Edexcel GCSE Biology Topic 6: Plant Structures and Their Functions Exam Questions

About Edexcel GCSE Biology Topic 6: Plant Structures and Their Functions

Topic 6 of Edexcel GCSE Biology is assessed on Paper 2. It covers photosynthesis and the factors that limit it, how water and mineral ions are absorbed and transported through the xylem, and how sucrose is moved in the phloem. GCSE Biology students also study how plants are adapted to extreme environments and how plant hormones control growth, with uses in agriculture. The core practical investigates the effect of light intensity on the rate of photosynthesis. Examiners often ask for limiting factor graph interpretation, inverse square law calculations (Higher tier), transpiration rates from potometers and explanations of phototropism.

What you need to know

• Photosynthesis Photosynthetic organisms are the main producers of food and therefore biomass. Photosynthesis is an endothermic reaction in chloroplasts: carbon dioxide + water -> glucose + oxygen, using light energy.
• Limiting factors Temperature, light intensity and carbon dioxide concentration can each limit the rate of photosynthesis. Higher tier: light intensity is inversely proportional to the square of the distance from the light source.
• Core practical: light intensity Investigate the effect of light intensity on the rate of photosynthesis, for example by counting oxygen bubbles from pondweed or measuring colour change of an indicator with algal balls at different distances from a lamp, controlling temperature and carbon dioxide.
• Water and mineral uptake Root hair cells have a large surface area for absorbing water by osmosis and mineral ions by active transport. Xylem is made of dead, lignified hollow tubes carrying water and mineral ions upwards.
• Phloem and translocation Phloem consists of living sieve tubes and companion cells and transports sucrose around the plant by translocation, in both directions.
• Transpiration and stomata Water evaporates from leaves through stomata, controlled by guard cells, pulling water up the xylem. The rate increases with light intensity, temperature and air movement and decreases with humidity. A potometer measures water uptake.
• Plant adaptations and hormones (Biology only) Plants are adapted to extreme environments, such as cacti with spines and thick waxy cuticles. Auxins cause phototropism and gravitropism; auxins are used as weedkillers and rooting powders, gibberellins in germination and fruit and flower production, and ethene to control fruit ripening.

Common mistakes in Topic 6: Plant Structures and Their Functions

• Saying light energy is turned into glucose. Light energy is transferred to chemical energy stored in glucose.
• Halving instead of quartering. Doubling the distance from the lamp reduces light intensity to one quarter.
• Saying phloem carries glucose. Sugars are transported in the phloem as sucrose.
• Saying root hair cells absorb mineral ions by diffusion. Mineral ions are usually absorbed by active transport against a concentration gradient.
• Saying high humidity speeds up transpiration. Humid air reduces the concentration gradient of water vapour, slowing transpiration.

Try three Topic 6: Plant Structures and Their Functions exam-style questions