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KCSE BIOLOGY
BIOLOGY ESSAY QUESTIONS WITH MARK SCHEMES
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
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swallowing or to be coughed out; reflex actions of coughing/sneezing/vomiting help
remove foreign materials from the respiratory tract/digestive 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
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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; 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
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