WAEC SSCE - Biology - 1992 (Essay)
Swali 1 Ripoti
(a) Mention six ways by which the government is contributing towards self-sufficiency in food production
(b) List five methods Of conserving soil fertility.
(c) Explain how three named agricultural practices can destroy the balance of an ecosystem.
(a) Six ways government contributes towards self-sufficiency in food production
- Granting agricultural loans and credit facilities to farmers at low interest.
- Subsidising farm inputs such as fertilizers, improved seeds, agro-chemicals and machinery.
- Providing agricultural research and extension services to teach farmers modern methods.
- Constructing irrigation schemes, dams and boreholes so that farming can continue in the dry season.
- Guaranteeing fair, stable prices for produce and establishing marketing boards to buy surplus crops.
- Providing storage, processing and preservation facilities (silos, cold rooms) to reduce post-harvest losses.
Other acceptable points: building access roads to farms, mechanisation programmes, and training of farmers.
(b) Five methods of conserving soil fertility
- Crop rotation, especially including leguminous crops that fix nitrogen.
- Application of organic manure and inorganic fertilizers to replace lost nutrients.
- Bush fallowing, resting the land to allow natural nutrient recovery.
- Mulching and cover cropping to protect the soil and add humus.
- Preventing erosion by contour ploughing, terracing and avoiding bush burning.
(c) How three named agricultural practices destroy the balance of an ecosystem
(i) Bush burning: it kills soil micro-organisms, insects and small animals, destroys vegetation that provides food and shelter, and exposes the soil to erosion. Food chains are broken and biodiversity is reduced.
(ii) Use of pesticides and herbicides: these chemicals kill non-target useful organisms such as bees, earthworms and predators. They accumulate along the food chain (bioaccumulation), poisoning higher consumers and upsetting predator-prey relationships.
(iii) Deforestation / clearing land for monoculture: removing natural forest destroys the habitats of many species, lowers biodiversity, alters the water cycle and local climate, and encourages soil erosion, all of which disturb the natural balance.
Maelezo ya Majibu
(a) Six ways government contributes towards self-sufficiency in food production
- Granting agricultural loans and credit facilities to farmers at low interest.
- Subsidising farm inputs such as fertilizers, improved seeds, agro-chemicals and machinery.
- Providing agricultural research and extension services to teach farmers modern methods.
- Constructing irrigation schemes, dams and boreholes so that farming can continue in the dry season.
- Guaranteeing fair, stable prices for produce and establishing marketing boards to buy surplus crops.
- Providing storage, processing and preservation facilities (silos, cold rooms) to reduce post-harvest losses.
Other acceptable points: building access roads to farms, mechanisation programmes, and training of farmers.
(b) Five methods of conserving soil fertility
- Crop rotation, especially including leguminous crops that fix nitrogen.
- Application of organic manure and inorganic fertilizers to replace lost nutrients.
- Bush fallowing, resting the land to allow natural nutrient recovery.
- Mulching and cover cropping to protect the soil and add humus.
- Preventing erosion by contour ploughing, terracing and avoiding bush burning.
(c) How three named agricultural practices destroy the balance of an ecosystem
(i) Bush burning: it kills soil micro-organisms, insects and small animals, destroys vegetation that provides food and shelter, and exposes the soil to erosion. Food chains are broken and biodiversity is reduced.
(ii) Use of pesticides and herbicides: these chemicals kill non-target useful organisms such as bees, earthworms and predators. They accumulate along the food chain (bioaccumulation), poisoning higher consumers and upsetting predator-prey relationships.
(iii) Deforestation / clearing land for monoculture: removing natural forest destroys the habitats of many species, lowers biodiversity, alters the water cycle and local climate, and encourages soil erosion, all of which disturb the natural balance.
Swali 2 Ripoti
(a) Explain the following terms: (i) voluntary action. (ii) involuntary action.
(b) State three functions each of: (I) insulin; (ii) auxins.
(c) Describe an experiment to show that plant roots respond positively to gravity.
(a)(1) Voluntary action - involves the response to a stimulus that is controlled at will by the brain. in this action, an impulse is carried from a sensory neurone via the spinal cord to the brain which interprets and sends the message back through the motor neurone to effector organ. The action is not automatic. e.g. running, writing, jumping, laughing, reading, smiling.
(II) Involuntary action or reflex action-It is a rapid or automatic response to a stimulus. It does not involve the brain for initiation. Therefore, the action is not under the control of the will, e.g. sneezing, coughing, knee jerk, salivation, secretion of grand, blinking
(b)(i) Functions of insulin:
(1) Assists in oxidation of glucose to produce energy
(2) regulates the amount or level of glucose in the blood
(3) assists in protein synthesis in some cells
(ii) Functions of auxin
(1) Promotes lateral bud development
(2) promotes reproduction, flowering and fruit formation in plants
(3) promotes the production of adventitious roots.
(c) Experiment to show that plant roots respond positively to gravity:
Aim - To demonstrate that plant roots respond positively to gravity.
Apparatus: A bean seedling, Wet blotting paper, damp saw dust, cupboard.
Procedure: Put some dust on a wet blotting paper and place the bean seedling on the saw dust horizontally. Carry the set up and place it inside a dark cupboard to eliminate light for few days.
Observation: When observed after few days, one will discover that the root has curved and growing downwards while the shoot grow upward. Conclusion: Since the root has grown downwards and the shoot upwards, we can say that roots respond to gravity, showing positive geotropism while the shoot shows negative geotropism.
Maelezo ya Majibu
(a)(1) Voluntary action - involves the response to a stimulus that is controlled at will by the brain. in this action, an impulse is carried from a sensory neurone via the spinal cord to the brain which interprets and sends the message back through the motor neurone to effector organ. The action is not automatic. e.g. running, writing, jumping, laughing, reading, smiling.
(II) Involuntary action or reflex action-It is a rapid or automatic response to a stimulus. It does not involve the brain for initiation. Therefore, the action is not under the control of the will, e.g. sneezing, coughing, knee jerk, salivation, secretion of grand, blinking
(b)(i) Functions of insulin:
(1) Assists in oxidation of glucose to produce energy
(2) regulates the amount or level of glucose in the blood
(3) assists in protein synthesis in some cells
(ii) Functions of auxin
(1) Promotes lateral bud development
(2) promotes reproduction, flowering and fruit formation in plants
(3) promotes the production of adventitious roots.
(c) Experiment to show that plant roots respond positively to gravity:
Aim - To demonstrate that plant roots respond positively to gravity.
Apparatus: A bean seedling, Wet blotting paper, damp saw dust, cupboard.
Procedure: Put some dust on a wet blotting paper and place the bean seedling on the saw dust horizontally. Carry the set up and place it inside a dark cupboard to eliminate light for few days.
Observation: When observed after few days, one will discover that the root has curved and growing downwards while the shoot grow upward. Conclusion: Since the root has grown downwards and the shoot upwards, we can say that roots respond to gravity, showing positive geotropism while the shoot shows negative geotropism.
Swali 3 Ripoti
(a) Describe briefly the female reproductive system of a named mammal. (A diagram is essential).
(b) List three differences between reproduction in mammals and in amphibians.
(c) Describe the structure and function of the male reproductive organ of a flowering plant.
(a) Female reproductive system of a named mammal (woman/human, diagram essential)
The labelled diagram (front view) should show and label:
- Two ovaries: almond-shaped organs that produce the ova (eggs) and secrete the hormones oestrogen and progesterone.
- Two oviducts (fallopian tubes): tubes with funnel-shaped, fringed openings (fimbriae) that receive the ovum and carry it towards the uterus; fertilisation takes place here.
- Uterus (womb): a muscular, pear-shaped organ with a soft inner lining (endometrium) in which the fertilised egg implants and the foetus develops.
- Cervix: the narrow neck of the uterus that opens into the vagina.
- Vagina: the muscular tube that receives the penis during mating and serves as the birth canal.
In brief, the ovaries release an ovum at ovulation; it passes into the oviduct where, if sperm are present, fertilisation occurs; the resulting zygote travels to the uterus, implants in its lining and develops into a foetus until birth.
(b) Three differences between reproduction in mammals and in amphibians
| Mammals | Amphibians |
|---|---|
| Fertilisation is internal | Fertilisation is external (in water) |
| Few young are produced | Very many eggs are produced |
| Development is internal (in the uterus); young are born alive (viviparous) | Development is external in water; eggs are laid and hatch (oviparous) |
| Much parental care; young are suckled with milk | Little or no parental care |
(c) Structure and function of the male reproductive organ of a flowering plant (the stamen)
The male reproductive organ is the stamen (androecium). Each stamen is made up of two parts:
- The anther: a two-lobed structure containing four pollen sacs. Inside these sacs the pollen grains are formed. The anther produces and stores the pollen grains, which carry the male gametes, and splits open (dehisces) at maturity to release them for pollination.
- The filament: the stalk that bears the anther. It holds up and supports the anther in a suitable position to expose the pollen for dispersal, and supplies it with water and nutrients through its vascular tissue.
Each mature pollen grain contains a generative nucleus (which divides to form two male gametes) and a tube nucleus (which controls the growth of the pollen tube during fertilisation). Thus the stamen's function is to produce the male gametes and make them available for pollination and fertilisation.
Maelezo ya Majibu
(a) Female reproductive system of a named mammal (woman/human, diagram essential)
The labelled diagram (front view) should show and label:
- Two ovaries: almond-shaped organs that produce the ova (eggs) and secrete the hormones oestrogen and progesterone.
- Two oviducts (fallopian tubes): tubes with funnel-shaped, fringed openings (fimbriae) that receive the ovum and carry it towards the uterus; fertilisation takes place here.
- Uterus (womb): a muscular, pear-shaped organ with a soft inner lining (endometrium) in which the fertilised egg implants and the foetus develops.
- Cervix: the narrow neck of the uterus that opens into the vagina.
- Vagina: the muscular tube that receives the penis during mating and serves as the birth canal.
In brief, the ovaries release an ovum at ovulation; it passes into the oviduct where, if sperm are present, fertilisation occurs; the resulting zygote travels to the uterus, implants in its lining and develops into a foetus until birth.
(b) Three differences between reproduction in mammals and in amphibians
| Mammals | Amphibians |
|---|---|
| Fertilisation is internal | Fertilisation is external (in water) |
| Few young are produced | Very many eggs are produced |
| Development is internal (in the uterus); young are born alive (viviparous) | Development is external in water; eggs are laid and hatch (oviparous) |
| Much parental care; young are suckled with milk | Little or no parental care |
(c) Structure and function of the male reproductive organ of a flowering plant (the stamen)
The male reproductive organ is the stamen (androecium). Each stamen is made up of two parts:
- The anther: a two-lobed structure containing four pollen sacs. Inside these sacs the pollen grains are formed. The anther produces and stores the pollen grains, which carry the male gametes, and splits open (dehisces) at maturity to release them for pollination.
- The filament: the stalk that bears the anther. It holds up and supports the anther in a suitable position to expose the pollen for dispersal, and supplies it with water and nutrients through its vascular tissue.
Each mature pollen grain contains a generative nucleus (which divides to form two male gametes) and a tube nucleus (which controls the growth of the pollen tube during fertilisation). Thus the stamen's function is to produce the male gametes and make them available for pollination and fertilisation.
Swali 4 Ripoti
(a) List the principal sense organs in mammals and their functions.
(b) (i) Describe the eye defect in which only distant objects are seen clearly.
(ii) How can it be corrected? Illustrate your answer with labelled diagrams.
(c) Make a large diagram of the vertical section through the mammalian skin.
(a) Principal sense organs in mammals and their functions
| Sense organ | Function |
|---|---|
| Eye | Sight – detects light, colour, shape, size and distance of objects. |
| Ear | Hearing (detects sound) and balance / sense of body position (equilibrium). |
| Nose | Smell (olfaction) – detects chemicals (odours) in the air. |
| Tongue | Taste – the taste buds detect dissolved chemicals (sweet, sour, salt, bitter). |
| Skin | Touch, pressure, pain, and temperature (heat and cold). |
(b)(i) The defect in which only distant objects are seen clearly
This defect is long sight (hypermetropia / far-sightedness). The person can see distant objects clearly but near objects appear blurred. It is caused by the eyeball being too short from front to back (or by the lens being too weak/flat and the ciliary muscles having lost their elasticity), so that light rays from a near object are brought to a focus behind the retina instead of exactly on it.
(b)(ii) Correction
Long sight is corrected by wearing spectacles fitted with a convex (converging) lens. The convex lens converges (bends inward) the diverging rays from a near object before they enter the eye, shortening the effective focal length so that the eye then brings them to a focus exactly on the retina, and near objects are seen clearly. The two diagrams below show the uncorrected eye (rays focusing behind the retina) and the corrected eye (a convex lens placed in front bringing the rays to a focus on the retina).
(c) Vertical section through the mammalian skin
The skin has two main layers: an outer epidermis (with a dead, cornified surface layer, a granular layer, and a living Malpighian / germinative layer that makes new cells and the pigment melanin) and, below it, the thicker dermis. The dermis contains the hair growing from its hair follicle, the erector (hair) muscle, the sebaceous (oil) gland, the coiled sweat gland opening at a sweat pore, sensory nerve endings, and blood capillaries. Beneath the dermis lies the subcutaneous fat (adipose) layer which stores fat and insulates the body. A large labelled vertical section is shown below.
Maelezo ya Majibu
(a) Principal sense organs in mammals and their functions
| Sense organ | Function |
|---|---|
| Eye | Sight – detects light, colour, shape, size and distance of objects. |
| Ear | Hearing (detects sound) and balance / sense of body position (equilibrium). |
| Nose | Smell (olfaction) – detects chemicals (odours) in the air. |
| Tongue | Taste – the taste buds detect dissolved chemicals (sweet, sour, salt, bitter). |
| Skin | Touch, pressure, pain, and temperature (heat and cold). |
(b)(i) The defect in which only distant objects are seen clearly
This defect is long sight (hypermetropia / far-sightedness). The person can see distant objects clearly but near objects appear blurred. It is caused by the eyeball being too short from front to back (or by the lens being too weak/flat and the ciliary muscles having lost their elasticity), so that light rays from a near object are brought to a focus behind the retina instead of exactly on it.
(b)(ii) Correction
Long sight is corrected by wearing spectacles fitted with a convex (converging) lens. The convex lens converges (bends inward) the diverging rays from a near object before they enter the eye, shortening the effective focal length so that the eye then brings them to a focus exactly on the retina, and near objects are seen clearly. The two diagrams below show the uncorrected eye (rays focusing behind the retina) and the corrected eye (a convex lens placed in front bringing the rays to a focus on the retina).
(c) Vertical section through the mammalian skin
The skin has two main layers: an outer epidermis (with a dead, cornified surface layer, a granular layer, and a living Malpighian / germinative layer that makes new cells and the pigment melanin) and, below it, the thicker dermis. The dermis contains the hair growing from its hair follicle, the erector (hair) muscle, the sebaceous (oil) gland, the coiled sweat gland opening at a sweat pore, sensory nerve endings, and blood capillaries. Beneath the dermis lies the subcutaneous fat (adipose) layer which stores fat and insulates the body. A large labelled vertical section is shown below.
