3.1.P SA:Vol Ratio and Gas Exchange Plants

• What adaptions do leaves have for an efficient gas exchange system?

  They are flat providing a large surface area. They have stroma which are pores to allow air to move in and out of the leaf. There are air spaces in the leaf which provide a short diffusion distance between mesophyll cells and air.
• Describe the diffusion of carbon dioxide for photosynthesis in a plant.

  Mesophyll cells photosynthesise which reduces the concentration of carbon dioxide in the cells, causing carbon dioxide to diffuse from the air spaces into the cells. This in turn reduces the concentration of carbon dioxide in the air spaces causing more carbon dioxide to move into the air spaces from the air outside of the leaf through the stroma.

  This all occurs because carbon dioxide moves from a place of high concentration to a place of low concentration.
• Describe the diffusion of oxygen out of the plant which is produced during photosynthesis.

  Mesophyll cells produce oxygen as a result of photosynthesis, the oxygen will diffuse into the air spaces from the cells increasing the concentration of oxygen in the air spaces. This causes oxygen to move from the air spaces to outside the leaf via the stroma.

  This all occurs because oxygen moves from a place of high concentration to a place of low concentration.
• What are some adaptations in plants to reduce water loss?

  The waxy cuticle is a waterproof layer which reduces the rate of water loss from the surface.

  Air spaces are saturated with water vapor from the xylem, causing water to diffuse out of the stroma and evaporate.

  At night, guard cells close the stroma to prevent water loss - Less carbon dioxide is required at this time of day due to the lack of available sunlight for photosynthesis.
• What are xerophytic plants

  Plants that are adapted to live in dry environments
• What adaptions do xerophytic plants have to reduce water loss? [6]

  ○ They have a reduced number of stroma, which results in less surface area for water loss.

  ○ Their stroma are in pits which reduces the concentration gradient .

  ○ They have hairs to trap water vapour which reduces the concentration gradient.

  ○ Their leaves are rolled which reduces the concentration gradient.

  ○ Leaves are reduced to spines which have a smaller surface area, reducing water loss.

  ○ They have thick waxy cuticles to increase the diffusion distance.
• How is surface area maximised in the gas exchange system of plants?

  Plants have numerous stomata, their leaves are long and flat, and they have a spongy mesophyll.
• How is the concentration gradient maintained in the gas exchange system of plants?

  It's maintained by photosynthesis and respiration
• How is the length of the diffusion pathway minimised in the gas exchange system of plants?

  No living cell is far from external air due to thin leaves and air spaces in the spongy mesophyll.