3: EXCHANGE SYSTEMS AND MASS TRANSPORT - GAS EXCHANGE IN PLANTS

Question 1

What is the main gas exchange surface in plants?

Answer 1

the surface of mesophyll cells in the leaf

Question 2

Describe the structure of a leaf

Answer 2

• waterproof waxy cuticle
• upper epidermis - layer of tightly packed cells
• palisade mesophyll layer - layer of elongated cells containing chloroplasts
• spongy mesophyll layer - layer of cells that contains an extensive network of air spaces
• stomata - pores (usually) on the underside of the leaf which allow air to enter
• guard cells - pairs of cells that control the opening and closing of the stomata
• lower epidermis - layer of tightly packed cells

Question 3

Describe gas exchange in plants

Answer 3

• when the guard cells are turgid (full of water) the stoma remains open allowing air to enter the leaf
• air spaces within the spongy mesophyll layer allows carbon dioxide to rapidly diffuse into cells
• the carbon dioxide is quickly used up in photosynthesis by cells containing chloroplasts, maintaining the concentration gradient

Question 4

What adaptations allow for efficient gas exchange in plants?

Answer 4

• lots of stomata provide large surface area
• short diffusion pathway as stomata are on the surface of the leaf
• well ventilated due to spaces between cells in spongy mesophyll

Question 5

What is a xerophyte?

Answer 5

a plant that is adapted to reduce water loss so it can survive in dry conditions

Question 6

What are adaptations of xerophytes?

Answer 6

• when dry, leaves roll up so stomata open up to enclosed space, water vapour accumulates in this space
• hairs on lower surface of leaf decrease air movement
• sunken stomata in pits to trap air and moisture
• thick waxy cuticle
• seasonal dormancy
• spines/hairs
• extensive root system
• water stored in stem