Adaptations for gas exchange in plants

Question 1

Cuticle

Answer 1

a waxy transparent layer. It 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

Palisade mesophyll

Answer 2

main photosynthetic layer packed with chloroplasts.

Question 3

Upper epidermis

Answer 3

transparent for light to easily penetrate to photosynthetic layers.

Question 4

Vascular bundle

Answer 4

containing xylem
(carrying water from roots), phloem (to carry sucrose to other parts of the plant) and bundle sheath parenchyma.

Question 5

Stomata

Answer 5

the stomatal pores allow the exchange of gases down a concentration gradient. The gases diffuse through intracellular spaces to and from the photosynthetic cells where they dissolve in the moist lining and diffuse into the cells. Guard cells open and close the stomata. The opening of the 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 the night reduces water loss

Question 6

Spongy mesophyll

Answer 6

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

Question 7

How are Leaves are adapted for photosynthesis

Answer 7

They have a large surface area and orientate
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 the
photosynthetic layers.
•They have palisade cells packed with
chloroplasts; cells are densely stacked with long axes
perpendicular to leaf surface

Question 8

Closed stomata

Answer 8

Flaccid guard cells meet in the middle, closingthe stomatal pore

Question 9

Open

Answer 9

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

Question 10

Opening and closing stomata for gas exchan

Answer 10

1. In light, chloroplasts in guard cells photosynthesise and produce ATP.
2. The ATP is used for the 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 bend as they swell, opening the stomatal pore.
6. The opposite occurs when there is no light closing the pore.