Exchange surfaces in leaves and fish

In a nutshell

Multicellular organisms need to have exchange surfaces to perform basic functions for survival, including respiration and photosynthesis. In this lesson, you will learn about exchange surfaces in leaves and fish.

Exchange surfaces in leaves

Biology; Cell biology; KS4 Year 10; Exchange surfaces in leaves and fish — 1. Waxy cuticle, 2. Upper epidermis, 3. Palisade mesophyll, 4. Spongy mesophyll, 5. Lower epidermis, 6. Guard cells, 7. Exchange of gases through stoma (plural stomata), 8. Air space, 9. Sunlight.

Stomata

Stomata are small holes that are found underneath a leaf. Carbon dioxide, which is needed for photosynthesis, diffuses through the stomata into the leaf. Water vapour and oxygen diffuse out of the leaf through the stomata. Guard cells control the size of stomata and the leaf’s flattened shape increases the area of its exchange surfaces.

Cell walls

Another exchange surface is the walls of the cells inside the leaf. Gases can diffuse into and out of the cells through these walls. Between cells, there are air spaces which increase the area of these surfaces.

Gas exchange in fish

Fish have gills which are their main gas exchange surface. Water containing oxygen flows into the mouth and out through the gills. In the gills, oxygen diffuses into the blood and carbon dioxide diffuses into the water.

Gills are adapted for gas exchange as they are made from many small, thin plates which gives them an increased surface area. The gill plates also have a good blood supply which increases the rate of diffusion. The diffusion distance is short, as the gill plates have a thin layer of surface cells.