Day and night breathing

The idea

Plants exchange gases by diffusion through stomata and large intercellular spaces, the direction set by conditions and needs: at night carbon dioxide is eliminated, while by day respiratory carbon dioxide goes into photosynthesis and oxygen is released.

A plant has no lungs

A plant has no nose or lungs, yet its cells need to exchange gases.

How do you think gases move in and out of a plant?

• By diffusion through tiny pores
• By being pumped by a heart
• They do not move at all

Day or night?

Choose Day and Night and watch which gas leaves the leaf.

Direction by need

Plants exchange gases by diffusion, through the stomata and the large intercellular spaces, which put all cells in contact with air. Carbon dioxide and oxygen can go into the cells or away from them. The direction depends on the conditions and the plant's needs. At night CO₂ elimination is the major exchange. By day the CO₂ from respiration is used up for photosynthesis, so oxygen release is the major event.

Plants exchange gases by diffusion through stomata and large intercellular spaces, the direction set by conditions and needs: at night carbon dioxide is eliminated, while by day respiratory carbon dioxide goes into photosynthesis and oxygen is released.

Notes

Plants exchange gases by diffusion through stomata and intercellular spaces: at night CO₂ leaves; by day respiratory CO₂ feeds photosynthesis and oxygen is released.

Check yourself

How do plants exchange gases?

At night, which gas exchange is the major one in a plant?

By day, what happens to the carbon dioxide made in respiration?

What decides the direction of gas diffusion in a plant?

• By a pumping heart. Plants have no heart; gases move by diffusion.
• By diffusion through stomata and large intercellular spaces — correct. Yes!
• By haemoglobin in red blood corpuscles. In human beings haemoglobin carries oxygen; plants exchange gases by diffusion.
• Oxygen release. Oxygen release is the major event by day.
• Carbon dioxide intake for photosynthesis. At night there is no photosynthesis occurring.
• Carbon dioxide elimination — correct. Yes!
• It is used up for photosynthesis — correct. Yes!
• It is eliminated through the stomata. By day there is no CO₂ release, because the CO₂ made in respiration is used up for photosynthesis.
• It is changed into haemoglobin. Haemoglobin is the respiratory pigment of human blood, not a product of plant respiration.
• Only the colour of the leaf. The book says the direction depends on the environmental conditions and the requirements of the plant.
• The environmental conditions and the plant's requirements — correct. Yes!
• Only the age of the roots. The book says the direction depends on the environmental conditions and the requirements of the plant.