Cambridge O Level Biology 5090 Syllabus

Explain the 'lock and key' model of enzyme action.

The enzyme has a specific active site whose shape is complementary to its substrate. The substrate fits into the active site (like a key in a lock), forms an enzyme-substrate complex, the reaction occurs, and products are released.

Explain why enzymes are specific.

Each enzyme has an active site of a particular shape that fits only one substrate (complementary shape). Therefore each enzyme catalyses only one type of reaction.

Describe the effect of increasing temperature on enzyme activity.

As temperature rises, rate increases (more kinetic energy and collisions) up to an optimum. Above the optimum the enzyme denatures (active site changes shape) and rate falls; at high temperature it stops.

What is meant by an enzyme being 'denatured'?

The enzyme's shape (its active site) is permanently changed by high temperature or extreme pH, so the substrate no longer fits and the enzyme can no longer function.

Describe the effect of pH on enzyme activity.

Each enzyme has an optimum pH at which it works best. Above or below this pH the rate decreases; extreme pH denatures the enzyme.

Write the word equation for photosynthesis.

Carbon dioxide + water --(light energy, chlorophyll)--> glucose + oxygen.

Write the balanced chemical equation for photosynthesis.

6CO2 + 6H2O --(light, chlorophyll)--> C6H12O6 + 6O2.

State the three external conditions that affect the rate of photosynthesis (limiting factors).

Light intensity, carbon dioxide concentration, and temperature.

What is a 'limiting factor' in photosynthesis?

A factor present in such short supply that it restricts (limits) the rate of photosynthesis; increasing it raises the rate until another factor becomes limiting.

Give three adaptations of a leaf for efficient photosynthesis.

Large flat surface area (to absorb light); thin (short diffusion distance for gases); many chloroplasts in palisade cells near the top; network of veins for transport; stomata for gas exchange.

What is the function of the xylem in a flowering plant?

Xylem transports water and dissolved mineral ions from the roots up to the leaves (one direction, upward). It also provides support.

What is the function of the phloem in a flowering plant?

Phloem transports (translocates) sucrose and amino acids (manufactured food) from the leaves to other parts of the plant, in both directions.

Define 'transpiration'.

The loss of water vapour from the leaves (and other aerial parts) of a plant by evaporation, mainly through the stomata, and its diffusion into the atmosphere.

State four factors that increase the rate of transpiration.

Increased temperature, increased light intensity (stomata open), decreased humidity, and increased air movement (wind).

How are root hair cells adapted for the absorption of water and mineral ions?

They have a long, thin extension (root hair) giving a large surface area for absorption, a thin cell wall for short diffusion distance, and many mitochondria for active uptake of mineral ions.

Define a 'balanced diet'.

A diet containing all the nutrients (carbohydrates, proteins, fats, vitamins, minerals, fibre and water) in the correct amounts and proportions to maintain good health.

State the deficiency disease caused by lack of vitamin C and lack of vitamin D.

Vitamin C deficiency causes scurvy. Vitamin D deficiency causes rickets (in children).

State the role of the mineral iron and the deficiency disease caused by lack of it.

Iron is needed to make haemoglobin in red blood cells. Its deficiency causes anaemia.

What is the role of dietary fibre (roughage) and what is its main source?

Fibre adds bulk to food, aids peristalsis and prevents constipation. Its source is plant material (e.g. cellulose cell walls in vegetables, fruits, wholegrains).

List, in order, the main regions of the alimentary canal from mouth to anus.

Mouth, oesophagus, stomach, small intestine (duodenum then ileum), large intestine (colon then rectum), anus.

Define 'ingestion', 'digestion', 'absorption' and 'egestion'.

Ingestion: taking food into the body (mouth). Digestion: breakdown of large insoluble molecules into small soluble ones. Absorption: movement of digested food into the blood. Egestion: removal of undigested food (faeces) through the anus.

What is peristalsis?

Waves of muscular contraction and relaxation of the circular and longitudinal muscles in the gut wall that push food along the alimentary canal.

Name the enzyme in saliva, its substrate and product.

Salivary amylase; it breaks down starch into maltose (a sugar).

State the functions of hydrochloric acid in the stomach.

It kills bacteria/microorganisms in food, and provides the acidic (low) pH that is the optimum for the enzyme pepsin (protease) to work.

What is the role of bile in digestion, where is it made and where is it stored?

Bile emulsifies fats (breaks large fat droplets into small ones, increasing surface area for lipase) and neutralises stomach acid. It is made in the liver and stored in the gall bladder.

Name the products of complete digestion of carbohydrates, proteins and fats.

Carbohydrates -> simple sugars (glucose). Proteins -> amino acids. Fats -> fatty acids and glycerol.

How is the small intestine (ileum) adapted for absorption?

It is long and has many villi and microvilli giving a very large surface area; villi have thin (one-cell-thick) walls, a good blood supply (capillaries) and a lacteal for fats, giving efficient absorption.

What is 'assimilation'?

The movement of digested food molecules into the cells of the body where they are used, becoming part of the cells (e.g. glucose used in respiration, amino acids built into proteins).

List the four components of human blood and one function of each.

Red blood cells (carry oxygen as oxyhaemoglobin); white blood cells (defence against pathogens); platelets (clotting); plasma (transports dissolved substances, e.g. CO2, nutrients, hormones, urea, heat).

How is a red blood cell adapted to its function?

Biconcave shape gives a large surface area for oxygen absorption; contains haemoglobin to carry oxygen; has no nucleus so it carries more haemoglobin; flexible to squeeze through capillaries.

State the function of the four chambers of the heart and which side carries oxygenated blood.

Right atrium and right ventricle pump deoxygenated blood to the lungs; left atrium and left ventricle pump oxygenated blood to the body. The left side carries oxygenated blood and has a thicker muscular wall.