6.4 - Gas Exchange In The Leaf Of A Plant

Question 1

What are leaf adaptations for photosynthesis

Answer 1

• large flat surface area - to absorb more light
• network of veins, containing xylem and phloem - for transport, help support the leaf upright to absorb more light
• thin - for gas exchange
• large air spaces - for gas exchange
• upper epidermis is thin and transparent - to absorb more light
• stomata allows gas exchange - for gas exchange, which may close to reduce water loss, most are on the lower epidermis.

Question 2

What is the role of guard cells in the stomata

Answer 2

• each stomata is surrounded by 2 guard cells
• guard cells turgid = pore open to allow gas exchange
• guard cells flaccid = pore closed to reduce water loss

Question 3

How does the waxy cuticle help to reduce water loss

Answer 3

• thick waxy cuticle means there is an impermeable layer which reduces evaporation from the surface. Its thickness also increases the distance for diffusion

Question 4

What are xerophytes?

Answer 4

Plants that live in environments with little water e.g cacti

Question 5

Adaptations of leaves to reduce water loss in xerophytes

Answer 5

• thicker leaves or needles so there is a smaller surface area for water loss
• thick waxy cuticle which is impermeable increases diffusion distance and reduces evaporation from the surface
• hairs on the surface of leaves trap a layer of moisture so there is water potential gradient is reduced
• sunken stomata are surrounded by a trapped layer of moisture which reduces the water potential gradient
• curled up leaves trap air saturated with water vapour which reduces the water potential gradient
• fewer stomata so there is a reduced surface area for water loss