BIOLOGY (231/2) REVISION QUESTIONS (ESSAYS): EXPECTED RESPONSES
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;
Max. 20 mks
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 sensation; 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; thinwalled; with dense cytoplasm; for
primary and secondary growth; Max. 20 mks
3. Describe how the mammalian body protects itself against infections
Pathogenic microbes are found on the skin, respiratory tract, mouth, vagina and the intestinal tract;
the skin; has a keratinised and waterproof cornified outer layer; that provides a mechanical barrier
to microbes/prevents entry of microbes; sebaceous gland; produces sebum; which has antiseptic
properties; the respiratory tract; produce mucus secretions that trap dust; cilia sweep/waft/propel
the microbes to the pharynx for swallowing or to be coughed out; reflex actions of
coughing/sneezing/vomiting help remove foreign materials from the respiratory tract/digestive
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, tract; lysozymes/enzymes in saliva/nasal secretions/tears; digest walls of bacteria destroying them;
gastric secretions such as hydrochloric acid lowers the pH in the stomach killing micro-organisms;
clotting of blood; prevents entry of microbes after damage of blood vessels; phagocytosis; by
phagocytes engulf and destroy microbes and other foreign bodies; lymphocytes are stimulated to
produce antibodies; by proteins present in microbes protecting the body; antibodies destroy/kill
micro-organisms through various ways: agglutinins; bind to pathogens making them clump
together; killing them; Lysins; bind to pathogens and make them burst or disintegrate; opsonins;
bind to pathogens making them easily recognized hence be engulfed/destroyed by other
lymphocytes; anti-toxins; bind and neutralize toxins produced by micro-organisms; vagina is
acidic; hence making it not conducive for growth and reproduction of micro-organisms; Max: 20
mks
4. 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;
Max. 20 mks
5. 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; Max. 20 mks
6. 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;
Page 2 of 31
, lipase digests the remaining lipids (oil) into fatty acids and glycerol; which is absorbed through the
lacteals of the villi; Max. 20 mks
7. 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 pancreaset 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; Max. 20 mks
8. Outline and explain the various homeostatic functions of the liver in mammals
Deamination; process of removal of an amino group from an amino acid molecule; the process gets
rid of excess amino acids in the body; as the body is not able to store them; the amino group enters
the ornithine cycle; where it is combined with carbon (IV) oxide to form urea; which is excreted in
urine through the kidney; Heat production; many metabolic activities take place in the liver;
releasing heat energy; that is distributed by the blood to other parts of the body; this helps in
thermoregulation; Storage of vitamins and mineral salts; Vitamins A, B, D, E and K; are stored in
the liver; worn-out red blood cells, are broken down to yield iron; which is stored in the liver in
form of ferritin; this is used later in case of shortage; Formation of red blood cells; occurs in the
liver of the foetus; the liver also breaks down old/exhausted red blood cells; leading to formation
of more in the bone marrow to replace the worn-out cells; to enhance oxygen and carbon (IV) oxide
distribution; Regulation of blood sugar level; liver cells convert excess glucose into glycogen and
fats under the influence of insulin hormone; the stored glycogen is however converted back to
glucose; when glucose levels are low; by the liver cells; under the influence of glucagon hormone;
Regulation of plasma proteins; plasma proteins such as prothrombin and fibrinogen are
manufactured in the liver using the amino acids found in the liver; they play a major role in blood
clotting; that prevents excessive blood loss and infection at the injured area; other plasma proteins
produced by the liver such as serum and albumen; contribute to the maintenance of osmotic
pressure in the body; non-essential amino acids are also synthesized by the liver; for use by the
body; Storage of blood; the liver is highly vascularised; hence it is capable of holding a large
volume of blood when the blood vessels dilate during hot conditions; when the temperatures are
low, the blood vessels constrict under the influence of the endocrine and nervous systems; hence
less blood is stored in the liver; this contributes to thermoregulation; Detoxification; this is the
Page 3 of 31
, process where harmful compounds such as drugs and poisons; are converted to less toxic
compounds in the liver; toxicity is caused by medication, drugs and microorganisms; the toxic
compounds are later excreted in urine; detoxification prevents the accumulation of toxins in body
cells; which could lead to death or malfunctioning of the body cells; Max. 20 mks
Page 4 of 31
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;
Max. 20 mks
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 sensation; 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; thinwalled; with dense cytoplasm; for
primary and secondary growth; Max. 20 mks
3. Describe how the mammalian body protects itself against infections
Pathogenic microbes are found on the skin, respiratory tract, mouth, vagina and the intestinal tract;
the skin; has a keratinised and waterproof cornified outer layer; that provides a mechanical barrier
to microbes/prevents entry of microbes; sebaceous gland; produces sebum; which has antiseptic
properties; the respiratory tract; produce mucus secretions that trap dust; cilia sweep/waft/propel
the microbes to the pharynx for swallowing or to be coughed out; reflex actions of
coughing/sneezing/vomiting help remove foreign materials from the respiratory tract/digestive
Page 1 of 31
, tract; lysozymes/enzymes in saliva/nasal secretions/tears; digest walls of bacteria destroying them;
gastric secretions such as hydrochloric acid lowers the pH in the stomach killing micro-organisms;
clotting of blood; prevents entry of microbes after damage of blood vessels; phagocytosis; by
phagocytes engulf and destroy microbes and other foreign bodies; lymphocytes are stimulated to
produce antibodies; by proteins present in microbes protecting the body; antibodies destroy/kill
micro-organisms through various ways: agglutinins; bind to pathogens making them clump
together; killing them; Lysins; bind to pathogens and make them burst or disintegrate; opsonins;
bind to pathogens making them easily recognized hence be engulfed/destroyed by other
lymphocytes; anti-toxins; bind and neutralize toxins produced by micro-organisms; vagina is
acidic; hence making it not conducive for growth and reproduction of micro-organisms; Max: 20
mks
4. 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;
Max. 20 mks
5. 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; Max. 20 mks
6. 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;
Page 2 of 31
, lipase digests the remaining lipids (oil) into fatty acids and glycerol; which is absorbed through the
lacteals of the villi; Max. 20 mks
7. 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 pancreaset 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; Max. 20 mks
8. Outline and explain the various homeostatic functions of the liver in mammals
Deamination; process of removal of an amino group from an amino acid molecule; the process gets
rid of excess amino acids in the body; as the body is not able to store them; the amino group enters
the ornithine cycle; where it is combined with carbon (IV) oxide to form urea; which is excreted in
urine through the kidney; Heat production; many metabolic activities take place in the liver;
releasing heat energy; that is distributed by the blood to other parts of the body; this helps in
thermoregulation; Storage of vitamins and mineral salts; Vitamins A, B, D, E and K; are stored in
the liver; worn-out red blood cells, are broken down to yield iron; which is stored in the liver in
form of ferritin; this is used later in case of shortage; Formation of red blood cells; occurs in the
liver of the foetus; the liver also breaks down old/exhausted red blood cells; leading to formation
of more in the bone marrow to replace the worn-out cells; to enhance oxygen and carbon (IV) oxide
distribution; Regulation of blood sugar level; liver cells convert excess glucose into glycogen and
fats under the influence of insulin hormone; the stored glycogen is however converted back to
glucose; when glucose levels are low; by the liver cells; under the influence of glucagon hormone;
Regulation of plasma proteins; plasma proteins such as prothrombin and fibrinogen are
manufactured in the liver using the amino acids found in the liver; they play a major role in blood
clotting; that prevents excessive blood loss and infection at the injured area; other plasma proteins
produced by the liver such as serum and albumen; contribute to the maintenance of osmotic
pressure in the body; non-essential amino acids are also synthesized by the liver; for use by the
body; Storage of blood; the liver is highly vascularised; hence it is capable of holding a large
volume of blood when the blood vessels dilate during hot conditions; when the temperatures are
low, the blood vessels constrict under the influence of the endocrine and nervous systems; hence
less blood is stored in the liver; this contributes to thermoregulation; Detoxification; this is the
Page 3 of 31
, process where harmful compounds such as drugs and poisons; are converted to less toxic
compounds in the liver; toxicity is caused by medication, drugs and microorganisms; the toxic
compounds are later excreted in urine; detoxification prevents the accumulation of toxins in body
cells; which could lead to death or malfunctioning of the body cells; Max. 20 mks
Page 4 of 31
