Photosynthesis and gas exchange

HideShow resource information

Adaptations of Leaves for Photosynthesis

1) Leaves are broad so there is a larger surface area being exposed to sunlight

2) The chloroplasts are usually found in the palisade layer. This is because it is closer to the surface of the cell where they can get the most light

3) The upper epidermis is transparent so that sunlight can pass through it and onto the palisade layer

4) There are a network of vascular bundles - these are the transport vessels xylem and phloem. They deliver water and other nutrients to every part of the leaf and take away the glucose produced by photosynthesis. They also help support the leaf structure

5) The waxy cuticle helps to prevent water loss by evaporation

6) The adaptations of leaves for efficient gas exchange also make photosynthesis more efficient. E,g, the lower surface is full of little holes called stomata which let CO2 diffuse directly into the leaf

1 of 3

Test for Starch

1) Using tweezers, dunk a leaf into boiling hot water to stop any chemical reactions happening in the leaf

2) To get rid of the chlorophyll, put the leaf in a boiling tube with some ethanol already inside it. The leaf should end up a pale white-ish colour

3) Rinse the leaf in cold water to rehydrate it and add a few drops of iodine solution. If starch is present it should turn a bluey-black colour

2 of 3

Adaptations of Leaves for Efficient Gas Exchange

  • Broad - larger surface area for diffusion
  • Thin - gases only travel a short distance to reach the cells where they're needed
  • Air spaces - lets gases like CO2 and O2 move easily between cells. Also increases surface area for gas exchange
  • Stomata - allow gases like CO2 and O2 diffuse in and out. Also allow water to escape (transpiration)
  • Stomata begin to close as it gets dark. Photosynthesis cannot happen in the dark, so they don't need to be open to let CO2 in. When the stomata are closed, water can't escape. This stops the plant from drying out
  • Stomata also close when supplies of water from the roots start to dry up. This stops the plant from photosynthesising, but if they didn't close, the plant might dry out and die
  • The opening and closing of stomata is controlled by the cells that surround them (called guard cells)
3 of 3


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Respiration and exercise resources »