B7.1 - transport in plants

Question 1

what are the general functions of the xylem and the phloem?

Answer 1

General functions: to transport substances from source where they are taken in or made to the sinks which are areas where the sources are used

To support the plant stem

Question 2

what is the function of the xylem?

Answer 2

Xylem: transport water and dissolved minerals from the root up to all the other parts of the plant

Question 3

what is the function of the phloem?

Answer 3

Phloem Vessels: The function of the phloem vessels is to transport food nutrients such as glucose from the leaves to other parts of the plant

Question 4

what is the definition of transpiration?

Answer 4

The loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by the diffusion of water vapour through the stomata.

Question 5

what is the process of transpiration?

Answer 5

1. Water leaves the mesophyll cells into air spaces created by the irregular shape of spongy mesophyll cells then diffuses out of the stomata.
2. This causes the plant to wilt as the water loss is greater than the re-uptake. Cells become flaccid and the tissues become limp
3. This causes more water to travel up the xylem through the transpirational pull and to create a water potential gradient that draws up columns of water molecules held together by cohesion.

Question 6

what are the factors which affect the transpiration rate?

Answer 6

light, humidity and temperature

Question 7

how does light affect transpiration rate?

Answer 7

• A lot of light increases the transpiration rate because the stomata opens which allows more photosynthesis to take place
• More light = higher photosynthesis rate = stomata opens constantly = more water is evaporated = larger transpirational pull

Question 8

how does humidity affect transpiration rate?

Answer 8

• Low humidity increases the water potential gradient between the leaf and the atmosphere which increases the transpiration rate.
• Humidity is the water density in air. If there is a higher density than water doesn’t need to be evaporated

Question 9

how does temperature affect transpiration rate?

Answer 9

• Higher temperature increases the water-holding capacity of air and increases the transpiration rate due to more water evaporating which then requires more water to travel from the roots of the plant to the leaves via the xylem
• Higher temperature increases energy in water particles so more water will be lose

Question 10

what is the pathway of water?

Answer 10

1. Water is first poured onto the soil either manually or by rain
2. Then water osmosis into the root hair cells due to water moving from a higher water potential to a lower water potential. Root hair cells are specialised with long projections which creates a large surface area for osmosis
3. Water then moves into the root cortex cells
4. Xylem vessels collect water from the root cortex and transport it up the plants system
5. When water reaches the leaf, water osmosis out of the xylem and into the leaves mesophyll cells where photosynthesis takes place.

Question 11

define translocation.

Answer 11

Is the movement of sucrose and amino acids from the source to an area of storage or usage in respiration and growth (sink).