Plant gas exchange

Question 1

List parts of a leaf (top to bottom)

Answer 1

• Wax cuticle
• Upper epidermis
• Palisade layer
• Spongy mesophyll
• Lower epidermis
  - Stomata & Guard cells

Question 2

What is the purpose of the wax cuticle and upper epidermis?

Answer 2

Wax cuticle: Prevents water loss & protects leaf

Upper epidermis: Transparent to light pass through

Question 3

What is the function of the palisade cells?

Answer 3

Contains many chloroplasts to absorb light energy for photosynthesis

Question 4

What is the function of spongy mesophyll?

Answer 4

Air spaces to increase SA for gas exchange

Question 5

What are the functions of stomata and guard cells?

Answer 5

Stomata: Light opens guard cells during day to allow gasses to enter and leave
Guard cells: Loss of water, less firm, changes shape and closes stoma, prevents further water loss

Question 6

What is the xylem?

Answer 6

Dead and hollow tube that transports water

Question 7

What is the phloem?

Answer 7

Contains companion cells to move sugars

Question 8

Describe the role of a potassium pump in stomata.

Answer 8

• Increased conc. of K+ ions in guard cells (flaccid stoma)
• Lower water potential in guard cells
• Water moves in by osmosis down water potential gradient (turgid stoma)

Question 9

What conditions to xerophytes live in?

Answer 9

Hot and dry

Question 10

Describe and explain three adaptations of xerophytes.

Answer 10

1. Hairs so ‘trap’ water vapour and water pot. gradient decreased
2. Stomata in pits so
   ‘trap’ water vapour and water pot. gradient decreased
3. Thick waxy cuticle so increases diffusion distance
4. Rolled leaves so
   ‘trap’ water vapour and water pot. gradient decreased
5. Needles so reduces SA:Vol

Question 11

List 3 adaptations of marram grass.

Answer 11

• Rolled leaf
• Thick waxy cuticle
• Inner surface has many hairs