WAEC SSCE - Biology - 2018

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Using contact lenses may lead to an eye infection. Contact lenses sit directly on the eye, and if they are not cleaned and stored properly, bacteria can accumulate on the lenses and cause an infection. Symptoms of an eye infection include redness, pain, sensitivity to light, and discharge. To prevent eye infections when wearing contact lenses, it is important to wash your hands thoroughly before handling them, clean and disinfect them regularly, and avoid wearing them for too long or while sleeping. It is also important to follow your eye doctor's instructions for proper use and care of your contact lenses. Convex lenses, biconcave lenses, and concave lenses are not likely to lead to an eye infection, as they are not worn directly on the eye and do not come into contact with it. These types of lenses are used to correct vision problems and do not pose a risk of infection unless they are contaminated and come into contact with the eye.

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Spirogyra is an organism composed of cells, so it belongs to the level of organization known as a "cell." Spirogyra is a type of filamentous green algae that consists of many individual cells arranged in a long chain, held together by a gel-like substance. Although Spirogyra cells can perform some specialized functions, such as photosynthesis, they are not organized into tissues or organs. Therefore, Spirogyra is not classified as a "tissue" or "organ" level of organization. Finally, since Spirogyra is an individual organism and not part of a larger system, it is also not classified as a "system" level of organization.

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The chemical bond that holds the base pairs of the two strands of DNA together is a hydrogen bond. DNA is composed of two strands of nucleotides, which are composed of a sugar molecule, a phosphate group, and a nitrogen-containing base. The nitrogen-containing bases in DNA are adenine (A), cytosine (C), guanine (G), and thymine (T). The two strands of DNA are held together by hydrogen bonds between the nitrogen-containing bases. Adenine always bonds with thymine, and cytosine always bonds with guanine. These hydrogen bonds are relatively weak, but they are strong enough to hold the two strands of DNA together. Therefore, the chemical bond that holds the base pairs of the two strands of DNA together is a hydrogen bond.

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The odontoid process is found on the axis vertebra. The axis is the second cervical (neck) vertebra, which is located just below the atlas vertebra. The odontoid process is a projection of bone that extends from the upper surface of the axis vertebra and serves as a pivot point for the rotation of the head.

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The organelle that is found only in plant cells is plastids. Plastids are organelles that are involved in the synthesis and storage of food, pigments, and other materials in plant cells. They are responsible for storing and converting energy, and they can also play a role in the coloration of plant tissues. Plastids come in several forms, including chloroplasts, which contain chlorophyll and are involved in photosynthesis, and chromoplasts, which contain pigments that give fruits and flowers their color. Mitochondria, ribosomes, and lysosomes are all found in both plant and animal cells.

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Genes that remain linked are those that are close to each other on the chromosomes. Chromosomes are structures in the cell that carry genetic information in the form of genes. Genes are segments of DNA that contain the instructions for making proteins, which are the building blocks of the body. In sexually reproducing organisms, such as humans, each parent contributes one chromosome to each pair of chromosomes in the offspring. As a result, offspring have two copies of each gene, one from each parent. Genes that are located close to each other on the same chromosome are more likely to be inherited together because they are physically close and cannot easily separate during the process of meiosis, which is the process by which cells divide to form gametes, such as sperm and eggs. Therefore, genes that remain linked are those that are close to each other on the chromosomes.

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A plant cell has 14 chromosomes prior to mitosis, but the number of chromosomes in the daughter cells depends on the type of cell division. During mitosis, the cell duplicates its chromosomes and then separates them equally into two identical daughter cells. This means that each daughter cell will receive the same number of chromosomes as the parent cell. So, after mitosis, each daughter cell will also have 14 chromosomes, the same as the parent cell. However, in other forms of cell division such as meiosis, the number of chromosomes in the daughter cells can be different from the parent cell. But for mitosis, the number of chromosomes in the daughter cells is the same as the parent cell.

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The correct statement is: "Intensity of stimulus must reach a threshold value before the neurons can be excited." Neurons, which are the basic building blocks of the nervous system, respond to various stimuli by transmitting electrical signals. However, not all stimuli are strong enough to trigger this response. The stimulus must reach a certain level of intensity or strength, known as the threshold, before the neuron will be excited and transmit an electrical signal. If the stimulus is below the threshold, the neuron will not respond. This is why neurons must receive a stimulus of sufficient intensity before they can be excited.

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The ascent of water in tall trees is mainly due to transpiration pull. Transpiration is the process by which water evaporates from the leaves of plants and creates a negative pressure or tension in the water column of the xylem, which is the tissue responsible for transporting water in plants. This negative pressure or tension, combined with the cohesive forces between water molecules, creates a continuous column of water that extends from the roots to the leaves of the tree. The cohesive forces between water molecules allow the water column to remain unbroken, while the transpiration pull provides the force that moves the water up the tree. Adhesive forces between the water and the cell walls of the xylem also help to keep the water column intact and prevent it from breaking under tension. Root pressure, which is the pressure created by the roots of a plant, can also play a role in moving water up a tree, but it is not the main mechanism responsible for water ascent in tall trees.

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Xerophytes have the following characteristics aimed at conserving water except broad leaf surfaces. Xerophytes are plants that have adaptations to survive in arid or desert environments where water is scarce. To conserve water, xerophytes have several adaptations, including: - Thick cuticle: A thick cuticle is a waxy layer on the surface of leaves that reduces water loss through transpiration. - Sunken stomata: Stomata are tiny pores on the surface of leaves that allow for gas exchange. In xerophytes, stomata are often sunken into the leaf surface, which reduces the surface area exposed to the air and reduces water loss. - Waxy cuticle: Like a thick cuticle, a waxy cuticle helps reduce water loss through transpiration. Broad leaf surfaces, on the other hand, increase the surface area of the leaf and can increase water loss through transpiration. Therefore, the characteristic of xerophytes aimed at conserving water that is not present is broad leaf surfaces.

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The digestion of starch, protein, and lipids would be affected if the duodenum of a person was surgically removed. The duodenum is the first part of the small intestine, where digestive enzymes from the pancreas and bile from the liver are mixed with partially digested food from the stomach. The enzymes in the duodenum help break down starch into smaller sugar molecules, protein into amino acids, and lipids into fatty acids and glycerol. If the duodenum is removed, the digestive enzymes and bile will not mix with the food, and the digestion of these substances will be impaired. Therefore, the person may have difficulty digesting starch, protein, and lipids, leading to malabsorption and other digestive problems.

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The hospital should have carried out an agglutination test on both patients X and Y before transfusing the blood from the donor. The agglutination test is a standard blood test that determines the compatibility between the donor's blood and the recipient's blood. The test checks for the presence of antigens and antibodies in the blood, which could trigger an adverse reaction in the recipient. In this case, patient X has blood group AO, which means they have A antigens on their red blood cells and anti-B antibodies in their plasma. Patient Y, on the other hand, has blood group AB, which means they have both A and B antigens on their red blood cells and no antibodies in their plasma. The blood transfusion from the donor may have contained B antigens, which would have triggered an immune response in patient X, causing difficulty in breathing. Therefore, the agglutination test would have prevented the transfusion of incompatible blood and avoided any adverse reactions.

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The scientist who introduced the system of naming organisms using two Latin names, known as binomial nomenclature, was Carolus Linnaeus. Linnaeus was a Swedish botanist and zoologist who lived in the 18th century. He created a system for classifying and naming all living things, which is still used today. In this system, each species is given a unique two-part name, consisting of the genus name and the species name, both written in Latin. For example, the scientific name for humans is Homo sapiens, where Homo is the genus name and sapiens is the species name. This system allows scientists to clearly and precisely communicate about specific species, and to understand their relationships to other species. Linnaeus' system of classification and naming has been incredibly important for the study of biology and the understanding of the diversity of life on Earth.

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Starch is a complex carbohydrate made up of many glucose units linked together. The process by which starch is converted into maltose is called hydrolysis. In hydrolysis, a water molecule is added to the bond between two glucose units, breaking the bond and forming two separate molecules of glucose. This process is catalyzed by an enzyme called amylase. Therefore, the correct answer is (a) Hydrolysis.

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The theory depicted in the illustration is known as Lamarckism or Lamarckian evolution, and it was proposed by Jean Lamarck. Lamarck proposed that organisms can acquire traits during their lifetime based on their environment and behavior, and these acquired traits can be passed on to their offspring. He believed that the environment could drive evolution by selecting for advantageous traits and gradually eliminating disadvantageous ones. However, this theory was later largely discredited by scientific evidence, and it was replaced by the theory of natural selection proposed by Charles Darwin.

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Conservation of wildlife is necessary for several reasons, one of the main reasons being to prevent extinction of species. Extinction means that a species is no longer found on the Earth and has disappeared forever. This is a serious problem because once a species is gone, it cannot be brought back. Additionally, loss of species can also have a cascading effect on the ecosystem and other species that rely on it. Another important reason for conservation is that many wild animals play important roles in the ecosystem. For example, predators help control populations of other species and maintain balance in the ecosystem. Wild species also provide valuable resources and ecosystem services, such as pollination and seed dispersal, that are essential for human well-being. Finally, conservation of wildlife is also important for cultural, educational, and aesthetic reasons. Many people derive pleasure from observing wild animals and appreciate their beauty and diversity. Wildlife also provides important opportunities for scientific study and research that can help us better understand the natural world and improve our ability to protect it. In conclusion, conservation of wildlife is necessary to protect species from extinction, maintain the balance of ecosystems, and provide cultural, educational, and aesthetic benefits.

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When large numbers of organisms share limited space and resources, the immediate result is competition. Competition occurs when organisms within a population compete with each other for resources such as food, water, shelter, and mates. As the population grows, resources become more scarce, and the competition intensifies. This can lead to natural selection, where individuals with advantageous traits for obtaining resources, such as better camouflage or faster running speed, are more likely to survive and reproduce. Those with less advantageous traits may struggle to compete and may not survive long enough to reproduce, which can lead to a decrease in their numbers over time. While some individuals may choose to emigrate or immigrate to find new resources, if the competition remains intense, it can lead to extinction for some species.

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The disease caused by a bacterium is syphilis. Syphilis is a sexually transmitted disease caused by the bacterium Treponema pallidum. It is transmitted through sexual contact and can also be transmitted from an infected mother to her unborn child. Syphilis can cause a variety of symptoms, including genital sores, skin rashes, and fever. If left untreated, syphilis can cause serious complications such as blindness, dementia, and even death. Syphilis can be treated effectively with antibiotics.

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Fossils are naturally preserved in rocks. When a plant or animal dies, its body may become buried in sediment, such as sand or mud. Over time, more layers of sediment can accumulate on top, which can compress and harden the lower layers into rock. As the body decays, minerals from the surrounding sediment can seep into the bones or other hard parts, replacing the organic material with rock-like minerals. This process is called fossilization, and it can preserve the remains of the organism for millions of years. Later on, erosion and weathering can expose these fossils, allowing us to study and learn about the organisms that lived long ago.

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The streaming movement of cytoplasm within the Paramecium is known as Cyclosis. Cytoplasm is the gel-like substance that makes up most of a cell's interior and contains all the organelles and other cellular structures. In the Paramecium, the cytoplasm moves in a continuous, circular flow, which is called Cyclosis. This flow helps distribute nutrients, waste, and other materials throughout the cell, and it also helps mix and distribute chemicals that are involved in various cellular processes. Overall, Cyclosis plays a critical role in maintaining the health and function of the Paramecium cell.

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Ultrafiltration in the kidney takes place in Bowman's capsule. Bowman's capsule is a cup-shaped structure located in the outer part of the kidney, called the cortex. It surrounds a cluster of blood vessels called the glomerulus. The glomerulus and Bowman's capsule together form a structure called the renal corpuscle. During ultrafiltration, blood from the glomerulus flows into Bowman's capsule. The glomerulus is made up of a network of capillaries with very small pores. These pores allow small molecules such as water, salts, and waste products to be filtered out of the blood and into the Bowman's capsule. The larger molecules such as proteins and blood cells cannot pass through the pores and remain in the bloodstream. The filtered fluid in Bowman's capsule is called the glomerular filtrate. It contains water, salts, glucose, and other small molecules. This filtrate then passes through the rest of the nephron, where it is further processed and modified before being excreted as urine. So, in summary, ultrafiltration in the kidney takes place in Bowman's capsule, where small molecules are filtered out of the blood and into the nephron to form the glomerular filtrate.

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Oxygen is not an excretory product of animals. Oxygen is essential for respiration, which is the process that releases energy from food. During respiration, animals take in oxygen and release carbon dioxide as a waste product. Urea is a waste product formed in the liver as a result of protein metabolism, and it is excreted by the kidneys. Sweat is also an excretory product that is produced by sweat glands to regulate body temperature and remove excess water and salts. Therefore, the correct answer is option D, which is oxygen.

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The process being investigated in this experiment is the ascent of water through the xylem. By placing the seedling in a solution of red ink, the red dye is able to travel up the xylem vessels along with the water. When a transverse section of the stem is examined under a microscope, the red dye can be seen in the xylem vessels, showing the path taken by water through the plant. This process is also known as transpiration, where water evaporates from the leaves and creates a negative pressure, which draws water up through the roots and into the xylem. The study of this process is important for understanding how plants transport water and nutrients from the roots to the rest of the plant.

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The most important factor(s) that influence(s) the ecological niche of an organism is/are the competition for food and space. Ecological niche refers to the role and position of a species within its habitat. It encompasses all the interactions between the species and its biotic and abiotic environment. Competition for resources such as food, water, and space is a major factor that shapes the ecological niche of an organism. The availability of these resources determines the survival and growth of a population, as well as the interactions between different species in the ecosystem. Therefore, the competition for food and space is a crucial factor that shapes the ecological niche of an organism.

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The association between living organisms in which one lives on and feeds at the expense of the other is called parasitism. In this relationship, one organism (the parasite) benefits while the other organism (the host) is harmed. The parasite lives on or within the host and uses its resources for food and shelter. Examples of parasites include tapeworms, lice, and mosquitoes.

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The greatest contribution to genetic studies was made by Gregor Mendel. Mendel was an Austrian monk who conducted a series of experiments in the mid-19th century with pea plants, which allowed him to discover the basic principles of inheritance and the patterns of transmission of genetic traits from parents to offspring. He established the laws of segregation and independent assortment, which provided a framework for understanding the mechanisms of genetic inheritance. His work laid the foundation for the modern science of genetics, and he is widely regarded as the father of genetics.

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The larva in the diagram is commonly referred to as a caterpillar. Caterpillars are the juvenile form of butterflies and moths. They have a worm-like appearance and are characterized by their multiple legs, which they use to move around and search for food. As they grow, they molt their skin several times, eventually transforming into a pupa or chrysalis, where they undergo metamorphosis and emerge as an adult butterfly or moth.

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Active transport differs from diffusion in that active transport allows the movement of substances against the concentration gradient. Diffusion is the process by which molecules move from an area of high concentration to an area of low concentration. This is driven by the natural tendency of molecules to distribute evenly in a system. Active transport, on the other hand, requires energy to move substances against the concentration gradient, from an area of low concentration to an area of high concentration. This process is important in cells because it allows the cell to take in nutrients, eliminate waste, and maintain a balance of ions and other substances inside and outside the cell. Therefore, active transport differs from diffusion in that active transport allows the movement of substances against the concentration gradient.

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The exchange of genes between homologous chromosomes is called crossing over. During meiosis, which is the process by which cells divide to form gametes, homologous chromosomes pair up and exchange segments of their genetic material. This exchange occurs at specific points called chiasmata, which are where the chromosomes break and rejoin with each other. Crossing over can result in the exchange of alleles, which are alternative versions of a gene, between the homologous chromosomes. This can lead to the production of new combinations of alleles that were not present in either parent, which contributes to genetic diversity. Back cross and test cross are different types of breeding experiments, while mutation refers to a change in the DNA sequence that can arise spontaneously or be induced by environmental factors.

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The social insect that is not included in the given list is the housefly. Houseflies are not social insects because they do not live in colonies or work together to maintain a nest or hive. Houseflies are solitary insects that do not exhibit any social behavior. In contrast, termites, honeybees, and ants are all social insects that live in colonies or hives and exhibit a division of labor where different individuals perform different tasks to maintain the colony. For example, in an ant colony, there are workers that gather food, soldiers that defend the colony, and a queen that lays eggs. The individuals in a social insect colony work together to ensure the survival and success of the colony.

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The thyroid gland is a part of the endocrine system, and it is located in the neck, specifically at the base of the neck. The gland is butterfly-shaped, with two lobes on either side of the trachea (windpipe) and connected by a thin strip of tissue called the isthmus. It produces hormones that regulate metabolism and other bodily functions.

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The instrument used to determine the turbidity of water is a Secchi disc. Turbidity refers to the cloudiness or haziness of a liquid, caused by the presence of suspended particles in the water. The Secchi disc is a simple, circular device that is used to measure water turbidity by determining the depth at which the disc is no longer visible when it is lowered into the water. The Secchi disc is typically painted in alternating black and white quadrants, and is used by lowering it into the water until it is no longer visible. The depth at which the disc disappears is recorded, and this measurement is used to estimate the turbidity of the water. Therefore, the instrument used to determine the turbidity of water is a Secchi disc.

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One major difference between plant and animal nutrition is the ability of plants to synthesize food. Plants are able to produce their own food through the process of photosynthesis, in which they use energy from sunlight to convert carbon dioxide and water into sugars and oxygen. Animals, on the other hand, cannot produce their own food and must obtain energy by consuming other organisms, either directly (as predators) or indirectly (as herbivores). This means that plants are autotrophic, while animals are heterotrophic. The ability to synthesize food is a key difference between plant and animal nutrition, and it is one of the reasons why plants are considered the primary producers in most ecosystems.

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(a) Conversion of food to chyme in the stomach

When food (the bolus) reaches the stomach, the gastric glands in the stomach wall secrete gastric juice, which contains hydrochloric acid, the enzyme pepsin(ogen) and rennin. The hydrochloric acid provides an acidic medium, kills harmful bacteria and activates pepsinogen into active pepsin. Pepsin digests proteins into shorter chains (peptones and polypeptides), while rennin curdles the soluble milk protein (caseinogen) into insoluble casein. At the same time the muscular wall of the stomach contracts rhythmically (churning / peristalsis), thoroughly mixing the food with the gastric juice. The food is gradually turned into a semi-liquid, acidic, partly digested paste called chyme, which is then released in small amounts into the small intestine.

(b) Completed table

(c) Experiment to show that carbon dioxide is necessary for photosynthesis

1. Destarch a potted plant by keeping it in the dark for about 48 hours, then test one leaf to confirm no starch is present.
2. Enclose one leaf (still attached) in a flask containing a little potassium hydroxide (KOH) or soda lime, which absorbs all the carbon dioxide inside; seal the neck with a split cork and vaseline so it is air-tight.
3. Set up a control: enclose another leaf in a flask containing sodium hydrogen carbonate solution (which supplies carbon dioxide).
4. Expose the whole plant to bright sunlight for several hours.
5. Remove both leaves and test each for starch (boil in water, decolourise in alcohol, then add iodine solution).

Result: the leaf deprived of carbon dioxide shows no starch (iodine stays brown), while the control leaf supplied with carbon dioxide turns blue-black, showing starch. Conclusion: carbon dioxide is necessary for photosynthesis.

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(a) Explanation of terms

Ecosystem: a natural unit made up of all the living organisms (the biotic components) in a given area together with the non-living surroundings (the abiotic components) with which they interact to form a stable, self-supporting system through which energy flows and nutrients are recycled.

Abiotic environment: the non-living physical and chemical part of a habitat, that is, factors such as light, temperature, water, dissolved oxygen, wind, pH and soil, which affect the organisms living in that habitat.

(b) Three ecological factors specific to each habitat

Aquatic habitats: salinity (of the water); turbidity (cloudiness of the water); water current (tidal/wave movement). Dissolved gases and density are also acceptable.

Terrestrial habitats: wind; humidity (of the air); topography (relief of the land). Soil (edaphic factors) and altitude are also acceptable.

(c) Relationship between green grass and a rabbit in a given habitat

The relationship is a feeding (food) relationship that also involves an exchange of gases:

• The green grass is the producer; it photosynthesises to manufacture its own food.
• The rabbit is a herbivore (primary consumer); it cannot make its own food and so feeds on the grass, thereby obtaining energy from it.
• During respiration the rabbit gives out carbon dioxide, which the grass uses for photosynthesis.
• During photosynthesis the grass releases oxygen, which the rabbit uses for respiration.
• When the rabbit defecates or dies, bacteria and fungi decompose the waste, forming humus/nutrients that the grass absorbs from the soil.

Energy therefore flows from the grass to the rabbit, while gases and nutrients are cycled between them.

(d) Pyramid of energy using four feeding levels

A pyramid of energy is drawn as horizontal bars stacked on one another, widest at the base (producers) and narrowing upwards, because usable energy is lost (mainly as heat during respiration) at each successive trophic level. The values shown (in kJ m^-2 yr^-1) are typical and confirm that each higher level contains far less energy than the one below it.

The base (producers) contains the greatest amount of energy and each higher feeding level contains progressively less, giving the upright, narrowing pyramid shape.

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(a) Five vertebrae in mammals and their locations

(b) One function each in a dicotyledonous leaf

• (i) Palisade: contains many chloroplasts and carries out most of the photosynthesis.
• (ii) Vascular bundle (vein): conducts water and mineral salts to the leaf (xylem) and food away from it (phloem), and supports the leaf.
• (iii) Epidermis: protects the inner tissues and (with its cuticle) reduces water loss.

(c) One function each in the stem of a flowering plant

• (i) Sieve tube: conducts (translocates) manufactured food such as sugars through the plant.
• (ii) Cortex: stores food and water and gives support to the stem.
• (iii) Pith: stores food and water in the centre of the stem.

(d) Stem versus root of a maize (monocot) seedling

(i) Two external structural differences

(ii) Two internal structural differences

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(a) Roles in respiration

(i) Glucose

• It is the respiratory substrate (fuel) that is broken down (oxidised) to release energy.
• Its breakdown yields ATP (energy), carbon dioxide and water for the cell's activities.

(ii) Oxygen

• It is used to oxidise glucose completely (it is the final acceptor of hydrogen/electrons).
• It makes aerobic respiration possible, releasing the maximum amount of energy and producing carbon dioxide and water.

(b) Two types of cellular respiration: aerobic respiration and anaerobic respiration.

(c) Structures of gaseous exchange

(d) Diagram of an open stoma

Draw the stoma 6 cm to 8 cm long showing two bean-shaped guard cells enclosing the open stomatal pore (aperture), with the following labels: guard cell, chloroplasts (inside the guard cells), nucleus, stomatal pore (opening), thick inner wall and thin outer wall of the guard cell, and the neighbouring epidermal cells.

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(a)(i) Type of teeth

• A: Canine.
• B: Molar.
• C: Incisor.

(a)(ii) Teeth found in positions I, II and IV

• I: Incisor.
• II: Canine.
• IV: Molar.

(a)(iii) One function of each

• A (canine): for tearing flesh and piercing food.
• B (molar): for breaking, crushing, chewing and grinding food.
• C (incisor): for cutting and biting food.

(a)(iv) One reason for each answer

• A (canine): it is conical, sharp and pointed.
• B (molar): it is broad with ridges (cusps) on its surface.
• C (incisor): it has a flat, sharp, chisel-shaped edge.

(b) Two factors that may cause decay of tooth B

• Accumulation of acid produced by bacteria acting on food remnants.
• Frequent eating of sweet, sugary or sticky foods with poor cleaning of the teeth.

(c) Total number in the dentition of an adult human

• A (canines): 4.
• B (molars): 12.
• C (incisors): 8.

(d) Tooth absent in a rabbit: the canine (A). A rabbit has a gap (diastema) in place of the canines.

(e)(i) Tooth in position III of diagram D: premolar.

(e)(ii) Part where a tooth is not found in an infant: position IV (the molar).

(f) Five ways of caring for the teeth

1. Brush the teeth regularly, after meals and before going to bed.
2. Reduce the intake of sweet, sticky and sugary foods.
3. Eat foods rich in vitamins and minerals, such as fruits, for strong teeth.
4. Visit the dentist at least twice a year (every six months) for check-ups.
5. Avoid using the teeth on hard objects (such as cracking bones or opening bottle tops) and avoid smoking and excessive alcohol.

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(a) Five processes involved in the water cycle

1. Evaporation (of water from seas, rivers and land).
2. Transpiration (loss of water vapour from plants).
3. Condensation (water vapour forming clouds).
4. Precipitation (rain, hail or snow).
5. Run-off (and infiltration into the ground).

(b) Instruments for measuring each physical factor

(c) Contributions to the cell theory

• Robert Hooke: using an early microscope he examined thin slices of cork and observed and named the tiny box-like compartments \'cells\', the first observation of cells.
• Theodore Schwann: he proposed that all animals are made of cells and, with Schleiden, stated that all living things are composed of cells, so the cell is the basic unit of life.

(d) Meaning of terms

• Nastism (nastic movement): a non-directional response of a plant part to a diffuse (non-directional) stimulus, for example the folding of Mimosa leaves when touched.
• Taxism (taxis): the movement of a whole organism towards or away from a directional stimulus, for example a Euglena swimming towards light.

(e) A diagram 6 to 8 cm long of the human tongue is required, showing and labelling the four taste areas: sweet (tip), salt (front sides), sour (back sides) and bitter (back of the tongue).

(f)(i) Four ways microorganisms enter the human body

1. Through the mouth in contaminated food and water.
2. Through the nose in inhaled air (droplets).
3. Through cuts, wounds or breaks in the skin.
4. Through the reproductive tract (sexual contact) or insect bites.

(f)(ii) Three harmful effects of microorganisms to humans

1. They cause diseases such as cholera, tuberculosis and malaria.
2. They cause food spoilage and food poisoning.
3. They produce toxins that poison the body and cause decay of body tissues (sepsis).

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(a)(i) Type of teeth in A, B and C:

• A = Canine
• B = Molar
• C = Incisor

(a)(ii) Teeth found in positions I, II and IV:

• I = Incisor
• II = Canine
• IV = Molar

(a)(iii) One function each

• A (canine): for tearing flesh and piercing food.
• B (molar): for breaking, crushing, chewing and grinding food.
• C (incisor): for cutting and biting food.

(a)(iv) One reason each

• A (canine): it is conical, sharp and pointed.
• B (molar): it is broad with ridges (cusps) on its surface.
• C (incisor): it has a flat, sharp, chisel-shaped edge.

(b) Two factors that may cause decay of tooth B

• Accumulation of acid together with bacterial (microbial) activity on the tooth.
• Food remnants from sweet, sugary or sticky foods, and lack of proper dental care.

(c) Total number in the dentition of an adult human

• A (canines): 4
• B (molars): 12
• C (incisors): 8

(d) Tooth absent in a rabbit: the canine (tooth A). A rabbit has a gap (diastema) in its place.

(e)(i) Tooth in position III of diagram D: premolar.

(e)(ii) Position where a tooth is not found in an infant: position IV (the molar), because molars are absent in the milk (deciduous) dentition.

(f) Five ways of caring for the teeth

1. Brush the teeth regularly, after meals and before going to bed.
2. Reduce the intake of sweet, sticky and sugary foods, and avoid smoking and excessive alcohol.
3. Eat foods rich in vitamins and minerals, such as fruits, for strong teeth.
4. Remove food particles with a tooth pick and floss the teeth.
5. Visit the dentist at least twice a year (every six months) for check-ups.

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(a)(i) Chemosynthesis

Chemosynthesis is a mode of nutrition in which certain autotrophic bacteria manufacture their own organic food using energy obtained from the oxidation of inorganic chemical substances, instead of using light energy as in photosynthesis.

(a)(ii) Two examples of chemosynthetic organisms: nitrifying bacteria (Nitrosomonas and Nitrobacter) and sulphur bacteria (Thiobacillus).

(b) Three atmospheric gases and their percentage composition

(c)(i) Four characteristics of a salt marsh habitat

• The water and soil have a high salt content (high salinity).
• The soil is soft, muddy and waterlogged with little oxygen (anaerobic).
• It is periodically flooded and drained by the tides.
• It is exposed to strong winds and wide changes in temperature.

(c)(ii) Modification of plants for anchorage

Salt marsh plants (e.g. mangroves) develop strong, widely spreading and prop / stilt roots that grow into the soft mud. These extensive roots anchor the plant firmly and prevent it from being swept away by the tides.

(d)(i) Four bacterial diseases linked to poor food hygiene: cholera, typhoid fever, bacterial food poisoning (salmonellosis) and bacillary dysentery.

(d)(ii) Three effects of poor food hygiene: contamination of food and food poisoning; spread of communicable diseases; ill-health and possible death, with economic loss.

(e) How lost blood is restored

The blood is restored by blood transfusion: blood of a compatible (matching) group is collected from a healthy donor and introduced into a vein of the accident victim. Intravenous fluids (a drip) may first be given to restore blood volume, and over time the body itself replaces the lost plasma and blood cells.

(f) Three differences between tillage and bush burning

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(a) Gases involved in photosynthesis: carbon dioxide (CO₂) and oxygen (O₂).

(b) Role of each gas

• Carbon dioxide: it is a raw material that is taken in and used to manufacture carbohydrate (glucose).
• Oxygen: it is the gas given off (released) as a by-product of photosynthesis.

(c)(i) What is a variegated leaf?

A variegated leaf is a leaf that has both green and non-green (white or yellow) patches, because chlorophyll is present only in the green parts.

(c)(ii) Only the green part of the leaf tests positive (turns blue-black) with iodine solution.

(c)(iii) Two reasons

• Only the green part contains chlorophyll, which traps light energy for photosynthesis.
• Therefore only the green part manufactures and stores starch; the non-green part has no chlorophyll and cannot make food.

(c)(iv) Mineral element needed to form chlorophyll: magnesium (nitrogen is also acceptable).

(d) Classification of the organisms by mode of nutrition

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(a)(i) Identity of the diagrams

• D = Sweep net (hand net) - a long-handled net with a mesh bag.
• E = Pooter (insect aspirator) - a jar carrying two tubes through its lid.
• F = Quadrat - a square frame of side 1 m divided into smaller squares.

(a)(ii) Names of the parts I to VIII

(a)(iii) One function each of I, III, IV, V and VII

• I (handle): provides a grip so the net can be held and swung to sweep up organisms.
• III (mouth tube): it is sucked to create a partial vacuum inside the jar, drawing the insect in through the inlet tube.
• IV (gauze): prevents the insect and debris from being sucked out of the jar into the collector's mouth.
• V (collecting jar): receives and holds the trapped insects for observation.
• VII (frame): marks out a fixed, known area (1 m by 1 m) within which organisms are counted.

(b) One use each of D, E and F

• D (sweep net): catching small, fast-moving animals such as flying insects (or aquatic organisms when swept through water).
• E (pooter): picking up small, delicate insects and other tiny arthropods from the ground or vegetation without harming them.
• F (quadrat): sampling to estimate the population density or percentage cover of plants and slow-moving/sessile animals in a habitat.

(c) Brief description of how each tool is used

D - Sweep net: The net is swung to and fro (or in a figure-of-eight) through vegetation, air or water while walking along a chosen line. Small animals are trapped in the mesh bag (II); the mouth of the bag is then closed and the catch is transferred into a container for counting and identification.

E - Pooter: The inlet tube (VI) is held close to or directly over the insect. The collector sucks sharply through the mouth tube (III); the suction draws the insect through the inlet tube into the jar (V). The gauze (IV) over the mouth tube keeps the insect inside the jar and stops it entering the mouth. The trapped insect is then examined or preserved.

F - Quadrat: The frame is thrown or placed at random points on the ground. At each placing, the organisms rooted or resting inside the frame are counted (or their cover estimated using the grid squares VIII). Several random placings are made and averaged. The area sampled is

\[ A_q = 1\,\text{m} \times 1\,\text{m} = 1\,\text{m}^2 \]

If \(N\) organisms are counted over \(n\) quadrats, the mean number per quadrat is \(\dfrac{N}{n}\), and since each quadrat covers \(1\,\text{m}^2\) the population density is

\[ \text{Density} = \frac{N}{n}\ \text{organisms per } \text{m}^2 \]

Multiplying this density by the total area \(A\) of the habitat gives an estimate of the whole population:

\[ \text{Estimated population} = \frac{N}{n} \times A \]

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(a) Explanation of terms

(i) Renewable natural resources: natural resources that can be replaced by natural processes or re-grown after use, so they are not permanently exhausted, for example forests, fish and water.

(ii) Non-renewable natural resources: natural resources that are present in fixed amounts and cannot be replaced within a human lifetime once used up, for example crude oil, coal and mineral ores.

(b) Two examples each

• (i) Renewable: forests (timber) and fish (wildlife). Water and solar energy are also acceptable.
• (ii) Non-renewable: crude oil (petroleum) and coal. Natural gas and metallic ores are also acceptable.

(c) Five ways of conserving forests

1. Afforestation and reafforestation (planting new trees to replace those felled).
2. Selective felling of only mature trees instead of clear felling.
3. Preventing and controlling bush burning.
4. Establishing and protecting forest reserves.
5. Enacting and enforcing laws against indiscriminate cutting of trees.

(d) Four effects of adding animal manure to garden soil

1. It adds humus and improves the fertility of the soil.
2. It improves the soil structure and aeration.
3. It increases the water-holding (moisture-retaining) capacity of the soil.
4. It increases the population of useful soil micro-organisms and releases nutrients as it decays.

(e) Possible genotypes in humans

Taking a single gene pair with a dominant allele and a recessive allele (for example alleles A and a), the three possible genotypes are:

• \(AA\) - homozygous dominant
• \(Aa\) - heterozygous
• \(aa\) - homozygous recessive

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(a)(i) Mendel's laws of inheritance

• Law of Segregation (First Law): the two alleles (factors) controlling a character separate during the formation of gametes, so that each gamete carries only one allele of the pair.
• Law of Independent Assortment (Second Law): the alleles of different genes (characters) are distributed to the gametes independently of one another during gamete formation.

(a)(ii) Five applications of genetics in medicine

1. Genetic counselling of couples to predict the risk of hereditary diseases in their children.
2. Diagnosis of inherited disorders such as sickle-cell anaemia and haemophilia.
3. Blood group determination for safe blood transfusion.
4. Production of medicines such as insulin and vaccines by genetic engineering.
5. Determination of paternity and identification through DNA (fingerprinting).

(a)(iii) Three disadvantages of inbreeding

1. It brings together harmful recessive genes, so hereditary defects appear more often.
2. It reduces genetic variation (leads to loss of hybrid vigour).
3. It can reduce fertility, vigour and resistance to disease in the offspring.

(b)(i) What is evolution?

Evolution is the gradual change in the characteristics of living organisms over a long period of time, so that new species arise from pre-existing ancestral forms.

(b)(ii) Convergent versus divergent evolution

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(a)(i) Identity of the organisms: A is a butterfly (Papilio sp.); B is a housefly (Musca sp.).

(a)(ii) Parts labelled I to X:

• I - head
• II - antenna
• III - thorax
• IV - forewing
• V - abdomen
• VI - antenna
• VII - head
• VIII - compound eye
• IX - wing
• X - leg

(b) Function of parts VI, VIII, IX and X

• VI (antenna): for feeling, and sensitivity to touch, smell and vibration.
• VIII (compound eye): for sight or vision.
• IX (wing): for flight and balancing during flight.
• X (leg): for walking, crawling and running.

(c) Specific habitats

A (butterfly) lives in gardens and farms among flowering plants and trees. B (housefly) lives around latrines, refuse dumps, sewage, exposed food and decaying organic matter.

(d) Three structural adaptations of organism A (butterfly)

• Large, broad wings for flight.
• A long, thin proboscis for sucking nectar from flowers.
• Long clubbed antennae and large compound eyes for sensitivity and wide vision.

(e)(i) Three structural similarities between A and B: both possess wings; both have the body divided into head, thorax and abdomen; both have a pair of antennae and a pair of compound eyes.

(e)(ii) Three structural differences between A and B

(f)(i) Class of A and B: Insecta.

(f)(ii) Three reasons: the body is divided into head, thorax and abdomen; there are three pairs of jointed legs on the thorax; there is one pair of antennae and a pair of compound eyes (with wings present).

(g) One biological importance of organism A (butterfly): it pollinates flowers (and also serves as a source of food for other organisms).

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(a) How the structure of each cell relates to its function

(i) Sperm cell

• It has a long, whip-like tail (flagellum) which lashes from side to side to propel the cell so that it can swim to reach the egg (ovum).
• Its head bears an acrosome filled with digestive enzymes that break down and penetrate the membrane of the egg at fertilisation.
• The head contains a haploid nucleus which fuses with the nucleus of the ovum during fertilisation to form the zygote.
• The middle piece is packed with mitochondria that release the energy (ATP) needed to power the beating of the tail during swimming.

(ii) Palisade cell

• It has a thin cell wall which allows easy penetration of light and rapid diffusion of gases.
• It contains numerous chloroplasts arranged in the peripheral cytoplasm for maximum absorption of sunlight for photosynthesis.
• It is long and column-shaped and closely packed just below the upper epidermis so that many chloroplasts are exposed to light.
• It has a large central vacuole containing cell sap which pushes the chloroplasts to the edges near the light and stores the products of photosynthesis temporarily.

(b) Drawing of the front (anterior) view of the human female reproductive system

The diagram below shows the front view of the female reproductive system, about 8-10 cm long when drawn, fully labelled.

(c) Two differences between reproduction in mammals and in amphibians

(d) Two methods of birth control in humans

• Use of contraceptive pills (hormonal method).
• Use of condoms (barrier method).

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(a) Explanation of terms

• (i) Gene: a unit of hereditary material, a length of DNA on a chromosome, that carries the code for a particular characteristic and is passed from parent to offspring.
• (ii) Hybrid: the offspring produced from a cross between two genetically different (unlike) parents; in genetics a heterozygote carrying two different alleles of a gene.
• (iii) Trait: an observable inherited characteristic or feature of an organism, such as flower colour or height.

(b) Cross between two heterozygous yellow flowers

Let \(Y\) = allele for yellow (dominant) and \(y\) = allele for the recessive colour. Each heterozygous parent is \(Yy\).

Parental genotypes: \(Yy \times Yy\)

Gametes: \(Y\) and \(y\) from each parent.

Genotypic ratio of F1: \(1\,YY : 2\,Yy : 1\,yy\).

Phenotypic ratio of F1: 3 yellow : 1 recessive (non-yellow), i.e. \(3:1\).

(c) Four transmitted (inherited) characters in plants

1. Flower colour.
2. Seed shape (round or wrinkled).
3. Height of the plant (tall or short).
4. Fruit or seed colour. Leaf shape is also acceptable.