WAEC SSCE - Biology - 2011

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Afforestation is an activity that promotes forest conservation. Afforestation involves the planting of new trees in areas where there was no forest before. This activity helps to increase the forest cover, which provides a habitat for many species of animals and plants, helps to reduce soil erosion, and prevents flooding. Additionally, afforestation helps to combat climate change by absorbing carbon dioxide from the atmosphere. Therefore, afforestation is an important activity that promotes the conservation of forests. The other options listed in the question, such as lumbering, use of firewood for cooking, and production of paper, can contribute to deforestation and degradation of forests.

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A xerophyte is a plant that has adapted to survive in environments with low water availability. To conserve water, xerophytes possess certain features such as a thick cuticle on leaves, sunken stomata to reduce water loss, and a fleshy stem to store water. However, xerophytes do not have broad leaves as this would result in increased transpiration and water loss, which is contrary to their water-conserving adaptation. Therefore, the correct answer is "broad leaves".

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Inhaled air is made warm and moist in the nasal cavity. The nasal cavity contains specialized structures called turbinates, which help to increase the surface area of the nasal cavity. As air passes through the nasal cavity, it comes into contact with the moist mucous membranes lining the cavity, which help to humidify the air and also trap any dust or particles in the air. Blood vessels in the mucous membranes also warm the air, bringing it closer to body temperature. Overall, the nasal cavity helps to prepare inhaled air for entry into the lungs, making it more suitable for respiration.

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The term used to describe differences in characteristics observed between individuals of the same species is "variation". Variation can be caused by a number of factors, including genetic differences, environmental factors, and interactions between genes and the environment. Variation can be observed in many different traits or characteristics, such as height, weight, color, behavior, and more. Understanding and studying variation is important in fields such as genetics, ecology, and evolution, as it can help us to understand how and why populations change over time.

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The practice that improves crop yield in a clayey soil is the addition of lime and humus. Clayey soils are often compact and have low nutrient levels, making it difficult for crops to grow properly. The addition of lime helps to reduce the acidity of the soil, which can be toxic to plants. The addition of humus helps to increase the organic matter content of the soil, which can improve soil structure and nutrient availability. Both lime and humus can help to improve soil fertility, making it easier for crops to grow and produce a higher yield.

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The correct answer is option C: diffusion. Water movement in the endodermis of plant roots is regulated by a specialized cell layer known as the Casparian strip. The Casparian strip prevents water and solutes from moving freely through the cell walls between endodermal cells, forcing them instead to cross the plasma membrane of the endodermal cells. Once inside the endodermal cells, water and solutes can move through two pathways: the apoplastic pathway, which is the space between the cell walls of adjacent cells, and the symplastic pathway, which is the cytoplasmic continuum that links adjacent cells through plasmodesmata. Water moves through the symplastic pathway by osmosis, driven by differences in solute concentration between the soil and the root. Active transport of solutes also plays a role in establishing these concentration gradients. Once inside the root, water and solutes can be transported to the xylem, which carries them to the rest of the plant. The process that is not involved in water movement in the endodermis is diffusion, which is the movement of solutes from an area of high concentration to an area of low concentration. While diffusion can occur in the apoplastic and symplastic pathways, it is not the primary driving force behind water movement through the endodermis.

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The capture-recapture method is used to estimate the total population size of a species in a given area. The formula for this method is: Total population size = (number marked in first sample * number in second sample) / number marked in second sample Using the values given in the question: Number marked in first sample = 200 Number in second sample = 120 Number marked in second sample = 40 Plugging in these values into the formula, we get: Total population size = (200 * 120) / 40 = 600 Therefore, the total number of organisms in the habitat is 600. So the answer is option C - 600.

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The appropriate method for the cultivation of cassava is stem cutting. This involves cutting stems of cassava plants into sections, usually 20-30 cm long, and planting them in soil. The stems will sprout and grow into new cassava plants. This method is commonly used because cassava does not produce true seeds and cannot be propagated through budding or fragmentation. Root cutting can be used, but it is less efficient than stem cutting because it takes longer for the roots to develop into new plants.

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When an amoeba is placed in a salt solution, the salt solution is hypertonic (higher concentration of solute) compared to the cytoplasm of the amoeba. As a result, water from the cytoplasm moves out of the cell through osmosis to the hypertonic salt solution, causing the amoeba to shrink. In response to this, the contractile vacuole in the amoeba would form more frequently to pump out the excess water from the cytoplasm in order to maintain the osmotic balance and prevent the amoeba from bursting. Therefore, the correct option is "be formed less frequently" as the opposite is true.

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Leguminous crops are incorporated into crop rotation in order to promote nitrogen fixation. Leguminous plants form a symbiotic relationship with nitrogen-fixing bacteria, Rhizobia, which live in nodules on their roots. These bacteria convert atmospheric nitrogen into a form that plants can use, such as ammonia or nitrates. When leguminous crops are grown and then plowed under the soil, the nitrogen-rich plant material breaks down and releases this essential nutrient into the soil, making it available for other crops to use in subsequent rotations. Therefore, leguminous crops are important in maintaining soil fertility, reducing the need for synthetic fertilizers, and increasing crop yields.

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The testes are the male reproductive organs responsible for producing sperm and the male hormone testosterone. In mammals, including humans, the testes initially form inside the abdomen, near the kidneys. However, for the production of healthy sperm, the testes need to be maintained at a temperature lower than the normal body temperature. Hence, during fetal development, a structure called the gubernaculum begins to pull the testes down towards the scrotal sac. As the testes move down, they are accompanied by blood vessels, nerves, and a duct called the vas deferens, which carry sperm from the testes to the urethra. Once the testes reach the scrotal sac, they are positioned outside the body, where the temperature is lower than the body temperature. This helps to keep the testes cool, which is important for the production of healthy sperm. Therefore, the testes in male mammals descend into the scrotal sac to maintain a relatively low temperature that is optimal for the production of healthy sperm.

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The food substance is likely to be a protein. When sodium hydroxide solution and a drop of copper sulphate solution are added to a protein, it forms a violet or purple color. This is due to the formation of a complex between the copper ions and the peptide bonds in the protein molecules. The intensity of the color depends on the concentration of the protein in the solution.

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During photosynthesis, plants produce glucose as a result of the conversion of carbon dioxide and water using sunlight. This glucose can be used to meet the energy requirements of the plant. However, since the plant can only use so much glucose at once, it needs to store the excess glucose for future use. The conversion of glucose to starch in the leaf during the day primarily enables the leaf to store the excess glucose as starch. Starch is a more compact and stable form of glucose storage, which is easily stored in the plant cells. By converting glucose to starch, the plant can store more glucose in a smaller space and keep it stable for longer periods. Thus, the conversion of glucose to starch in the leaf is an essential process that enables plants to store excess glucose and meet their energy needs efficiently.

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Haemoglobin is an oxygen-carrying pigment found in the red blood cells of mammals. It is responsible for transporting oxygen from the lungs to other tissues in the body, and it also helps to transport carbon dioxide from the tissues back to the lungs for exhalation. Therefore, the statement that best describes haemoglobin is that it is an oxygen-carrying pigment.

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Vaccination results in the production of antibodies which destroy toxins of germs. When a vaccine is introduced into the body, it triggers an immune response, causing the immune system to produce specific antibodies against the pathogen. These antibodies circulate in the body and are ready to attack the pathogen if it enters the body. In this way, the body is able to quickly and effectively fight off the pathogen and prevent the development of the disease. This is the primary mechanism by which vaccination protects against infectious diseases.

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Filtrate in the Bowman's capsule contains vitamins because they have a low molecular weight. Vitamins are organic compounds that the body needs in small amounts to maintain normal physiological function. Due to their small size and molecular weight, they can easily pass through the glomerulus and into the Bowman's capsule during filtration in the kidney. Once in the filtrate, vitamins can be reabsorbed into the bloodstream and utilized by the body, or excreted in the urine if they are present in excess. Therefore, the correct option is "they have low molecular weight".

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Adenine pairs with thymine because one is a purine base (adenine) and the other is a pyrimidine base (thymine). The structure of DNA requires that the nitrogenous bases, which make up the "rungs" of the DNA ladder, pair in a specific way: purines (adenine and guanine) must pair with pyrimidines (thymine and cytosine). Adenine has a complementary hydrogen-bonding pattern with thymine, which allows them to pair together, forming two hydrogen bonds between them. This specific pairing between the bases is important for DNA replication and the accurate transmission of genetic information.

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Cells that utilize a lot of energy require a lot of ATP, the energy currency of cells. Mitochondria are the organelles responsible for producing ATP in cells through cellular respiration. Therefore, cells that use a lot of energy, such as muscle cells or neurons, will have a large number of mitochondria to produce the ATP they require. So, the correct answer is mitochondria.

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During sexual reproduction in Paramecium, the zygote undergoes meiosis to form four haploid nuclei. These haploid nuclei then undergo two rounds of mitosis to produce eight nuclei. Therefore, the zygote divides three times to produce eight nuclei. The correct answer is 3.

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The structure that produces the greatest variety of digestive enzymes is the pancreas. The pancreas is an organ located behind the stomach and it secretes digestive enzymes that help in the breakdown of carbohydrates, fats, and proteins in the small intestine. The enzymes produced by the pancreas include amylase, lipase, and protease, which can break down carbohydrates, fats, and proteins respectively. The salivary glands produce amylase which helps in the breakdown of carbohydrates in the mouth, while the stomach produces pepsin, which breaks down proteins. The colon, on the other hand, absorbs water and electrolytes, and is not primarily involved in enzyme production. Therefore, the correct answer is the pancreas.

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The process whereby electrons are emitted from chlorophyll and returned to it unchanged is known as cyclic photophosphorylation. During this process, light energy is absorbed by chlorophyll and used to excite electrons, which then move along an electron transport chain and ultimately return to the chlorophyll molecule. This results in the generation of ATP (adenosine triphosphate), which is an important energy source for the cell. Unlike non-cyclic photophosphorylation, which involves the transfer of electrons to an electron acceptor and the subsequent generation of NADPH in addition to ATP, cyclic photophosphorylation only generates ATP.

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Sensory neurons may not have myelin sheath. Sensory neurons are responsible for transmitting signals from the sensory receptors (such as those in the skin, eyes, ears, nose, and tongue) to the central nervous system (brain and spinal cord). Some sensory neurons have long axons that extend from the periphery to the spinal cord or brain, and these axons may be covered by myelin sheath produced by Schwann cells. However, not all sensory neurons have myelin sheath. For example, some sensory neurons that are involved in transmitting pain signals may have very short or no myelin sheath. This lack of myelin sheath can contribute to the sensation of pain, as it allows the signal to be transmitted more slowly and with greater intensity.

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Somatic cells are not regarded as specialized cells. Somatic cells are the body cells that make up most of the body tissues and organs. They perform general functions in the body such as providing structural support, protection, and nutrient transport. In contrast, specialized cells have specific functions and characteristics that allow them to perform specific tasks. For example, sperm cells are specialized cells that are involved in reproduction, muscle cells are specialized cells that are involved in movement, and root hair cells are specialized cells that are involved in nutrient uptake.

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Effector organs are the organs that carry out the response or action in response to a stimulus. Among the given options, the skin is an effector organ as it responds to stimuli such as heat, cold, pressure, and pain, by activating various physiological mechanisms such as sweating, shivering, and blood vessel constriction or dilation, to maintain the body's internal balance or homeostasis. The tongue, nose bridge, and ear glands are not considered effector organs as they do not have a direct role in carrying out a physiological response to a stimulus.

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The branch of biology that deals with the principles of classification of organisms is known as taxonomy. Taxonomy is the scientific study of how living things are classified or grouped based on their characteristics and relationships with one another. This involves identifying, naming, and organizing species into hierarchical categories or taxonomic ranks, such as kingdom, phylum, class, order, family, genus, and species. The aim of taxonomy is to provide a systematic and logical framework for the study of biodiversity and the relationships among different organisms.

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If a person has two alleles of the sickle cell anaemia gene, the person has the disease. Sickle cell anaemia is an autosomal recessive genetic disorder, which means that two copies of the abnormal gene are required to have the disease. A person with one abnormal and one normal gene is a carrier and does not have the disease but can pass the abnormal gene to their offspring. A person with two abnormal genes has the disease and may experience symptoms such as pain, fatigue, and anemia.

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If the population size is stable, it means that the birth rate (natality) and immigration rate are equal to the death rate (mortality) and emigration rate respectively. However, if there is a ten percent increase in natality and a twenty percent increase in immigration, the population size will begin to increase. This is because the number of individuals added to the population through births and immigration will exceed the number lost through deaths and emigration, resulting in a net increase in population size. Therefore, the correct answer is "begin to increase."

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Kreb's cycle, also known as the citric acid cycle or TCA cycle, occurs in the mitochondria. It is a series of chemical reactions that occur in the presence of oxygen and play a critical role in the production of energy in the form of ATP during cellular respiration. The cycle starts with the entry of acetyl-CoA into the cycle, which then undergoes a series of reactions to produce NADH and FADH2, which are important electron carriers. These electron carriers then go on to participate in the electron transport chain, leading to the production of ATP.

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Hibiscus and Spirogyra are plants that are capable of producing their own food through photosynthesis. Cactus is also a plant that is capable of producing food, although it uses a specialized form of photosynthesis called CAM photosynthesis. On the other hand, Mushroom is not a plant and is not capable of producing its own food. It is a fungus that obtains its nutrients by decomposing organic matter. Therefore, Mushroom is the organism in the given options that is not a producer.

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Phloem is responsible for the transportation of the products of photosynthesis, including sugar and other nutrients from the leaves to other parts of the plant, including the roots. If all the phloem tissues of the stem of a plant close to the root system are removed for a long period of time, the roots will not receive the necessary nutrients to survive. Without the products of photosynthesis, the roots will not have enough energy to carry out important processes such as respiration and growth. Therefore, the most likely outcome of this scenario is that the plant will wither and eventually die.

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The man has blood group IA IA, which means that he has two copies of the A allele. The woman has blood group IA IO, which means she has one A allele and one O allele. When they have a child, each parent passes one allele to their child. The possible combinations of alleles that their child can inherit are IA from the father and IA or IO from the mother. So, the child can have blood group IA IA, IA IO, or IO IO. However, the child cannot have blood group B or AB because neither parent has the B allele. Therefore, the likely blood group of their son is A.

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The statement that is not true about continuous variation is: "is usually controlled by one or two pair(s) of genes". Continuous variation is a type of variation that shows a wide range of possible values for a particular trait, and is usually controlled by several genes, with each gene contributing a small amount to the final phenotype. Continuous variation can also be influenced by environmental factors, such as nutrition or exposure to certain chemicals. The distribution of continuous variation usually follows a normal distribution curve, with most individuals clustering around the mean value and fewer individuals at the extremes of the distribution. Therefore, the statement that is not true is that continuous variation is usually controlled by one or two pair(s) of genes.

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The falling off of leaves of deciduous trees is helpful to the plant because it reduces the rate of transpiration. Deciduous trees shed their leaves during the dry season to conserve water. The leaves of these trees have stomata that can lose water through transpiration. Shedding of leaves helps reduce the surface area of the plant that can lose water through transpiration, thus conserving water. Additionally, the fallen leaves decompose, adding nutrients to the soil, which are later used by the plant to produce new leaves.

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The statement that is not true about photosynthesis is "Plants can photosynthesize without an increase in dry weight." Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy stored in organic compounds such as sugars. This process occurs in specialized organelles called chloroplasts, which are found in the cells of the plant's leaves, stems, and sometimes roots. During photosynthesis, carbon dioxide and water are converted into glucose and oxygen, with the help of chlorophyll and other pigments that absorb light energy. The oxygen produced during photosynthesis comes from the splitting of water molecules, not the breakdown of water. And, photosynthesis does lead to an increase in dry weight, as the plant stores the energy in the form of organic compounds.

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A vestigial structure in humans is a structure that has lost its original function due to evolution. In other words, it served a purpose in an ancestor of the species, but is no longer necessary or useful in the current form of the species. In humans, the tail bone or coccyx is considered a vestigial structure because it was used for balance and mobility in our primate ancestors, but has no apparent function in humans.

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The correct answer is "Pyruvate and cellulose" because both pyruvate and cellulose are not six-carbon compounds. Pyruvate is a three-carbon compound produced during glycolysis, while cellulose is a polymer made up of repeating glucose units and has a much larger molecular weight than glucose. The other options contain at least one six-carbon compound: glucose has six carbons, lactose is made up of glucose and galactose (both six-carbon compounds), and cellulose contains repeating glucose units.

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The structure that is not involved in respiration is the stomach. Respiration is the process of gas exchange, which involves taking in oxygen and releasing carbon dioxide. The lungs, mouth, and trachea are all involved in respiration. The lungs are the primary organ of respiration where gas exchange occurs. The trachea, also known as the windpipe, is the tube that carries air from the mouth and nose to the lungs. The mouth serves as an opening for air to enter the respiratory system. The stomach, on the other hand, is involved in the digestion of food, which is a separate process from respiration.

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The enzyme that is active in the duodenum is Trypsin. When food leaves the stomach, it enters the duodenum of the small intestine. Trypsin is produced by the pancreas and is released into the duodenum. Its function is to break down proteins into smaller peptides. This process aids in digestion and allows for the absorption of essential amino acids by the body. Therefore, the correct option is Trypsin.

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Ecological investigation in a habitat includes choosing a habitat, identification of specimens, and measuring abiotic and biotic factors. Determining the genetic makeup of specimens is not typically included as part of ecological investigation in a habitat. Genetic makeup is more relevant in genetic research or population genetics, which is a different field of study from ecology. Ecological investigation is focused on the study of the relationships and interactions between living organisms and their environment. This involves examining the physical and chemical factors of the environment, as well as the diversity and distribution of species in the ecosystem.

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More sweat is produced during muscular exercise because the temperature of the body rises. When muscles contract during exercise, they generate heat which raises the body temperature. To prevent the body from overheating, sweat glands are stimulated to produce sweat. Sweat, which is mostly composed of water and salt, evaporates from the skin surface and removes heat from the body, thus reducing the body temperature. This process is known as evaporative cooling. Therefore, the more a person exercises, the more heat is produced, and the more sweat is produced to cool the body down.

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The component of Lamarck's theory of evolution that is considered faulty is "Changes that result in individuals of the same species are transmitted to offspring." This idea, also known as the inheritance of acquired characteristics, suggests that an organism can pass on characteristics it has acquired during its lifetime to its offspring. However, this has been disproven by modern genetics, which shows that inherited traits are determined by an organism's DNA and not influenced by its experiences during life. Therefore, traits acquired during an individual's lifetime cannot be inherited by its offspring.

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The answer is "bacteria". Bacteria are living organisms and are part of the biotic components of an ecosystem. The other options, temperature, oxygen, and soil, are abiotic components of an ecosystem. Abiotic factors are non-living components of an ecosystem that can affect the growth and survival of living organisms. Temperature affects the rate of biological processes, oxygen is necessary for respiration, and soil provides nutrients and support for plants.

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Secondary growth in plants refers to the increase in the girth or thickness of the plant stem or root. This process is brought about by the activity of the vascular cambium, a lateral meristem responsible for the production of secondary xylem and phloem. The vascular cambium divides actively, producing new cells towards the inner side (secondary xylem) and the outer side (secondary phloem). As a result, the stem or root increases in girth over time. The other options, phellogen and phelloderm, are involved in the formation of the protective outer bark in woody plants.

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(a)(i) Effect of gravity on plant growth

Gravity determines the direction of growth of plant organs. The root grows downwards towards the pull of gravity (it is positively geotropic), while the shoot grows upwards away from gravity (it is negatively geotropic). This response is called geotropism (gravitropism).

(a)(ii) Experiment to demonstrate the effect of gravity on roots

1. Soak and germinate several bean seeds until the radicle (root) appears.
2. Pin two or three germinating seeds to a cork so that their roots point in different directions (some horizontal, some upward).
3. Place the cork inside a bell jar or wide jar containing moist cotton wool to keep the air humid, and keep it in the dark to remove the effect of light.
4. Set up a control in which an identical cork with seeds is fixed to a slowly rotating clinostat (this nullifies the one-sided pull of gravity).
5. Leave both set-ups for two to three days and observe.

Observation: in the stationary set-up all the roots curve downwards, whatever their starting direction; on the clinostat the roots grow straight. Conclusion: gravity causes roots to grow downwards (positive geotropism).

(b) How bitter taste is detected in humans

Bitter substances in food dissolve in the saliva and stimulate the taste buds located mainly at the back of the tongue. The chemical stimulates the receptor (gustatory) cells, which generate nerve impulses. The impulses are carried by sensory nerves to the brain (cerebral cortex), where they are interpreted as a bitter taste.

(c) Endocrine glands and their functions

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None

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(a) Relative position of organs in the mammalian gut

A large labelled diagram (8 to 10 cm long) should show the stomach on the left, leading into the C-shaped duodenum; the pancreas lying in the loop of the duodenum; the liver above and to the right of the stomach; and the gall bladder tucked under the liver, with its bile duct joining the pancreatic duct to enter the duodenum.

(b)(i) Two diseases of the liver

1. Hepatitis (inflammation of the liver)
2. Liver cirrhosis (jaundice/liver cancer also accepted)

(b)(ii) Five effects of liver disease on the body

1. Jaundice (yellowing of the skin and eyes) from build-up of bile pigment.
2. Poor digestion and absorption of fats because bile production falls.
3. Accumulation of toxins in the blood, as the liver can no longer detoxify them.
4. Failure of blood clotting, leading to easy bleeding (reduced fibrinogen/prothrombin).
5. General weakness, loss of appetite and swelling of the abdomen (accumulation of fluid).

(c) Vitamin deficiency symptoms

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(a)(i) Difference between genotype and phenotype

The genotype is the genetic constitution of an individual, that is, the actual set of alleles (genes) it carries for a trait, for example BB, Bb or bb. The phenotype is the observable physical or physiological expression of that trait, for example black coat colour or white coat colour, which results from the genotype interacting with the environment.

(a)(ii) Two factors that determine each term

Genotype is determined by:

• the genotypes (alleles) of the parents from which the individual inherits its genes;
• mutation, that is, changes in the genes or chromosomes.

Phenotype is determined by:

• the genotype of the individual;
• the environment (for example diet, temperature and general health).

(b) Breeding experiment: BB (black) × bb (white)

Let B = allele for black coat (dominant) and b = allele for white coat (recessive).

Parental cross (P): a homozygous black dog (BB) crossed with a homozygous white dog (bb). Each parent contributes one gamete type, so every offspring receives one B and one b allele. All the first filial generation (F1) are therefore Bb (black).

F1 × F1 cross: Bb × Bb. The genetic diagram (Punnett square) below shows the F2 offspring.

From the genetic diagram the F2 genotypes are 1 BB : 2 Bb : 1 bb, giving a phenotypic ratio of 3 black : 1 white.

Total number of F2 puppies = 240.

(b)(i) Number of white puppies

White puppies (bb) form \(\tfrac{1}{4}\) of the offspring:

(b)(ii) Number of black puppies

Black puppies (BB and Bb) form \(\tfrac{3}{4}\) of the offspring:

Answers: 60 white puppies and 180 black puppies in the second filial generation.

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(a)(i) The second law of thermodynamics

The second law of thermodynamics states that whenever energy is converted from one form to another, some of the energy is always lost as heat, so that no energy transfer or transformation is 100% efficient; the entropy (disorder) of the universe always tends to increase.

(a)(ii) Applying it to energy flow in a food chain

Energy enters a food chain when green plants (producers) trap sunlight in photosynthesis. As energy passes from one trophic level to the next (producer to primary consumer to secondary consumer, and so on), only about 10% is passed on and stored in the next level. The other roughly 90% is lost as heat through respiration and in movement, and some is lost in undigested waste and death. Because of this loss at each transfer, less and less energy is available at higher trophic levels. This is why energy flow is one-directional (it does not cycle) and why food chains usually have only four or five links, and why there are fewer organisms at the top than at the bottom (the pyramid of energy).

(b)(i) Three factors that limit the size of human populations

1. Food supply (availability of food).
2. Disease and epidemics.
3. Space / shelter and availability of water (war and natural disasters also accepted).

(b)(ii) Two ways each of overcoming the factors

• Food supply: increase food production through mechanised and improved farming; improve storage, preservation and distribution of food.
• Disease: provide immunisation/vaccination and good medical services; improve sanitation, clean water and public health education.
• Space / water: build more houses and develop new settlements/urban planning; provide dams, boreholes and pipe-borne water and manage resources wisely.