Gas Exchange In Plants

Question 1

Movement of gases in plants

Answer 1

When photosynthesising, uses up lots of CO2 leaving hardly any, hence more CO2 diffuses into leaf

Simultaneously, lots of CO2 made as waste product, some used in respiration but rest diffuses out through stomata

Question 2

How light intensity affects gas exchange

Answer 2

In day - high light so more oxygen produced in photosynthesis than used in respiration - release oxygen and use up more CO2 than release - take in CO2

At night - low light so only respire hence take in O2 and release CO2

Question 3

How are leaves adapted for efficient gas exchange? (4 reasons)

Answer 3

• leaves are broad (large SA for diffusion)
• air spaces in leaf (easy movement and increases SA)
• Stomata on lower surface (allow gases in and out and TRANSPIRATION - water escape)
• close at night (photosynthesis can’t happen)
  stops drying out
• close when water supplies from roots dry up (guard cells)

Question 4

Hydrogen Carbonate Indicator colours

Answer 4

Solution in air is orange
If CO2 increases becomes yellow
If concentration decreases, CO2 leaves solution making it purple

Question 5

Experiment to show how light affects gas exchange

Answer 5

• add hydrogen carbonate to four tubes
• put similar sized healthy looking leaves into three tubes and deal with rubber bung. Trap stem leaf with bu got stop falling and keep tube as control
• one wrapped in foil and second in gauze
• all tubes in bright light
• leave for hour

Question 6

Role of stomata in gas exchange

Answer 6

Guard cells regulate opening and closing of stomata
During day, absorb water and become turgid - opening stomata
At night are flaccid - close stomata