Topic 13 - Transport in Plants

Question 1

Transport system

Answer 1

A system that provides a constant supply of necessary substances through a medium to cells via an exchange surface - e.g., circulatory system

Question 2

Why multicellular organisms need transport systems

Answer 2

• Small surface area to volume ratio
• Therefore inefficient rate of diffusion, preventing cells from relying on diffusion to transport necessary substances in and out of the cell
• Hence, multicellular organisms rely on transport systems to provide a constant supply of necessary substances through a medium to their cells via an exchange surface

Question 3

Xylem

Answer 3

A plant tissue which transports water, mineral ions, and solutes from the roots to the leaves

Process: transpiration stream

Question 4

Phloem

Answer 4

A plant tissue which transports food materials (mainly sucrose and amino acids) made by the plant from photosynthesising leaves to non-photosynthesising regions in the roots and stem

Process: translocation

Question 5

How water is absorbed by root hair cells

Answer 5

There is usually a higher water potential in the soil than there is inside the plant, so the water is draw into the root hair cell by osmosis down the concentration gradient.

Question 6

Transpiration

Answer 6

The loss of water vapour from the plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by diffusion of water vapour through the stomata

Question 7

How humidity affects rate of transpiration

Answer 7

Humidity levels need to be low so that water vapour can diffuse out due to the steep concentration gradient of water.

Low humidity levels increase rate of transpiration.

Question 8

How temperature affects rate of transpiration

Answer 8

Temperature needs to be high (but not too high, as enzymes denature).

High temperature increases rate of transpiration. Average kinetic energy of water molecules increase, which will cause an increase in the rate of diffusion of water out of the stomata.

Question 9

How wind speed affects rate of transpiration

Answer 9

Wind speeds need to be high because this means water vapour from transpiration can get carried away from the surface of the leaf faster.

Question 10

How light intensity affects rate of transpiration

Answer 10

Light intensity needs to be high as light provides warmth and chloroplasts absorb light energy for photosynthesis.

Light intensity ↑
Transpiration ↑
Rate of photosynthesis ↑
Loss of water from the stomata ↑

Guard cells open stomata during the day for photosynthesis