Stomata

• Stomata


  Tiny pores on the surface of the plant, which allow CO2 and oxygen to diffuse directly in and out of a leaf
• Stomata


  • Allow water vapour to escape during transpiration
  • They open and close automatically
• Stomata


  Able to open and close to control the amount of water lost from the leaves
• Guard cells


  Cells surrounding the stomata, which change shape to control the size of the pore
• Opening and closing of stomata

  1. Guard cells are turgid (swollen with water), stomata are open

  2. Guard cells are flaccid (low on water and limp), stomata are closed
• Supplies of water start to dry up

  Stomata close automatically
• It's night time


  Stomata close to save water without losing out on photosynthesis
• Changes in ion concentration inside guard cells

  1. In response to stimuli like light, potassium ions (K+) are pumped into guard cells

  2. This increases the solute concentration of the guard cells, which decreases the concentration of water molecules

  3. Water then moves into the guard cells by osmosis

  4. This makes the guard cells turgid and the stoma opens

  5. When potassium ions leave the guard cells, the concentration of water molecules in the cell increases

  6. Water then moves out by osmosis, the guard cells become flaccid and the stoma closes
• If the plant's really short of water, the cytoplasm inside its cells starts to shrink and the membrane pulls away from the cell wall. A cell in this condition is said to be plasmolysed.
• Viewing stomata, xylem and phloem under a microscope

  1. Prepare a slide to view stomata

  2. Observe xylem and phloem in thin sections of a plant's stem
• Stomata can be observed using a light microscope
• Preparing a slide to view stomata

  1. Paint two thin layers of clear nail varnish onto the leaf

  2. Leave the varnish to dry in between each coat

  3. Put a piece of clear sticky tape over the top of the painted leaf and use it to peel the varnish off slowly

  4. Stick the tape with the varnish onto a microscope slide
• You should be able to count the stomata and guard cells from the impression on the varnish
• Comparing the top and bottom surfaces of a leaf

  There are more stomata on the bottom of the leaf
• Observing the structure of xylem and phloem

  1. Leave a stem upright in a beaker of eosin dye

  2. The dye will travel up the stem, staining the xylem red

  3. Take a thin section of the stem and view it on a slide under a microscope