Lesson 5 - Gas exchange in plants

Question 1

function waxy cuticle

Answer 1

reduces water loss from the leaf surface

Question 2

function air spaces

Answer 2

interconnecting spaces that run throughout the mesophyll layer, which are adapted to provide a network of gases to allow gases to quickly diffuse in and out of leaf and to access photosynthesising cells

Question 3

function palisade mesophyll cells

Answer 3

cells located beneath the upper epidermis to carry out photosynthesis

Question 4

function spongy mesophyll cells

Answer 4

dispersed and irregular-shaped cells located beneath the palisade mesophyll layer to carry out photosynthesis. They are adapted by having a large surface area to maximise diffusion

Question 5

function stomata

Answer 5

small pores on the underside of the leaf which open and close via guard cells to allow air to enter into leaf. The stomata open and close when it’s suitable for photosynthesis, allowing the diffusion of oxygen and carbon dioxide, and to minimise water loss

Question 6

function lower epidermis

Answer 6

bottom layer of leaf which contains stomata and guard cells

Question 7

function vascular tissue

Answer 7

transports water and nutrients

Question 8

how do plants minimise water loss

Answer 8

-Have a waterproof waxy cuticle on their leaves
-Have guard cells which close the stomata when needed

Question 9

meaning xerophytes

Answer 9

plants adapted to living in dry environments with limited water availability

Question 10

describe 6 adaptations of xerophytes to reduce water loss

Answer 10

-Thick waxy cuticle reduces water loss through evaporation
-Folding of leaves closes the stomata on the lower surface to reduce air flow and the evaporation of water
-Hairs on leaves traps the moist air against the leaf surface to reduce the concentration gradient of water vapour
-Sunken stomata in pits reduces air flow and the evaporation of water
-Small, needle-like leaves reduces the surface area across which water can be lost
-Water storage organs conserves water when it is in low supply

Question 11

meaning lenticles

Answer 11

spongy areas with loosely packed cells that are the site of gas exchange in woody stems and roots

Question 12

how do the stomatal pores open

Answer 12

when conditions are favourable for photosynthesis and carbon dioxide is needed, solutes such as potassium ions are moved into the guard cells by active transport. Water then moves into the guard cells from the surrounding epidermal cells by osmosis, and the guard cells swell so the turgor pressure increases. The stomatal pores open because the uneven bendings of the inner cellulose cell wall

Question 13

how do stomatal pores close

Answer 13

when conditions are less favourable for photosynthesis, or when it is dark, the active pumping of potassium ions into the cell stops and potassium ions are excreted. So, water leaves the cell by osmosis, turgor is reduced and the guard cells become flaccid, closing the stomatal pores