Gas exchange in plants

• why do plants respire all the time?

  as, like animals, they need to generate energy constantly
• when is photosynthesis carried out?

  during the day for plant cells that contain chloroplasts
• what do plants do during the day?

  plant cells that contain chloroplasts carry out photosynthesis - so during the day plants both respire and photosynthesise
• where is the carbon dioxide needed for photosynthesis provided from?

  some of the carbon dioxide is provided by their respiration but most diffuses into the leaves from the atmosphere
• where is the oxygen produced from photosynthesis used?

  some of the oxygen produced is used in respiration but most diffuses out of leaves
• what do plants do at night?

  • plants respire only and so they need oxygen from the atmosphere
  • some oxygen enters the stem and roots by diffusion, but most gas exchange takes place at the leaves
• when do all aerobic organisms use oxygen?

  all the time, day and night
• what can produce oxygen?

  its produced only by plants, some protoctista and some prokaryotes and only during the day
• is the rate of photosynthesis or respiration faster during the day?

  the rate of photosynthesis is faster
• why is the overall gas released oxygen during the day?

  as more oxygen is produced in photosynthesis than is used in respiration
• why is the overall gas released during the night carbon dioxide?

  as photosynthesis doesn’t occur at night so no oxygen is produced
• what is the diffusion pathway like in leaves?

  its short
• why is the diffusion pathway short in leaves?

  as leaves are thin
• what is this a diagram of?

  the structure of a leaf

  
• how do gases diffuse through the stomata?

  down a concentration gradient
• what does the direction of diffusion depend on in leaves?

  it depends on the concentration of gases in the atmosphere and the reactions in the plant cells
• what are the diffusion gradients of oxygen and carbon dioxide between the inside and outside of the leaf maintained by?

  by mitochondria carrying out respiration and by chloroplasts carrying out photosynthesis
• why is the large surface area of a leaf significant for gas exchange?

  room for many stomata
• why is the large surface area of a leaf significant for photosynthesis?

  to capture as much light as possible
• why is the leaf being thin significant for gas exchange?

  diffusion pathways for gases entering and leaving is short
• why is the leaf being thin significant for photosynthesis?

  light penetrates through the leaf
• why is the cuticle and epidermis being transparent significant for photosynthesis?

  light penetrates to the mesophyll
• why is the palisade cells being elongated in a leaf significant for photosynthesis?

  it can accommodate a large number
• why is the palisade cells being packed with chloroplasts in a leaf significant for photosynthesis?

  captures as much light as possible
• why is the chloroplasts being able to rotate and move within mesophyll cells in a leaf significant for photosynthesis?

  they move into the best positions for maximum absorption of light
• why is the leaves having air spaces in the spongy mesophyll significant for gas exchange?

  it allows oxygen and carbon dioxide to diffuse between the stomata and the cells
• why is the leaves having air spaces in the spongy mesophyll significant for photosynthesis?

  it allows carbon dioxide to diffuse to the photosynthesising cells
• why is the leaf having stomatal pores significant for gas exchange?

  allows gas exchange in and out of the leaf
• what is a cuticle?

  waxy covering on a leaf, secreted by epidermal cells, which reduces water loss
• what is a stomata?

  pores on lower leaf surface, and other aerial parts of a plant, bounded by 2 guard cells, through which gases and water vapour diffuse