1'6'6 Exchanging Gases in Plants'

1
1.6.6 Exchanging Gases in Plants.

• Objectives
• Understand the site of gas exchange.
• Be able to describe the cross-section of a leaf.
• Be able to describe the differences between
  exchange during the day and night.

2
The Leaf.

• The leaf has three major layers
• The cuticle a layer containing suberin (wax)
  that prevents water loss.
• The epidermis the outer layer of cells usually
  with guard cells surrounding the stomata.
• The mesophyll inner layer of cells with a moist
  surface.
• Draw fig 2 p100.

3
Gas exchange.

• Gases pass into and out of the leaf through the
  stomata (sing. stoma).
• Guard cells can change shape to prevent excessive
  water loss.
• Gases diffuse into the leaf and are exchanged
  through the surface of the mesophyll cells.
• Waste gases diffuse out of the cells into the
  intercellular spaces.

4
Day and Night.

• During the day plants use up carbon dioxide and
  release more oxygen during photosynthesis.
• Compared to the amount of carbon dioxide produced
  and oxygen used up during respiration.
• Consequently carbon dioxide diffuses into the
  leaf and oxygen diffuses out.
• What happens at night?
• Psyn stops, respiration continues so the plant
  takes in oxygen and gives out carbon dioxide.

5
Homework.

• 1.6.7 Efficient exchange surfaces.
• Read p102/3
• Using the information produce a table of how
  mammals, fish and plants meet their gas exchange
  needs.

6
Suggestion.