Biology Examination — Questions and Complete Solutions
Questions
Question 1
(a) Explain the following terms:
i. Ovoviviparity (2½ marks)
ii. Moulting (2½ marks)
iii. Glands (2½ marks)
iv. Chiasmata (2½ marks)
(b) A child with blood group AB is a source of dispute between two contesting fathers: Father P, with blood group B, and Father Z, with blood group O. The mother of the child has blood group A. Using crossings, show how the blood groups of the child, disputing fathers, and mother can be used in resolving the dispute. (20 marks)
© Fill in the blank spaces:
i. The two types of cells in photoreceptors are a and b.
ii. c, d, and e are types of gaseous exchange found in the class Amphibia.
iii. The f gland is known to maintain hormonal balance in the body.
iv. The g eye defect can be corrected by use of a concave lens.
v. The h form the structural and functional unit of the i system that specializes in the transmission of nerve impulses.
vi. j is the main site of cellular respiration and is also involved in energy storage in a cell.
Question 2
Write short notes on the following:
a) Autonomic nervous system (10 marks)
b) Mouth-to-mouth resuscitation (10 marks)
Question 3
Outline ten (10) characteristics of the class Mammalia. (20 marks)
Question 4
a) Explain how low and high blood glucose levels are returned to normal. (15 marks)
b) Outline five (5) functions of connective tissues. (5 marks)
Question 5
With the aid of well-labeled diagrams, explain the process of conjugation in Paramecium. (20 marks)
Question 6
(a) Mention the characteristics of the following muscle cells:
i. Skeletal (5 marks)
ii. Cardiac (5 marks)
iii. Smooth (5 marks)
(b) Outline the functions of the mammalian skin. (5 marks)
Solutions
Question 1(a) — Definitions
i. Ovoviviparity
A mode of reproduction in which eggs are retained and hatched inside the mother’s body, with the embryo nourished by the egg yolk rather than directly via a placenta. The young are born live. It is intermediate between oviparity (egg-laying) and viviparity (live birth with placental nourishment). Examples include some sharks, snakes, and lizards.
ii. Moulting (ecdysis)
The periodic shedding of the exoskeleton in arthropods, or of feathers, skin, or hair in other animals, to allow growth and renewal. In insects and crustaceans, the rigid exoskeleton cannot grow, so it is shed and replaced with a new, larger one under the control of the hormone ecdysone; the animal is soft and vulnerable between moults. In reptiles, the outer layer of skin is shed periodically.
iii. Glands
Specialized organs or groups of cells that synthesize and secrete specific chemical substances, such as hormones, enzymes, mucus, or sweat. Exocrine glands have ducts carrying secretions to specific locations (e.g. salivary, sweat, and sebaceous glands), while endocrine glands are ductless and secrete hormones directly into the bloodstream (e.g. pituitary, thyroid, adrenal glands).
iv. Chiasmata
X-shaped points of contact between homologous chromosomes during prophase I of meiosis, where crossing over occurs. Non-sister chromatids break and exchange segments of genetic material at these points, producing recombination and increased genetic variation in offspring; the number and position of chiasmata vary and contribute to genetic diversity.
Question 1(b) — Blood group genetics / paternity dispute
Given: Child’s blood group AB; mother’s blood group A; Father P’s blood group B; Father Z’s blood group O.
| Individual | Blood Group | Possible Genotypes |
|---|---|---|
| Child | AB | I^A I^B (only possibility) |
| Mother | A | I^A I^A or I^A i |
| Father P | B | I^B I^B or I^B i |
| Father Z | O | ii (only possibility) |
Since the child is I^A I^B, one allele (I^A) must come from one parent and one allele (I^B) from the other. For the child to be AB, the mother must contribute I^A (so her genotype is I^A i), and the father must contribute I^B.
Cross: Mother (I^A i) × Father P (I^B i)
| I^B | i | |
|---|---|---|
| I^A | I^A I^B (AB) | I^A i (A) |
| i | I^B i (B) | ii (O) |
An AB child is possible from this cross.
Cross: Mother (I^A i) × Father Z (ii)
| i | i | |
|---|---|---|
| I^A | I^A i (A) | I^A i (A) |
| i | ii (O) | ii (O) |
Only blood groups A and O are possible from this cross; blood group AB is impossible.
Conclusion: Father P (blood group B) is the biological father of the AB child. Father Z (blood group O) cannot be, since a cross between him and the mother cannot produce an AB child. The dispute is resolved in favour of Father P.
Question 1© — Fill in the blanks
| Letter | Answer |
|---|---|
| a | Rods |
| b | Cones |
| c | Cutaneous respiration (skin) |
| d | Buccal (buccopharyngeal) |
| e | Pulmonary (lungs) |
| f | Pituitary (hypothalamus/pituitary) |
| g | Myopia (short-sightedness) |
| h | Neurons (neurones) |
| i | Nervous |
| j | Mitochondria |
Question 2
(a) Autonomic nervous system
The autonomic nervous system is the division of the peripheral nervous system that controls involuntary body functions such as heart rate, digestion, respiration rate, pupil dilation, glandular secretion, and blood vessel diameter. It has two subdivisions with largely opposing effects.
The sympathetic nervous system prepares the body for stressful or emergency situations. It originates from the thoracic and lumbar regions of the spinal cord and uses noradrenaline as its neurotransmitter. Its effects include increased heart rate, pupil dilation, inhibited digestion, dilated bronchioles, stimulated adrenaline release, and redirected blood flow to muscles.
The parasympathetic nervous system returns the body to a resting state after stress. It originates from the cranial nerves and sacral region of the spinal cord and uses acetylcholine as its neurotransmitter. Its effects include decreased heart rate, constricted pupils, stimulated digestion and peristalsis, constricted bronchioles, and promoted glandular secretion.
The ANS uses two-neuron pathways (preganglionic and postganglionic neurons) with a ganglion in between, controls smooth muscle, cardiac muscle, and glands, works alongside the endocrine system to maintain homeostasis, and is primarily controlled by the hypothalamus.
(b) Mouth-to-mouth resuscitation
An emergency first-aid procedure to restore breathing in a person who has stopped breathing but still has a pulse, forming part of cardiopulmonary resuscitation (CPR).
Procedure:
- Ensure the environment is safe for both rescuer and victim.
- Check responsiveness; call for emergency help if unresponsive.
- Lay the person flat on their back on a firm surface.
- Open the airway using the head-tilt chin-lift maneuver.
- Check for breathing for no more than 10 seconds.
- Pinch the victim’s nostrils shut.
- Take a normal breath, seal your mouth over the victim’s, and breathe out steadily for about 1 second, watching for the chest to rise.
- Remove your mouth and allow the chest to fall as air escapes.
- Give 2 rescue breaths, then check pulse; continue at about 12–20 breaths per minute for adults.
Exhaled air contains about 16–17% oxygen (compared to 21% in atmospheric air), which is sufficient to sustain life; the carbon dioxide in exhaled air can also stimulate the victim’s respiratory centre if it remains partially functional. When combined with chest compressions, the ratio used is 30 compressions to 2 rescue breaths.
Question 3 — Ten characteristics of class Mammalia
- Presence of mammary glands in females, producing milk to nourish offspring — the defining characteristic of the class.
- Body covered with hair or fur at some stage of life, providing insulation, camouflage, and sensory function.
- Warm-blooded (endothermic), maintaining a constant body temperature regardless of the environment.
- Viviparity in most species, with the embryo nourished via a placenta (except monotremes, which lay eggs).
- Highly developed brain with a large cerebral cortex, capable of complex behaviour, learning, and memory.
- Four-chambered heart, giving complete separation of oxygenated and deoxygenated blood.
- A diaphragm separating the thoracic and abdominal cavities, assisting breathing; unique to mammals.
- Heterodont, thecodont dentition — different tooth types (incisors, canines, premolars, molars) set in sockets.
- Three middle ear ossicles (malleus, incus, stapes), transmitting sound vibrations; unique to mammals.
- Extended parental care, with behavioural learning passed from parent to young.
Question 4
(a) Regulation of blood glucose levels
Blood glucose is normally maintained at approximately 80–120 mg per 100 cm³ of blood, regulated primarily by the islets of Langerhans in the pancreas through two antagonistic hormones.
When blood glucose is too high (hyperglycaemia), beta cells of the islets of Langerhans detect the rise and secrete insulin, which acts on liver and muscle cells to increase glucose uptake, convert excess glucose to glycogen (glycogenesis), promote conversion of glucose to fat (lipogenesis), and increase cellular respiration of glucose, bringing blood glucose back to normal.
When blood glucose is too low (hypoglycaemia), alpha cells detect the fall and secrete glucagon, which acts on the liver to convert stored glycogen back to glucose (glycogenolysis) and synthesize glucose from non-carbohydrate sources such as amino acids and fats (gluconeogenesis). Adrenaline from the adrenal medulla also promotes glycogenolysis during stress, raising blood glucose back to normal.
This is an example of negative feedback control, where the hormonal response opposes the change that triggered it, restoring homeostasis.
(b) Five functions of connective tissues
- Support and structural framework — provides mechanical support to organs and tissues, e.g. cartilage supporting the ear and trachea, bone supporting the body.
- Binding and connection — tendons connect muscles to bones, and ligaments connect bones to bones.
- Protection — bone protects the brain, spinal cord, and heart; adipose tissue cushions organs.
- Transport — blood, a fluid connective tissue, transports oxygen, nutrients, hormones, and waste.
- Storage — adipose tissue stores fat, bone stores calcium and phosphorus, and red bone marrow produces and stores blood cells.
Question 5 — Conjugation in Paramecium
Conjugation in Paramecium is a form of sexual reproduction involving the temporary union of two compatible mating-type individuals for the exchange of genetic material. It does not immediately produce new organisms but results in genetic recombination.
- Recognition and pairing: two compatible Paramecium cells attach at their oral grooves, forming a conjugation bridge.
- Micronuclear division: the macronucleus of each cell begins to disintegrate, while the micronucleus undergoes meiosis to produce four haploid micronuclei.
- Degeneration: three of the four haploid micronuclei degenerate, leaving one functional micronucleus in each conjugant.
- Mitotic division: the remaining haploid micronucleus divides by mitosis into a stationary (female) pronucleus and a migratory (male) pronucleus.
- Exchange: the migratory micronuclei are exchanged between the two conjugants through the cytoplasmic bridge.
- Fusion (karyogamy): in each conjugant, the received migratory nucleus fuses with the stationary nucleus, forming a diploid synkaryon.
- Separation: the two cells separate as ex-conjugants.
- Nuclear reorganization: the synkaryon divides mitotically several times, with some nuclei becoming new macronuclei and others new micronuclei.
- Cell division: the ex-conjugants may undergo binary fission, producing daughter cells with new genetic combinations.
Conjugation produces genetic variation through recombination and restores vitality to aging cell lines; it is a method of exchanging genes rather than increasing cell number. A diagram should show two Paramecium cells joined at the oral groove, meiosis of the micronuclei, exchange of migratory nuclei across the bridge, fusion, and separation.
Question 6
(a) Characteristics of muscle cell types
i. Skeletal muscle (striated/voluntary)
- Voluntary, under conscious control.
- Striated, showing alternating light and dark bands from the arrangement of actin and myosin filaments.
- Multinucleate, with many nuclei located at the periphery of each fibre.
- Long, cylindrical fibres, sometimes up to 30 cm.
- Contracts rapidly but fatigues quickly, suited to short bursts of powerful activity.
- Attached to bones by tendons; responsible for body movement and locomotion.
ii. Cardiac muscle
- Involuntary, contracting automatically.
- Striated, similar to skeletal muscle.
- Uninucleate, with one (occasionally two) centrally placed nucleus per cell.
- Branched, interconnected cells joined by intercalated discs, allowing coordinated contraction as a unit.
- Never fatigues, contracting rhythmically and continuously throughout life.
- Found only in the heart wall (myocardium), where it pumps blood.
iii. Smooth muscle (involuntary/visceral)
- Involuntary, controlled by the autonomic nervous system.
- Non-striated, lacking organized sarcomere structure.
- Uninucleate, with a single, centrally located, oval nucleus per cell.
- Spindle-shaped cells, tapering at both ends.
- Contracts slowly but sustained, resisting fatigue.
- Found in the walls of hollow organs, such as the gut, uterus, blood vessels, and bladder, controlling peristalsis and vasoconstriction.
(b) Functions of the mammalian skin
- Protection — a physical barrier against injury, pathogens, UV radiation, and chemical damage.
- Thermoregulation — regulates body temperature via sweating, vasodilation/vasoconstriction, and hair erection.
- Sensation — contains receptors for touch, pressure, pain, temperature, and vibration.
- Excretion — sweat glands excrete small amounts of urea, salts, and water.
- Synthesis of vitamin D — converts 7-dehydrocholesterol to vitamin D₃ upon UV exposure, aiding calcium absorption and bone development.
- Storage — the adipose layer in the dermis stores energy and provides insulation.