Transpiration and Translocation — Practice Questions

Question 1

Transpiration is best described as:

Accepted Answer

The loss of water vapour from the leaves — Transpiration is the evaporation of water from mesophyll cells and its diffusion out of the leaf as vapour through the stomata.

Question 2

Which change would increase the rate of transpiration?

Accepted Answer

An increase in wind speed — Wind carries water vapour away from the leaf, keeping the diffusion gradient steep, so transpiration speeds up.

Question 3

Increasing the humidity of the air around a leaf will:

Accepted Answer

Decrease transpiration — Humid air reduces the difference in water vapour concentration between the leaf and the air, slowing diffusion and transpiration.

Question 4

Through which structures does most water vapour leave a leaf?

Accepted Answer

The stomata — Water vapour diffuses out of the leaf mainly through the stomata, most of which are on the lower surface.

Question 5

Raising the temperature usually increases transpiration because it:

Accepted Answer

Speeds up the evaporation of water — Higher temperature gives water molecules more energy, so they evaporate faster from the mesophyll and diffuse out more quickly.

Question 6

Translocation is the transport of:

Accepted Answer

Sucrose and amino acids in the phloem — Translocation is the movement of dissolved food, mainly sucrose and amino acids, through the phloem.

Question 7

In translocation, substances move from a source to a sink. A 'sink' is a region where substances are:

Accepted Answer

Used or stored, such as a growing root — A sink is any part that uses or stores food, for example growing roots, fruits or storage organs.

Question 8

A potometer is used to measure:

Accepted Answer

The rate of water uptake by a shoot — A potometer measures the rate at which a cut shoot takes up water, which is closely linked to the rate of transpiration.

Question 9

Why does a plant wilt on a hot, windy day?

Accepted Answer

Water is lost by transpiration faster than it is taken up — When transpiration exceeds water uptake, the cells lose water and become flaccid, so the plant wilts.

Question 10

Which statement comparing xylem and phloem transport is correct?

Accepted Answer

Xylem carries water upward; phloem carries food up or down — Xylem moves water in one direction (upward), while phloem can translocate dissolved food both up and down the plant.