3.2 Gas exchange in plants

Question 1

what is the direction of net movement of oxygen during the day in plants and why

Answer 1

the net movement of oxygen is outwards because the rate of photosynthesis is greater than the rate of respiration during the day

Question 2

what is the direction of net movement of water vapour during the night in plants and why

Answer 2

the net movement of water vapour goes outwards because the rate of respiration is greater than the rate of photosynthesis during the night

Question 3

describe the internal structure of a leaf

Answer 3

waxy cuticle, upper epidermis, mesophyll (consists of the palisade mesophyll and the spongy mesophyll), lower epidermis, air space, stoma, guard cell, waxy cuticle

Question 4

what is the role and properties of the waxy cuticle in a leaf

Answer 4

it is impermeable to water and so reduces water loss by evaporation

Question 5

what is the role and properties of the upper epidermis in a leaf

Answer 5

it is transparent and so allows light to pass through, it also protects against mechanical damage

Question 6

what is the role of the palisade mesophyll in a leaf

Answer 6

it is the main site of photosynthesis, has the highest density of chloroplasts

Question 7

what is the role of the spongy mesophyll in a leaf

Answer 7

it is the site of gas exchange, contains the vascular bundle (phloem/xylem)

Question 8

what is the role of the lower epidermis in a leaf

Answer 8

protects leaf tissue from mechanical damage

Question 9

what is the role of the stoma in a leaf

Answer 9

to allow entry and exit of gases

Question 10

what is the role of the air space in a leaf

Answer 10

for gas exchange

Question 11

what is the role of the guard cell in a leaf

Answer 11

open and close the stomata, only lower epidermal cells

Question 12

how do you calculate the area of the field of view in mm² of a leaf down a microscope

Answer 12

measure the diameter of the field of view in epu
convert to micrometers (using conversion factor)
convert to mm (/ by 1000)
calculate area of field of view using pi r squared

Question 13

how do you calculate stomatal density using a microscope and leaf

Answer 13

mean number of stomata in field of view
/
area of field of view in mm²

Question 14

in relation to gas exchange, explain how the leaf is adapted to provide a large surface area

Answer 14

leaf has a very broad surface

Question 15

in relation to gas exchange, explain how the leaf is adapted to reduce the length of the diffusion pathway

Answer 15

leaf is very thin, mesophyll has many air spaces allowing gases to diffuse in the gaseous phase which is quicker than in the liquid phase

Question 16

in relation to gas exchange, explain how the leaf is adapted to maintain a steep concentration gradient

Answer 16

stomata open and close to control oxygen and carbon dioxide entering and leaving the leaf