gas exchange in plants Flashcards
describe the movement of gases in and out of the plant
-when plants photosynthesises it uses lots of CO2, leaving little inside the leaf. CO2 diffuses into the leave from an area of higher concentration to an area of lower concentration
-O2 is made as a waste product of photosynthesis. Some is used in respiration. The rest diffuses out through the stomata from an area of higher concentration to an area of lower concentration
how are leaves adapted for efficient gas exchange
-leaves are broad, larger surface area for diffusion
-leaves are thin, reducing the diffusion distance to reach the cells where they are needed in
-air spaces in the lead allows gases to move easily between cells. Also increases surface area for gas exchange
-stomata lets gases diffuse in and out, and water to escape
-stomata close at dark, preventing water from escaping and stopping the plant from drying out(no CO2 is needed in the plant at dark)
-stomata close when water supply from roots starts to dry up, stopping the plant from photosynthesising but preventing the plant from drying out
-guard cells that surround the stomata control the opening and closing of stomata.
how do guard cells change volume
-In bright light the guard cells take in water by osmosis and become plump and turgid
-In low light the guard cells lose water and become flaccid, causing the stomata to close
practical to investigate effect of light on net gas exchange from a leaf using hydrogen carbonate indicator
-add same volume of hydrogen carbonate indicator to four boiling tubes
-put similar sized healthy looking leaves into three of the tubes and seal with a rubber bung. Trap the stem with the bung to stop it from falling into the solution
-keep fourth tube empty
wrap one tube in aluminium foil, and the second tube in gauze
-place all tubes in bright light
-leaves tubes for an hour, then check the colour of the indicator
-control tube no change
-tube in foil to go yellow, no photosynthesis, but respiration occurs
-tube in gauze stays same colour, little photosynthesis and some respiration = equal amounts of CO2 taken up and produced
-uncovered tube = purple, some respiration, lots of photosynthesis
