IGCSE BIO EXP

Explain four adaptations of villi for absorption.

1. Villi and microvilli provide a large surface area. 2. The epithelium is one cell thick, giving a short diffusion distance. 3. A rich capillary supply carries away absorbed glucose and amino acids, maintaining concentration gradients. 4. Lacteals absorb products of fat digestion.

Explain four adaptations of alveoli for gas exchange.

1. Numerous alveoli provide a large surface area. 2. Walls are one cell thick, giving a short diffusion distance. 3. Moist lining allows gases to dissolve. 4. Rich blood supply and ventilation maintain steep concentration gradients.

Explain how the small intestine absorbs digested nutrients efficiently.

1. Villi and microvilli increase surface area. 2. Thin epithelium shortens diffusion distance. 3. Blood flow maintains concentration gradients. 4. Glucose and amino acids enter capillaries; absorbed lipids enter lacteals.

Explain how temperature affects enzyme activity.

1. Increasing temperature raises kinetic energy. 2. Enzyme and substrate collide more frequently. 3. Rate rises to the optimum temperature. 4. Above optimum, the active site changes shape as the enzyme denatures, reducing the rate.

Explain how pH affects enzyme activity.

1. Each enzyme has an optimum pH. 2. Changes in pH disrupt bonds maintaining enzyme structure. 3. The active site changes shape, so the substrate binds less effectively. 4. Extreme pH may denature the enzyme.

Explain four ways smoking damages the respiratory system.

1. Tar damages cilia, allowing mucus to accumulate. 2. Pathogens and particles are removed less effectively. 3. Alveolar walls can break down, reducing surface area. 4. Carbon monoxide binds to haemoglobin, reducing oxygen transport.

Explain why heart rate increases during exercise.

1. Muscles respire faster and require more oxygen and glucose. 2. Increased blood flow delivers these substances faster. 3. Faster circulation removes carbon dioxide. 4. More energy can be released to support muscle contraction.

Explain four adaptations of a leaf for photosynthesis.

1. Broad and flat, providing a large surface area for light absorption. 2. Thin, allowing rapid gas diffusion. 3. Palisade cells contain many chloroplasts. 4. Stomata allow carbon dioxide to enter.

Explain how root hair cells absorb mineral ions.

1. Root hairs provide a large surface area. 2. Mineral ions may be at a lower concentration in soil than inside cells. 3. Active transport moves ions against the concentration gradient. 4. This requires energy from respiration.

Explain how water moves from roots to leaves.

1. Water enters root hair cells by osmosis. 2. Water moves into the xylem. 3. Transpiration from leaves creates a pulling force. 4. Cohesion between water molecules helps maintain a continuous column in the xylem.

Explain how vaccination protects against a pathogen.

1. Vaccine introduces harmless antigens. 2. Lymphocytes produce specific antibodies. 3. Memory cells remain. 4. On later exposure, they produce a faster response, helping destroy the pathogen before serious illness develops.

Explain how antibiotic resistance develops.

1. Random mutations create genetic variation. 2. Some bacteria have resistance alleles. 3. Antibiotics kill susceptible bacteria while resistant bacteria survive. 4. Resistant bacteria reproduce and pass resistance alleles to offspring.

Explain how genetic engineering produces human insulin.

1. A restriction enzyme cuts out the human insulin gene. 2. The same enzyme cuts a bacterial plasmid. 3. DNA ligase joins the gene into the plasmid. 4. The recombinant plasmid enters bacteria, which multiply and produce insulin.

Explain why energy is lost between trophic levels.

1. Not all organisms or biomass are eaten. 2. Some ingested material is indigestible and egested. 3. Some material is lost in excretion. 4. Energy is transferred to the surroundings as heat during respiration.

Explain how deforestation reduces biodiversity.

1. Habitats are destroyed. 2. Organisms lose food and shelter. 3. Populations decline or become extinct. 4. Food webs are disrupted, reducing the variety of species.

Explain how eutrophication occurs.

1. Fertiliser runoff adds nitrates to water. 2. Algae grow rapidly, forming a bloom. 3. Algae die and decomposers break them down, using oxygen in respiration. 4. Dissolved oxygen falls, killing aquatic organisms.

Explain how the kidneys help maintain water balance.

1. Blood is ultrafiltered in the glomerulus. 2. Useful substances are selectively reabsorbed. 3. Water is reabsorbed by osmosis. 4. ADH increases collecting-duct permeability, increasing water reabsorption.

Explain how insulin lowers blood glucose.

1. The pancreas detects raised blood glucose. 2. It releases insulin. 3. Body cells take up more glucose. 4. The liver and muscles convert glucose to glycogen.

Explain why transpiration increases on a hot, windy day.

1. Higher temperature increases evaporation from mesophyll cells. 2. Wind removes humid air around the leaf. 3. The water-vapour concentration gradient increases. 4. The rate of transpiration rises.

Explain how high biodiversity benefits an ecosystem.

1. More species provide varied food sources and habitats. 2. More complex food webs may be more resilient to change. 3. Biodiversity provides resources such as food and medicines. 4. Genetic diversity may help populations adapt to environmental changes.

Explain how the placenta supports a developing fetus.

1. It provides a large exchange surface. 2. Oxygen and nutrients pass from maternal to fetal blood. 3. Carbon dioxide and other wastes pass to maternal blood. 4. Maternal and fetal blood normally remain separate, reducing direct mixing.

Explain how stomata control water loss.

1. Guard cells control stomatal opening. 2. When guard cells lose water, they become less turgid. 3. Stomata close. 4. Less water vapour diffuses out, reducing transpiration.

Explain why a plant wilts when it loses too much water.

1. Water leaves plant cells by osmosis. 2. Vacuoles shrink. 3. Turgor pressure decreases and cells become flaccid. 4. Tissues lose support, causing wilting.

Explain why large organisms need specialised exchange surfaces.

1. Larger organisms have a smaller surface-area-to-volume ratio. 2. Their surface cannot exchange enough substances to meet the needs of all cells. 3. Diffusion distances inside the body are greater. 4. Specialised exchange surfaces and transport systems improve supply and removal.

Explain how a reflex action protects the body.

1. A receptor detects a stimulus. 2. A sensory neurone carries impulses to the central nervous system. 3. A relay neurone passes the impulse to a motor neurone. 4. The motor neurone stimulates an effector to produce a rapid response.

Explain the role of decomposers in the carbon cycle.

1. Decomposers break down dead organisms and waste. 2. They respire. 3. Respiration releases carbon dioxide. 4. Decomposition returns mineral nutrients to the soil.

Explain how exercise increases oxygen delivery to muscles.

1. Heart rate increases. 2. Cardiac output increases. 3. More oxygenated blood reaches the muscles per minute. 4. Oxygen is used for aerobic respiration.

Explain how the body cools itself when it is too hot.

1. Skin arterioles dilate, increasing blood flow near the surface. 2. More energy is transferred to the surroundings. 3. Sweat production increases. 4. Evaporation of sweat removes heat from the body.

Explain how the body conserves heat when it is too cold.

1. Skin arterioles constrict, reducing blood flow near the surface. 2. Less heat is lost from the skin. 3. Sweating decreases. 4. Muscle shivering increases respiration and heat production.

Explain how a high carbon dioxide concentration affects breathing.

1. Carbon dioxide concentration in the blood rises. 2. Blood pH falls. 3. Receptors detect the change. 4. The breathing rate and depth increase to remove more carbon dioxide.