6.4 - Gas Exchange in Plants

Question 1

Adaptations of leaf structures for gas exchange (3):

Answer 1

1. air spaces - provide a network for gases to quickly diffuse in and out of the leaf and access photosynthesising cells
2. Mesophyll cells - dispersed throughout the leaf, provides a large SA across which agsers can diffuse
3. Stomata - Open when conditions are suitable for photosynthesis, allows inward diffusion of CO2 and outward diffusion of O2, and close to minimise water loss

Question 2

Important structures of a leaf (6):

Answer 2

1. upper epidermis with waxy cuticle - reduces water loss from the leaf surface
2. air spaces - interconnecting spaces that run throughout the mesophyll layer
3. mesophyll cells - cells within the mesophyll tissue, located between the upper and lower epidermis
4. Stomata - small pores surrouneded by guard cells on the underside of leaves that can open and close
5. Lower epidermis - bottom layer of cells in a leaf that contains the stomat and guard cells
6. Vascular tissue - transports water and nutrients

Question 3

Key Adaptations of xerophytes to reduce water loss (6):

Answer 3

1. thick waxy cuticle - reduces water loss through evaporation
2. rolling or folding of leaves - encloses the stomata on the lower surface to reduce air flow and the evaporation of water
3. Hairs on leaves - trap moist air against the leaf surface to reduce the diffusion gradient of water vapour
4. Sunken stomata in pits - reduce air flow and evaporation of water
5. small, needle-like leaves - reduce the SA across which water can be lost
6. water storage organs - conserve water for when it’s low in supply

Question 4

What are Xerophytes?

Answer 4

plants adapted to living in dry environments with limited water availability otherwise they become desiccated and die

Question 5

Limiting water loss in plants (2):

Answer 5

1. they have a waterproof waxy cuticle on their leaves
2. they have guard cells that can close stomata when needed