Transport in Plants Flashcards

All 15 cards in this deck

What is transpiration?

The movement of water from the roots, up the xylem and out of the leaves, driven by evaporation of water from the leaves through the stomata.

Name the cells that change the size of the stomata.

Guard cells.
e.g. when they lose water and become flaccid the stomata get smaller, reducing water loss.

True or false? In most leaves the stomata are found mainly on the upper surface.

False. Most stomata are on the lower surface — this reduces water loss by evaporation while still allowing gas exchange for photosynthesis.

What is translocation?

The movement of sugars, as sucrose, from the leaves through the living sieve cells of the phloem to sinks in the plant where the sucrose is needed.

Why does translocation of sucrose require energy from the plant?

Sucrose is moved into and along the phloem by active transport, which uses energy from respiration.

Give two differences between transpiration and translocation.

Transpiration moves water (and mineral ions) through dead, lignified xylem cells in one direction only; translocation moves sucrose through living sieve cells of the phloem in both directions.

What effect does an increase in light intensity have on the rate of water uptake by a plant?

It increases it — the stomata open wider in the light, so more water evaporates from the leaves.

What effect does increased air movement (e.g. a fan) have on the rate of water uptake by a plant?

It increases it — moving air removes water vapour from around the leaf, increasing evaporation/diffusion of water vapour from the leaf, so the plant takes up more water.

What effect does an increase in temperature have on the rate of water uptake by a plant?

It increases it — water evaporates and diffuses out of the leaves faster.

What is the equation for the rate of water uptake measured with a potometer?

rate of water uptake = volume of water taken up ÷ time taken (e.g. mm³ per minute)

In an experiment on the effect of a fan on water uptake, why is the volume of water taken up also measured with the fan switched off?

As a control, to compare the effect / to give a baseline measurement.

Which gases move in and out of a leaf through the stomata?

Carbon dioxide and oxygen diffuse in and out (in the light, carbon dioxide goes in for photosynthesis and oxygen comes out). Water vapour also escapes through them during transpiration.

How are mineral ions carried from the roots to the leaves?

Dissolved in water, up the xylem in the transpiration stream.

What happens to a stoma when its guard cells become turgid?

It opens — the guard cells swell with water and the pore between them widens.

Why does a potometer only give an estimate of the rate of transpiration?

It measures water uptake, not water loss; it assumes the plant loses as much water from its leaves as it takes up.