QUESTIONS
1. (a) Explain the following:
i) Plasmids
ii) Economic importance of termites
iii) Mouth to mouth resuscitation
iv) Feeding in Planaria
(b) Assuming uniform colour (C) is dominant over spotted (c) in cattle. When a cross is made between a pure breed (homozygous) black bull (BBCC) with a white spotted cow (bbcc):
i) Use 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 that are possible when two of the F₁ generations 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 stores fat and cushions and insulates the body.
ii) Energy-producing mitochondria, small organelles found free-floating in the ______ of the cell.
iii) The type of respiration that occurs through the skin is called ______ respiration.
iv) DNA consists of ______ polynucleotide chains.
v) ______ removal of metabolic waste products from the body of mammals.
vi) ______ links the nervous system to endocrine system.
vii) The two systems ______, and ______ regulation of biological activities in the body.
viii) ______ is the tissue that forms the tooth from the dental crown to the tooth root.
ix) ______ produces bile which aids in digesting fat.
2. (a) Explain the process of regulation of blood sugar in blood.
(b) Outline five (5) economic importance of annelids.
3. (a) Explain the gene theory of inheritance.
(b) Briefly explain the blood circulation system in fish.
4. (a) Draw and label the transverse section of a mammalian heart with arrows to show the direction of blood flow.
(b) Give one function of each chamber of the heart drawn.
5. (a) Explain the mechanism of perception of taste in man.
(b) Mention five (5) adaptations of a toad.
6. (a) Explain the adaptations of reproductive egg cell of mammals.
(b) Outline five (5) characteristics of mosquito larva.
ANSWERS
1. (a) i) Plasmids
Plasmids are small, circular, double-stranded DNA molecules found in the cytoplasm of bacteria, separate from the main chromosomal DNA. They are capable of independent (autonomous) replication and often carry genes conferring advantageous traits such as antibiotic resistance. Plasmids can be transferred between bacteria through conjugation and are widely used in genetic engineering as vectors for inserting foreign genes into host cells.
ii) Economic importance of termites
Termites decompose dead wood and plant material, recycling nutrients back into the soil and improving soil aeration and fertility. However, they are economically destructive as they damage wooden buildings, furniture, and structural timber, destroy crops and stored agricultural produce, and damage paper, books, and fabric materials, causing significant financial losses.
iii) Mouth to mouth resuscitation
Mouth-to-mouth resuscitation is an emergency first-aid procedure used to manually ventilate a person who has stopped breathing. The rescuer tilts the victim's head back to open the airway, pinches the victim's nose shut, seals their mouth over the victim's mouth, and exhales air into the victim's lungs, causing the chest to rise. This is alternated with chest compressions (as part of CPR) to restore spontaneous breathing and circulation.
iv) Feeding in Planaria
Planaria is a carnivorous flatworm that feeds using a muscular, protrusible pharynx located mid-ventrally on its body. When feeding, the pharynx is extended out of the mouth and applied to the prey or food source; digestive enzymes are secreted to partially digest the food externally, after which the softened material is sucked into the highly branched intestine (gastrovascular cavity), where digestion is completed and nutrients are absorbed and distributed through the branches to all parts of the body.
(b)
Cross: BBCC (black, uniform colour) × bbcc (white, spotted)
i) Punnett square (F₁ generation)
Gametes from BBCC parent: BC
Gametes from bbcc parent: bc
| BC | |
|---|---|
| bc | BbCc |
All F₁ offspring genotype: BbCc
ii) Phenotype of F₁ calves
All F₁ calves are black with uniform colour (BbCc), since both black colour (B) and uniform colour (C) are dominant.
iii) F₁ × F₁ cross (BbCc × BbCc) — types and ratio of offspring
Gametes from each parent: 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 |
Phenotypic ratio:
- Black, uniform colour (B_C_) = 9
- Black, spotted (B_cc) = 3
- White, uniform colour (bbC_) = 3
- White, spotted (bbcc) = 1
Ratio = 9 : 3 : 3 : 1
iv) New combinations arising from the cross
The new combinations (recombinants) not present in either original parent are:
- Black, spotted (B_cc)
- White, uniform colour (bbC_)
(c) Fill in the blanks
i) Adipose tissue
ii) Cytoplasm
iii) Cutaneous respiration
iv) Two (double) polynucleotide chains
v) Excretion
vi) Hypothalamus
vii) Nervous system, and Endocrine system
viii) Dentine
ix) Liver
Question 2
(a) Regulation of blood sugar in blood
Blood sugar (glucose) level is regulated mainly by the pancreas through the hormones insulin and glucagon, in a negative feedback mechanism:
- When blood glucose level rises (e.g., after a meal), the beta cells of the Islets of Langerhans in the pancreas secrete insulin. Insulin stimulates liver and muscle cells to take up glucose from the blood and convert it into glycogen (glycogenesis) for storage, and promotes uptake of glucose into body cells for respiration, thereby lowering blood glucose level.
- When blood glucose level falls (e.g., during fasting or exercise), the alpha cells of the Islets of Langerhans secrete glucagon. Glucagon stimulates the liver to break down stored glycogen into glucose (glycogenolysis) and release it into the bloodstream, raising blood glucose level back to normal.
- Additional hormones such as adrenaline (from the adrenal medulla) also raise blood glucose during stress by stimulating glycogenolysis.
This homeostatic mechanism maintains blood glucose within a narrow normal range (approximately 70–110 mg/100ml).
(b) Five economic importance of annelids
- Earthworms improve soil fertility and structure by burrowing, which aerates the soil and enhances drainage.
- Earthworm castings enrich the soil with nutrients, acting as a natural fertilizer.
- Some annelids (e.g., ragworms, earthworms) serve as fishing bait.
- Certain annelids, such as Eunice (palolo worm), are used as a food source in some cultures.
- Leeches are used medicinally for bloodletting and in microsurgery to prevent blood clotting and restore circulation in reattached tissue.
Question 3
(a) Gene theory of inheritance
The gene theory of inheritance states that hereditary characteristics are controlled by discrete units called genes, which are located on chromosomes and are passed from parents to offspring during reproduction. Each gene occupies a specific position (locus) on a chromosome and may exist in alternative forms called alleles. Genes are composed of DNA, which carries the genetic code determining the structure and function of proteins responsible for an organism's traits. During gamete formation (meiosis), genes segregate independently and are transmitted to offspring according to Mendelian principles, such as the Law of Segregation and the Law of Independent Assortment, accounting for the patterns of inheritance observed across generations.
(b) Blood circulation system in fish
Fish possess a single circulatory system with a two-chambered heart consisting of one atrium and one ventricle. Deoxygenated blood from the body returns to the atrium, is passed to the ventricle, and is then pumped through the ventral aorta to the gills, where gas exchange occurs and the blood becomes oxygenated. The oxygenated blood then flows through the dorsal aorta to be distributed to all parts of the body. Because blood passes through the heart only once in each complete circuit (heart → gills → body → heart), this is referred to as single circulation, and the blood pressure is relatively low compared to double circulatory systems.
Question 4
(a) Transverse section of a mammalian heart
[Diagram to be hand-drawn, showing: right atrium, right ventricle, left atrium, left ventricle, septum, tricuspid valve, bicuspid (mitral) valve, pulmonary artery, pulmonary vein, vena cava, aorta, semilunar valves. Arrows should indicate: deoxygenated blood entering right atrium from vena cava → right ventricle → pulmonary artery to lungs; oxygenated blood entering left atrium from pulmonary vein → left ventricle → aorta to the body.]
(b) Function of each chamber
- Right atrium: Receives deoxygenated blood from the body via the vena cava.
- Right ventricle: Pumps deoxygenated blood to the lungs via the pulmonary artery.
- Left atrium: Receives oxygenated blood from the lungs via the pulmonary vein.
- Left ventricle: Pumps oxygenated blood to the rest of the body via the aorta.
Question 5
(a) Mechanism of perception of taste in man
Taste is perceived through taste buds, which are sensory receptor structures located mainly on the papillae of the tongue, and also on the soft palate and epiglottis. Each taste bud contains gustatory (taste) receptor cells with microvilli (hair-like projections) that extend into a taste pore. When food substances dissolved in saliva come into contact with these receptor cells, they bind to specific receptor proteins on the microvilli, triggering a depolarization of the receptor cell membrane. This generates a nerve impulse, which is transmitted via sensory nerve fibres (facial, glossopharyngeal, and vagus nerves) to the taste centre in the cerebral cortex of the brain, where the impulse is interpreted as one of the basic tastes: sweet, sour, salty, bitter, or umami.
(b) Five adaptations of a toad
- Moist, glandular skin that facilitates cutaneous respiration and gaseous exchange.
- Webbed hind feet that aid in swimming.
- Protruding eyes positioned on top of the head, allowing vision while the rest of the body remains submerged in water.
- A long, sticky, extensible tongue for capturing insect prey.
- Poison (parotoid) glands behind the eyes that secrete toxic substances as a defence mechanism against predators.
- Powerful hind limbs adapted for jumping/leaping to escape predators.
(Any five of the above.)
Question 6
(a) Adaptations of the reproductive egg cell of mammals
- The egg (ovum) is surrounded by a protective glycoprotein layer called the zona pellucida, which is involved in species-specific sperm recognition and prevents polyspermy (entry of more than one sperm) after fertilization.
- The egg contains cortical granules beneath the plasma membrane, which release their contents upon fertilization to harden the zona pellucida, further blocking polyspermy.
- The egg is a large cell containing abundant cytoplasm and nutrient reserves to support the early stages of embryonic development.
- The egg is non-motile, relying on the motile sperm to reach it for fertilization, and is surrounded by follicular (cumulus) cells that support its maturation and transport along the oviduct.
- It is haploid, containing half the chromosome number, ensuring that fusion with a haploid sperm restores the diploid chromosome number in the zygote.
(b) Five characteristics of mosquito larva
- Aquatic, living in stagnant water bodies such as ponds, puddles, and containers.
- Elongated, segmented body divided into head, thorax, and abdomen.
- Possesses a breathing siphon (respiratory tube) at the posterior end of the abdomen, used to obtain atmospheric air at the water surface.
- Exhibits characteristic wriggling (jerky) movement in water, giving it the common name "wriggler."
- Lacks true legs but possesses setae (bristles) and mouth brushes used for filter-feeding on microorganisms and organic debris in water.
- Undergoes several moults (instars) before developing into the pupal stage.
(Any five of the above.)