GAS EXCHANGE IN PLANTS

Question 1

Gas exchange during the day vs night (2)

Answer 1

• During the day respire and photosynthesise

- During the night respire only

Question 2

How does oxygen enter the stem and roots

Answer 2

• via diffusion

Question 3

how do gases travel in a leaf

Answer 3

• down a concentration gradient
• in substomatal air chambers diffuse through inter cellular spaces between spongy mesophyll into cells
• direction of diffusion depends on concentration of gases

Question 4

large SA leaf significance for gas exchange and photosynthesis (2)

Answer 4

• room for many stomata

- capture as much light as possible

Question 5

thin leaf significance for gas exchange and photosynthesis (2)

Answer 5

• short diffusion pathway for gases

- light penetrates through leaf

Question 6

transparent cuticle and epidermis significance photosynthesis

Answer 6

• light penetrates to mesophyll

Question 7

elongated palisade cells significance for photosynthesis

Answer 7

• accommodate a large number

Question 8

palisade cells packed with chloroplasts significance for photosynthesis

Answer 8

• capture as much light as possible

Question 9

chloroplasts rotate and move within mesophyll significance for photosynthesis

Answer 9

• move into best positions for maximum absorption of light

Question 10

air spaces in spongy mesophyll significance for gas exchange and photosynthesis? (2)

Answer 10

• allow o2 and co2 to diffuse between stomata and cells

- allow co2 diffuse to photosynthesising cells

Question 11

stomatal pores significance for gas exchange

Answer 11

• allow in and out of leaf

Question 12

stomata (2)

Answer 12

• small pores on bottom of leaves

- where gas exchange occurs

Question 13

guard cell (2)

Answer 13

• epidermal cells with chloroplasts

- unevenly thickened walls - inner > outer

Question 14

how do guard cells work during the day? (2)

Answer 14

• water enters the guard cells they become turgid and swell, opening the pore
• water leaves the guard cell, they become flaccid and the pore closes

Question 15

guard cells work during the day because… (5)

Answer 15

• chloroplasts in the guard cells photosynthesise producing ATP
• ATP provides energy for active transport of K+ into the guard cells
• stored starch converted to malate
• K+ and malate ions lower water potential in guard cells so water enters via osmosis
• guard cells are uneven, absorb water in the thin spots, less in the thick areas

Question 16

why do stomata close? (3)

Answer 16

• at night to prevent water loss (bc no LDR)
• in bright light to prevent water loss due to evaporation
• if there is excessive water loss