B. A. C. Name structures A to C. What is the function of stomata? Where are they found and why? How do they work? To exchange oxygen, carbon dioxide and water with the atmosphere. They are mostly found on the underside of the leaf, as less evaporation will occur here. When water enters the guard cells, they swell and bulge (turgor pressure) so that there is an opening (stomata) between them, when water leaves the guard cells, they shrink (low turgor pressure) and relax to close the opening. The surface of a tobacco leaf has approximately 12,000 stomata per square centimeter of surface area C.

Q) Explain how this opening and closing of stomata is advantageous to the plant. When also might this cycle change? Open to get carbon dioxide in for photosynthesis, during the day when there it light for chlorophyll to trap. Close at night to prevent the loss of water. This cycle may change in very dry conditions as the water being lost by transpiration is not being replaced by water form the soil.

Factors affecting transpiration Light Temperature Humidity Air movement

Light Light causes stomata to open H+ ions out of guard cells increased light intensity = increased rate of transpiration Light causes stomata to open H+ ions out of guard cells K+ ions into guard cells Starch -> malate K ions + malate cause water to enter guard cells by osmosis The increase in hydrostatic pressure causes the inner thicker wall of the guard cell to change shape (bend) hydrostatic pressure = the positive pressure built up when water is compressed

Temperature Water evaporates faster at higher temperatures increased temperature = increased rate of transpiration Water evaporates faster at higher temperatures

Cross section of a xerophyte (e.g. cactus)

Humidity Air outside leaf already saturated with water Increased humidity = decreased rate of transpiration Air outside leaf already saturated with water So ψ gradient lower, so transpiration slower

Air Movement Increased air movement = increased rate of transpiration Air movement moves the saturated air from around the leaf so the ψ gradient is steeper

                                             

Higher or lower! http://www.tellytunes.com/tv-theme-tune.asp?theme_title=Play%20Your%20Cards%20Right

Cold so LOWER

Deserts are hot so it would be HIGHER

Its very humid in a tropical rainforest so transpiration would be HIGHER

Windy so HIGHER, but not a lot of light so could also be LOWER!