IGCSE Biology Past Paper Common Questions

Practice flashcards covering key concepts and exam questions across all chapters in IGCSE Biology, including cell structure, enzymes, plant transport, human organ systems, genetics, ecology, and biotechnology.

How is a species defined?

A group of organisms that can reproduce to produce fertile offspring.

What structural features distinguish bacteria from other groups of organisms?

They have a peptidoglycan or murein cell wall, no nucleus or nuclear membrane (a nucleoid), a loop of DNA, no mitochondria, no chloroplasts, no vacuoles, smaller ribosomes, pili, and a capsule.

What structural features distinguish the cells of a Protoctista from a prokaryote?

Protoctista cells have a nucleus or nuclear membrane, membrane-bound organelles, linear chromosomes, and cell walls with a different composition if present.

What is the primary function of the cell nucleus?

It stores genetic information in chromosomes, genes, or DNA, controls cell activities, development, and growth, and contains instructions for protein synthesis.

What happens during the process of plasmolysis in plant cells?

The cytoplasm and vacuole decrease in volume, causing the cell membrane to pull away from the cell wall, leaving the cell flaccid with reduced turgor pressure.

According to the gas exchange chart, what color changes does hydrogencarbonate indicator undergo at different concentrations of $CO_2$?

Yellow at the highest concentration of $CO_2$, orange at higher levels, red at normal atmospheric levels, magenta at low levels, and purple at the lowest concentration of $CO_2$.

What are the common symptoms shared by marasmus and kwashiorkor?

Both cause diarrhoea, low body mass, poor growth, tiredness or irritability, muscle wastage, dry skin, brittle hair or hair color change, fatty liver, and anaemia.

How is a catalyst defined in biological processes?

A substance that increases the rate of chemical reactions and is not changed during or by the reaction.

How are palisade mesophyll cells adapted to maximize photosynthesis?

They contain many chloroplasts, are tightly packed and columnar-shaped, arranged vertically near the top surface of the leaf to capture light.

What is the role of bile in the human digestive system?

It emulsifies fat droplets to increase surface area for lipase, neutralizes stomach acid to raise pH for intestinal enzymes, and denatures pepsin.

By what mechanism does the pathogen cholera cause diarrhoea?

It releases a toxin that binds to the small intestine wall, causing chloride ion secretion into the lumen which lowers water potential and draws water out of cells into the gut by osmosis.

What mechanism is responsible for the continuous movement of water up xylem vessels?

Transpiration pull, created as water evaporates from mesophyll walls and diffuses through stomata, generating tension that pulls a cohesive continuous column of water upwards.

Why is regular exercise recommended for individuals at high risk of coronary heart disease (CHD)?

Exercise prevents blocked blood vessels, lowers blood pressure, reduces cholesterol and fats, aids weight loss, strengthens heart muscle, and lowers resting pulse rate.

How does a vaccine provide long-term active immunity against a pathogen?

It introduces harmless pathogens containing specific antigens that stimulate lymphocytes to produce complementary antibodies and long-lasting memory cells.

What key features make gas exchange surfaces efficient for diffusion?

A large surface area, thin wall providing a short diffusion distance, good blood supply, efficient ventilation, permeability, and a moist surface.

How are nerve impulses transmitted across a synaptic cleft?

Vesicles release neurotransmitters into the synaptic cleft, which diffuse across and bind to complementary receptors on the post-synaptic neurone membrane.

How does a renal dialysis machine filter waste products from the patient's blood?

Blood flows past a partially permeable membrane; urea and excess salts diffuse into dialysis fluid down concentration gradients, excess water leaves by osmosis, while proteins and glucose are retained.

What structural adaptations distinguish insect-pollinated flowers from wind-pollinated flowers?

Insect-pollinated flowers have large, brightly colored petals, nectar, scent, and sticky spiky pollen, with anthers and stigmas positioned inside the flower.

What vital roles does the placenta perform for the developing fetus?

It facilitates gas exchange, nutrient transfer, waste excretion, secretes essential pregnancy hormones, and allows transfer of maternal antibodies for passive immunity.

What is meant by the genetic term co-dominance?

A condition where both alleles in a heterozygous organism are expressed, resulting in a phenotype that combines or shows both traits.

How does eutrophication in rivers lead to severe fish mortality?

Leached nutrient ions cause algal bloom that blocks sunlight, killing aquatic plants; aerobic bacteria then decompose dead organic matter, depleting dissolved oxygen during respiration.

What structural features enable xerophytes to minimize water loss in arid environments?

Thick cuticles, sunken stomata, low stomatal density, rolled leaves, leaf hairs, small or reduced leaves, and stomata that close during the day.

Based on marking criteria, what harmful effects do non-biodegradable plastics have on organisms and ecosystems?

Plastics persist for long periods, cause ingestion and digestive blockages, entangle or suffocate organisms, block light needed for photosynthesis, release toxic chemicals, reduce water aeration, and cause bioaccumulation.

Why is it more energy efficient for humans to consume plant products directly rather than eating meat from plant-fed animals?

Eating plants involves fewer trophic levels; approximately $90\%$ of energy is lost at each stage through respiration, heat, and excretion, transferring only about $10\%$ to the consumer.

Why are single-celled fungi and bacteria well-suited for industrial biotechnology?

They reproduce rapidly, possess plasmids, share a universal genetic code, produce complex molecules, require minimal space and cheap growth mediums, and raise fewer ethical concerns.