Science: Biology Essentials

Which part of a plant cell is not found in an animal cell?

• AThe nucleus
• BThe cell membrane
• CThe cytoplasm
• DThe cell wall✓

Answer: Plant cells have a cellulose cell wall (as well as chloroplasts and a permanent vacuole) that animal cells lack. Both types of cell have a nucleus, a cell membrane and cytoplasm.

Which word equation correctly summarises aerobic respiration?

• Acarbon dioxide + water → glucose + oxygen
• Bglucose + water → oxygen + carbon dioxide
• Cglucose + oxygen → carbon dioxide + water✓
• Dglucose → lactic acid

Answer: Aerobic respiration releases energy by reacting glucose with oxygen to produce carbon dioxide and water. The reverse equation is photosynthesis, and glucose → lactic acid is anaerobic respiration in muscle.

Which process moves water across a partially permeable membrane from a dilute solution to a more concentrated one?

• AOsmosis✓
• BDiffusion of solute
• CActive transport
• DTranspiration

Answer: Osmosis is the movement of water molecules across a partially permeable membrane from a region of higher water concentration to lower. Active transport moves substances against a gradient using energy, and transpiration is water loss from leaves.

Which of these is a communicable (infectious) disease?

• AType 2 diabetes
• BMeasles✓
• CLung cancer
• DCoronary heart disease

Answer: Measles is caused by a virus and spreads from person to person, so it is communicable. Diabetes, heart disease and cancer are non-communicable: they are not passed between people.

In humans, the allele for brown eyes (B) is dominant over blue (b). Two parents are both Bb. What proportion of their children would be expected to have blue eyes?

• A1 in 4✓
• B3 in 4
• C1 in 2
• DNone

Answer: A Punnett square for Bb × Bb gives BB, Bb, Bb and bb in equal proportions. Only bb produces blue eyes, so the expected proportion is 1 in 4 (25%); 3 in 4 have brown eyes.

What is the role of enzymes in digestion?

• AThey absorb digested food into the bloodstream
• BThey speed up the breakdown of large food molecules into smaller soluble ones✓
• CThey provide the chemical energy needed to push food along the length of the gut by peristalsis
• DThey kill bacteria that enter the stomach with food

Answer: Enzymes are biological catalysts: amylase, proteases and lipases break carbohydrates, proteins and fats into small soluble molecules that can be absorbed. Stomach acid kills bacteria, muscles move food, and the small intestine absorbs it.

Which blood vessel carries oxygenated blood from the lungs to the heart?

• AThe pulmonary vein✓
• BThe aorta
• CThe pulmonary artery
• DThe vena cava

Answer: The pulmonary vein is the exception to the rule that veins carry deoxygenated blood: it brings oxygenated blood from the lungs to the left atrium. The pulmonary artery carries deoxygenated blood to the lungs, the aorta carries oxygenated blood to the body, and the vena cava returns deoxygenated blood to the heart.

What is the function of red blood cells?

• ATo help the blood to clot at a wound
• BTo fight infection by producing antibodies
• CTo carry dissolved food and hormones
• DTo transport oxygen around the body using haemoglobin✓

Answer: Red blood cells are packed with haemoglobin, which binds oxygen in the lungs and releases it in the tissues. White blood cells fight infection, platelets clot the blood, and plasma carries dissolved substances.

In photosynthesis, which two substances do plants take in and which two do they produce?

• AThey take in nitrogen and water and produce glucose and carbon dioxide
• BThey take in carbon dioxide and water and produce glucose and oxygen✓
• CThey take in carbon dioxide and oxygen and produce water and glucose
• DThey take in oxygen and glucose and produce carbon dioxide and water

Answer: The word equation is carbon dioxide + water → glucose + oxygen, using light energy absorbed by chlorophyll. The reverse process is respiration.

A student investigates how light intensity affects the rate of photosynthesis in pondweed by counting bubbles. Which variable should be kept constant?

• AThe temperature of the water✓
• BThe number of bubbles counted
• CThe rate of photosynthesis
• DThe distance of the lamp from the pondweed

Answer: Light intensity is the independent variable (changed by moving the lamp), the bubble count is the dependent variable, and the rate is what is being measured. Temperature would also affect the rate, so it must be controlled.

Which of these describes natural selection?

• AOrganisms choose which of their characteristics to pass on to their offspring so that the next generation is better suited
• BIndividuals with characteristics best suited to the environment are more likely to survive and reproduce✓
• CIndividuals change their characteristics during their lifetime to suit the environment
• DAll individuals in a species are identical at birth, so which of them survive and reproduce is entirely a matter of chance

Answer: Natural selection works on existing variation: better-adapted individuals survive and breed, passing on the alleles responsible. Characteristics acquired during life are not inherited, and no choice is involved.

Which organ produces insulin?

• AThe kidney
• BThe pancreas✓
• CThe liver
• DThe stomach

Answer: Insulin is a hormone made by the pancreas that lowers blood glucose by causing cells to take it up. The liver stores glucose as glycogen in response to insulin but does not make the hormone.