WAEC SSCE - Biology - 1998

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Ultrafiltration takes place in the Bowman's capsule of the kidney. The Bowman's capsule is a small, cup-shaped structure at the beginning of the nephron, which is the functional unit of the kidney. The Bowman's capsule surrounds a cluster of tiny blood vessels called the glomerulus. As blood flows through the glomerulus, high pressure forces fluid and small molecules, such as ions, glucose, and amino acids, out of the blood and into the Bowman's capsule. This process is called ultrafiltration. The ultrafiltrate, which is the fluid and molecules that are filtered out of the blood, then enters the proximal convoluted tubule where most of the valuable substances like glucose and amino acids are reabsorbed, and water and waste products continue to flow through the rest of the nephron to eventually be eliminated from the body as urine.

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Artificial vegetative propagation is a type of asexual reproduction in plants where new plants are produced from existing vegetative structures. Layering is a method of artificial vegetative propagation where a stem is bent down and covered with soil, while it is still attached to the parent plant. Roots will grow from the buried portion of the stem, and when it is cut and planted separately, it will grow into a new plant that is genetically identical to the parent plant. Therefore, the answer is "Layering".

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In a plant of genotype Tt, the T and t are alleles of a gene, and each parent contributes one allele to their offspring. Therefore, the plant can produce two types of gametes - one with the T allele and another with the t allele. Since the plant is heterozygous (Tt), each type of gamete (T or t) has an equal chance of being produced. Thus, the probability of a gamete containing gene t is 1/2 or 50%. Therefore, the answer is/2.

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The question cannot be answered definitively without the diagram itself or a more specific description of the diagram. However, the options given suggest that the diagram is likely related to ecology or biology. If the diagram shows different sizes of organisms, it could be illustrating the concept of scale in ecology and the relative sizes of different organisms. If the diagram shows different types of organisms in a habitat, it could be illustrating the biodiversity of a specific ecosystem. If the diagram shows the flow of energy in a habitat, it could be illustrating a food web or energy pyramid, which shows how energy is transferred from one trophic level to another. If the diagram shows the hierarchy of organisms in a habitat, it could be illustrating a food chain or trophic levels. In summary, without further information about the diagram, it is difficult to determine what it is illustrating.

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The statement that "Poliomyelitis is a bacterial disease" is not correct. Poliomyelitis, commonly known as polio, is actually a viral disease caused by the poliovirus. It can affect the central nervous system, leading to paralysis or even death in some cases. It primarily affects children under the age of 5, but can also affect adults. Polio can be prevented through immunization with the polio vaccine, which is a safe and effective way to protect against the disease. The virus attacks the motor neurons in the spinal cord, which can result in paralysis and muscle wasting, particularly in the limbs.

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A herbivore is an organism that feeds on plants. Among the options given, the organism that is a herbivore is the phytoplankton. Phytoplankton are tiny, microscopic plants that float on the surface of water bodies, and are consumed by a variety of aquatic organisms. Therefore, the correct answer is Phytoplankton.

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The mode of nutrition which describes feeding habit in animals is holozoic. Holozoic nutrition is a mode of nutrition in which animals consume complex organic food materials, such as plants or other animals, and then break them down into simpler substances through the process of digestion. These simpler substances are then absorbed and utilized by the animal for energy, growth, and maintenance. In contrast, autotrophic nutrition is the process by which organisms, such as plants, use energy from the sun or inorganic compounds to create their own food through photosynthesis. Photosynthetic nutrition is similar to autotrophic nutrition but is specifically used to describe the feeding habits of plants. Saprophytic nutrition involves the breakdown and absorption of dead organic matter by decomposers, such as fungi and bacteria. Holophytic nutrition is a less commonly used term that is similar to photosynthetic nutrition and describes the feeding habits of organisms that use light energy to create their own food. This term is most often used in reference to certain types of algae and bacteria. Therefore, the correct mode of nutrition that describes the feeding habit in animals is holozoic.

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The stomata of a leaf perform a similar function to the spiracles of insects. Stomata are small pores located on the underside of leaves that allow for gas exchange between the plant and the atmosphere. They open and close in response to environmental conditions, such as light, temperature, and humidity. During photosynthesis, stomata allow carbon dioxide to enter the plant and oxygen to exit. In addition, water vapor can also be released through the stomata in a process called transpiration. Similarly, spiracles are small pores located on the exoskeleton of insects that allow for gas exchange between the insect and the atmosphere. They also open and close in response to environmental conditions. Oxygen enters the insect through the spiracles and carbon dioxide exits. Some insects can also release excess water through their spiracles. So, both stomata and spiracles perform a similar function of facilitating gas exchange between the organism and the environment, allowing for respiration and photosynthesis to occur.

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The liver is the organ that is concerned with detoxication of harmful compounds. The liver is a vital organ that performs many functions in the body, including filtering the blood and removing harmful toxins and waste products from the body. The liver breaks down these harmful substances, such as alcohol and drugs, into less harmful compounds that can be eliminated from the body through urine or feces. It also produces bile, a fluid that helps to digest fats in the small intestine. The kidney filters waste products from the blood and helps to regulate fluid and electrolyte balance, but it is not primarily responsible for detoxication. The lungs help to exchange gases between the body and the environment, but they do not play a significant role in detoxication. The gallbladder stores bile produced by the liver, but it does not directly detoxify harmful compounds. The pancreas produces enzymes that help to digest food in the small intestine, but it is not primarily responsible for detoxication.

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The presence of stilt and breathing roots are features of plants found in mangrove forests. Mangrove forests are unique ecosystems found in tropical and subtropical regions where the land meets the sea. The plants in these forests have adapted to the salty and muddy environment by developing specialized roots. Stilt roots are aerial roots that grow from the trunk and branches of the tree and extend down to the soil to provide additional support. Breathing roots, also known as pneumatophores, are vertical roots that grow upward from the muddy soil to help the tree get oxygen. These adaptations allow mangrove trees to survive in an environment with fluctuating tides and low oxygen levels.

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In a food chain, each stage represents a trophic level. A trophic level refers to a hierarchical level in an ecosystem, based on the organism's source of energy and nutrients. The first level is occupied by primary producers, such as plants, which produce their food through photosynthesis. The second level consists of primary consumers, such as herbivores, that feed on the primary producers. The third level comprises secondary consumers, such as carnivores, that eat the primary consumers. The fourth level is occupied by tertiary consumers, which are carnivores that feed on other carnivores. The trophic level of an organism determines its position in the food chain and its role in the transfer of energy and nutrients through the ecosystem.

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The mammalian heart has four chambers - two atria (also called auricles) and two ventricles. One major difference between the auricles and the ventricles is that the walls of the ventricles are more muscular than those of the auricles. This is because the ventricles are responsible for pumping blood out of the heart and into the rest of the body, while the auricles receive blood returning to the heart. Additionally, the ventricles carry deoxygenated blood to the lungs or oxygenated blood to the rest of the body, while the auricles receive blood from the veins and have valves to prevent backflow. The ventricles also have outlets (arteries) that carry blood away from the heart, while the auricles do not.

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In this cross, the dominant trait is the red flower color (R), while the recessive trait is the white flower color (r). The heterozygous plant (Rr) has one dominant allele and one recessive allele, while the white-flowered plant (rr) has two recessive alleles. When these two plants are crossed, the possible gametes that the heterozygous plant (Rr) can produce are R and r, while the white-flowered plant (rr) can only produce r. Therefore, the possible offspring genotypes are: Rr (red-flowered) and rr (white-flowered). The probability of an offspring inheriting the R allele from the heterozygous plant (Rr) is 1/2, as there is an equal chance of the gamete carrying the R or r allele. The probability of an offspring inheriting the r allele from the white-flowered plant (rr) is 1, as the gamete can only carry the r allele. To determine the probability of an offspring being Rr, we need to multiply the probability of inheriting R from the heterozygous plant (1/2) by the probability of inheriting r from the white-flowered plant (1). Therefore, the probability of an offspring being Rr is 1/2 x 1 = 1/2. So the correct answer is 1/2.

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The process of meiosis results in the formation of gametes (sperm or egg cells) that contain half the number of chromosomes as compared to the parent cell. Therefore, if the somatic cell has eight chromosomes, the gamete will have half that number, which is 4 chromosomes. Hence, the correct answer is 4.

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Sundew is the carnivorous plant in the options given. Sundew plant catches and digests insects to get nutrients such as nitrogen and phosphorus, which are present in low concentrations in the soil where it grows. The sundew plant has leaves covered with small, hair-like structures that produce a sticky, mucilaginous substance. The substance traps small insects, which are then digested by the plant. This adaptation is necessary for survival in nutrient-poor environments. Therefore, Sundew is a carnivorous plant.

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The mammalian feature that acts as a shock-absorber to the developing embryo is the amniotic fluid. The amniotic fluid is a clear liquid that surrounds the developing embryo in the uterus of a pregnant mammal. The amniotic fluid serves several functions, one of which is to act as a cushion to protect the embryo from mechanical shock or injury. The fluid is contained within the amniotic sac, which is made up of two membranes called the amnion and the chorion. The amnion is the innermost membrane that directly surrounds the embryo, while the chorion is the outermost membrane that lines the inside of the uterus. Together, these membranes and the amniotic fluid create a protective environment for the developing embryo, allowing it to grow and develop in safety.

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Sweat is not an excretory product of plants. Plants do not have sweat glands or any mechanism for sweating. Instead, plants excrete waste products such as tannins, gums, alkaloids, and anthocyanins through various mechanisms such as leaf shedding, root exudation, and secretion through specialized cells.

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If the petals of a flowering plant are removed, the process that is likely to be affected is Pollination. Pollination is the process by which pollen from the male reproductive organs of a flower (anther) is transferred to the female reproductive organs of another flower (stigma) or the same flower, leading to fertilization and seed production. Petals play an important role in pollination by attracting pollinators such as bees, butterflies, and birds, which are responsible for transferring pollen between flowers. Without petals, pollinators may not be attracted to the flower, reducing the chances of pollination and seed production. Therefore, if the petals of a flowering plant are removed, pollination may be affected, and the plant may not be able to reproduce successfully. Transpiration, germination, photosynthesis, and dispersal are not directly dependent on the presence of petals.

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The difference between mitosis and meiosis is that meiosis involves the pairing of homologous chromosomes, while mitosis does not. Both mitosis and meiosis are types of cell division, but they have different purposes. Mitosis is responsible for the growth and repair of somatic (body) cells, while meiosis is responsible for the production of gametes (sex cells) for sexual reproduction. During meiosis, homologous chromosomes pair up, crossing over each other to exchange genetic material before they separate. This results in a shuffling of genetic information and the creation of genetically diverse gametes. In contrast, during mitosis, the chromosomes replicate and the cell divides into two identical daughter cells, each with the same number of chromosomes as the parent cell.

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The major difference between osmosis and diffusion is that diffusion does not need a semipermeable membrane, while osmosis does. Diffusion is the movement of particles from an area of high concentration to an area of low concentration, while osmosis is the movement of water molecules across a semipermeable membrane from an area of high water concentration to an area of low water concentration. Diffusion can take place in both liquid and gaseous mediums, and can be demonstrated experimentally.

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The process that removes CO2 from the atmosphere is photosynthesis. Photosynthesis is the process by which plants, algae, and some bacteria use light energy to convert carbon dioxide and water into organic compounds such as glucose, releasing oxygen in the process. During photosynthesis, carbon dioxide is taken in from the atmosphere through small pores in plant leaves called stomata. Inside the chloroplasts of plant cells, the carbon dioxide is combined with water to produce glucose and oxygen. This process of photosynthesis is critical to maintaining the balance of gases in the Earth's atmosphere. As plants and other organisms that perform photosynthesis remove carbon dioxide from the atmosphere, they also release oxygen, which is necessary for the survival of most living organisms. The carbon dioxide that is taken in during photosynthesis is used to build plant tissues and stored in the plant or eventually returned to the atmosphere through respiration or combustion. Therefore, photosynthesis is the process that removes CO2 from the atmosphere and plays a vital role in maintaining the balance of gases that support life on Earth.

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The collective name for the female parts of the flower is gynoecium. The gynoecium is the reproductive part of the flower that contains one or more female reproductive organs called carpels or pistils. Each carpel consists of three parts: the stigma, the style, and the ovary. The stigma is the sticky part at the top of the carpel that receives the pollen, the style is the stalk-like part that connects the stigma to the ovary, and the ovary is the enlarged base of the carpel that contains the ovules, which are the structures that will become seeds after fertilization. The androecium, on the other hand, is the collective name for the male parts of the flower, which include the stamen, anther, and filament.

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The hormone that promotes secondary sexual characteristics in females is called estrogen. Estrogen is a group of hormones responsible for developing and maintaining female reproductive system and promoting secondary sex characteristics such as breast development, wider hips, and distribution of body fat to the buttocks and thighs. It also plays a role in regulating the menstrual cycle and supporting pregnancy.

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Amoeba is the organism that respires through the body surface. Amoeba is a unicellular organism that belongs to the protist kingdom. The exchange of gases (oxygen and carbon dioxide) in amoeba takes place through the process of diffusion across the cell membrane. The cell membrane of amoeba is thin, flexible and permeable to gases, which allows for the exchange of gases to take place between the environment and the cytoplasm of the cell. The other options - Man, Fish, Tridax and Hibiscus - have specialized respiratory organs like lungs or gills that are adapted for respiration.

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The statement that is not correct is: "The oxygenated blood enters the lungs through the pulmonary vein." In fact, the pulmonary vein carries oxygenated blood from the lungs to the left atrium of the heart, not the other way around. The right ventricle pumps deoxygenated blood to the lungs through the pulmonary artery, where it is oxygenated, and then returned to the left atrium via the pulmonary veins.

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The part labelled II in the diagram is the axon. The function of the axon is to transmit impulses from the cell body to the axon terminals or to other neurons, muscles or glands. The axon is covered with a fatty substance called myelin sheath which insulates and protects it, and helps in speeding up the transmission of nerve impulses.

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The pancreatic duct is a tube that carries digestive enzymes from the pancreas to the small intestine. It opens into the first part of the small intestine, called the duodenum, which is located just after the stomach. The enzymes secreted by the pancreas are important for the digestion of carbohydrates, proteins, and fats in the small intestine, and their release into the duodenum is regulated by the hormone secretin.

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The correct answer is: Queen, drones, and workers make up the bee caste. Explanation: Bees have three distinct castes: Queen, drones, and workers. The Queen is the reproductive female in the colony and is responsible for laying eggs. Drones are male bees that are responsible for mating with the queen. Workers are sterile female bees that perform all other duties within the hive, including cleaning, feeding the young, and foraging for food. Soldiers are not a part of the bee caste; this term is usually used to refer to certain types of ants that have specialized roles in defending the colony.

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Termites are called social insects because they live together in communities and have a division of labor. There are different types of termites with specialized roles, such as the queen, king, soldiers, and workers. The queen allocates duties to the workers and the function of the workers and soldiers are very important for the survival of the colony. They work together in a coordinated way to maintain and defend the nest, obtain food, and take care of the young. This social structure is similar to that of other social insects like ants and bees.

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The earthworm is important because it aerates the soil. Earthworms burrow through the soil, creating tunnels that allow air, water and nutrients to penetrate deeper into the soil. This improves the structure of the soil, making it easier for roots to grow and helping to prevent soil erosion. Additionally, as earthworms feed on organic matter in the soil, they help to break it down and release nutrients that plants can use for growth.

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During inspiration, the diaphragm contracts and moves downward, the intercostal muscles between the ribs contract, causing the ribs to move up and out, and the thoracic cavity increases in size, which results in a decrease in internal air pressure, allowing air to rush into the lungs. Therefore, the option that does not happen during inspiration is "Diaphragm relaxes". During inspiration, the diaphragm contracts and flattens, increasing the volume of the thoracic cavity and causing air to flow into the lungs. When the diaphragm relaxes, it moves back up into its dome-shaped position, decreasing the volume of the thoracic cavity and causing air to flow out of the lungs during expiration.

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Hydra feeds by digesting its food extra-cellularly. This means that Hydra releases enzymes (special proteins) outside its body to break down the food it has caught into smaller pieces. These small pieces are then absorbed by Hydra's cells and used for energy and growth. Unlike animals that chew their food or plants that make their own food through photosynthesis, Hydra does not masticate its food or synthesize its own food chemically. Hydra also does not absorb food that has already been digested by other organisms or have a symbiotic association with other species to obtain food.

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The feature of wind-pollinated flowers is that they have smooth, light, and numerous pollen grains. This is because wind-pollinated flowers rely on the wind to carry their pollen from the male part of the flower (the stamen) to the female part of another flower (the stigma). Unlike insect-pollinated flowers, wind-pollinated flowers do not need to attract insects with colorful petals, sweet scents, or nectar. Instead, their pollen grains need to be small and lightweight, so they can easily be carried by the wind to other flowers. The absence of pollen guides, which are structures that help insects find the nectar and pollen, is also a feature of wind-pollinated flowers.

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The role of bacteria in the nitrogen cycle is very important, and it includes several processes. One of them is the conversion of ammonia to nitrites, followed by the conversion of nitrites to nitrates. These nitrates are then available for plant uptake and utilization. Another important role of some bacteria is fixing atmospheric nitrogen, which is a process that converts nitrogen gas from the atmosphere into a form that plants can use. Bacteria can also play a role in the decay of dead organisms, which releases nitrogen back into the soil. However, converting carbohydrates to carbon dioxide is not a role of bacteria in the nitrogen cycle, as this process is related to cellular respiration, which is different from the nitrogen cycle. Therefore, the correct answer is "Converting carbohydrates to carbon dioxide."

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The excessive loss of water from the leaf is prevented by the cuticle. The cuticle is a waxy layer found on the outermost layer of the leaf that reduces the rate of transpiration by preventing the loss of water through the leaf surface. It helps to retain water within the leaf and prevents desiccation of the plant. The cuticle also provides a barrier to pathogen attack and reduces the loss of nutrients from the leaf surface.

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The instrument that can be used to measure relative humidity is a hygrometer. Relative humidity refers to the amount of moisture or water vapor in the air compared to the maximum amount the air can hold at a given temperature. A hygrometer measures the amount of moisture in the air and gives a reading of the relative humidity. There are different types of hygrometers, such as mechanical, electronic, and psychrometric hygrometers. Some of these instruments work by measuring the change in electrical resistance or capacitance caused by moisture, while others use a wet and dry bulb thermometer to measure the difference in temperature between a dry and wet surface. An anemometer measures wind speed, a wind gauge measures wind direction, a barometer measures atmospheric pressure, and a thermometer measures temperature. While these instruments may be useful in predicting or indicating changes in relative humidity, they do not directly measure it.

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The enzyme that acts on milk in the stomach is renin. Renin is produced by special cells in the stomach called chief cells. It is an enzyme that coagulates milk proteins in the stomach, making them easier to digest. This coagulation process is important for young mammals that rely on milk for their nutrition. Renin helps to slow down the passage of milk through the stomach, giving it more time to be broken down by other digestive enzymes. It is particularly important for the digestion of milk in infants, but its production decreases as we grow older and start consuming more solid foods.

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The above diagram represents a longitudinal section of a root. A root is the part of the plant that typically lies below the surface of the soil and serves to anchor the plant in place and absorb water and nutrients from the soil. A longitudinal section is a cut that runs lengthwise through the root, dividing it into two halves. The diagram shows various parts of the root, including the root cap, which protects the tip of the root as it grows through the soil, the root hairs, which increase the surface area of the root for better absorption of water and nutrients, and the vascular cylinder, which contains the xylem and phloem that transport water, nutrients, and sugars throughout the plant.

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The organism with homodont dentition is lizard. Homodont dentition is a type of tooth arrangement in which all teeth in the mouth are of the same shape and size. This is different from heterodont dentition, which is the type of tooth arrangement in which teeth are different in shape and size. Out of the given options, lizard is the only organism that has homodont dentition. The other organisms have different types of teeth with different shapes and sizes.

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The correct answer is: "Distribution of bile". Blood has several important functions in the body, including maintenance of body temperature, formation of clots to prevent blood loss from injuries, transportation of oxygen and nutrients to the body tissues, removal of waste products from the body, and distribution of hormones to their target organs. However, bile is produced by the liver and stored in the gallbladder, and it is released into the small intestine to help with the digestion of fats. Bile is not transported by the blood.

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Euglena exhibits both plant and animal characteristics. Euglena is a type of unicellular organism that has chloroplasts, which are used for photosynthesis like plants, and a flagellum, which is used for movement like animals. Euglena is able to switch between autotrophic and heterotrophic modes of nutrition, meaning it can produce its own food like plants or consume other organisms like animals.

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The organ responsible for equalizing air pressure in the ear is the Eustachian tube. The Eustachian tube is a small passage that connects the middle ear to the back of the throat. Its main function is to equalize the air pressure on both sides of the eardrum. When the pressure outside the ear changes, such as during takeoff or landing on a plane, the Eustachian tube opens briefly to allow air to flow into or out of the middle ear, which equalizes the pressure. If the Eustachian tube is blocked or does not function properly, it can lead to a feeling of fullness in the ear, hearing loss, or even ear infections. Therefore, it is important for the Eustachian tube to be functioning properly for proper hearing and ear health. In summary, the Eustachian tube is the organ responsible for equalizing air pressure in the ear.

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In animals, the main protective covering is found in the epithelial tissues. These tissues cover the external surfaces of the body as well as the internal surfaces of organs and body cavities. They protect the body from physical, chemical, and biological damage by providing a barrier between the external environment and the internal tissues and organs. The skin is a good example of the protective function of epithelial tissues, as it prevents the entry of harmful microorganisms, chemicals, and UV radiation. Additionally, epithelial tissues also play a role in absorption, secretion, and sensation.

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The correct option is "Production of bile". Bile is not produced by the kidneys, but rather by the liver. The other options all relate to the functions of the kidneys. The kidneys are responsible for producing urine by filtering waste products from the blood. They also play a vital role in maintaining the acid-base balance of the body, regulating the osmotic pressure of bodily fluids, and removing urea from the blood.

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(a) Four castes in a termite nest

Queen, king, workers, and soldiers.

(b)(i) Role of each caste

• Queen: the only fully fertile female; she lays all the eggs and so reproduces to build up the colony.
• King: the fertile male that mates with the queen to fertilise her eggs.
• Workers: sterile insects that build and repair the nest, gather food, feed the queen, king and young, and keep the nest clean.
• Soldiers: sterile insects with large heads and strong jaws that defend the colony against enemies.

(b)(ii) Two economic importances of termites to man

• Harmful: they destroy wooden buildings, furniture, books, crops and paper, causing great loss.
• Useful: they help to break down (decompose) dead wood and plant matter, enriching and aerating the soil; their mounds provide fertile soil; and they serve as food (source of protein) for people and animals.

(c)(i) Two types of courtship behaviour in lower animals

Sound/vocal display (for example croaking in male toads, chirping in crickets), colour/visual display (for example nodding and colour change in the Agama lizard), release of scent (pheromones), and nuptial dance/movement display. (Any two.)

(c)(ii) Two importances of courtship behaviour in reproduction

• It attracts a mate of the same species and of the opposite sex, ensuring successful mating.
• It prepares the partners and synchronises the release of gametes, so that fertilization succeeds and interbreeding between different species is avoided.

(d) Courtship behaviour of the Agama lizard

The male Agama lizard (rainbow lizard) attracts a female by a display of colour and movement. During courtship the male develops bright colours, with an orange or reddish head and a bluish body. He carries out repeated up-and-down movements of the head and the front part of the body (head-bobbing or press-up movements), often on a raised surface, to attract the attention of the female. This display also warns off rival males and marks his territory. When a female is attracted and becomes receptive, the two mate.

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(a) Four floral parts of a flower

Sepals (calyx), petals (corolla), stamens (androecium, the male part), and carpels/pistil (gynoecium, the female part).

(b)(i) Differences between wind- and insect-pollinated flowers

(b)(ii) Examples

• Wind-pollinated: maize (also grasses, guinea corn).
• Insect-pollinated: Hibiscus (also flamboyant, Crotalaria).

(c)(i) Three agents of fruit and seed dispersal

Wind, water, animals (and explosive/self mechanism).

(c)(ii) Examples dispersed by each

• Wind: Tridax / cotton seed (light, winged or hairy fruits and seeds).
• Water: coconut (buoyant fruit).
• Animals: Desmodium / cactus (hooked or fleshy fruits); also mango eaten by animals.
• Explosive mechanism: Crotalaria / oil bean (pods that burst open).

(d)(i) Hormones

Hormones are chemical substances produced in small quantities by an organism which are transported to other parts of the body where they control and coordinate growth, development and other activities.

(d)(ii) One plant hormone

Auxin (others: gibberellin, cytokinin, abscisic acid, ethylene/ethene).

(d)(iii) Two effects of plant hormones

• They promote cell elongation and growth of stems and roots (and control tropisms, that is, growth movements towards or away from a stimulus).
• They control the ripening of fruits, formation of fruits, and flowering.
• They control leaf and fruit fall (abscission) and seed/bud dormancy.

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(a)(i) Two stages of photosynthesis

The light stage (light-dependent reaction) and the dark stage (light-independent reaction / Calvin cycle).

(a)(ii) Equation for the first (light) stage

In the light stage, water is split by light energy (photolysis) to release oxygen, hydrogen and energy:

\[ 2H_2O \xrightarrow{\text{light energy / chlorophyll}} 4H^+ + 4e^- + O_2 \]

(In words: water is split in the presence of light and chlorophyll to give hydrogen ions, electrons and oxygen. The energy is trapped as ATP.)

(b)(i) Six modes of nutrition

Autotrophic (holophytic), heterotrophic (holozoic), saprophytic, parasitic, symbiotic, and chemosynthetic nutrition (carnivorous/insectivorous also acceptable).

(b)(ii) Feature that makes feeding possible

• I. Paramecium: cilia (which sweep food into the oral groove / gullet).
• II. Spirogyra: chloroplasts (containing chlorophyll for photosynthesis).
• III. Rhizopus: rhizoids/hyphae which secrete enzymes and absorb digested food (saprophytic feeding).
• IV. Tapeworm: hooks and suckers (scolex) for attachment, and a thin body surface for absorbing already-digested food from the host.

(c) Balanced diet

A balanced diet is a diet that contains all the classes of food (carbohydrates, proteins, fats and oils, vitamins, mineral salts and water) in the correct proportions needed by the body for good health.

(d)(i) Three characteristics of enzymes

• They are proteins and act as biological catalysts.
• They are specific in their action.
• They are affected by temperature and pH (denatured by high temperature).

(d)(ii) Ptyalin and pepsin

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(a) Organic evolution

Organic evolution is the gradual change in living organisms from simple earlier forms to more complex and better-adapted forms over a very long period of time; that is, the process by which present-day organisms have descended, with modification, from earlier ancestral forms.

(b) Contributions to organic evolution

• (i) Lamarck: proposed the theory of the inheritance of acquired characteristics. He held that characters an organism develops during its lifetime through use and disuse of parts (for example the long neck of the giraffe from constantly stretching to reach high leaves) are passed on to its offspring, and that in this way organisms change over generations. He was the first to put forward a clear theory of how evolution could occur.
• (ii) Darwin: proposed the theory of evolution by natural selection (survival of the fittest). He observed that organisms produce more offspring than can survive, that there is variation among individuals, and that there is a struggle for existence. Individuals with favourable variations are better adapted, survive and reproduce, passing on their favourable characters, while the less-adapted die out. Over many generations this leads to new, better-adapted species.

(c) Three evidences of organic evolution

• Fossil records (palaeontology), which show a graded series of extinct forms leading to modern ones.
• Comparative anatomy, especially homologous organs (for example the pentadactyl limb of different vertebrates) showing common ancestry.
• Comparative embryology, in which the early embryos of different vertebrates are strikingly similar.
• Vestigial structures (such as the appendix in man) and geographical distribution of organisms. (Any three.)

(d) Role in the formation of new species

• (i) Mutation: a mutation is a sudden heritable change in the genetic material (genes or chromosomes). It produces new inheritable variations in a population. If a mutation is favourable, it is preserved by natural selection and spreads, so that over time the population becomes different from the original and a new species may arise.
• (ii) Isolation: isolation (for example by a geographical barrier such as a mountain, river or sea) separates a population into groups that can no longer interbreed. Each isolated group accumulates its own variations and adapts to its own conditions. In time the groups become so different that even when brought together they can no longer interbreed, and thus new species are formed.