Gas exchange - flowering plants

• how do plants exchange gas?

  • through diffusion
  • photosynthesis in plant takes up lots of CO2 - hardly any inside leaf - more CO2 move into leaf through diffusion
  • lots of O2 as waste product of photosynthesis - some in respiration - rest diffuses out of stomata
• how does net exchange of gas depend on light intensity?

  • photosynthesis occurs only throughout the day - plants respire all the time - to get energy required for living
  • during day - more oxygen production by photosynthesis than used in respiration - daylight - release of oxygen and use up more CO2 than produced so they take in CO2
  • At night - very low light intensity for photosynthesis - plants only respire - take in oxygen and release CO2
• how are leaves adapted for efficient gas exchange?

  • the air spaces inside a leaf allows CO2 or O2 to move easily between cells and increase SA of gas exchange
  • stomata - lets gases CO2 and O2 diffuse in and out - allow transpiration
• how does the stomata operate?

  • stomata closes as its dark - no photosynthesis in dark - not open to let CO2 in. No water escape - plant doesn't dry out
  • Stomata closes when supplies of water from the roots start to dry up. This stops the plant from photosynthesising - if didn't close the plant will dry out and die
  • opening and closing of stomata controlled by guard cells - done by changing shape and volume - increase volume to open stomata and decrease volume to close stomata