Questions
1. (a) Explain the following:
i) Ribosomes
ii) Economic importance of earthworms
iii) The recovery position in first aid
iv) Feeding in Amoeba
(b) Assuming grey fur (G) is dominant over white fur (g) in rabbits, and long ears (L) is dominant over short ears (l). When a cross is made between a pure breed (homozygous) grey, long-eared buck (GGLL) with a white, short-eared doe (ggll):
i) Use a Punnett diagram to show the result of the F₁ generation.
ii) What will be the phenotype of the offspring 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).
(c) Fill in the blank spaces.
i) ______ is the connective tissue that joins muscle to bone.
ii) The powerhouse of the cell, releasing energy through respiration, is the ______.
iii) The type of respiration that occurs through gills is called ______ respiration.
iv) RNA, unlike DNA, consists of ______ polynucleotide chain(s).
v) ______ is the process by which excess water is removed from the body of freshwater fish.
vi) ______ connects a muscle to a bone.
vii) The two systems ______ and ______ work together to coordinate rapid and slow responses in the body.
viii) ______ is the hard, calcified tissue that covers the crown of a tooth.
ix) ______ produces insulin and glucagon to regulate blood sugar.
2. (a) Explain the process of thermoregulation in mammals.
(b) Outline five (5) economic importance of arthropods.
3. (a) Explain the chromosome theory of inheritance.
(b) Briefly explain the blood circulation system in amphibians (frog).
4. (a) Draw and label the longitudinal section of a mammalian kidney with arrows to show the direction of blood and filtrate flow.
(b) Give one function of each part of the kidney drawn.
5. (a) Explain the mechanism of perception of smell (olfaction) in man.
(b) Mention five (5) adaptations of a bony fish to aquatic life.
6. (a) Explain the adaptations of the sperm (spermatozoon) cell of mammals.
(b) Outline five (5) characteristics of housefly larva (maggot).
Answers
1. (a) i) Ribosomes
Ribosomes are small, granular, non-membrane-bound organelles composed of ribosomal RNA and protein, found either free in the cytoplasm or attached to the rough endoplasmic reticulum. They are the site of protein synthesis (translation), where messenger RNA is read and amino acids are assembled into polypeptide chains according to the genetic code.
ii) Economic importance of earthworms
Earthworms burrow through soil, improving aeration, drainage, and structure, and their castings enrich soil with nutrients, acting as a natural fertilizer that boosts agricultural productivity. They are also economically useful as fishing bait and as a protein source in some vermiculture and animal feed systems, though large populations can occasionally damage lawns and golf courses through excessive casting.
iii) The recovery position in first aid
The recovery position is a first-aid technique used to keep an unconscious but breathing casualty's airway open and clear. The casualty is turned onto their side with the head tilted slightly back and downward, the upper leg bent for stability, so that fluids such as vomit or saliva can drain from the mouth rather than obstruct the airway or be inhaled into the lungs.
iv) Feeding in Amoeba
Amoeba is a heterotrophic protozoan that feeds by phagocytosis. When it encounters a food particle, it extends pseudopodia (temporary cytoplasmic projections) around the particle, engulfing it to form a food vacuole within the cytoplasm. Digestive enzymes are secreted into the vacuole to break down the food, and the digested nutrients diffuse into the surrounding cytoplasm, while undigested waste is expelled by exocytosis at the cell surface.
(b)
Cross: GGLL (grey, long ears) × ggll (white, short ears)
i) Punnett square (F₁ generation)
Gametes from GGLL parent: GL
Gametes from ggll parent: gl
| × | gl |
|---|---|
| GL | GgLl |
All F₁ offspring genotype: GgLl
ii) Phenotype of F₁ offspring
All F₁ rabbits are grey with long ears (GgLl), since both grey fur (G) and long ears (L) are dominant.
iii) F₁ × F₁ cross (GgLl × GgLl) — types and ratio of offspring
Gametes from each parent: GL, Gl, gL, gl
| × | GL | Gl | gL | gl |
|---|---|---|---|---|
| GL | GGLL | GGLl | GgLL | GgLl |
| Gl | GGLl | GGll | GgLl | Ggll |
| gL | GgLL | GgLl | ggLL | ggLl |
| gl | GgLl | Ggll | ggLl | ggll |
Phenotypic ratio:
- Grey, long ears (G_L_) = 9
- Grey, short ears (G_ll) = 3
- White, long ears (ggL_) = 3
- White, short ears (ggll) = 1
Ratio = 9 : 3 : 3 : 1
iv) New combinations arising from the cross
The new combinations (recombinants) not present in either original parent are:
- Grey, short ears (G_ll)
- White, long ears (ggL_)
(c) Fill in the blanks
i) Tendon
ii) Mitochondria
iii) Branchial (gill) respiration
iv) One (single) polynucleotide chain
v) Osmoregulation
vi) Tendon
vii) Nervous system, and Endocrine system
viii) Enamel
ix) Pancreas
Question 2
(a) Thermoregulation in mammals
Mammals maintain a constant internal body temperature (homeothermy) through mechanisms controlled by the hypothalamus, which acts as the body's thermostat, using negative feedback:
- When body temperature rises above normal, the hypothalamus triggers vasodilation (widening of skin blood vessels), increasing blood flow to the skin surface for greater heat loss by radiation. Sweat glands are also stimulated to secrete sweat, which cools the body through evaporation, and hair/fur is flattened (erector muscles relax) to reduce insulation.
- When body temperature falls below normal, the hypothalamus triggers vasoconstriction (narrowing of skin blood vessels), reducing blood flow to the skin and minimizing heat loss. Erector pili muscles contract, raising hair/fur to trap an insulating layer of air, and shivering (rapid involuntary muscle contraction) generates additional metabolic heat.
- Behavioural responses, such as seeking shade or shelter, also assist in maintaining a stable body temperature.
This homeostatic mechanism keeps body temperature within a narrow normal range regardless of external conditions.
(b) Five economic importance of arthropods
- Honeybees produce honey and beeswax, and pollinate crops, boosting agricultural yields.
- Crustaceans such as crabs, prawns, and lobsters serve as valuable sources of food and income through fisheries.
- Silkworms (larvae of the silk moth) produce silk, an important raw material for the textile industry.
- Some insects, such as ladybirds, act as biological control agents by preying on crop pests.
- Certain arthropods (e.g., mosquitoes, ticks, tsetse flies) are vectors of disease, causing significant economic losses through illness in humans and livestock.
Question 3
(a) Chromosome theory of inheritance
The chromosome theory of inheritance states that genes, the units of heredity, are located on chromosomes within the nucleus of a cell, and that the behaviour of chromosomes during meiosis accounts for the patterns of inheritance described by Mendel's laws. Chromosomes occur in homologous pairs, one inherited from each parent, and each gene occupies a specific locus on a particular chromosome. During meiosis, homologous chromosomes segregate independently into separate gametes (explaining the Law of Segregation), and chromosomes of different pairs assort independently of one another (explaining the Law of Independent Assortment). This theory, developed from the work of Sutton and Boveri, provided the physical basis for Mendelian genetics by linking hereditary factors directly to observable chromosomal behaviour.
(b) Blood circulation system in amphibians (frog)
Frogs possess a double circulatory system with an incomplete separation of blood, using a three-chambered heart consisting of two atria and one ventricle. Deoxygenated blood from the body enters the right atrium, while oxygenated blood from the lungs and skin enters the left atrium; both empty into the single ventricle, where some mixing of oxygenated and deoxygenated blood occurs. From the ventricle, blood is pumped out through the truncus arteriosus, which directs blood partly to the lungs and skin for oxygenation (pulmonary-cutaneous circuit) and partly to the rest of the body (systemic circuit). Because blood passes through the heart twice in each complete circuit, this is referred to as double circulation, although it is incomplete due to the mixing in the single ventricle.
Question 4
(a) Longitudinal section of a mammalian kidney
[Diagram to be hand-drawn, showing: renal cortex, renal medulla (with renal pyramids), renal pelvis, renal artery, renal vein, ureter, calyx. Arrows should indicate: blood entering via the renal artery → cortex/medulla (nephrons) for filtration → filtered blood leaving via the renal vein; filtrate/urine formed in nephrons → collecting ducts → renal pelvis → ureter to the bladder.]
(b) Function of each part
- Renal cortex: Contains the glomeruli and convoluted tubules, where blood filtration and selective reabsorption take place.
- Renal medulla: Contains the loops of Henle and collecting ducts, involved in concentrating urine through water reabsorption.
- Renal pelvis: Collects urine from the collecting ducts and channels it into the ureter.
- Renal artery: Supplies oxygenated blood carrying waste products to the kidney for filtration.
- Renal vein: Carries filtered (cleaned) blood away from the kidney back to circulation.
- Ureter: Transports urine from the renal pelvis to the urinary bladder for storage.
Question 5
(a) Mechanism of perception of smell (olfaction) in man
Smell is perceived through olfactory receptor cells located in the olfactory epithelium, a specialized region high in the nasal cavity. Each receptor cell bears cilia (hair-like projections) that extend into a layer of mucus. When airborne odour molecules dissolve in this mucus, they bind to specific receptor proteins on the cilia, triggering depolarization of the receptor cell membrane. This generates a nerve impulse, which travels along the olfactory nerve (cranial nerve I) through the olfactory bulb to the olfactory centre in the temporal lobe of the cerebral cortex, where the impulse is interpreted as a particular smell.
(b) Five adaptations of a bony fish to aquatic life
- Streamlined, fusiform body shape that reduces water resistance during swimming.
- Gills with numerous thin-walled filaments and a large surface area for efficient gaseous exchange underwater.
- Fins (dorsal, pectoral, pelvic, caudal, anal) that provide balance, steering, and propulsion in water.
- A swim bladder that regulates buoyancy, allowing the fish to remain at a desired depth without expending energy.
- A lateral line system that detects vibrations and pressure changes in water, aiding in predator/prey detection and navigation.
- Overlapping scales covered in mucus, which reduce friction with water and protect against infection.
(Any five of the above.)
Question 6
(a) Adaptations of the sperm (spermatozoon) cell of mammals
- The sperm has a whip-like tail (flagellum) that provides motility, propelling it through fluid to reach and fertilize the egg.
- The head contains an acrosome, a cap-like structure filled with digestive enzymes that break down the outer layers of the egg to allow penetration during fertilization.
- The mid-piece is packed with numerous mitochondria, which supply the large amounts of ATP energy required for the beating of the tail.
- The sperm is a small, streamlined cell with little cytoplasm, reducing its mass and making it highly motile.
- It is haploid, containing half the chromosome number, so that fusion with a haploid egg restores the diploid chromosome number in the zygote.
(b) Five characteristics of housefly larva (maggot)
- Legless (apodous), soft-bodied, and worm-like in appearance.
- Elongated body tapering towards the head end, with a blunt posterior end.
- Lacks a distinct head capsule; mouth region bears small hooks used for feeding.
- Possesses spiracles (breathing pores) at the posterior end for gaseous exchange.
- Feeds on decaying organic matter, such as rotting food, faeces, and carrion.