Transport In Plants.

Question 1

What are the two vessels of the vascular system: Name them.

Answer 1

• Xylem vessels.
• Phloem vessels.

Question 2

What is the function of xylem vessels?

Answer 2

Transport water and minerals ions and support the plant.

Question 3

What is the function of phloem vessels?

Answer 3

Transport sucrose and amino acids.

Question 4

What is the direction of movement in the xylem and phloem?

Answer 4

Movement in the xylem only takes place in one direction (from roots to leaves) unlike phloem where movement takes place in different directions.

Question 5

What are the three adaptations of the xylem?

Answer 5

• Cells are joined end to end with no cross walls to form a long continuous tube.
• Cells are dead, without cell contents, to allow free passage of water.
• Outer walls are thickened with a substance called lignin, strengthening the tubes, which help support the plant.

Question 6

What are the two adaptations of phloem vessels?

Answer 6

• The cells are joined end to end and contain holes in the end cell walls (called sieve plates) which allow easy flow of substances from one cell to the next.
• Phloem tubes are made of living cells.

Question 7

What are root hairs?

Answer 7

Root hairs are single-celled extensions of epidermis cells in the root.

Question 8

What is the function of root hairs?

Answer 8

The function of root hairs is to absorb water and mineral ions from the soil.

Question 9

How does water uptake happen?

Answer 9

• Water enters the root hairs by osmosis,
• Water passes across the root from cell to cell by osmosis.
• Water is drawn up the xylem vessels.

Question 10

What is the function of the large surface area of root hairs?

Answer 10

The large surface area of root hairs increases the uptake of water and mineral ions.

Question 11

What is the pathway of water from the root hair cell?

Answer 11

root hair cell → root cortex cells → xylem → leaf mesophyll cells.

Question 12

What is transpiration?

Answer 12

Transpiration is defined as the loss of water vapor from plant leaves.

Question 13

How does transpiration happen?

Answer 13

Transpiration is defined as the loss of water vapor from plant leaves:

By evaporation of water at the surfaces of the mesophyll cells into the air spaces followed by diffusion of water vapor through the stomata.

Question 14

Describe the transpiration stream.

Answer 14

• Water enters root hairs by osmosis.
• Water containing dissolved mineral ions moves up the root and stem in xylem vessels.
• Water evaporates from the leaves.

Question 15

What are the four functions of transpiration in plants?

Answer 15

• Transporting mineral ions.
• Providing water to keep cells turgid in order to support the structure of the plant.
• Providing water to leaf cells for photosynthesis.
• Respiration.

Question 16

What is the effect of temperature on transpiration rates?

Answer 16

The higher the temperature, the greater the kinetic energy of water molecules. This means that water evaporates faster from the surface of the mesophyll cells, and the water vapour diffuses out of the leaf into the air more quickly.

Question 17

What is the effect of humidity on transpiration rates?
Humidity means the moisture content of the air.

Answer 17

The higher the humidity of the air outside the leaf the lower the transpiration rate because water usually diffuses down a concentration gradient, but if the air outside is already saturated with water, there is more likely to be a net movement of water into the leaf (providing the stomata are open) rather than out.

Question 18

Evaporation takes place from the surfaces of spongy mesophyll cells. How do the interconnecting air spaces between these cells increase the rate of evaporation?

Answer 18

The many interconnecting air spaces between these spongy mesophyll cells and the stomata create a large surface area meaning evaporation can happen rapidly when stomata are open.

Question 19

Explain the transpirational pull.

Answer 19

As water is lost from the plant by transpiration, this creates tension in the xylem.
Water moves upwards as it replaces the water that is lost. It travels up the xylem due to the cohesion within the water, this meaning the property of water molecules that make them stick to each other.

NOTE - Water molecules are drawn up the xylem by transpiration pull (NOT OSMOSIS).

Question 20

Define transpirational pull.

Answer 20

Transpiration pull is the force that aids in drawing water upwards from roots to leaves.

Question 21

What is the effect of wind speed on transpiration rates?

Answer 21

The faster the wind speed, the faster the water is moved away from the plant, creating a steeper gradient and increasing the transpiration rate.

Question 22

What is wilting and what is the effect of this?

Answer 22

This is when all the cells of the plant are not full of water, so the strength of the cell walls cannot support the plant and it starts to collapse.

Question 23

How and why does wilting occur?

Answer 23

If more water evaporates from the leaves of a plant than is available in the soil to move into the root by osmosis, then wilting will occur.

Question 24

What is translocation?

Answer 24

This is the movement of sucrose and amino acids in the phloem from sources to sinks.

Question 25

What are the sources of translocation?

Answer 25

Sources as the parts of plants that release sucrose or amino acids.

Question 26

What are the sinks of translocation?

Answer 26

Sinks as the part of plants that use or store sucrose or amino acids.