3.4The breathing system and excretion

Plant exchange and excretion

3.4The breathing system and excretion

Large surface area

Thin structure

Network of veins

Lots of chlorophyll

Structure of the Leaf

Transparent

Packed with chloroplasts

Lots of air spaces

Holes

3.4The breathing system and excretion

Gas exchange in the leafThe structure of the leaf allows plants to carry out gas

exchange.

carbon dioxide in (daytime) : photosynthesis

Oxygen in: respiration.

Oxygen + water vapour : OUT

3.4The breathing system and excretionWide spaces between ground cells – diffusion

3.4The breathing system and excretion

The Stomata• The function of the stomata is gas exchange.

Each stoma is a gap that is found in between two Guard cells.

The Guard cells control the opening and closing of the stoma.

3.4The breathing system and excretion

When water leaves the guard cells they shrink and the gap between the two cells (the stoma) closes.

When water enters the guard cells they swell and have a curved shape. The gap ( the stoma) opens up between the two cells.

The stoma and the guard cells

3.4The breathing system and excretion

3.4The breathing system and excretion

The stoma (open) and the guard cells

3.4The breathing system and excretion

Carbon dioxide controls the stoma• The opening and closing of the stoma depends on

the levels of carbon dioxide in the plant.

• When CO2 levels become low inside the plant water enters the guard cells and the stoma opens up.

3.4The breathing system and excretion

Carbon dioxide controls the stoma• When CO2 levels are high in the plant water leaves the

guard cells and they close.

3.4The breathing system and excretion

3.4The breathing system and excretion

Lenticels• Lenticels are small openings in the bark of a tree

where gas exchange happens.

3.4The breathing system and excretionWhat about trees and woody plants ?

Lenticels often look like tiny raised blisters on a branch or twig.

3.4The breathing system and excretionWinter twig – showing lenticels

3.4The breathing system and excretion

Plant excretionDef Excretion is getting rid of waste of the

metabolism from the body

Plants do not need to excrete a lot of waste:

• They make their own food so they have reduced food waste to get rid of

• They use most of the products of their metabolism in their bodies – i.e. oxygen is produced as a product of photosynthesis but is used for respiration.

Stomata and lenticels are the only organs of excretion.

They excrete oxygen and water vapour.