6. Transport in Plants - xylem

Question 1

What is the function of the xylem?

Answer 1

Its a tissue which transports water and mineral ions in solution.
Substances move up the plant from the roots to the leaves.

Question 2

What is the function of the phloem?

Answer 2

Its a tissue which transports organic substances like sugars in solution up and down the plant.

Question 3

What are the xylem and phloem classed as?

Answer 3

Mass transport systems as they move substances over large distances.

Question 4

What are the xylem vessels?

Answer 4

Part which transport water and ions.

Question 5

What is the structure of the xylem vessels?

Answer 5

Very long, tube-structures formed from dead cells joined end to end.
No end cells.

Question 6

The xylem has no end cells, what does this mean?

Answer 6

Water can pass through the middle easy as its uninterrupted.

Question 7

How does water move up a plant and what theory is used to describe it?

Answer 7

Water moves up a plant against the force of gravity, from roots to leaves.
Explained by cohesion and tension theory of water transport.

Question 8

Bullet point the stages in the cohesion and tension theory of water transport.

Answer 8

4. Water enters.
5. Cohesion.
6. Tension.
7. Water evaporates.

Question 9

What happens in step one of the cohesion and tension theory of water transport.
WATER EVAPORATES.

Answer 9

Water evaporates from leaves at the top of the xylem, through process of transpiration.

Question 10

What happens in step two of the cohesion and tension theory of water transport.
TENSION.

Answer 10

The previous step creates tension which pulls more water into leaf.

Question 11

What happens in step three of the cohesion and tension theory of water transport.
COHESION.

Answer 11

Water molecules ate cohesive, so when some pulled into leaf others follow.
Meaning the whole column of water in the xylem from the leaves down to the roots, moves upwards.

Question 12

What happens in step four of the cohesion and tension theory of water transport.
WATER ENTERS.

Answer 12

Water enters stem through roots.

Question 13

As water movement up a plant increases…

Answer 13

Transpiration rate increases.

Question 14

Define transpiration.

Answer 14

It is the evaporation of water from a plants surface, especially the leaves.
Water evaporates from moist cell walls and accumulates in the spaces between the cells in the leaf.
When stomata opens, it moves out of leaf down the water potential gradient.

Question 15

Why does the water move down a water potential gradient?

Answer 15

As there is more water inside the leaf than in the air outside.

Question 16

List 4 factors affecting transpiration rate?

Answer 16

Light intensity.
Temperature.
Humidity.
Wind.

Question 17

How does LIGHT INTENSITY affect the rate of transpiration?

Answer 17

Lighter it is = faster transpiration rate.
Stomata opens when it gets light to let in CO2 for photosynthesis.
Stomata is closed when its dark, little transpiration.

Question 18

How does TEMPERATURE affect the rate of transpiration?

Answer 18

Higher temperature = faster transpiration rate.
Warmer water molecules have more energy so they evaporate from the cells inside leaf faster.
Increases water potential gradient between the inside and outside of the leaf, making diffusion faster.

Question 19

How does HUMIDITY affect the rate of transpiration?

Answer 19

Lower the humidity = faster the rate of transpiration.

Air around plant is dry, water potential gradient between leaf and air increases, increasing transpiration.

Question 20

How does WIND affect the rate of transpiration?

Answer 20

Windier it is = faster rate of transpiration.
Lots of air movement blows away water molecules from around the stomata.
Increases water potential gradient, increases rate of transpiration.

Question 21

What is a potometer?

Answer 21

Special piece of apparatus used to estimate transpiration rate.

Question 22

What is a potometer used for?

Answer 22

Measuring water uptake by a plant.

Its assumed that water uptake by the plant is directly related to water loss by leaves.

Question 23

Initially, why do we use the potometer under water and cut the shoot on a slant?

Answer 23

To prevent air from entering the xylem.
AND.
To increase surface area for water uptake.

Question 24

What does the bubble movement represent when using the potometer?

Answer 24

An estimation of the transpiration rate.

Question 25

What must you remember to do when carrying out the potometer test?

Answer 25

To change only ONE variable.

All other conditions must be kept the same/constant.

Question 26

Transpiration is a side effect of what?

Answer 26

Photosynthesis.

Stomata needs to open to let CO2 in so it can produce glucose, but this also lets water out.

Question 27

How is transpiration rate different to water uptake by a plant?

Answer 27

Some water is used in reactions eg photosynthesis and to support the plant.

Question 28

What do you need to do if you want to compare water loss from different types of plants?

Answer 28

Measure the surface area of the leaves because it will vary with each type of plant.

Question 29

What is the air bubble sometimes called?

Answer 29

Air-water meniscus.

Question 30

How do you work out the rate of water uptake in mm3 per minute?

Answer 30

Measure the distance moved by bubble per minute and diameter of the capillary tube.

Question 31

What can be plotted from the data used from the distance moved by the bubble per minute?

Answer 31

Distance-time graph.

Gradient of line shows rate of water uptake.