WAEC SSCE - Biology - 2005 (Essay)
Pergunta 1 Relatório
(a) Define enzymes.
(b) State six characteristics of enzymes.
(c) Describe the role of pancreatic juice in the digestion of carbohydrates and proteins in a mammal.
(d) In what form is carbohydrate stored in (i) animals (ii) plants
(e) Describe the saprophytic nutrition of Rhizopus.
(a) Definition of enzymes
Enzymes are organic catalysts, made of protein, produced by living cells, which speed up the rate of biochemical reactions without themselves being used up or altered in the process.
(b) Six characteristics of enzymes
- They are proteins in nature.
- They are specific in action (each enzyme acts on one substrate or type of reaction).
- They are required in very small quantities.
- They are not used up in the reaction, so they can be used again (catalysts).
- Their activity is affected by temperature and is destroyed (denatured) by high temperature.
- Their activity is affected by pH; each works best at an optimum pH.
(Also acceptable: their action can be reversible; their activity is affected by substrate concentration.)
(c) Role of pancreatic juice in digestion of carbohydrates and proteins
Pancreatic juice is poured into the duodenum and contains several enzymes:
- Pancreatic amylase digests starch (carbohydrate) into maltose.
- Trypsin (secreted as inactive trypsinogen and activated by enterokinase) digests proteins and peptones into smaller peptides and amino acids.
The juice is also alkaline, providing the correct pH for these enzymes to work.
(d) Form in which carbohydrate is stored
(i) In animals: glycogen (in the liver and muscles).
(ii) In plants: starch.
(e) Saprophytic nutrition of Rhizopus
Rhizopus (bread mould) feeds saprophytically on dead organic matter such as bread. It grows fine thread-like hyphae; the root-like rhizoids penetrate the food and secrete digestive enzymes onto it. These enzymes digest the food externally (extracellular digestion), breaking down starch and proteins into soluble substances. The soluble products are then absorbed through the hyphae into the fungus and used for energy and growth, while excess food is stored.
Detalhes da Resposta
(a) Definition of enzymes
Enzymes are organic catalysts, made of protein, produced by living cells, which speed up the rate of biochemical reactions without themselves being used up or altered in the process.
(b) Six characteristics of enzymes
- They are proteins in nature.
- They are specific in action (each enzyme acts on one substrate or type of reaction).
- They are required in very small quantities.
- They are not used up in the reaction, so they can be used again (catalysts).
- Their activity is affected by temperature and is destroyed (denatured) by high temperature.
- Their activity is affected by pH; each works best at an optimum pH.
(Also acceptable: their action can be reversible; their activity is affected by substrate concentration.)
(c) Role of pancreatic juice in digestion of carbohydrates and proteins
Pancreatic juice is poured into the duodenum and contains several enzymes:
- Pancreatic amylase digests starch (carbohydrate) into maltose.
- Trypsin (secreted as inactive trypsinogen and activated by enterokinase) digests proteins and peptones into smaller peptides and amino acids.
The juice is also alkaline, providing the correct pH for these enzymes to work.
(d) Form in which carbohydrate is stored
(i) In animals: glycogen (in the liver and muscles).
(ii) In plants: starch.
(e) Saprophytic nutrition of Rhizopus
Rhizopus (bread mould) feeds saprophytically on dead organic matter such as bread. It grows fine thread-like hyphae; the root-like rhizoids penetrate the food and secrete digestive enzymes onto it. These enzymes digest the food externally (extracellular digestion), breaking down starch and proteins into soluble substances. The soluble products are then absorbed through the hyphae into the fungus and used for energy and growth, while excess food is stored.
Pergunta 2 Relatório
(a) Explain the following terms:
(i) trait
(ii) recessive gene
(iii) test cross
(iv) heterozygous
(b) How do you determine whether a man with blood group '0' and married to a woman with blood group 'AB' is the father of a child with blood group 'AB' born to them?
(c) (i) In rabbit brown hair is dominant over white hair colour. How could you determine that a brown coloured male rabbit is homozygous?
(ii) What is the difference between the chromosome number of a gamete and that of the body cell of the same organism?
(a) Explanation of terms
- (i) Trait: a distinct inherited characteristic or feature of an organism, e.g. eye colour, height or blood group.
- (ii) Recessive gene: an allele whose effect is masked in the presence of a dominant allele; it is only expressed when it is present in the homozygous condition (two recessive alleles together).
- (iii) Test cross: a cross between an individual of unknown genotype (showing the dominant trait) and a homozygous recessive individual, done to find out whether the unknown is homozygous or heterozygous.
- (iv) Heterozygous: having two different alleles of a gene for a particular trait, e.g. Bb.
(b) Determining fatherhood using blood groups
A person with blood group O has the genotype ii; he can only pass on an i allele. A person with blood group AB has the genotype IAIB. A child of blood group AB must have received IA from one parent and IB from the other. Since the group-O man can only give i, he cannot supply either IA or IB. Therefore a group-O man cannot be the biological father of an AB child; the AB child cannot be his.
(c)(i) Determining that a brown male rabbit is homozygous
Carry out a test cross: mate the brown male with several white (homozygous recessive, ww) females. If the male is homozygous WW, all the offspring will be brown. If any white offspring appear, the male is heterozygous Ww. So if all offspring are brown, the male is homozygous.
(c)(ii) Difference in chromosome number
A gamete has the haploid number of chromosomes (n), which is half the number in a body cell. A body (somatic) cell has the diploid number (2n), which is twice that of the gamete.
Detalhes da Resposta
(a) Explanation of terms
- (i) Trait: a distinct inherited characteristic or feature of an organism, e.g. eye colour, height or blood group.
- (ii) Recessive gene: an allele whose effect is masked in the presence of a dominant allele; it is only expressed when it is present in the homozygous condition (two recessive alleles together).
- (iii) Test cross: a cross between an individual of unknown genotype (showing the dominant trait) and a homozygous recessive individual, done to find out whether the unknown is homozygous or heterozygous.
- (iv) Heterozygous: having two different alleles of a gene for a particular trait, e.g. Bb.
(b) Determining fatherhood using blood groups
A person with blood group O has the genotype ii; he can only pass on an i allele. A person with blood group AB has the genotype IAIB. A child of blood group AB must have received IA from one parent and IB from the other. Since the group-O man can only give i, he cannot supply either IA or IB. Therefore a group-O man cannot be the biological father of an AB child; the AB child cannot be his.
(c)(i) Determining that a brown male rabbit is homozygous
Carry out a test cross: mate the brown male with several white (homozygous recessive, ww) females. If the male is homozygous WW, all the offspring will be brown. If any white offspring appear, the male is heterozygous Ww. So if all offspring are brown, the male is homozygous.
(c)(ii) Difference in chromosome number
A gamete has the haploid number of chromosomes (n), which is half the number in a body cell. A body (somatic) cell has the diploid number (2n), which is twice that of the gamete.
Pergunta 3 Relatório
(a) (i) Define asexual reproduction.
(ii) Name two types of asexual reproduction which occur in animals giving one example in each case.
(b) In a tabular form outline four differences between sexual and asexual reproduction.
(c) Make a large, labelled diagram 8 - 10cm long of the human spermatozoon to show its structure.
(d) State one function each of any three organelles found in the spermatozoon.
(a)(i) Definition of asexual reproduction
Asexual reproduction is the production of a new individual (offspring) from a single parent without the fusion of gametes (no fertilization) and without any change in the chromosome number. The offspring produced are genetically identical to the parent.
(a)(ii) Two types of asexual reproduction in animals (with one example each)
- Binary fission - the parent divides into two equal daughter cells. Example: Amoeba (or Paramecium).
- Budding - a small outgrowth (bud) develops on the parent and later detaches to form a new individual. Example: Hydra (or Obelia).
(Sporulation in Plasmodium, or parthenogenesis in aphids and honey bees, are also acceptable.)
(b) Four differences between sexual and asexual reproduction
| Sexual reproduction | Asexual reproduction |
|---|---|
| Two parents are usually involved | Only one parent is involved |
| Gametes (sex cells) are formed and fuse in fertilization to form a zygote | No gametes are formed; there is no fertilization and no zygote |
| Meiosis is involved; offspring show genetic variation | Only mitosis is involved; offspring are genetically identical to the parent |
| It is a slower mode of reproduction, producing fewer individuals | It is a rapid mode of reproduction, producing many individuals |
(c) Large, labelled diagram of the human spermatozoon (8 - 10 cm long)
The spermatozoon is divided into three main regions: the head (bearing the acrosome and the haploid nucleus), the middle piece (packed with mitochondria arranged in a spiral around the axial filament), and the long whip-like tail (flagellum) used for swimming.
(d) One function each of three organelles found in the spermatozoon
- Acrosome (cap of the head): contains digestive (lytic) enzymes that dissolve the membranes surrounding the ovum, allowing the sperm to penetrate and fertilize the egg.
- Nucleus (in the head): carries the haploid number of chromosomes (the male genetic material / DNA) that combine with those of the ovum at fertilization.
- Mitochondria (in the middle piece): contain respiratory enzymes and release energy (ATP) that powers the beating of the tail for the sperm's movement.
Detalhes da Resposta
(a)(i) Definition of asexual reproduction
Asexual reproduction is the production of a new individual (offspring) from a single parent without the fusion of gametes (no fertilization) and without any change in the chromosome number. The offspring produced are genetically identical to the parent.
(a)(ii) Two types of asexual reproduction in animals (with one example each)
- Binary fission - the parent divides into two equal daughter cells. Example: Amoeba (or Paramecium).
- Budding - a small outgrowth (bud) develops on the parent and later detaches to form a new individual. Example: Hydra (or Obelia).
(Sporulation in Plasmodium, or parthenogenesis in aphids and honey bees, are also acceptable.)
(b) Four differences between sexual and asexual reproduction
| Sexual reproduction | Asexual reproduction |
|---|---|
| Two parents are usually involved | Only one parent is involved |
| Gametes (sex cells) are formed and fuse in fertilization to form a zygote | No gametes are formed; there is no fertilization and no zygote |
| Meiosis is involved; offspring show genetic variation | Only mitosis is involved; offspring are genetically identical to the parent |
| It is a slower mode of reproduction, producing fewer individuals | It is a rapid mode of reproduction, producing many individuals |
(c) Large, labelled diagram of the human spermatozoon (8 - 10 cm long)
The spermatozoon is divided into three main regions: the head (bearing the acrosome and the haploid nucleus), the middle piece (packed with mitochondria arranged in a spiral around the axial filament), and the long whip-like tail (flagellum) used for swimming.
(d) One function each of three organelles found in the spermatozoon
- Acrosome (cap of the head): contains digestive (lytic) enzymes that dissolve the membranes surrounding the ovum, allowing the sperm to penetrate and fertilize the egg.
- Nucleus (in the head): carries the haploid number of chromosomes (the male genetic material / DNA) that combine with those of the ovum at fertilization.
- Mitochondria (in the middle piece): contain respiratory enzymes and release energy (ATP) that powers the beating of the tail for the sperm's movement.
Pergunta 4 Relatório
(a) List four functions of.the mammalian skeleton and name a particular part of the skeleton which performs each of these functions.
(b) Briefly describe how muscles and bones bring about movement at the elbow.
(c) How is support provided for in each of the following plants? (i) Herbaceous plants (ii) Woody plants.
(d) Name one vitamin and one mineral element necessary for healthy development of bones.
(a) Four functions of the mammalian skeleton and the part that performs each
| Function | Part of the skeleton |
|---|---|
| Protection of delicate organs | Cranium (protects the brain); rib cage (protects heart and lungs) |
| Support / gives shape to the body | Vertebral column (backbone) |
| Movement / locomotion (attachment for muscles) | Limb bones (femur, humerus) |
| Manufacture of blood cells | Red bone marrow of long bones such as the femur |
(b) How muscles and bones bring about movement at the elbow
The elbow is a hinge joint between the humerus (upper arm) and the radius and ulna (forearm). Two muscles act as an antagonistic pair: the biceps (a flexor) on the front and the triceps (an extensor) at the back. To bend (flex) the arm, the biceps contracts and shortens while the triceps relaxes, pulling the forearm up. To straighten (extend) the arm, the triceps contracts and the biceps relaxes, pulling the forearm down. Because each muscle can only pull (not push), the two work in opposition to move the bones about the joint.
(c) Support in plants
(i) Herbaceous plants: support comes mainly from the turgidity of their cells; water in the vacuoles keeps the cells firm, and the collenchyma and turgid parenchyma keep the soft stem upright.
(ii) Woody plants: support comes from the lignified (woody) xylem tissue and sclerenchyma, and from secondary thickening of the stem, which provide rigid mechanical strength.
(d) One vitamin and one mineral for healthy bones
Vitamin: vitamin D. Mineral element: calcium (phosphorus is also acceptable).
Detalhes da Resposta
(a) Four functions of the mammalian skeleton and the part that performs each
| Function | Part of the skeleton |
|---|---|
| Protection of delicate organs | Cranium (protects the brain); rib cage (protects heart and lungs) |
| Support / gives shape to the body | Vertebral column (backbone) |
| Movement / locomotion (attachment for muscles) | Limb bones (femur, humerus) |
| Manufacture of blood cells | Red bone marrow of long bones such as the femur |
(b) How muscles and bones bring about movement at the elbow
The elbow is a hinge joint between the humerus (upper arm) and the radius and ulna (forearm). Two muscles act as an antagonistic pair: the biceps (a flexor) on the front and the triceps (an extensor) at the back. To bend (flex) the arm, the biceps contracts and shortens while the triceps relaxes, pulling the forearm up. To straighten (extend) the arm, the triceps contracts and the biceps relaxes, pulling the forearm down. Because each muscle can only pull (not push), the two work in opposition to move the bones about the joint.
(c) Support in plants
(i) Herbaceous plants: support comes mainly from the turgidity of their cells; water in the vacuoles keeps the cells firm, and the collenchyma and turgid parenchyma keep the soft stem upright.
(ii) Woody plants: support comes from the lignified (woody) xylem tissue and sclerenchyma, and from secondary thickening of the stem, which provide rigid mechanical strength.
(d) One vitamin and one mineral for healthy bones
Vitamin: vitamin D. Mineral element: calcium (phosphorus is also acceptable).
Pergunta 5 Relatório
(a) Write short notes on the following:
(i) habitat
(ii) ecological niche.
(b) (i) List three instruments used in the measurement of different ecological factors.
(ii) Briefly state what each instrument listed in (b) (i) above is used for.
(c) Name; (i) three plants (ii) two animals found in savannah vegetation.
(a) Short notes
(i) Habitat: the particular natural place or type of environment where an organism lives, providing it with the conditions and resources it needs, e.g. a pond, a forest floor or the soil. It answers the question 'where does the organism live?'
(ii) Ecological niche: the role or function of an organism within its habitat, including how it obtains food, its relationships with other organisms and the conditions it requires. It answers 'what does the organism do and how does it fit into the community?' No two species can occupy exactly the same niche indefinitely.
(b)(i) and (ii) Instruments for measuring ecological factors and their uses
| Instrument | Use |
|---|---|
| Thermometer | Measures temperature of air, water or soil |
| Rain gauge | Measures the amount of rainfall |
| Hygrometer | Measures the relative humidity of the air |
(Other acceptable instruments: wind vane - wind direction; anemometer - wind speed; photometer/light meter - light intensity; pH meter - acidity/alkalinity of soil or water.)
(c) Organisms found in savannah vegetation
(i) Three plants: shea butter tree (Vitellaria), locust bean tree (Parkia), baobab, acacia, elephant grass or spear grass (any three).
(ii) Two animals: grasscutter (cane rat), antelope, grasshopper, lion, hare or guinea fowl (any two).
Detalhes da Resposta
(a) Short notes
(i) Habitat: the particular natural place or type of environment where an organism lives, providing it with the conditions and resources it needs, e.g. a pond, a forest floor or the soil. It answers the question 'where does the organism live?'
(ii) Ecological niche: the role or function of an organism within its habitat, including how it obtains food, its relationships with other organisms and the conditions it requires. It answers 'what does the organism do and how does it fit into the community?' No two species can occupy exactly the same niche indefinitely.
(b)(i) and (ii) Instruments for measuring ecological factors and their uses
| Instrument | Use |
|---|---|
| Thermometer | Measures temperature of air, water or soil |
| Rain gauge | Measures the amount of rainfall |
| Hygrometer | Measures the relative humidity of the air |
(Other acceptable instruments: wind vane - wind direction; anemometer - wind speed; photometer/light meter - light intensity; pH meter - acidity/alkalinity of soil or water.)
(c) Organisms found in savannah vegetation
(i) Three plants: shea butter tree (Vitellaria), locust bean tree (Parkia), baobab, acacia, elephant grass or spear grass (any three).
(ii) Two animals: grasscutter (cane rat), antelope, grasshopper, lion, hare or guinea fowl (any two).
Pergunta 6 Relatório
(a) Write a short note on the importance of the presence of an effective transport system in mammals.
(b) state eight functions of blood in mammals.
(c) list four materials transported in the bodies of flowering plants.
(a) Importance of an effective transport system in mammals
Mammals are large, active, warm-blooded animals with a high metabolic rate and a small surface-area-to-volume ratio, so diffusion alone cannot supply their deep-lying cells fast enough. An effective transport system (the blood circulatory system) is therefore essential to carry oxygen and digested food to all the cells, to remove carbon dioxide and other waste products to the excretory organs, to distribute heat and hormones round the body, and to defend the body against disease. Without it the cells would be starved of nutrients and poisoned by accumulated wastes.
(b) Eight functions of blood in mammals
- Transport of oxygen from the lungs to the tissues.
- Transport of carbon dioxide from the tissues to the lungs.
- Transport of digested food (glucose, amino acids) to the cells.
- Transport of nitrogenous waste (urea) to the kidneys for excretion.
- Transport of hormones from endocrine glands to their target organs.
- Distribution of heat to regulate body temperature.
- Defence against disease by white blood cells and antibodies.
- Clotting of blood to seal wounds and prevent loss of blood.
(c) Four materials transported in the bodies of flowering plants
- Water (through the xylem).
- Dissolved mineral salts (through the xylem).
- Manufactured food, especially sucrose (through the phloem).
- Amino acids and other organic solutes (through the phloem).
Detalhes da Resposta
(a) Importance of an effective transport system in mammals
Mammals are large, active, warm-blooded animals with a high metabolic rate and a small surface-area-to-volume ratio, so diffusion alone cannot supply their deep-lying cells fast enough. An effective transport system (the blood circulatory system) is therefore essential to carry oxygen and digested food to all the cells, to remove carbon dioxide and other waste products to the excretory organs, to distribute heat and hormones round the body, and to defend the body against disease. Without it the cells would be starved of nutrients and poisoned by accumulated wastes.
(b) Eight functions of blood in mammals
- Transport of oxygen from the lungs to the tissues.
- Transport of carbon dioxide from the tissues to the lungs.
- Transport of digested food (glucose, amino acids) to the cells.
- Transport of nitrogenous waste (urea) to the kidneys for excretion.
- Transport of hormones from endocrine glands to their target organs.
- Distribution of heat to regulate body temperature.
- Defence against disease by white blood cells and antibodies.
- Clotting of blood to seal wounds and prevent loss of blood.
(c) Four materials transported in the bodies of flowering plants
- Water (through the xylem).
- Dissolved mineral salts (through the xylem).
- Manufactured food, especially sucrose (through the phloem).
- Amino acids and other organic solutes (through the phloem).
