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Biology Component 3 > Gas Exchange in Plants > Flashcards

Gas Exchange in Plants Flashcards

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1
Q

What do plants do all the time?

A

They respire so need to generate energy constantly.

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2
Q

What do plants do during the day?

A

They both respire and photosynthesise as the plant cells which contain chloroplasts can carry out photosynthesis.

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3
Q

Explain gas exchange during the day in terms of photosynthesis and respiration?

A

Some of the CO2 needed in photosynthesis is provided by respiration but most does diffuse into the cells from the atmosphere. Some of the oxygen produced in photosynthesis is used in respiration but most of fuses out of the leaf.

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4
Q

What do plants do at night time?

A

They can only respire.

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5
Q

Explain gas exchange during night time in terms of photosynthesis and respiration?

A

As they can respire they require oxygen from the atmosphere. Some oxygen enters the stem and roots by diffusion but most gas exchange takes place at the leaves.

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6
Q

What are the two processes which need gas exchange?

A

Photosynthesis and respiration

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7
Q

During the day what rate is fastest?

A

The rate of photosynthesis is faster than the rate of respiration as more oxygen is produced in photosynthesis that is needed in respiration so the overall gas released is oxygen

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8
Q

During the night what rate is fastest?

A

As photosynthesis doesn’t occur no oxygen is produced so CO2 is released. It is an exchange of CO2 and oxygen in relation to respiration and photosynthesis

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9
Q

What adaptions are needed for efficient gas exchange in a leaf?

A

Thin and flat with a large surface area
Large spaces in the spongy mesophyll which allows gas circulation.
There are other air spaces which are smaller found between cells of all the tissues.
Stomatal pores are present which open for gas exchange.

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10
Q

Describe gas exchange of a plant?

A

Gases diffused to the stomata down a concentration gradient. Once inside the leaves the gases in the substomatal chambers diffuse through the intracellular spaces between the spongy mesophyll and into the cells. Gases dissolve in the film of water covering the cells and in the cellulose cell wall then the gases diffuse into the cell.

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11
Q

What happens during daylight in terms of the direction of gases?

A

Photosynthesis is dominant without respiration is still happening.
Carbon dioxide IN
Oxygen OUT
CO2 is produced during respiration which is used in photosynthesis however more CO2 is needed so it diffuses in.
Some O2 is used in respiration but most diffuses out of the leaf.

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12
Q

What happens during darkness in terms of the direction of gases?

A

Respiration is dominant
O2 OUT
CO2 IN
No photosynthesis occurs so O2 diffuses in and CO2 out

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13
Q

What is the direction of diffusion depend on?

A

The concentration of gases in the atmosphere and the reactions in the plant cells.

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14
Q

What is the significance of having a large surface area?

A

G.E - Room for many stomata

P - Capture as much light as possible

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15
Q

What is the significance of being thin?

A

G.E - Diffusion pathway for gases entering and leaving is short
P- Light penetrates through the leaf

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16
Q

What is the significance of having elongated palisade cells?

A

P- Can accommodate a large number

17
Q

What is the significance of having a transparent cuticle and epidermis

A

P- Light penetrates to the mesophyll

18
Q

What is the significance of having palisade cells packed with chloroplast?

A

P- Capture as much light as possible

19
Q

What is the significance of chloroplasts rotating and moving within mesophyll cells?

A

P- They move into the best positions for maximum absorption of light or move away for strong light to avoid damage.

20
Q

What is the significance of air spaces within the spongy mesophyll?

A

G.E- Allow CO2 and O2 to diffuse between the stomata and the cells.
P - Allow CO2 to diffuse to the photosynthesising cells

21
Q

What is the significance of stomatal pores?

A

G.E - Gas exchange in and out the leaf

22
Q

What is the cuticle secreted by?

A

The epidermal cells, the epidermis

23
Q

What is the cuticle?

A

It is a thick waxy layer which acts as a waterproofing agent reducing water loss through the epidermis the thicker the layer the less water lost.

24
Q

Where is the cuticle found?

A

It is found on the upper and lower epidermis.

25
Q

What does the cuticle prevent?

A

It prevents water loss and also prevents gas exchange. The stomata allows water and gases through.

26
Q

Where are the stomata found?

A

They found on the aboveground parts of plants and occur mostly on the lower surfaces of leaves. Each part is bounded by two guard cells

27
Q

Describe the structure of a guard cell?

A

It has chloroplasts and unevenly thickened walls with the inner wall next to the pore being thicker than the outer wall (normal epidermal cells are transparent with no chloroplasts).

28
Q

What does the stoma control?

A

Gas exchange between the atmosphere and the internal tissues of the leaf. When closed gas exchange and water loss is reduced. When open water loss of gas exchange increases.

29
Q

What happens to the guard cells when they open and close the stoma?

A

They change shape.

30
Q

What happens when water enters the guard cells?

A

They become turgid and swell and the pore opens. They cover away from each other because the inner wall is thicker and inelastic compared to the outer wall.

31
Q

What happens when the water flows out of the guard cells?

A

They become flaccid and the pore closes. As the inner walls meet again.

32
Q

What happens in darkness with the mechanism of the opening and closing of the stoma?

A
  1. K+ ions diffuse OUT the guard cells down their concentration gradient
  2. Malate is converted into starch
  3. Both of the above raise the water potential of the guard cells
  4. Water flows down its water potential gradient out of the cell.
  5. Tutor of the guard cells decreases and the guard cells change shape and the stoma closes.
33
Q

What happens in the light with the mechanism of the opening and closing of the stoma?

A
  1. K+ ions move into the guard cells via AT
  2. Starch is converted into malate lowering the WP of the guard cell
  3. Water flows into the guard cell down a WP gradient by osmosis
  4. Turgor increases and the guard cell changes shape opening the stoma
34
Q

Why does the guard cells have chloroplast?

A

To produce ATP required to the AT of K+

35
Q

Why is there extra thickening on walls next to the stoma?

A

It ensures that the guard cells bend when turgid

36
Q

When does the stomata close?

A

At night to prevent water loss as there is insufficient light for photosynthesis.
There is bright light as it is accompanied by intense heat which increases evaporation.
There is excessive water loss

Biology Component 3 (9 decks)

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