Question 1
(a) Explain the following terms:
i. Fatty acids
ii. Endocrine glands
iii. Cellular respiration
iv. Diploblastic organization
(b)
i. Using appropriate genetic symbols and showing your crossings, explain the possible blood groups of children whose father and mother are heterozygous with blood group A and blood group B respectively.
ii. Assuming these parents have non-identical twins, what is the probability that the twins will have blood group A? Show your crossings.
© Fill in the blank spaces:
i. a__, b__, c__, and d__ are different tastes which can be detected by taste neurons in humans.
ii. The arteries going from the right ventricle of the heart take blood to the e.
iii. Each replicated chromosome consists of two identical/sister f.
iv. The haploid sex gamete in males is known as g.
v. Blinking of the eyes is an example of h.
vi. The highly muscular pharynx of Ascaris is for i from the host.
vii. j is a major element in the synthesis of bones and teeth.
Question 2
(a) Define:
i. Reflex arc
ii. Reflex action
(b) Draw a large (8–9 cm) labeled diagram of a reflex arc and explain its components.
Question 3
(a) Draw a labeled diagram (8–9 cm) of the tracheal system of insects.
(b) Mention three (3) functions of each of the following in insects:
i. Antennae
ii. Cuticle
iii. Wings
iv. Abdomen
© List any four (4) reasons for locomotion in animals.
Question 4
(a) Explain the mechanism of perception of smell in man.
(b) Outline five (5) characteristics of the taxonomic class Arachnida.
Question 5
Write short notes on any four (4) of the following:
a) Smoking preservation
b) Photoreceptors
c) Albinism in man
d) Red blood cell
e) Factors affecting growth in animals
Question 6
In a tabular form, name ten (10) organelles of an animal cell and give one function of each.
Solutions
Question 1
(a) Definitions
i. Fatty acids
Long-chain organic (carboxylic) acids consisting of a hydrocarbon chain with a carboxyl group (–COOH) at one end, and the basic building blocks of lipids. They may be saturated (no double bonds, e.g. stearic acid) or unsaturated (one or more double bonds, e.g. oleic acid). They serve as a major energy source and are components of cell membranes.
ii. Endocrine glands
Ductless glands that secrete hormones directly into the bloodstream, which are transported to target organs to regulate specific physiological processes. Examples include the pituitary gland, thyroid gland, adrenal gland, pancreas (islets of Langerhans), and gonads.
iii. Cellular respiration
The biochemical process by which living cells break down organic molecules, primarily glucose, to release energy as ATP. Aerobic respiration (requiring oxygen) yields about 38 ATP per glucose molecule; anaerobic respiration (without oxygen) yields lactic acid or ethanol and only small amounts of ATP. It occurs in the cytoplasm and mitochondria.
iv. Diploblastic organization
The body plan of animals whose body wall is derived from only two embryonic germ layers: the ectoderm (outer layer, forming skin and nervous tissue) and the endoderm (inner layer, forming the gut lining), with no mesoderm. A gelatinous, non-cellular mesoglea lies between the two layers. Examples include phylum Cnidaria (jellyfish, Hydra, corals) and Porifera (sponges).
(b) Genetics — blood group crosses
Given: Father, heterozygous blood group A (I^A i); mother, heterozygous blood group B (I^B i).
| I^A | i | |
|---|---|---|
| I^B | I^A I^B | I^B i |
| i | I^A i | ii |
| Genotype | Blood Group | Ratio |
|---|---|---|
| I^A I^B | AB | 1/4 (25%) |
| I^B i | B | 1/4 (25%) |
| I^A i | A | 1/4 (25%) |
| ii | O | 1/4 (25%) |
Possible blood groups of children: A, B, AB, and O.
(b)(ii) Probability that non-identical twins both have blood group A
Probability of one child having blood group A = 1/4. Since non-identical (dizygotic) twins are conceived independently, the probability that both have blood group A = 1/4 × 1/4 = 1/16.
© Fill in the blanks
| Letter | Answer |
|---|---|
| a, b, c, d | Sweet, sour, salty, bitter |
| e | Lungs (via the pulmonary artery) |
| f | Chromatids |
| g | Spermatozoon/sperm |
| h | Reflex action |
| i | Obtaining food/nutrients (sucking/ingesting food) |
| j | Calcium |
Question 2
(a) Definitions
i. Reflex arc
The neural pathway taken by a nerve impulse during a reflex action — the simplest functional unit of the nervous system, consisting of: receptor → sensory neurone → relay/association neurone (in the CNS) → motor neurone → effector.
ii. Reflex action
An automatic, involuntary, rapid, stereotyped response to a stimulus, occurring without direct involvement of conscious thought and coordinated by the spinal cord. Examples include the knee-jerk reflex, withdrawal from a hot object, and blinking.
(b) Components of a reflex arc
The pathway runs: stimulus → receptor → sensory neurone → spinal cord (relay/interneurone) → motor neurone → effector → response.
- Receptor — detects the stimulus (e.g. pain, heat) and converts it into a nerve impulse; example: skin receptor.
- Sensory (afferent) neurone — carries the impulse from the receptor to the spinal cord; has its cell body in the dorsal root ganglion.
- Relay/association neurone (interneurone) — located in the grey matter of the spinal cord; connects sensory and motor neurones and processes the impulse.
- Motor (efferent) neurone — carries the impulse from the spinal cord to the effector, exiting via the ventral root.
- Effector — the muscle or gland that produces the response, e.g. a muscle contracting to withdraw a limb.
- Synapse — the junction between neurones, where chemical neurotransmitters (e.g. acetylcholine) transmit the impulse.
Question 3
(a) Tracheal system of insects
Key structures to label: spiracles (openings on the body surface for gas exchange, with a valve to open/close), tracheae (main air tubes reinforced with taenidia, spiral chitin rings, to prevent collapse), tracheoles (fine, non-chitinized branches reaching individual cells), air sacs (enlarged tracheal sacs that store air and aid ventilation), and body cells (where oxygen is delivered and carbon dioxide collected).
(b) Functions of insect structures
i. Antennae
- Detection of smell/odour for locating food, mates, or predators.
- Detection of touch and mechanical vibrations.
- Detection of humidity and temperature changes.
ii. Cuticle
- Protection of internal organs from mechanical injury and desiccation.
- Prevention of water loss due to the waxy epicuticle layer.
- Structural support, serving as an exoskeleton for muscle attachment.
iii. Wings
- Flight, for locomotion through the air.
- Escape from predators.
- Finding food and mates over long distances.
iv. Abdomen
- Houses vital organs, including the digestive system, Malpighian tubules, and reproductive organs.
- Site of gas exchange, with spiracles for tracheal breathing.
- Reproduction, housing gonads and, in females, the ovipositor for egg laying.
© Four reasons for locomotion in animals
- Search for food and nutrients.
- Escape from predators or danger.
- Search for mates.
- Migration or seeking favourable climatic and breeding conditions.
Question 4
(a) Mechanism of perception of smell in man
- Odorous (volatile) chemical substances dissolve in the mucus lining the nasal epithelium.
- The dissolved chemicals bind to chemoreceptors on the cilia of olfactory receptor cells in the olfactory epithelium.
- Binding triggers a nerve impulse in the receptor cells.
- Impulses travel along the olfactory nerve (Cranial Nerve I) through the cribriform plate of the ethmoid bone.
- The impulses reach the olfactory bulb, where initial processing occurs.
- Signals are relayed via the olfactory tract to the olfactory cortex, where the smell is interpreted and identified.
- The limbic system links smell to memory and emotion.
(b) Five characteristics of class Arachnida
- Body divided into two regions — the cephalothorax (prosoma) and abdomen (opisthosoma) — with no distinct head.
- Four pairs of walking legs (eight legs total) attached to the cephalothorax; no antennae.
- Two pairs of appendages on the cephalothorax: chelicerae (for feeding/defense) and pedipalps (for sensing/reproduction).
- Respiration by book lungs, tracheae, or both.
- Excretion by Malpighian tubules and/or coxal glands; mostly terrestrial.
Question 5 — Short notes (any four)
(a) Smoking preservation
A method of food preservation, commonly for fish and meat, involving exposure to smoke from burning wood. Heat removes moisture, inhibiting microbial growth; antimicrobial chemicals in smoke, such as phenols and aldehydes, kill or inhibit bacteria and fungi; and a protective surface layer forms that reduces recontamination. It extends shelf life and imparts flavour, and is widely used in West Africa for preserving fish such as smoked catfish.
(b) Photoreceptors
Specialized sensory cells in the retina that respond to light and convert it into nerve impulses. Rods, more numerous, are located mainly at the periphery of the retina, function in low light, detect only shades of grey, and contain rhodopsin. Cones, fewer in number and concentrated at the fovea centralis, function in bright light, provide colour vision and fine detail, and contain pigments sensitive to red, green, or blue wavelengths. Impulses travel via the optic nerve to the visual cortex.
© Albinism in man
A genetic disorder marked by absence or reduction of melanin, caused by a mutation in the gene encoding tyrosinase, the enzyme needed to convert tyrosine into melanin. It is inherited as an autosomal recessive trait (genotype aa). Features include very light skin and hair, pink or pale eyes, poor eyesight, and a high risk of sunburn and skin cancer due to reduced UV protection. A cross of Aa × Aa gives a 1:2:1 ratio (AA : Aa : aa), meaning a 25% chance of albino offspring.
(d) Red blood cell (erythrocyte)
The most abundant blood cell, produced in the red bone marrow by erythropoiesis. It has a biconcave disc shape that increases surface area for gas exchange, and mature mammalian red blood cells are anucleate, maximizing space for haemoglobin, which binds oxygen for transport from lungs to tissues and helps carry carbon dioxide back to the lungs. Lifespan is about 120 days, with old cells destroyed in the spleen and liver; diameter is about 7–8 micrometres, and normal count is roughly 4.5–5.5 million per mm³ of blood.
(e) Factors affecting growth in animals
- Genetics/heredity — genes determine the maximum potential size and growth rate.
- Nutrition — adequate protein, carbohydrate, fat, vitamin, and mineral intake is essential; malnutrition stunts growth.
- Hormones — growth hormone, thyroid hormones, insulin, and sex hormones regulate growth.
- Temperature — affects metabolic rate; extremes inhibit growth, especially in ectotherms.
- Disease and health status — chronic illness, parasites, and infections divert energy from growth.
- Exercise/physical activity — stimulates muscle and bone growth through mechanical stress.
Question 6 — Animal cell organelles and functions
| # | Organelle | Function |
|---|---|---|
| 1 | Nucleus | Contains genetic material (DNA); controls cell activities and heredity |
| 2 | Mitochondria | Site of aerobic cellular respiration; produces ATP |
| 3 | Ribosomes | Site of protein synthesis |
| 4 | Rough endoplasmic reticulum (RER) | Synthesis and transport of proteins; studded with ribosomes |
| 5 | Smooth endoplasmic reticulum (SER) | Synthesis of lipids and steroids; detoxification of drugs |
| 6 | Golgi apparatus | Modifies, packages, and dispatches proteins and lipids |
| 7 | Lysosomes | Contain digestive enzymes; break down worn-out organelles and foreign particles |
| 8 | Centrioles | Form spindle fibres during mitosis and meiosis |
| 9 | Cell (plasma) membrane | Regulates entry and exit of substances via selective permeability |
| 10 | Vacuoles | Temporary storage of water, food, or waste materials |