Gas Exchange For Gas Exchange In Plants

Question 1

Function and structure of cuticle on leaf

Answer 1

A waxy transparent layer. Allows light to pass through to the photosynthetic palisade mesophyll below but reduces water lost by evaporation through the top surface of the leaf

Question 2

Function and structure on the upper epidermis in a leaf

Answer 2

Transparent for light to easily penetrate to photosynthetic layers

Question 3

Function and structure of palisade mesophyll in the leaf

Answer 3

Main photosynthetic layer packed with chloroplast

Question 4

What is the vascular bundle

Answer 4

Containing xylem (carries water from roots), phloem (carry sucrose to other parts of plant) and bundle sheath parenchyma

Question 5

Structure and function of spongy mesophyll

Answer 5

Surrounded by air spaces for easy diffusion of gases. The mesophyll cell membranes are the site of gas exchange

Question 6

What is the structure and function of stomata

Answer 6

The stomatal pores allow the gas exchange of gases down a concentration gradient.the gases diffuse through intracellular spaces to and from the photosynthetic cells where they diffuse into the cells.

Question 7

What’s the function of the guard cells

Answer 7

Open and close stomata during the day. Allows carbon dioxide to enter the air spaces and then the cells to be used in photosynthesis. The closing of the stomata during night reduces water loss

Question 8

How have leaves adapted to photosynthesis

Answer 8

• they have large surface area and orientated perpendicular to the sun for maximum light absorption
• they are thin with a transparent cuticle and upper epidermis for light to penetrate into the leaf and also for efficient diffusion of gases from the stomata up through the gas spaces to photosynthetic layers
  -they have palisade cells packed with chloroplasts; cells are densely stacked with long axes perpendicular to leaf structure

Question 10

What happens to guard cells when the stomata is open

Answer 10

Turgid guard cells bend due to thickened inner walls, opening stomatal pore

Question 11

What happens to guard cells when stomata is closed

Answer 11

Flaccid guard cells meet in the middle, closing The stomatal pore

Question 12

How do plants open and close the stomata form gas exchange

Answer 12

1. In light, chloroplasts in guard cells photosynthesise and produce ATP
2. The ATP is used for active transport of potassium ions into guard cells
3. Starch is converted to malate
4. Malate and potassium ions lower water potential of guard cells and water is drawn in by osmosis
5. Uneven thickening of guard cell inner walls causes them to end as they swell opening stomatal pore
6. The opposite occurs when there is no light closing The pore

Question 13

What happens to stomata during the day

Answer 13

If stomata are open, rate of photosynthesis is high as CO2 can diffuse in from the air and excess oxygen can diffuse out
Higher temperatures increase evaporation from leaves and water can be lost quickly

Question 14

What happens to the stomata at night

Answer 14

Only respiration takes place. O2 diffused in and CO2 diffuses out

Question 15

What are the differences in a dicot and a monocot leaf

Answer 15

Dicots - stomata are arranged randomly reflecting the network of vascular bundle. The thickening in the wall of their guard cells is also different, therefore open differently
Monocots - stomata are arranged in parallel lines reflecting the arrangement of vascular bundles

Question 16

Structure of guard cells

Answer 16

Contains chloroplast
Rings of thicker cellulose in the cell wall around guard cell
Inner wall if guard cells is thicker than outer wall