WAEC SSCE - Biology - 1988

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The constituent of the exhaust gases of motor vehicles that causes serious air pollution is carbon monoxide. Carbon monoxide (CO) is a colorless, odorless gas that is produced when fuel is burned. Incomplete combustion of gasoline, diesel, or other fossil fuels in vehicles' engines releases CO into the air. CO is dangerous because it binds to hemoglobin in the blood and reduces the amount of oxygen that can be carried, causing dizziness, headaches, and even death in high concentrations. It is also a significant contributor to the formation of smog and can worsen respiratory problems like asthma. Therefore, reducing CO emissions from motor vehicles is essential to improving air quality and public health.

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The ability of organisms to maintain a constant internal environment is known as homeostasis. It's like having a thermostat in your house that keeps the temperature steady, no matter what the temperature is outside. Our bodies are able to regulate things like temperature, pH, and blood sugar levels to keep us healthy and functioning properly. This balance is crucial to the survival of all living organisms.

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The causative organism of sleeping sickness is a type of parasite called Trypanosome. It is transmitted to humans through the bite of the tsetse fly, which is found in sub-Saharan Africa. Once inside the human body, the trypanosomes multiply and can cause symptoms such as fever, headaches, and fatigue. As the disease progresses, it can lead to disruption of the sleep-wake cycle, resulting in daytime sleepiness and nighttime insomnia. Without treatment, sleeping sickness can be fatal.

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The change in color of the chameleon serves as a means of camouflage from predators. Chameleons have the unique ability to change the color of their skin to blend in with their surroundings. This helps them avoid being detected by predators and increases their chances of survival. The color change is achieved through the manipulation of pigments in the skin cells called chromatophores, which expand or contract to reveal different colors. Therefore, the color change is not for attracting a mate, repelling enemies, regulating body temperature, or producing a variety of skin pigments, but rather for camouflage purposes.

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Flowering plants primarily contain chlorophyll pigments, which are responsible for their green coloration and essential for photosynthesis. However, some plants also contain accessory pigments such as carotenoids, xanthophylls, and anthocyanins, which give them additional colors such as yellow, orange, and red. So, even though some flowering plants contain these accessory pigments, they still contain chlorophyll pigment. In fact, the presence of these accessory pigments doesn't affect the presence of chlorophyll in plants; instead, they complement and enhance their visual appeal.

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The symptoms described in the question are typical of a nutrient deficiency, and the specific symptoms of poor growth and yellowing of leaves suggest that the plant may be deficient in an essential mineral nutrient. Among the options provided, calcium, phosphorus, iron, zinc, and copper are all essential mineral nutrients for plants. However, of these options, iron is most commonly associated with the symptoms described, as a lack of iron can result in yellowing of leaves due to a reduction in chlorophyll synthesis. This condition is known as iron chlorosis. Therefore, the most likely answer is iron.

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The haploid number of chromosomes in humans is 23. Haploid refers to the number of chromosomes in a cell that contains only one set of chromosomes. In humans, the cells that are haploid are the sperm and egg cells. Each human cell normally contains 46 chromosomes, which are arranged in 23 pairs. When a sperm cell fertilizes an egg cell, the resulting zygote (fertilized egg) contains 23 pairs of chromosomes, or a total of 46 chromosomes. During the process of meiosis, which occurs in the cells that produce sperm and egg cells, the number of chromosomes is reduced from 46 to 23. This is because the cells divide twice, but the chromosomes only replicate once. As a result, each of the four resulting cells has only 23 chromosomes, which is the haploid number for humans.

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The option that is not part of the objectives of conservation of natural resources is: - To eliminate wild animals in order to enable other plants and animals survive Conservation of natural resources is a practice aimed at protecting and preserving the environment for the benefit of present and future generations. The objectives of conservation of natural resources include using resources on a sustained yield basis, guarding against indiscriminate killing of plants and animals, guarding against the extinction and exhaustion of natural resources, and protecting the environment. However, the elimination of wild animals goes against the objectives of conservation as it disrupts the natural ecosystem and may lead to negative consequences such as a decrease in biodiversity.

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The statement that is not true about gene mutation is that it always affects the chromosome number. Gene mutation refers to any change that occurs in the DNA sequence of a gene, and it can result in different outcomes. For instance, gene mutation can introduce new traits into a population by altering the sequence of nucleotides in a gene, which can lead to changes in the phenotype (observable traits). However, some mutations may have an unnoticeable effect on the phenotype, and the individual carrying the mutation may appear normal. Gene mutations do not always affect the chromosome number, and there are two types of mutations that affect the chromosome number, which are called chromosomal mutations. These mutations involve changes in the structure or number of chromosomes, and they can lead to genetic disorders or conditions such as Down syndrome. In summary, gene mutation can introduce new traits into a population, cause changes in the DNA, have unnoticeable effects on the phenotype, and be a source of new genes. However, gene mutation does not always affect the chromosome number.

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Gregor Mendel is known for his work on the inheritance of traits in pea plants, which led to the discovery of the basic principles of genetics. One of the major ideas that he proved was that characteristics of an organism are controlled by genes occurring in pairs. Mendel conducted experiments in which he crossed pea plants with different traits, such as tall and short plants, and observed the characteristics of their offspring. He found that certain traits, such as tallness, were dominant over others, such as shortness, and that these traits were passed down from one generation to the next in predictable patterns. Mendel's work established the concept of dominant and recessive traits, and laid the foundation for the modern study of genetics. It demonstrated that traits are not blended in offspring, but instead are inherited as discrete units, which we now call genes. Therefore, the major idea proved by Gregor Mendel was that characteristics of an organism are controlled by genes occurring in pairs.

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The pulmonary artery carries deoxygenated blood from the right ventricle of the heart to the lungs. This means that the blood in the pulmonary artery is low in oxygen and needs to be replenished by picking up oxygen in the lungs. Once the blood has been oxygenated in the lungs, it will be carried back to the heart through the pulmonary veins and sent to the rest of the body.

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The process of animals within the same class and order becoming more specialized in their structure and function to survive in new and different environments is known as adaptive radiation. This means that over time, the animals develop specific adaptations to fit the unique conditions of their environment, such as changes in their diet or physical characteristics. For example, a group of finches on the Galapagos Islands developed different beak shapes to suit their specific diets. This process is important for the survival and success of species in changing environments.

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The relationship between a herbivore and the bacteria that live in its caecum is known as "symbiosis." Symbiosis is a close and long-term interaction between two different species, where both species benefit from the relationship. In this case, the herbivore provides a warm and nutrient-rich environment in its caecum for the bacteria to live in, and the bacteria help the herbivore digest tough plant material, breaking down cellulose into simpler compounds that the herbivore can absorb as nutrients. This mutualistic relationship benefits both the herbivore and the bacteria, and they depend on each other for survival.

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Auxins are a type of plant hormone that play a crucial role in growth and development. They are primarily produced in the apical regions of both roots and shoots. These regions are responsible for the growth of the plant, so the production of auxins in these areas allows for the regulation of growth and development throughout the plant. While auxins can also be found in other parts of the plant such as the parenchyma of roots and shoots, and the epidermis of roots and shoots, their primary site of production is in the apical regions.

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The sheet of muscle that separates the thoracic cavity from the abdominal cavity is called the diaphragm. The diaphragm is a large, dome-shaped muscle that sits at the bottom of the rib cage and helps with breathing by contracting and relaxing. When it contracts, it moves downward, which increases the volume of the thoracic cavity and allows the lungs to expand and take in air. When it relaxes, it moves upward, which decreases the volume of the thoracic cavity and helps to expel air from the lungs. Therefore, the diaphragm plays an essential role in the respiratory system and is crucial for breathing.

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The step that would not be taken to protect or conserve fishing grounds from over-exploitation is the use of nets with all sizes of mesh. This is because using nets with all sizes of mesh can result in the unintentional capture and killing of juvenile fish and other non-targeted species. This can disrupt the ecological balance of the fishing grounds and lead to a decline in fish populations. Instead, a better option would be to use nets with a particular mesh size that is suitable for the targeted species and does not harm non-targeted species. Additionally, banning the harvesting of some species, regulating the size of ships allowed into fishing grounds, and limiting the period of fishing in the waters are all effective measures that can be taken to protect and conserve fishing grounds from over-exploitation.

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The organisms that can keep their body temperature almost constant within a narrow range are called homotherms. This means that their internal body temperature remains stable even when the external temperature changes. Unlike poikilotherms, which have body temperatures that fluctuate with the environment around them, homotherms maintain a stable body temperature through various mechanisms like sweating, panting, or shivering. Some examples of homothermic animals are humans, dogs, and birds.

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Uracil is not a constituent of DNA. DNA (deoxyribonucleic acid) is made up of four basic building blocks, called nucleotides, which consist of a phosphate group, a sugar molecule called deoxyribose, and a nitrogenous base. The four nitrogenous bases found in DNA are adenine (A), guanine (G), cytosine (C), and thymine (T). Uracil is a nitrogenous base that is found in RNA (ribonucleic acid), which is a related molecule to DNA but has a slightly different structure. RNA also contains a phosphate group and a sugar molecule (ribose) but instead of thymine, it contains uracil as one of its four nitrogenous bases.

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Deamination is the process through which excess amino acids are broken down into ammonia and a keto acid. Amino acids are the building blocks of proteins, and when we consume more protein than our body needs, the excess amino acids must be eliminated. The process of deamination takes place in the liver and kidneys, where enzymes remove the amino group from the amino acid and convert it into ammonia. The ammonia is then converted into urea and eliminated from the body in urine. The remaining keto acid can be used for energy or converted into glucose or fat for storage.

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The pituitary gland is called the 'master gland' because it controls the functions of many other glands in the body. It does this by producing and secreting hormones that stimulate or inhibit the production of hormones from other glands. So, it acts as a central regulator of the endocrine system, which is responsible for maintaining the body's internal balance and regulating various physiological processes. Additionally, the pituitary gland is located in the brain and is connected to the hypothalamus, which is a key region that controls many essential bodily functions such as hunger, thirst, and temperature regulation.

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The characteristic feature of tropical rain-forest habitat that is not listed is "fewer canopy strata than the savannah." Tropical rainforests have a multi-layered canopy with several strata, each containing various species of trees and other plants. The canopy layers can range from 30-40 meters high to as low as 3-5 meters. In contrast, savannahs have a much simpler structure, with fewer and shorter trees that do not form a complex canopy. This difference in the number of canopy strata is due to the fact that the rainforest receives more rainfall than the savannah, allowing for more plant growth and diversity. Therefore, the correct option is the one that mentions the "fewer canopy strata" characteristic.

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The habitat that is not classified as a terrestrial habitat is the Littoral zone. The littoral zone is a marine habitat, which refers to the area of the shore that is covered and uncovered by the tides. It is the region that lies between the highest and lowest water marks on the shore. In contrast, terrestrial habitats are those habitats that are found on land, such as forests, savannahs, alpine areas, and deserts.

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When large numbers of organisms share limited space and resources, the result is competition. Competition occurs when organisms struggle to obtain resources like food, water, and shelter in an environment where there are limited supplies. The organisms that are better adapted to the environment and able to obtain the resources they need are more likely to survive and reproduce, while those that are not as well adapted may die off or become extinct. This process of natural selection helps to ensure that the fittest organisms are able to survive and pass on their genes to future generations.

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The brain and the spinal cord make up the central nervous system (CNS). The CNS is responsible for processing and coordinating information from the senses, controlling movements, and regulating body functions. It receives information from the peripheral nervous system (PNS), which consists of the nerves that extend from the CNS to the rest of the body. The CNS is responsible for many of the body's important functions, including consciousness, thought, memory, and emotion.

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The pigment responsible for skin coloration in the malphigian layer is called melanin. Melanin is produced by specialized cells called melanocytes found in the skin's epidermis. The amount and type of melanin produced by these cells determine a person's skin color. Melanin also plays a role in protecting the skin from the harmful effects of the sun's ultraviolet (UV) radiation. Individuals with more melanin in their skin have a higher level of natural protection against UV radiation, while those with less melanin are more susceptible to sunburn and skin damage.

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The statement that is not true of a climax vegetation is that it eliminates competition. Climax vegetation is a stable community of plants and animals that has reached a state of equilibrium and is able to persist over time under prevailing environmental conditions. However, competition between different species in the community can still occur, although it may be reduced compared to earlier stages of succession. The development of climax vegetation is the result of a process called succession, in which different plant and animal communities replace one another over time until a stable, diverse community is established. The colonization of a habitat by plants and animals is a key aspect of this process.

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Double fertilization is a unique process that occurs in flowering plants during sexual reproduction. In this process, two sperm cells from a single pollen grain fertilize two different nuclei in the female reproductive structure of the flower. The first sperm fertilizes the egg cell, forming a zygote, which eventually develops into an embryo. The second sperm fuses with the polar nuclei, which results in the formation of the endosperm. The endosperm is a food-rich tissue that provides nourishment to the developing embryo. So, the correct option is "one embryo and endosperm nucleus are formed." Double fertilization leads to the formation of both an embryo and the endosperm, which provides nutrients for the developing embryo to grow into a mature seed.

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Coordination in the body of mammals is primarily achieved through the action of the endocrine and nervous systems working together. The nervous system consists of the brain, spinal cord, and nerves that transmit electrical impulses, while the endocrine system consists of glands that produce hormones that travel through the bloodstream to target organs and tissues. Together, these systems regulate and control bodily functions such as movement, sensation, digestion, and metabolism, ensuring that all parts of the body work together in harmony. While the skeletal, muscular, and circulatory systems are also important for movement and support, they do not play as significant a role in overall coordination as the endocrine and nervous systems.

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The vector of the malarial parasite is the female Anopheles mosquito. This is because female Anopheles mosquitoes feed on the blood of humans and animals, and when they bite an infected person, they can transmit the malaria parasite from that person's blood to their own. The parasite then multiplies inside the mosquito, and when the mosquito bites another person, it can transmit the parasite to them, thus spreading the disease. It is important to note that male mosquitoes do not feed on blood, and therefore cannot transmit the malaria parasite.

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The structure in the maize grain that stores food is called the endosperm. It is a tissue that surrounds and nourishes the embryo of the seed. The endosperm is rich in starch, which serves as a source of energy for the growing embryo. During germination, the enzymes released by the embryo break down the starch in the endosperm to release the stored energy, which is then used by the developing plant to grow and establish itself. In other words, the endosperm is the part of the maize grain that provides the nourishment for the growing plant until it is capable of producing its own food through photosynthesis.

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The specialized structures that are stimulated by touch, pressure, pain, heat and cold are called receptors. Receptors are specialized cells or structures that detect changes in the environment, including changes in temperature, pressure, and pain. They are found throughout the body, including in the skin, muscles, and internal organs, and are responsible for transmitting information about the environment to the brain and spinal cord. Once the receptors are stimulated, they generate electrical impulses that travel along sensory neurons to the spinal cord and brain, where they are processed and interpreted to give rise to our sensory experiences.

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The bicuspid valve, also known as the mitral valve, is located between the left auricle (the upper chamber on the left side of the heart) and the left ventricle (the lower chamber on the left side of the heart). It allows blood to flow from the left atrium into the left ventricle, but prevents blood from flowing back into the atrium when the ventricle contracts and pumps blood out to the body.

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The factor that is not associated with aquatic habitat is humidity. Humidity refers to the amount of water vapor present in the air, and it is a factor that is more relevant to terrestrial habitats rather than aquatic ones. Aquatic habitats are characterized by factors such as temperature, light intensity, turbidity, and wave action, which can significantly affect the survival and behavior of aquatic organisms. Temperature is important because it affects the metabolic rate of organisms and influences their growth and reproduction. Light intensity is crucial because it drives photosynthesis in aquatic plants and affects the behavior and distribution of aquatic animals. Turbidity is significant because it influences the amount of light penetration and can affect the feeding and predator-prey interactions of aquatic organisms. Wave action is important because it determines the level of water movement, which can affect the distribution and behavior of organisms in the water column.

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Fungi, viruses, bacteria, and nematodes are all causative organisms of plant diseases. Fungi are a type of organism that can cause diseases in plants. They are responsible for many common plant diseases, such as powdery mildew, rust, and black spot. Viruses are another type of organism that can cause diseases in plants. They can cause a wide range of symptoms, such as yellowing or mottling of leaves, stunting of growth, and even death of the plant. Bacteria are also known to cause plant diseases. They can infect plants through wounds or natural openings, causing symptoms such as wilting, leaf spots, and rot. Nematodes are tiny, worm-like organisms that can live in the soil and infect plant roots, causing damage to the plant's root system and reducing its ability to take up water and nutrients. Cercariae, on the other hand, are not causative organisms of plant diseases. They are a type of larva that can infect snails and other animals, but they do not infect plants.

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Among the options given, the process of "carbondioxide is evolved" does not occur during photosynthesis. During photosynthesis, plants use energy from sunlight to convert water and carbon dioxide into glucose (a type of sugar) and oxygen. This process takes place in the chloroplasts of plant cells and involves a series of complex biochemical reactions. During the light-dependent reactions, energy from sunlight is absorbed by pigments such as chlorophyll and converted into chemical energy in the form of ATP and NADPH. These energy-rich molecules are then used in the light-independent reactions (also called the Calvin cycle) to fix carbon dioxide into glucose. Throughout the process, oxygen is released as a byproduct of photosynthesis, which is essential for sustaining life on Earth. In contrast, carbon dioxide is not evolved, but rather utilized by plants to create organic compounds such as glucose.

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Hormones are chemical messengers produced by various glands and organs in the body. They are secreted directly into the bloodstream and travel to target organs or tissues, where they bind to specific receptors and initiate a response. Therefore, the correct statement about hormones is that they are secreted directly into the bloodstream. Hormones are highly specific in their mode of action, and their effects depend on the target tissue or organ.

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Erythrocytes, also known as red blood cells, have the greatest affinity for oxygen and carbon dioxide. This is because they contain a protein called hemoglobin, which binds to oxygen and carbon dioxide and transports them throughout the body. Hemoglobin has a high affinity for oxygen, which allows it to pick up oxygen in the lungs and deliver it to tissues throughout the body that need it. Hemoglobin also has a moderate affinity for carbon dioxide, which allows it to pick up carbon dioxide from tissues and transport it back to the lungs to be exhaled. Therefore, erythrocytes are essential for maintaining proper oxygen and carbon dioxide levels in the body.

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(a) Four modes of nutrition in plants

• Autotrophic (holophytic) nutrition: green plants manufacture their own food by photosynthesis, e.g. most green plants.
• Saprophytic nutrition: feeding on dead organic matter, e.g. Mucor, Rhizopus, mushroom.
• Parasitic nutrition: feeding on a living host, e.g. Cuscuta (dodder), mistletoe.
• Carnivorous (insectivorous) nutrition: trapping and digesting insects, e.g. sundew, pitcher plant, bladderwort.

(Symbiotic nutrition, e.g. lichen, is also acceptable.)

(b) Light and dark reactions of photosynthesis

Light reaction (light-dependent stage):

• Takes place in the grana of the chloroplast and requires light.
• Chlorophyll absorbs (traps) light energy.
• The trapped energy splits water molecules into hydrogen and oxygen (photolysis of water); the oxygen is released as a by-product.
• The light energy is used to form energy-rich ATP, and hydrogen is picked up by a carrier (NADP) to form reduced NADP (NADPH₂).

Dark reaction (light-independent stage / Calvin cycle):

• Takes place in the stroma of the chloroplast and does not need light directly.
• Carbon dioxide is fixed (combined) using the hydrogen (from reduced NADP) and the energy (from ATP) produced in the light stage.
• This reduces carbon dioxide to form simple sugar (glucose), which may then be built up into starch.

Overall: \[ 6CO_2 + 6H_2O \xrightarrow{\text{light, chlorophyll}} C_6H_{12}O_6 + 6O_2 \]

(c) Modifications and mechanisms of feeding habits

• (i) Filter feeding in mosquito larva: the larva lives in water and hangs just below the surface. It has a pair of brushes of fine hairs (mouth brushes) around the mouth. These hairs beat rapidly and set up water currents that sweep small floating food particles (plankton, tiny organisms and organic matter) in the water towards the mouth, where they are filtered out and swallowed. In this way the larva strains (filters) food from the water.
• (ii) Parasitic feeding in tapeworm: the tapeworm lives in the small intestine of its host (man), where digested food is abundant. It has a head (scolex) bearing hooks and suckers for firm attachment to the intestinal wall, so that it is not swept away. It has no mouth and no gut; instead it has a thin, flat, ribbon-like body with a very large surface area covered by a resistant cuticle that protects it from the host's digestive enzymes. It simply absorbs already-digested, soluble food from the host through its whole body surface (osmosis and diffusion). Its long, segmented body also allows it to produce large numbers of eggs for reproduction.

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(a)(i) Definition of population

A population is a group of organisms of the same species living together in the same habitat at a particular time, and which are able to interbreed to produce fertile offspring.

(a)(ii) Factors affecting population growth

Biotic factors (living factors):

• Availability of food - abundant food supports growth while scarcity limits it.
• Predation, competition, parasitism and disease - these reduce numbers by increasing the death rate.

Abiotic factors (non-living factors):

• Temperature - extreme heat or cold slows reproduction and raises mortality.
• Availability of water, light and space - shortage of any of these restricts survival and reproduction.

(b) Effects of food shortage on a population

• Increased competition among members for the limited food, both intraspecific and interspecific.
• Increased death rate (higher mortality) as the weaker individuals starve.
• Reduced reproductive rate (lower natality) because underfed organisms produce fewer offspring.
• Migration or emigration of some members in search of food, reducing the local population.
• Stunted growth and poor health, making individuals more prone to disease.
• Overall the population size falls until it matches the available food (the carrying capacity).

(c) Methods and their principles

(i) Improving crop yield

• Application of fertilizers (manuring) - Principle: fertilizers add essential mineral nutrients such as nitrogen, phosphorus and potassium to the soil, which the crops need for the manufacture of proteins and healthy growth, thereby raising yield.
• Use of improved (high-yielding) varieties through selective breeding - Principle: plants with desirable genes (fast growth, disease resistance, large produce) are selected and bred so that these favourable characteristics are passed on, giving heavier harvests.

Other acceptable methods: irrigation (supplies water for photosynthesis and transport of nutrients) and pest and weed control (removes organisms that compete with or destroy the crop).

(ii) Preserving and storing food

• Refrigeration or freezing (low temperature) - Principle: low temperatures slow down the activity of enzymes and inhibit the growth and multiplication of decay-causing micro-organisms (bacteria and fungi), so the food does not spoil quickly.
• Drying (dehydration) - Principle: removing moisture from the food deprives micro-organisms of the water they need to grow and reproduce, thereby preventing decay.

Other acceptable methods: salting or sugaring (high salt/sugar concentration draws water out of microbial cells by osmosis, killing or inhibiting them) and canning/pasteurisation (heat kills micro-organisms and sealing prevents re-entry of air and microbes).

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(a) Conservation of natural resources

Conservation of natural resources is the careful and wise management, protection and use of the earth's natural resources so that they are not wasted, destroyed or exhausted, and so that they remain available for the benefit of both present and future generations.

(b) Natural resources to be conserved and the benefits

(c) Problems often encountered in ensuring conservation

• Rapid population growth increases demand for land, food, timber and fuel, causing over-exploitation.
• Poverty and unemployment force people to exploit resources such as forests and wildlife for survival.
• Ignorance and lack of public awareness about the importance and methods of conservation.
• Poor enforcement of conservation laws and inadequate funding of enforcement agencies.
• Bush burning, illegal logging, poaching and over-grazing that destroy resources faster than they can be replaced.
• Industrialisation and urbanisation leading to pollution and destruction of natural habitats.
• Corruption and conflict of interest between economic development and conservation.

(d) Efforts employed in my country to ensure conservation

• Establishment of national parks, game reserves and forest reserves to protect wildlife and vegetation.
• Enactment and enforcement of conservation and anti-poaching laws, and a ban on indiscriminate bush burning and illegal logging.
• Afforestation and reforestation programmes (tree-planting campaigns) to replace felled trees.
• Setting up agencies such as environmental protection and forestry commissions to regulate resource use.
• Public enlightenment and environmental education in schools and the media to create awareness.
• Encouraging controlled or selective harvesting, crop rotation and use of alternative energy to reduce pressure on resources.
• Control of pollution through laws on waste disposal and treatment of industrial effluents.

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(a)(i) Labelled drawing of a typical plant cell

(a)(ii) Functions of two labelled organelles

1. Mitochondrion: it is the site of aerobic respiration, where energy is released from food and trapped in ATP for the activities of the cell.
2. Chloroplast: it contains chlorophyll, which absorbs light energy for the manufacture of food during photosynthesis.

(b) Two levels of cell organisation

1. Tissue level: a tissue is a group of similar cells working together to perform a particular function. For example, xylem tissue in a plant conducts water and mineral salts; muscle tissue in an animal brings about movement.
2. Organ level: an organ is made up of different tissues working together to carry out one or more functions. For example, a leaf is a plant organ for photosynthesis and gaseous exchange, while the heart is an animal organ that pumps blood.

(c) Roles of processes in a living cell

1. Osmosis: this is the movement of water molecules through a selectively permeable membrane from a region of higher water potential, or more dilute solution, to a region of lower water potential, or more concentrated solution. It enables root-hair cells to absorb water from the soil and keeps plant cells turgid for support. It also helps to maintain the water balance of cells.
2. Diffusion: this is the movement of particles from a region of higher concentration to a region of lower concentration. It enables cells to take in oxygen and soluble food substances and to remove wastes such as carbon dioxide. Thus, it is important in gaseous exchange and in movement of nutrients from tissue fluid into cells.