Gas exchange in plants

Question 1

What is considered a complex plant?

Answer 1

Flowering plants or angiosperms

Question 2

What are the three places where gas exchange occurs in a plant?

Answer 2

Leaf

Stem

Roots

Question 3

What is the cuticle?

Answer 3

a waxy compound on the very outer surface of the upper epidermis.

Question 4

What does the upper epidermis do?

Answer 4

one or two cells thick.

Protects against water loss by the cuticle or by epidermal hairs which trap moisture and reflect light.

Protects against invasion by pathogens so that the moist inner leaf is sterile.

Question 5

What does the cuticle do?

Answer 5

May reduce water loss by evaporation

Question 6

What does the palisade mesophyll do?

Answer 6

major site of photosynthesis.

Cells are packed vertically with many chloroplasts which may move by cytoplasmic streaming to the optimal position in the cell for light absorption and photosynthesis.

Question 7

What does the xylem do?

Answer 7

transports water and mineral salts to the leaves.

Question 8

What does the phloem do?

Answer 8

Transports sugars around the plant and may import amino acids.

Question 9

What does the spongy mesophyll do?

Answer 9

irregular shaped cells that fit loosely together to leave large air spaces which permit diffusion of gases through leaves.

Question 10

What does the lower epidermis do?

Answer 10

similar protective functions to the upper epidermis. Cuticle.

Question 11

How do guard cell work?

Answer 11

Uneven thickening of cellulose wall permits opening/closing of the stomatal pore as turgidity changes.

Have chloroplast

Question 12

What is a stomatal pore?

Answer 12

can be opened ( to allow diffusion of O2 and CO2 down concentration gradients) or closed (to limit water losses by evaporation to a drier atmosphere).

Question 13

What are 2 functions of the stomata?

Answer 13

Allow the exchange of CO2 and O2 between the inside of the leaf and the surrounding atmosphere.
Permit the escape of water vapour from the leaf (transpiration)

Question 14

What happens when the stomata is open?

Answer 14

If the stomata are open the plant can lose excess water vapour, especially in dry habitats.

Question 15

What happens when the stomata is closed?

Answer 15

If the plant closes the stomata it may run short of CO2 and O2.

Plants overcome this problem by not opening stomata for longer than necessary.

Question 16

What controls the opening and closing of the stomata?

Answer 16

Stomata opening and closing is controlled by the turgor of the guard cells on either side of the stoma (pore).
Stomata opens when guard cells absorb water and close when they lose water.

Question 17

How does the stomata close?

Answer 17

If water is drawn into the guard cells by osmosis, the cells expand and their turgidity is increased.

Question 18

How does the stomata open?

Answer 18

As the expansion is not uniform, this results in the guard cells drawing apart and the stoma(pore) opening.

Question 19

How does gas exchange occur in stems that have bark?

Answer 19

The bark of trees is a barrier to the entry of gases.

There are areas in the bark called lenticels, that are openings and allow the exchange of gases with cells of the stem beneath the bark.

Question 20

How does gas exchange occur in the roots?

Answer 20

Aerated soils that are not waterlogged contain air.

Oxygen from the air spaces in the soil can diffuse into the root hair cells or epidermal cells and enter the roots.
Carbon dioxide can diffuse in the opposite direction out of the root.

Question 21

How does gas exchange occur in plants?

Answer 21

Occurs locally throughout the plant through the process of passive diffusion.

Question 22

Why are leaves well adapted for gas exchange?

Answer 22

as they are large and are always flat, maximising the S.A compared to the relatively small volume of each leaf.

Question 23

Why do plants not need a transport system?

Answer 23

As the movement of gases in leaves depends on simple diffusion and happens locally over short distances.

Question 24

What are 5 conditions that can override the effects of light with the timing of opening and closing of the stomata?

Answer 24

Temperature

Water availability

Concentration of CO2 inside the plant

levels of humidity

severe water stress (drought)

Question 25

What mostly controls the timing of the opening and closing of the stomata under natural conditions?

Answer 25

Light

Stomata opens at daybreak and closes at night.

Question 26

How can temperature override light affecting the timing of the opening and closing of the stomata?

Answer 26

In daylight, if temperature increases, water vapour can be lost through the stomata .

If water loss exceeds the uptake of water from the soil, water content of the plants falls, guard cells begin to lose their water, and the stomata closes.

Question 27

How can water availability override light affecting the timing of the opening and closing of the stomata?

Answer 27

Under conditions of decreased water availability, stomata closes and thus photosynthesis may be reduced and the concentration of CO2 inside the leaf will rise.

Question 28

How can the internal concentration of CO2 override light affecting the timing of the opening and closing of the stomata?

Answer 28

A rise in internal concentration of CO2 causes the stomata to close and so no further excess of CO2 enters.

A fall in internal concentration of CO2 can cause the stomata to open, allowing carbon dioxide to diffuse into the plant.

Question 29

How can levels of humidity override light affecting the timing of the opening and closing of the stomata?

Answer 29

If the air is saturated with water vapour, the rate of water loss is reduced, stomata remains open. Though water is also lost through the water vapour, if water loss is in excess, the plant wilts.

Question 30

How can plants adapt to water loss?

Answer 30

Plants need to balance their gaseous requirements with their ability to withstand water loss

Question 31

How can situations of severe water loss (droughts) override light affecting the timing of the opening and closing of the stomata?

Answer 31

Guard cells may lose water during the day and close the stomata, though this reduces the loss of water it also cuts off the supply of CO2.

Question 32

How can situations of severe water loss do to a plant beside override the timing of the opening and closing of the stomata?

Answer 32

Due to the stomata closing, It can restrict the capacity of photosynthesis, thus restricting the overall growth of the plant.

Question 33

How can some plants adapt to situations of severe water loss?

Answer 33

Plants like pineapples and cactuses.

Have evolved mechanisms where they open their stomata during the evening when its cooler, effectively store CO2 for use in the day time and close their stomata during the hottest parts of the day

Question 34

How does gas exchange occur in bryophyte (moss) occur?

Answer 34

Through the stomata, simple diffusion occurs through the outer surfaces.