Cambridge IGCSE Biology 8 Transport in Plants Exam Questions

About Cambridge IGCSE Biology 8 Transport in Plants

Transport in plants explains how water, mineral ions and food move through a flowering plant in Cambridge IGCSE Biology. You need to identify xylem and phloem in sections of roots, stems and leaves, describe the pathway of water from root hair cells to the leaf, and define transpiration. Practical questions often use a potometer or a stained celery stalk. Extended candidates explain transpiration pull using cohesion between water molecules, the effects of temperature, wind and humidity, wilting, and translocation of sucrose and amino acids from sources to sinks. This topic builds on osmosis, active transport and leaf structure.

What you need to know

• 8.1 Xylem and phloem Xylem transports water and mineral ions and gives support. Phloem transports sucrose and amino acids. Extended: xylem vessels are made of dead, hollow cells with no cross walls and thick walls strengthened with lignin.
• 8.2 Water uptake Root hair cells increase the surface area for absorbing water by osmosis and mineral ions by active transport. Water passes through the root cortex cells to the xylem, up the stem and into the mesophyll cells of the leaf.
• 8.3 Transpiration Transpiration is the loss of water vapour from leaves. Water evaporates from the surfaces of mesophyll cells into the air spaces, then diffuses out through the stomata.
• 8.3 Factors affecting transpiration Rate increases with higher temperature and wind speed, and decreases with higher humidity. Measure it with a potometer by timing how far an air bubble moves. Extended: explain using kinetic energy of water molecules and the concentration gradient of water vapour.
• 8.3 Transpiration pull (Extended) Water loss from leaves creates a pull on the water column in the xylem. Cohesion (attractive forces between water molecules) means the whole column moves up as one. If water loss exceeds uptake, cells lose turgor and the plant wilts.
• 8.4 Translocation (Extended) Translocation is the movement of sucrose and amino acids in phloem from sources (where they are made or released from storage) to sinks (where they are used or stored). Some parts, such as roots storing starch, can be a source at one time and a sink at another.

Common mistakes in 8 Transport in Plants

• Saying water evaporates from the stomata. Water evaporates from mesophyll cell surfaces into air spaces and then diffuses out of the stomata as water vapour.
• Saying phloem transports glucose. Phloem transports sucrose and amino acids.
• Saying a potometer measures transpiration directly. It measures water uptake, which is used as an estimate of transpiration.
• Saying root hair cells absorb mineral ions by osmosis. Water enters by osmosis; mineral ions mostly enter by active transport.
• Saying higher humidity increases transpiration. Humid air reduces the water vapour concentration gradient, so transpiration slows.

Try three 8 Transport in Plants exam-style questions