Plants and Gas Exchange

Question 1

What is the role of diffusion in gas exchange?

Answer 1

Gases such as oxygen and carbon dioxide can move in and out of cells easily.

Question 2

How is the leaf shape adapted for photosynthesis?

Answer 2

It has a large surface area and is thin, to maximise absorption of sunlight by photosynthetic cells. It also increases the number of stomata, so that carbon dioxide can diffuse quicker.

Question 3

How is the leaf shape adapted for photosynthesis?

Answer 3

It has a large surface area and is thin, to maximise absorption of sunlight by photosynthetic cells. It also increases number of stomata so that carbon dioxide can diffuse quicker.

Question 4

How is the upper epidermis adapted for photosynthesis?

Answer 4

It’s transparent, allowing light to penetrate to the mesophyll.

Question 5

How are the palisade cells adapted for photosynthesis?

Answer 5

They are long and thin and tightly packed. They contain large number of chloroplasts. This maximises the absorption of sunlight energy. The palisade mesophyll is the main sight of photosynthesis.

Question 6

How are the stomata adapted for photosynthesis?

Answer 6

They allow gases to diffuse into the air spaces of the leaf. This provides a short diffusion distance for carbon dioxide.

Question 7

What does the xylem do for photosynthesis?

Answer 7

Transports water (absorbed by the roots) into the leaves. This then provides a short distance for water to diffuse into the photosynthesising cells.

Question 8

What does the phloem do for photosynthesis?

Answer 8

Transports sugars made by photosynthesis to other parts of the plant.

Question 9

What happens to stomata at night time?

Answer 9

They begin to close as it gets dark. This is because there’s no more sunlight so photosynthesis can’t occur, so they don’t need to be open to let carbon dioxide in. When the stomata are closed, water can’t escape so prevents the plant from drying out

Question 10

What is another reason for stomata to close?

Answer 10

If supplies of water from the roots begin to dry up. This reduced chance of the plant dying from drying up.

Question 11

What controls the opening and closing of the stomata? How do they do this?

Answer 11

Guard cells increase in volume to open the stomata and decrease in volume to close them.

Question 12

What does the xlyem do?

Answer 12

Transports water and mineral ions taking in from the roots to the rest of the plant, including the leaves. Travels in the transpiration stream.

Question 13

How is water absorbed by root hair cells?

Answer 13

The cells on plant roots grown into long ‘hairs’ which stick out into the soil. Each branch of a root will be covered in millions of these microscopic hairs. This gives the plant a big surface area for absorbing water from the soil. Water is taken in by osmosis, as there’s usually a higher concentration of water in the soil than inside the plant, so water is drawn in by the process of osmosis.

Question 14

Define transpiration?

Answer 14

The evaporation of water from the surface of a plant.

Question 15

What are the 5 factors affecting the rate of transpiration?

Answer 15

-Humidity
-Wind speed
-Temperature
-Light intensity
-Water supply

Question 16

How does humidity affect rate of transpiration?

Answer 16

The higher the humidity, the lower the rate of transpiration. This is because there’s a smaller concentration gradient of water outside the plant to inside the plant, so transpiration slows down.

Question 17

How does wind speed affect rate of transpiration?

Answer 17

The faster the wind speed, the faster the rate of transpiration. This is because water vapour will be blown away from the leaf as it diffuses out. In still air, the region around a leaf will be saturated with water vapour so that no more/little can escape from the leaf, causing transpiration to slow down.

Question 18

How does temperature affect rate of transpiration?

Answer 18

The higher the temperature, the faster the rate of transpiration. This is because the higher the temperature, the more kinetic energy water particles have and therefor they evaporate from the surface quicker.

Question 19

How does light intensity affect rate of transpiration?

Answer 19

The higher the light intensity, the faster the rate of diffusion. This is because in day light the stomata are open to photosynthesise, meaning more water is able to diffuse out of the leaves and into the atmosphere.

Question 20

How does water supply affect rate of transpiration?

Answer 20

If water is in short supply and the plant is losing water by transpiration faster than it is being taken up by the roots, the plant way start to wilt. Before this happens the guard cells become flaccid and the stomata start to close, therefor reducing transpiration and delaying wilting.

Question 21

What can we use and what are the steps to measuring the rate of transpiration?

Answer 21

We use a potometer.

1) The potometer must be set up underwater, this prevents any air bubbles from entering the system and blocking the xylem.

2) Cut the stem of a shoot.

3) Put the shoot stem into the bung, grease the joint with plenty of petroleum jelly to prevent water loss and air entry.

4) Put the bung into the potometer.

5) Make sure the tap is closed and full of water (no bubbles). Then lift the potometer out of the water.

6) Leave the end of the capillary tube out of the water until an air bubble forms then put the end into a beaker of water.

7) You can measure the transpiration rate as distance the bubble travels in 5 minutes (or the time taken for a bubble to travel a set distance). You should take a number of readings and calculate a mean rate.

Question 22

What can you use to change the wind speed when doing a transpiration experiment?

Answer 22

A hairdryer.

Question 23

What can you use to change the humidity when doing a transpiration experiment?

Answer 23

A clear plastic bag over the plant.