Gas and Solute Exchange
Exchange Surfaces are adapted for use:
- Very thin- substances have short distance to diffuse
- Large surface area- lots of substances can diffuse at once
- In animals they are often Ventilated- air moves in and out
- Carbon Dioxide fuses into air spaces within the leaf, then it diffuses into the cells where photosynthesis happens.
- The leaf's structure is adapted so this can happen easily.
- The under leaf is called the exchange surface and covered with stomata which the carbon dioxide diffuses through.
- Oxygen and water vapour also diffuse out of the stomata.
- The size of stomata are controlled by guard cells. These close the stomata when the plant is losing water faster than it is being replaced by the roots. Without these guard cells the plant would soon wilt.
- The flattened shape of the leaf increases the area of exchange surface so its more effective.
- The walls of cells inside the leaf, form another exchange surface. The air spaces inside the leaf increase the area so there’s more chance for carbon dioxide to get into the cells.
The water vapour evaporates from inside the leaf. Then it escapes by diffusion because there's a lot of it inside the leaf and less of it in the air outside. Evaporation is quickest in hot, dry, windy conditions.
The lungs are in the Thorax, which is in the top part of your body. It is…