Questions
1(a) Explain the following terms:
i. Colour blindness
ii. Co-dominance
iii. Co-enzymes
iv. Heterogamic sex
(b) Assuming uniform colour © is dominant over spotted © in cattle. When a cross is made between a pure breed (homozygous) black bull (BBCC) with a white spotted cow (bbcc):
i. Use a Punnett diagram to show the result of the F₁ generation.
ii. What will be the phenotype of the calves in the F₁ generation?
iii. Show the types and ratio of offspring possible when two of the F₁ generation are mated.
iv. Name all the new combinations that have arisen from the cross above (1b iii).
© Fill in the blank spaces. Spellings of one-word answers and scientific names must be correct to score:
i. A nucleotide has __________, __________ and __________ components.
ii. Sucrose is digested to __________ and __________.
iii. The “bleeders’ disease” is known as __________.
v. A condition in which a gene fails to express itself in the presence of a dominant allele is __________.
vi. The scientific name of the giant African land snail is __________.
vii. Urine is approximately 95% __________, 2% __________, 1% sodium chloride, and other smaller amounts of nitrogenous compounds and mineral salts.
2. Give four adaptations of the following vertebrate taxa:
i. Proboscidea
ii. Pythonidae
iii. Chamaeleonidae
iv. Chiroptera
3.
a) Outline fifteen (15) characteristics of the phylum Arthropoda.
b) List any five (5) economic importance of Protozoa.
4.
a) Make a large (8–9 cm) diagram of the lateral view of a bony fish.
b) Mention the adaptations of a bony fish for efficient movement in water.
5. Write short notes on any four (4) of the following:
a) Osmoregulation
b) Short-sightedness
c) Involuntary/reflex action
d) Economic importance of phylum Annelida
e) Gene pool
6.
a) Enumerate any six (6) primary functions of the liver.
b) Write notes on:
i. Closed circulation
ii. Open circulation
Complete Solutions
Question 1(a) — Explanation of terms
i. Colour blindness
A sex-linked recessive genetic condition in which a person cannot distinguish certain colours, most commonly red and green. It results from a defective gene on the X chromosome. It is more common in males (XᶜY) than females (XᶜXᶜ) because males need only one defective allele to be affected, while females need two; females are usually carriers (XᶜX).
ii. Co-dominance
A form of inheritance in which both alleles of a gene are equally expressed in the phenotype of a heterozygous individual, with neither dominant nor recessive over the other. Example: the AB blood group, where both Iᴬ and Iᴮ alleles are fully expressed.
iii. Co-enzymes
Non-protein organic molecules that bind to an enzyme (apoenzyme) to form an active complex called a holoenzyme. They assist enzymes in catalysing reactions by carrying electrons, atoms, or chemical groups. Examples: NAD⁺, FAD, and Coenzyme A, many derived from B-complex vitamins.
iv. Heterogamic sex
The sex that produces two different types of gametes, one carrying an X chromosome and one a Y chromosome. In humans and most mammals, the male (XY) is the heterogamic sex; in birds and some insects, the female is heterogamic.
Question 1(b) — Genetics cross
Given: Uniform colour © dominant over spotted ©; black (B) dominant over white (b). Black bull = BBCC; white spotted cow = bbcc.
i. Punnett diagram — F₁ generation
Black bull gametes: BC. White spotted cow gametes: bc.
| BC | |
|---|---|
| bc | BbCc |
All F₁ offspring = BbCc.
ii. Phenotype of F₁ calves
Since B is dominant over b and C is dominant over c, all F₁ calves (BbCc) are Black and Uniform coloured — 100% Black Uniform.
iii. F₁ × F₁ cross (BbCc × BbCc)
Gametes of BbCc: BC, Bc, bC, bc.
| BC | Bc | bC | bc | |
|---|---|---|---|---|
| BC | BBCC | BBCc | BbCC | BbCc |
| Bc | BBCc | BBcc | BbCc | Bbcc |
| bC | BbCC | BbCc | bbCC | bbCc |
| bc | BbCc | Bbcc | bbCc | bbcc |
| Phenotype | Genotypes | Number | Ratio |
|---|---|---|---|
| Black Uniform | B_C_ | 9 | 9 |
| Black Spotted | B_cc | 3 | 3 |
| White Uniform | bbC_ | 3 | 3 |
| White Spotted | bbcc | 1 | 1 |
Ratio = 9 Black Uniform : 3 Black Spotted : 3 White Uniform : 1 White Spotted.
iv. New combinations from the cross
The parental phenotypes were Black Uniform and White Spotted. The new (recombinant) combinations arising in the F₂ generation are:
- Black Spotted (B_cc)
- White Uniform (bbC_)
Question 1© — Fill in the blanks
i. A nucleotide has a phosphate group, a pentose sugar, and a nitrogenous base.
ii. Sucrose is digested to glucose and fructose.
iii. The “bleeders’ disease” is known as haemophilia.
v. A condition in which a gene fails to express itself in the presence of a dominant allele is epistasis (recessiveness).
vi. The scientific name of the giant African land snail is Achatina achatina.
vii. Urine is approximately 95% water, 2% urea, and 1% sodium chloride, with smaller amounts of other nitrogenous compounds and mineral salts.
Question 2 — Four adaptations of vertebrate taxa
i. Proboscidea (elephants)
- Elongated trunk (proboscis), a muscular fusion of nose and upper lip, used for grasping food, drinking, and social interaction.
- Large, pillar-like legs with dense, near-vertical bones to support enormous body weight.
- Large, fan-shaped, blood-vessel-rich ears used for thermoregulation.
- Tusks (modified upper incisors) used for digging, stripping bark, and defense.
ii. Pythonidae (pythons)
- Flexible, ligament-joined jaws allowing them to swallow prey larger than their head diameter.
- Vestigial pelvic girdle and hind-limb remnants (pelvic spurs) as evidence of limbed ancestry.
- Heat-sensitive labial pit organs that detect infrared radiation from warm-blooded prey.
- Muscular, scale-covered body enabling constriction of prey; scales reduce water loss and aid movement.
iii. Chamaeleonidae (chameleons)
- Zygodactyl feet with toes fused in opposing groups for firm grip on branches.
- Chromatophore-containing skin enabling rapid colour change for camouflage, communication, and thermoregulation.
- Long, projectile tongue that can extend up to 1.5 times body length to catch insects.
- Independently mobile eyes that rotate and focus separately, giving near-360° vision.
iv. Chiroptera (bats)
- Modified forelimbs with elongated finger bones supporting a wing membrane (patagium) for true, sustained flight.
- Echolocation: emission of ultrasonic sounds and interpretation of returning echoes for navigation and hunting.
- Roosting posture (hanging upside down) enabled by tendons that lock without muscle effort, allowing quick take-off.
- Nocturnal adaptations, including large eyes or well-developed hearing, and torpor to conserve energy during the day.
Question 3
a) Fifteen characteristics of phylum Arthropoda
- Segmented body divided into distinct regions (head, thorax, abdomen).
- Bilaterally symmetrical body plan.
- Exoskeleton made of chitin, providing protection and support.
- Periodic moulting (ecdysis) to allow growth.
- Jointed appendages used for locomotion, feeding, and sensory functions.
- Triploblastic — three germ layers (ectoderm, mesoderm, endoderm).
- Coelomate, with a true, though reduced, body cavity.
- Open circulatory system with a dorsal heart and haemocoel.
- Ventral nerve cord with a dorsal brain (cerebral ganglia).
- Compound eyes and simple eyes (ocelli) for vision.
- Specialized mouthparts adapted for different feeding methods.
- Respiration varies: gills (crustaceans), tracheae (insects), book lungs (arachnids).
- Excretion by Malpighian tubules (insects) or green glands (crustaceans).
- Separate sexes (dioecious); mostly sexual reproduction, with some parthenogenesis.
- Well-developed sensory organs, including antennae, statocysts, and proprioceptors.
b) Five economic importance of Protozoa
- Disease causation: Plasmodium causes malaria, Trypanosoma causes sleeping sickness, and Entamoeba causes amoebic dysentery, leading to economic losses through medical costs and reduced productivity.
- Soil fertility: free-living soil protozoa feed on bacteria, regulating populations and releasing nutrients such as nitrogen.
- Food chain: ciliates and flagellates are primary consumers of bacteria and algae, supporting fish and other aquatic organisms.
- Indicator organisms: certain protozoa serve as bioindicators of water quality and pollution.
- Research and medicine: protozoa are used as model organisms in cell biology and genetics, aiding development of antiparasitic drugs.
Question 4
a) Diagram — lateral view of a bony fish
A clearly labeled 8–9 cm diagram should be drawn showing the following structures: mouth, eye, operculum (gill cover), lateral line, dorsal fin, pectoral fin, pelvic fin, anal fin, caudal fin, scales, and nostril.
b) Adaptations of a bony fish for efficient movement in water
- Streamlined (fusiform) body shape, reducing water resistance.
- Fins: dorsal and anal fins provide stability; pectoral and pelvic fins control steering and vertical movement; the caudal fin provides propulsive thrust.
- Mucus-covered, overlapping scales reduce friction with water.
- Swim bladder regulates buoyancy, allowing the fish to remain at a given depth without expending energy.
- Lateral line system detects pressure changes and water currents, aiding orientation.
- Powerful trunk and tail muscles (myotomes) arranged in W-shaped blocks generate undulating movements for propulsion.
- Flexible vertebral column allows the side-to-side body undulation needed for swimming.
Question 5 — Short notes on any four
a) Osmoregulation
The physiological process by which organisms regulate the concentration of water and dissolved solutes in body fluids to maintain homeostasis. In humans this is carried out mainly by the kidneys, which filter blood and produce urine of variable concentration. The hypothalamus monitors blood osmotic pressure and triggers release of antidiuretic hormone (ADH) from the posterior pituitary to increase water reabsorption when the body is dehydrated.
b) Short-sightedness (myopia)
A defect of vision in which near objects are seen clearly but distant objects appear blurred. It occurs when the eyeball is too long or the cornea/lens too curved, causing light from distant objects to focus in front of the retina rather than on it. It is corrected with a concave (diverging) lens, which pushes the focal point back onto the retina.
c) Involuntary/reflex action
A rapid, automatic, unconscious response to a stimulus that does not require direct brain involvement, coordinated through the spinal cord via a reflex arc: receptor → sensory neuron → relay neuron (spinal cord) → motor neuron → effector. Examples include the knee-jerk reflex, withdrawal from a hot object, and blinking. Reflex actions protect the body and allow rapid responses without the delay of conscious thought.
d) Economic importance of phylum Annelida
- Soil aeration and fertility: earthworms burrow through soil, improving aeration, drainage, and organic matter mixing.
- Food: some polychaetes and earthworms are eaten by humans in certain cultures and used as fish bait.
- Indicators of soil health: earthworm population density is used as a bioindicator of soil quality.
- Medicine: leeches are used in hirudotherapy; their saliva contains hirudin, an anticoagulant used in microsurgery.
- Ecological role: annelids serve as prey for birds, fish, and other animals within food chains.
e) Gene pool
The total collection of all alleles present in a breeding population at a given time, representing the population’s available genetic diversity. A large gene pool indicates high genetic diversity, making a population more adaptable and less susceptible to extinction, while a small gene pool (as in inbreeding) leads to reduced variation and greater risk of recessive disorders and extinction.
Question 6
a) Six primary functions of the liver
- Bile production: produces bile, stored in the gallbladder, which emulsifies fats to aid digestion and absorption.
- Detoxification: breaks down and neutralizes toxic substances such as alcohol, drugs, and ammonia.
- Deamination: removes the amino group from excess amino acids, converting it to ammonia and then urea (via the ornithine cycle) for excretion by the kidneys.
- Glycogen storage and regulation: converts excess glucose to glycogen for storage and breaks it down when blood sugar is low, maintaining glucose homeostasis.
- Plasma protein synthesis: produces blood proteins including albumin, fibrinogen, and globulins.
- Thermoregulation: generates heat as a by-product of its high metabolic activity, helping maintain body temperature.
(Other functions include fat metabolism, storage of vitamins A, D, and B₁₂, iron storage, and destruction of red blood cells.)
b) Notes on circulation types
i. Closed circulation
Blood remains enclosed within blood vessels (arteries, veins, capillaries) throughout its circuit and never directly bathes tissues; exchange occurs by diffusion through capillary walls. It allows higher blood pressure and faster, more efficient delivery of oxygen and nutrients. Found in annelids, echinoderms, and vertebrates. Example: the human circulatory system, where blood flows heart → arteries → capillaries → veins → heart.
ii. Open circulation
Blood (haemolymph) is not always enclosed in vessels but flows into open body cavities called haemocoels, directly bathing organs and tissues. The heart pumps haemolymph into arteries that open into the haemocoel, and it returns to the heart through pores called ostia. It operates at lower pressure and is less efficient than closed circulation. Found in most arthropods and molluscs. Example: the cockroach, where haemolymph flows tubular heart → arteries → haemocoel → ostia → heart.