage;

Proteins; used for growth and repair of worn out tissues; provide energy incase of acute shortage of carbohydrates/starvation; bind and transport specific molecules from one part of the body to another;structural proteins support tissues in the body e.g. bone and cartilage tissues; act as metabolic regulators such as enzymes and hormones;

Carbohydrates; used to produce energy/store energy;

Lipids produce energy; form of storage of energy; insulate the body; major structural components of the cell membrane; when oxidised, it provides metabolic water;

Vitamins; defense against infections; form coenzymes which activate enzymes;

Water; a universal solvent; medium for chemical reactions; used as coolant because of its high specific heat capacity; maintains the shape of cells; hydrolysis of many substances; transport medium in the body;

Mineral salts; formation of teeth and bones; formation of hormones (e.g. thyroxine); formation of blood; maintenance of osmotic pressure of body fluid; transmission of nerve impulses;

Roughage; makes food to be bulk; promotes peristalsis; and absorption of water in the large intestines; induces mucus production;

9. Explain the factors that affect enzyme activity

Temperature; enzymes are protein in nature; and hence sensitive to temperature changes; as temperature increases, enzyme activity also increases until optimum/maximum; above this optimum the reaction decreases sharply; due to the destruction of the enzyme structure/become denatured; making the enzyme ineffective/nonfunctional; most enzymes have optimum temperature of between 35oC and 40oC; when temperature decreases, the rate of enzyme reaction decreases as the enzyme becomes inactivated;

pH/acidity or alkalinity; most enzymes have optimum pH of close to 7/neutral which is the intracellular pH;however some enzymes work best in an alkaline medium while others work best in an acidic medium/condition; as the pH exceeds optimum, the enzyme activity decreases; extreme acidity or alkalinity denatures most enzymes;

Substrate concentration and enzyme concentration; enzyme reaction increases with increase in substrate concentration; up to a certain level where further increase in substrate concentration does not increase the rate of enzyme reaction; this is because when substrate concentration is increased, all the active sites of the enzyme are occupied; however, when the enzyme molecules are increased, there is a proportional increase in the maximum rate of enzyme action; enzymes are however required in small amounts hence; they speed up the rate of biochemical reactions without altering the equilibrium;

Enzyme cofactors/coenzymes; these are non-proteinous substances which activate the enzymes; most enzymes will not work without them; examples of cofactors are metallic ions such as iron, magnesium, zinc,copper and also vitamins as enzyme coenzymes; these substances are required in small amounts and areused repeatedly/can be recycled;

Enzyme inhibitors; these are substances that inhibit enzyme action by competing with the normal substrate for the active sites; there are two types: competitive and non-competitive; competitive inhibitors have no permanent effect on the enzyme action; while non-competitive inhibitors combine permanently with theenzyme molecules thus distorting or blocking the active sites permanently; examples of these inhibitors include cyanides, mercury, silver; inhibition can be reduced by reducing the concentration of the inhibitors; or by increasing the substrate concentration;