WAEC SSCE - Biology - 2015 (Essay)
Pregunta 1 Informe
(a)(i) What is sewage?
(ii) State five effects of releasing untreated sewage into a stagnant water body.
(b) Explain surface terracing as a soil conservation method.
(c) Explain the term adaptation.
(d) Explain two ways each by which the following organisms adapt to their habitats:
(i) hydrophytes
(ii) xerophytes.
(a)(i) Sewage is the liquid and solid waste matter, including human excreta, waste water and refuse, that is carried away from homes, industries and towns in drains and sewers.
(ii) Five effects of releasing untreated sewage into a stagnant water body
- It causes water pollution, making the water unfit for drinking and domestic use.
- It introduces disease-causing organisms (typhoid, cholera, dysentery).
- It promotes rapid growth of algae (eutrophication), forming an algal bloom.
- Decomposition of the sewage and dead algae by bacteria uses up dissolved oxygen, killing fish and other aquatic organisms.
- It produces foul (offensive) odours and breeds mosquitoes and other vectors.
(b) Surface (bench) terracing: this is a soil-conservation method used on steep slopes in which the slope is cut into a series of broad, level, step-like platforms (terraces) supported by ridges or walls along the contour. The flat terraces reduce the speed of run-off water, allow it to soak into the soil, and so check soil erosion while retaining water and nutrients for crops.
(c) Adaptation is the possession of special structural, physiological or behavioural features that enable an organism to survive and reproduce successfully in its particular environment.
(d) Two ways each of adaptation
- (i) Hydrophytes (water plants): possess many large air spaces (aerenchyma) for buoyancy and gaseous exchange; have poorly developed roots and thin/dissected leaves; stomata are on the upper leaf surface (in floating leaves).
- (ii) Xerophytes (dry-habitat plants): have reduced leaves or spines and a thick waxy cuticle to reduce water loss; have sunken stomata and deep or extensive roots; store water in fleshy (succulent) tissues.
Detalles de la respuesta
(a)(i) Sewage is the liquid and solid waste matter, including human excreta, waste water and refuse, that is carried away from homes, industries and towns in drains and sewers.
(ii) Five effects of releasing untreated sewage into a stagnant water body
- It causes water pollution, making the water unfit for drinking and domestic use.
- It introduces disease-causing organisms (typhoid, cholera, dysentery).
- It promotes rapid growth of algae (eutrophication), forming an algal bloom.
- Decomposition of the sewage and dead algae by bacteria uses up dissolved oxygen, killing fish and other aquatic organisms.
- It produces foul (offensive) odours and breeds mosquitoes and other vectors.
(b) Surface (bench) terracing: this is a soil-conservation method used on steep slopes in which the slope is cut into a series of broad, level, step-like platforms (terraces) supported by ridges or walls along the contour. The flat terraces reduce the speed of run-off water, allow it to soak into the soil, and so check soil erosion while retaining water and nutrients for crops.
(c) Adaptation is the possession of special structural, physiological or behavioural features that enable an organism to survive and reproduce successfully in its particular environment.
(d) Two ways each of adaptation
- (i) Hydrophytes (water plants): possess many large air spaces (aerenchyma) for buoyancy and gaseous exchange; have poorly developed roots and thin/dissected leaves; stomata are on the upper leaf surface (in floating leaves).
- (ii) Xerophytes (dry-habitat plants): have reduced leaves or spines and a thick waxy cuticle to reduce water loss; have sunken stomata and deep or extensive roots; store water in fleshy (succulent) tissues.
Pregunta 2 Informe
(a) Copy and complete the table below
| Disease | one effect | one remedy |
| kidney stones | ||
| Nephritis | ||
| Diuresis |
(b) Make a labelled diagram of the carbon cycle.
(c)(i) What is Estuarine habitat?
(ii) Construct a food chain typical of an Estuarine habitat.
(d)(i) Name two diseases that can attack plant crops.
(ii) State three ways of controlling plant diseases.
(e) State four functions of a public health authority
(f) State four ways of maintaining food hygiene in the community.
(a) Completed table
| Disease | One effect | One remedy |
|---|---|---|
| Kidney stones | Blockage of the urinary tract causing severe pain and difficulty in passing urine | Drink plenty of water; remove the stones by surgery or lithotripsy |
| Nephritis | Inflammation of the kidney (nephrons) which impairs filtration, so protein and blood appear in the urine | Treat with antibiotics and rest; use dialysis and a low-salt diet in severe cases |
| Diuresis | Excessive and frequent production of urine, leading to loss of water and dehydration | Treat the underlying cause (e.g. control diabetes); reduce intake of diuretics and take prescribed medication |
(b) Diagram of the carbon cycle
Draw a labelled cycle showing: carbon dioxide in the atmosphere; uptake of CO2 by green plants in photosynthesis; passage of carbon compounds to animals through feeding; return of CO2 to the air through the respiration of plants and animals; release of CO2 through the decay/decomposition of dead plants and animals by micro-organisms; and release of CO2 through the combustion (burning) of wood and fossil fuels.
(c)(i) Estuarine habitat
An estuarine habitat is the region where a river meets the sea, containing brackish water (a mixture of fresh water and salt water) whose salinity rises and falls with the tides.
(c)(ii) A food chain typical of an estuary
Phytoplankton (diatoms) → zooplankton → small fish (mullet) → large fish / heron.
(d)(i) Two diseases that attack crops: cassava mosaic disease and rice blast (leaf spot and rust are also acceptable).
(d)(ii) Three ways of controlling plant diseases: use disease-resistant varieties; spray with the correct fungicide/pesticide; practise crop rotation; remove and burn infected plants.
(e) Four functions of a public health authority
- Provide clean, safe drinking water for the community.
- Organise proper disposal of refuse and sewage.
- Carry out immunisation and control the spread of diseases.
- Give health education and inspect food and food premises.
(f) Four ways of maintaining food hygiene in the community
- Wash the hands with soap before handling or eating food.
- Cover food to protect it from flies and dust.
- Cook food thoroughly and store or refrigerate it properly.
- Use clean water and clean utensils in preparing food.
Detalles de la respuesta
(a) Completed table
| Disease | One effect | One remedy |
|---|---|---|
| Kidney stones | Blockage of the urinary tract causing severe pain and difficulty in passing urine | Drink plenty of water; remove the stones by surgery or lithotripsy |
| Nephritis | Inflammation of the kidney (nephrons) which impairs filtration, so protein and blood appear in the urine | Treat with antibiotics and rest; use dialysis and a low-salt diet in severe cases |
| Diuresis | Excessive and frequent production of urine, leading to loss of water and dehydration | Treat the underlying cause (e.g. control diabetes); reduce intake of diuretics and take prescribed medication |
(b) Diagram of the carbon cycle
Draw a labelled cycle showing: carbon dioxide in the atmosphere; uptake of CO2 by green plants in photosynthesis; passage of carbon compounds to animals through feeding; return of CO2 to the air through the respiration of plants and animals; release of CO2 through the decay/decomposition of dead plants and animals by micro-organisms; and release of CO2 through the combustion (burning) of wood and fossil fuels.
(c)(i) Estuarine habitat
An estuarine habitat is the region where a river meets the sea, containing brackish water (a mixture of fresh water and salt water) whose salinity rises and falls with the tides.
(c)(ii) A food chain typical of an estuary
Phytoplankton (diatoms) → zooplankton → small fish (mullet) → large fish / heron.
(d)(i) Two diseases that attack crops: cassava mosaic disease and rice blast (leaf spot and rust are also acceptable).
(d)(ii) Three ways of controlling plant diseases: use disease-resistant varieties; spray with the correct fungicide/pesticide; practise crop rotation; remove and burn infected plants.
(e) Four functions of a public health authority
- Provide clean, safe drinking water for the community.
- Organise proper disposal of refuse and sewage.
- Carry out immunisation and control the spread of diseases.
- Give health education and inspect food and food premises.
(f) Four ways of maintaining food hygiene in the community
- Wash the hands with soap before handling or eating food.
- Cover food to protect it from flies and dust.
- Cook food thoroughly and store or refrigerate it properly.
- Use clean water and clean utensils in preparing food.
Pregunta 3 Informe
(a) Explain the following terms:
(i) test cross
(ii) monohybrid cross.
(b) In a mango plant the, the allele for bean-shaped seed is r and is recessive to round-shaped seed R. With the aid of a genetic diagram, determine the genotypes of the offspring if:
(i) a homozygous bean-shaped parent with a homozygous round shaped parent;
(ii) a heterozygous bean-shaped parent is crossed with a heterozygous round shaped parent.
(a)(i) Test cross: This is the crossing of an organism showing a dominant character, but whose genotype is unknown, with a homozygous recessive organism in order to determine the unknown genotype.
(a)(ii) Monohybrid cross: This is a genetic cross involving one pair of contrasting alleles, used to study the inheritance of a single character.
(b) Let R represent the allele for round-shaped seed (dominant) and r represent the allele for bean-shaped seed (recessive).
(i) Homozygous bean-shaped parent × homozygous round-shaped parent
Parental genotypes: \(rr \times RR\)
All the offspring have genotype \(Rr\). Therefore, all the offspring are round-shaped.
Genotypic ratio: 100% \(Rr\)
Phenotypic ratio: 100% round-shaped seeds.
(ii) Heterozygous cross
A bean-shaped plant cannot be heterozygous because the heterozygous genotype \(Rr\) produces round-shaped seeds. Thus, the stated heterozygous parents have genotype \(Rr\), and the genetic cross is \(Rr \times Rr\).
Offspring genotypes are \(RR, Rr, Rr\), and \(rr\).
Genotypic ratio: \(1RR : 2Rr : 1rr\).
Phenotypic ratio: \(3\) round-shaped seeds : \(1\) bean-shaped seed.
Detalles de la respuesta
(a)(i) Test cross: This is the crossing of an organism showing a dominant character, but whose genotype is unknown, with a homozygous recessive organism in order to determine the unknown genotype.
(a)(ii) Monohybrid cross: This is a genetic cross involving one pair of contrasting alleles, used to study the inheritance of a single character.
(b) Let R represent the allele for round-shaped seed (dominant) and r represent the allele for bean-shaped seed (recessive).
(i) Homozygous bean-shaped parent × homozygous round-shaped parent
Parental genotypes: \(rr \times RR\)
All the offspring have genotype \(Rr\). Therefore, all the offspring are round-shaped.
Genotypic ratio: 100% \(Rr\)
Phenotypic ratio: 100% round-shaped seeds.
(ii) Heterozygous cross
A bean-shaped plant cannot be heterozygous because the heterozygous genotype \(Rr\) produces round-shaped seeds. Thus, the stated heterozygous parents have genotype \(Rr\), and the genetic cross is \(Rr \times Rr\).
Offspring genotypes are \(RR, Rr, Rr\), and \(rr\).
Genotypic ratio: \(1RR : 2Rr : 1rr\).
Phenotypic ratio: \(3\) round-shaped seeds : \(1\) bean-shaped seed.
Pregunta 4 Informe
(a) Explain how the leaf of a flowering plant is adapted for photosynthesis.
(b) Describe briefly the mode of feeding in tapeworm.
(c) Name one mineral element each needed for the proper functioning of :
(i) bones (ii) red blood cells
(iii) thyroid gland.
(d)(i) State three benefits of including roughages in the diet of humans.
(ii) State three reasons why proteins are important to humans.
(a) How the leaf is adapted for photosynthesis
- Broad, flat lamina gives a large surface area to trap maximum sunlight.
- Thin lamina so that light and gases diffuse quickly to the inner cells.
- Abundant chloroplasts (rich in chlorophyll), especially in the palisade layer, to absorb light energy.
- Palisade cells are elongated and packed near the upper surface to catch the most light.
- Many stomata allow entry of carbon dioxide and exit of oxygen.
- Air spaces in the spongy mesophyll allow rapid diffusion of gases.
- A network of veins (xylem) supplies water and (phloem) removes manufactured food.
- Leaves are arranged in a mosaic (leaf mosaic) to avoid overshadowing one another.
(b) Mode of feeding in tapeworm: the tapeworm lives in the host's small intestine and feeds by absorbing already-digested food (mainly soluble sugars and amino acids) directly through its flat body wall over its whole large surface area. It has no mouth or gut of its own; it secretes anti-enzymes to protect itself from being digested and simply absorbs the host's nutrients (parasitic nutrition).
(c) One mineral element needed for the proper functioning of
- (i) Bones: calcium (phosphorus also acceptable).
- (ii) Red blood cells: iron.
- (iii) Thyroid gland: iodine.
(d)(i) Three benefits of roughage in the diet
- Adds bulk to food and stimulates peristalsis, aiding movement of food through the gut.
- Prevents constipation and helps regular egestion of faeces.
- Helps prevent bowel disorders (such as colon cancer) and absorbs/removes harmful substances.
(ii) Three reasons why proteins are important to humans
- For growth and formation of new cells and tissues.
- For repair of worn-out and damaged tissues.
- For making enzymes, hormones and antibodies.
Detalles de la respuesta
(a) How the leaf is adapted for photosynthesis
- Broad, flat lamina gives a large surface area to trap maximum sunlight.
- Thin lamina so that light and gases diffuse quickly to the inner cells.
- Abundant chloroplasts (rich in chlorophyll), especially in the palisade layer, to absorb light energy.
- Palisade cells are elongated and packed near the upper surface to catch the most light.
- Many stomata allow entry of carbon dioxide and exit of oxygen.
- Air spaces in the spongy mesophyll allow rapid diffusion of gases.
- A network of veins (xylem) supplies water and (phloem) removes manufactured food.
- Leaves are arranged in a mosaic (leaf mosaic) to avoid overshadowing one another.
(b) Mode of feeding in tapeworm: the tapeworm lives in the host's small intestine and feeds by absorbing already-digested food (mainly soluble sugars and amino acids) directly through its flat body wall over its whole large surface area. It has no mouth or gut of its own; it secretes anti-enzymes to protect itself from being digested and simply absorbs the host's nutrients (parasitic nutrition).
(c) One mineral element needed for the proper functioning of
- (i) Bones: calcium (phosphorus also acceptable).
- (ii) Red blood cells: iron.
- (iii) Thyroid gland: iodine.
(d)(i) Three benefits of roughage in the diet
- Adds bulk to food and stimulates peristalsis, aiding movement of food through the gut.
- Prevents constipation and helps regular egestion of faeces.
- Helps prevent bowel disorders (such as colon cancer) and absorbs/removes harmful substances.
(ii) Three reasons why proteins are important to humans
- For growth and formation of new cells and tissues.
- For repair of worn-out and damaged tissues.
- For making enzymes, hormones and antibodies.
Pregunta 5 Informe
(a) Explain briefly sexual reproduction in Rhizopus.
(b) A student suddenly stepped on a big snake, he cried for help and ran away.
(i) Name the hormone produced in the body for the reaction.
(ii) In which part of the human body is the hormone named in (b) (i) produced?
(iii) State five changes that must have taken place as a result of the hormone named in (a) (i).
(c) (i) In tabular form, state three differences between excretion in flowering plants and excretion in humans,
(ii) List two organelles found in plant cell that are responsible for the excretion of metabolic wastes.
(a) Sexual reproduction in Rhizopus: when two hyphae from opposite mating strains (+ and -) grow close together, each puts out a short side branch called a progametangium. The tips swell and are cut off by cross-walls to form two gametangia, each containing many nuclei (gametes). The walls between the touching gametangia dissolve and their contents fuse (plasmogamy then karyogamy). This produces a thick-walled, resistant zygospore. The zygospore undergoes a resting period, then germinates by meiosis to produce a sporangium that releases haploid spores which grow into new mycelia.
(b)(i) Hormone produced: adrenaline (epinephrine).
(ii) Site of production: the adrenal (suprarenal) glands, specifically the adrenal medulla, located above each kidney.
(iii) Five changes caused by adrenaline
- Increased heart rate and force of heartbeat.
- Increased rate and depth of breathing.
- Raised blood sugar level (conversion of glycogen to glucose in the liver).
- Widening (dilation) of the pupils of the eyes.
- Diversion of blood from the gut and skin to the muscles (and erection of body hair; increased sweating).
(c)(i) Three differences between excretion in flowering plants and in humans
| Excretion in flowering plants | Excretion in humans |
|---|---|
| No specialised excretory organs | Has specialised organs (kidneys, lungs, skin) |
| Wastes produced slowly and in small amounts | Wastes produced rapidly and in larger amounts |
| Some wastes are reused (e.g. oxygen, carbon dioxide) or stored in tissues | Wastes are mostly removed from the body, not reused |
| Nitrogenous waste is little; main products are oxygen, carbon dioxide and water | Produces much nitrogenous waste (urea) |
(ii) Two organelles in plant cells responsible for excreting metabolic wastes: the vacuole (stores waste in the cell sap) and the plastids/chloroplasts (release oxygen and other products). (Golgi bodies are also acceptable.)
Detalles de la respuesta
(a) Sexual reproduction in Rhizopus: when two hyphae from opposite mating strains (+ and -) grow close together, each puts out a short side branch called a progametangium. The tips swell and are cut off by cross-walls to form two gametangia, each containing many nuclei (gametes). The walls between the touching gametangia dissolve and their contents fuse (plasmogamy then karyogamy). This produces a thick-walled, resistant zygospore. The zygospore undergoes a resting period, then germinates by meiosis to produce a sporangium that releases haploid spores which grow into new mycelia.
(b)(i) Hormone produced: adrenaline (epinephrine).
(ii) Site of production: the adrenal (suprarenal) glands, specifically the adrenal medulla, located above each kidney.
(iii) Five changes caused by adrenaline
- Increased heart rate and force of heartbeat.
- Increased rate and depth of breathing.
- Raised blood sugar level (conversion of glycogen to glucose in the liver).
- Widening (dilation) of the pupils of the eyes.
- Diversion of blood from the gut and skin to the muscles (and erection of body hair; increased sweating).
(c)(i) Three differences between excretion in flowering plants and in humans
| Excretion in flowering plants | Excretion in humans |
|---|---|
| No specialised excretory organs | Has specialised organs (kidneys, lungs, skin) |
| Wastes produced slowly and in small amounts | Wastes produced rapidly and in larger amounts |
| Some wastes are reused (e.g. oxygen, carbon dioxide) or stored in tissues | Wastes are mostly removed from the body, not reused |
| Nitrogenous waste is little; main products are oxygen, carbon dioxide and water | Produces much nitrogenous waste (urea) |
(ii) Two organelles in plant cells responsible for excreting metabolic wastes: the vacuole (stores waste in the cell sap) and the plastids/chloroplasts (release oxygen and other products). (Golgi bodies are also acceptable.)
