WAEC SSCE - Biology - 2014 (Essay)
Vraag 1 Verslag
(a) Define the following in
(i) elimination
(ii) excretion
(iii) secretion.
(b) Describe the digestion of boiled fish in the gut of humans
(c) Make a diagram 8cm - 10am long of a longitudinal section of a villus and label fully.
(a) Definitions
- (i) Elimination (egestion): the removal of undigested food materials (faeces) from the alimentary canal through the anus.
- (ii) Excretion: the removal from the body of waste products of metabolism, such as carbon dioxide, urea and excess water and salts.
- (iii) Secretion: the production and release of useful substances (such as enzymes, hormones and mucus) by cells or glands for use in the body.
(b) Digestion of boiled fish (protein) in the human gut
- Mouth: the fish is chewed and mixed with saliva to form a bolus; no chemical digestion of protein occurs here.
- Stomach: gastric juice containing hydrochloric acid and the enzyme pepsin acts on the protein. Pepsin digests proteins into peptones and polypeptides. \(\text{Proteins} \rightarrow \text{peptones/polypeptides}\)
- Duodenum: pancreatic juice adds trypsin, which continues breaking proteins and peptones into smaller peptides.
- Ileum: intestinal juice contains peptidase (erepsin) which completes digestion, converting peptides into amino acids. \(\text{Peptides} \rightarrow \text{amino acids}\)
- The soluble amino acids are then absorbed into the bloodstream through the villi.
(c) A labelled longitudinal-section diagram of a villus, 8-10 cm long, is required (showing epithelium, lacteal, blood capillary network, arteriole, venule and goblet cells).
Antwoorddetails
(a) Definitions
- (i) Elimination (egestion): the removal of undigested food materials (faeces) from the alimentary canal through the anus.
- (ii) Excretion: the removal from the body of waste products of metabolism, such as carbon dioxide, urea and excess water and salts.
- (iii) Secretion: the production and release of useful substances (such as enzymes, hormones and mucus) by cells or glands for use in the body.
(b) Digestion of boiled fish (protein) in the human gut
- Mouth: the fish is chewed and mixed with saliva to form a bolus; no chemical digestion of protein occurs here.
- Stomach: gastric juice containing hydrochloric acid and the enzyme pepsin acts on the protein. Pepsin digests proteins into peptones and polypeptides. \(\text{Proteins} \rightarrow \text{peptones/polypeptides}\)
- Duodenum: pancreatic juice adds trypsin, which continues breaking proteins and peptones into smaller peptides.
- Ileum: intestinal juice contains peptidase (erepsin) which completes digestion, converting peptides into amino acids. \(\text{Peptides} \rightarrow \text{amino acids}\)
- The soluble amino acids are then absorbed into the bloodstream through the villi.
(c) A labelled longitudinal-section diagram of a villus, 8-10 cm long, is required (showing epithelium, lacteal, blood capillary network, arteriole, venule and goblet cells).
Vraag 2 Verslag
(a) Explain briefly the following ecological terms:
(i) biosphere
(ii) habitat
(b) Describe the mode of nutrition in a named carnivorous plant.
(c) State three reasons why the dispersal of fruits and seeds are important.
(d) State six methods of conserving soil.
(a) Ecological terms
- (i) Biosphere: the part of the earth (land, water and air) and its atmosphere in which living organisms exist and can survive.
- (ii) Habitat: the specific place or natural environment where an organism (or community) lives, feeds and reproduces.
(b) Mode of nutrition in a named carnivorous plant (Sundew, Drosera): the sundew is a green plant that photosynthesises but grows in nitrogen-poor soil, so it supplements its nitrogen by trapping insects. Its leaves bear tentacles tipped with a sticky, glistening fluid that attracts and traps insects. When an insect lands, the tentacles bend inwards and hold it fast. The leaf then secretes digestive enzymes that break down the insect's proteins into soluble nitrogenous compounds, which are absorbed by the leaf. (Pitcher plant or Venus fly-trap are equally acceptable.)
(c) Three reasons why dispersal of fruits and seeds is important
- To reduce overcrowding and competition for light, water, space and nutrients between parent and offspring.
- To spread the species to new areas and colonise fresh habitats.
- To reduce the spread of diseases and pests among plants of the same kind.
(d) Six methods of conserving soil
- Crop rotation.
- Terracing on slopes.
- Contour ploughing/ridging.
- Afforestation and planting cover crops (mulching).
- Strip cropping.
- Building of windbreaks/shelter belts and avoiding overgrazing/bush burning.
Antwoorddetails
(a) Ecological terms
- (i) Biosphere: the part of the earth (land, water and air) and its atmosphere in which living organisms exist and can survive.
- (ii) Habitat: the specific place or natural environment where an organism (or community) lives, feeds and reproduces.
(b) Mode of nutrition in a named carnivorous plant (Sundew, Drosera): the sundew is a green plant that photosynthesises but grows in nitrogen-poor soil, so it supplements its nitrogen by trapping insects. Its leaves bear tentacles tipped with a sticky, glistening fluid that attracts and traps insects. When an insect lands, the tentacles bend inwards and hold it fast. The leaf then secretes digestive enzymes that break down the insect's proteins into soluble nitrogenous compounds, which are absorbed by the leaf. (Pitcher plant or Venus fly-trap are equally acceptable.)
(c) Three reasons why dispersal of fruits and seeds is important
- To reduce overcrowding and competition for light, water, space and nutrients between parent and offspring.
- To spread the species to new areas and colonise fresh habitats.
- To reduce the spread of diseases and pests among plants of the same kind.
(d) Six methods of conserving soil
- Crop rotation.
- Terracing on slopes.
- Contour ploughing/ridging.
- Afforestation and planting cover crops (mulching).
- Strip cropping.
- Building of windbreaks/shelter belts and avoiding overgrazing/bush burning.
Vraag 3 Verslag
(a) State five reasons why animals move from place to place.
(b) State one function each of the following structures found in plants:
(i) epidermis
(ii) phloem
(iii) sclerenchyma.
(c) Give two examples each of the following types of organisms:
(i) parasitic plants
(ii) saprophytes.
(d) State two adaptive features of plants which inhabit salt water swamp.
(e) State two factors each which result in
(i) increase
(ii) decrease, in population density.
(f) Mention four ways in which modern agricultural activities may threaten the survival of species.
(g) State three reasons why mitosis is important to living organisms
(h) State three causes of food spoilage.
(a) Five reasons why animals move from place to place
- To search for food.
- To find water.
- To escape from predators and danger.
- To search for a mate for reproduction.
- To seek shelter or favourable conditions (suitable temperature, breeding sites).
(b) One function each of plant structures
- (i) Epidermis: protects the inner tissues and (in leaves) reduces water loss.
- (ii) Phloem: transports (translocates) manufactured food from the leaves to other parts of the plant.
- (iii) Sclerenchyma: provides mechanical support and strength to the plant.
(c) Two examples each
- (i) Parasitic plants: mistletoe and dodder (Cassytha).
- (ii) Saprophytes: Mucor and Rhizopus (mushrooms/toadstools also acceptable).
(d) Two adaptive features of salt-water-swamp (mangrove) plants: possession of breathing roots (pneumatophores) for gaseous exchange in waterlogged mud; and viviparous germination (seeds germinate while still attached to the parent) with prop/stilt roots for support.
(e) Population density
- (i) Increase: high birth rate (natality) and immigration (or abundant food).
- (ii) Decrease: high death rate (mortality) and emigration (or disease/predation).
(f) Four ways modern agriculture threatens species survival
- Clearing of forests (deforestation) destroys natural habitats.
- Use of pesticides and herbicides kills non-target organisms.
- Bush burning destroys organisms and their habitats.
- Monoculture and drainage of wetlands reduce biodiversity; overgrazing degrades land.
(g) Three reasons why mitosis is important
- It brings about growth by increasing the number of cells.
- It enables repair and replacement of worn-out or damaged cells.
- It maintains a constant chromosome number and enables asexual reproduction.
(h) Three causes of food spoilage: activity of microorganisms (bacteria and fungi); action of enzymes in the food (autolysis); and attack by pests/insects (also moisture, heat and improper storage).
Antwoorddetails
(a) Five reasons why animals move from place to place
- To search for food.
- To find water.
- To escape from predators and danger.
- To search for a mate for reproduction.
- To seek shelter or favourable conditions (suitable temperature, breeding sites).
(b) One function each of plant structures
- (i) Epidermis: protects the inner tissues and (in leaves) reduces water loss.
- (ii) Phloem: transports (translocates) manufactured food from the leaves to other parts of the plant.
- (iii) Sclerenchyma: provides mechanical support and strength to the plant.
(c) Two examples each
- (i) Parasitic plants: mistletoe and dodder (Cassytha).
- (ii) Saprophytes: Mucor and Rhizopus (mushrooms/toadstools also acceptable).
(d) Two adaptive features of salt-water-swamp (mangrove) plants: possession of breathing roots (pneumatophores) for gaseous exchange in waterlogged mud; and viviparous germination (seeds germinate while still attached to the parent) with prop/stilt roots for support.
(e) Population density
- (i) Increase: high birth rate (natality) and immigration (or abundant food).
- (ii) Decrease: high death rate (mortality) and emigration (or disease/predation).
(f) Four ways modern agriculture threatens species survival
- Clearing of forests (deforestation) destroys natural habitats.
- Use of pesticides and herbicides kills non-target organisms.
- Bush burning destroys organisms and their habitats.
- Monoculture and drainage of wetlands reduce biodiversity; overgrazing degrades land.
(g) Three reasons why mitosis is important
- It brings about growth by increasing the number of cells.
- It enables repair and replacement of worn-out or damaged cells.
- It maintains a constant chromosome number and enables asexual reproduction.
(h) Three causes of food spoilage: activity of microorganisms (bacteria and fungi); action of enzymes in the food (autolysis); and attack by pests/insects (also moisture, heat and improper storage).
Vraag 4 Verslag
(a)(i) Explain the term co-ordinance.
(ii) Calculate the number of individuals with co-dominant blood group.
(iii) What is the total number of individuals in the table that are able to donate blood to an accident victim with blood group B?
(b) A man whose blood group is heterozygous A is married to a woman whose blood group is AB. With the aid of a genetic diagram, suggest the possible blood groups of their children.
A survey to determine blood groups was carried out on 250 people living in a community. The results are represented in the table below.
| Blood group | Percentage |
| A | 8.0 |
| B | 14.0 |
| AB | 32.8 |
| O | 45.2 |
(a)(i) Co-dominance
Co-dominance is a condition in which both alleles of a gene are fully and equally expressed in a heterozygous individual. Neither allele masks the other. For example, \(I^A\) and \(I^B\) are co-dominant alleles; hence \(I^AI^B\) produces blood group AB.
Survey calculations
| Blood group | Percentage | Number out of 250 |
|---|---|---|
| A | 8.0% | 20 |
| B | 14.0% | 35 |
| AB | 32.8% | 82 |
| O | 45.2% | 113 |
(a)(ii) The co-dominant blood group is AB.
\[\frac{32.8}{100}\times250=82\]
Therefore, 82 individuals have the co-dominant blood group.
(a)(iii) A person with blood group B can receive blood from persons with blood groups B and O.
\[\text{Number with group B}=\frac{14.0}{100}\times250=35\]
\[\text{Number with group O}=\frac{45.2}{100}\times250=113\]
\[35+113=148\]
Therefore, 148 individuals can donate blood to the accident victim with blood group B.
(b) Genetic diagram
Heterozygous blood group A man: \(I^Ai\)
Blood group AB woman: \(I^AI^B\)
Gametes from the man are \(I^A\) and \(i\), while gametes from the woman are \(I^A\) and \(I^B\).
The possible genotypes and phenotypes of the children are:
- \(I^AI^A\): blood group A
- \(I^Ai\): blood group A
- \(I^AI^B\): blood group AB
- \(I^Bi\): blood group B
Thus, the possible blood groups are A, AB and B, in the ratio:
\[2\text{ A}:1\text{ AB}:1\text{ B}\]
That is, 50% blood group A, 25% blood group AB and 25% blood group B. No child will have blood group O.
Antwoorddetails
(a)(i) Co-dominance
Co-dominance is a condition in which both alleles of a gene are fully and equally expressed in a heterozygous individual. Neither allele masks the other. For example, \(I^A\) and \(I^B\) are co-dominant alleles; hence \(I^AI^B\) produces blood group AB.
Survey calculations
| Blood group | Percentage | Number out of 250 |
|---|---|---|
| A | 8.0% | 20 |
| B | 14.0% | 35 |
| AB | 32.8% | 82 |
| O | 45.2% | 113 |
(a)(ii) The co-dominant blood group is AB.
\[\frac{32.8}{100}\times250=82\]
Therefore, 82 individuals have the co-dominant blood group.
(a)(iii) A person with blood group B can receive blood from persons with blood groups B and O.
\[\text{Number with group B}=\frac{14.0}{100}\times250=35\]
\[\text{Number with group O}=\frac{45.2}{100}\times250=113\]
\[35+113=148\]
Therefore, 148 individuals can donate blood to the accident victim with blood group B.
(b) Genetic diagram
Heterozygous blood group A man: \(I^Ai\)
Blood group AB woman: \(I^AI^B\)
Gametes from the man are \(I^A\) and \(i\), while gametes from the woman are \(I^A\) and \(I^B\).
The possible genotypes and phenotypes of the children are:
- \(I^AI^A\): blood group A
- \(I^Ai\): blood group A
- \(I^AI^B\): blood group AB
- \(I^Bi\): blood group B
Thus, the possible blood groups are A, AB and B, in the ratio:
\[2\text{ A}:1\text{ AB}:1\text{ B}\]
That is, 50% blood group A, 25% blood group AB and 25% blood group B. No child will have blood group O.
Vraag 5 Verslag
(a) (i) List three characteristics of living organisms.
(ii) Explain briefly the characteristics listed in (a)(i) above.
(b) In a tabular form, state four differences between plants and animals.
(c)(i) Name one organism that exhibits both plant and animal features.
(ii) State four animal features and two plant features possessed by the organism named in (c)(i) above.
(a)(i) Three characteristics of living organisms: nutrition, respiration, and movement (growth, reproduction, excretion, irritability/sensitivity are also valid).
(ii) Brief explanation
- Nutrition: the taking in and use of food materials for energy, growth and repair of the body.
- Respiration: the breakdown of food in cells to release energy needed for life activities.
- Movement: the ability of an organism, or parts of it, to change position or place.
(b) Four differences between plants and animals
| Plants | Animals |
|---|---|
| Manufacture their own food (autotrophic) | Feed on ready-made food (heterotrophic) |
| Possess chlorophyll | Lack chlorophyll |
| Cells have a cellulose cell wall | Cells lack a cell wall |
| Growth occurs at the tips (apical), and is usually indefinite | Growth occurs all over the body, and is usually definite |
| Cannot move from place to place (fixed) | Can move from place to place (locomotion) |
(c)(i) Organism exhibiting both plant and animal features: Euglena.
(ii) Four animal features: moves using a flagellum; has a contractile vacuole; has an eyespot (stigma) sensitive to light; lacks a cellulose cell wall (has a flexible pellicle) and can feed heterotrophically.
Two plant features: possesses chloroplasts and carries out photosynthesis; contains pyrenoids associated with food (starch) storage.
Antwoorddetails
(a)(i) Three characteristics of living organisms: nutrition, respiration, and movement (growth, reproduction, excretion, irritability/sensitivity are also valid).
(ii) Brief explanation
- Nutrition: the taking in and use of food materials for energy, growth and repair of the body.
- Respiration: the breakdown of food in cells to release energy needed for life activities.
- Movement: the ability of an organism, or parts of it, to change position or place.
(b) Four differences between plants and animals
| Plants | Animals |
|---|---|
| Manufacture their own food (autotrophic) | Feed on ready-made food (heterotrophic) |
| Possess chlorophyll | Lack chlorophyll |
| Cells have a cellulose cell wall | Cells lack a cell wall |
| Growth occurs at the tips (apical), and is usually indefinite | Growth occurs all over the body, and is usually definite |
| Cannot move from place to place (fixed) | Can move from place to place (locomotion) |
(c)(i) Organism exhibiting both plant and animal features: Euglena.
(ii) Four animal features: moves using a flagellum; has a contractile vacuole; has an eyespot (stigma) sensitive to light; lacks a cellulose cell wall (has a flexible pellicle) and can feed heterotrophically.
Two plant features: possesses chloroplasts and carries out photosynthesis; contains pyrenoids associated with food (starch) storage.
