Unit 8

Question 1

What is the function of the xylem?

Answer 1

To transport water and mineral salts from the roots to the leaves.

Question 2

What is the function of the phloem?

Answer 2

To transport food up and down the plant.

Question 3

What function do vascular bundles perform aside from transportation?

Answer 3

To support the stem of a plant.

Question 4

What is the cortex?

Answer 4

The cells packed between the epidermis and vascular bundles in a root or stem of a plant.

Question 5

What is the pith?

Answer 5

The central tissue of a plant stem.

Question 6

What is a root cap?

Answer 6

The layers of cells found at the tip of a root which are continually worn away as a root grows and pushes into the soil.

Question 7

Through what processes do root hairs absorb water and mineral salts?

Answer 7

Water is absorbed through osmosis and mineral salts are absorbed through active transport.

Question 8

What are root hairs?

Answer 8

Tiny tube-like outgrowths from a root which absorb water and mineral salts.

Question 9

How does water pass from root hairs to xylem vessels?

Answer 9

When water is absorbed through osmosis into a roots hair cell, the turgor pressure is raised. This increased turgor pressure forces the water through the cell wall of the root hair to the next cell over and then onto the the next cell and so on, right through the cortex of the root to the xylem vessels.

Question 10

What is transpiration?

Answer 10

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

Question 11

How does transpiration occur?

Answer 11

When the cell sap in a mesophyll cell exerts turgor pressure on the cell wall, water passes through the cell wall into other mesophyll cells but also into the air space between cells and then out of the stomata.

Question 12

What are the characteristics of a flaccid leaf?

Answer 12

A leaf with flaccid cells will be limp and its stem will droop.

Question 13

What happens when cell vacuoles lose water?

Answer 13

The cells will lose their turgor and become flaccid.

Question 14

Why does a plant wilt?

Answer 14

Because its cells lose their turgor pressure due to insufficient water in their vacuoles.

Question 15

What do root hairs do?

Answer 15

The increase the surface area across which water can be absorbed by osmosis and ions by active transport. This increases the rate of absorption.

Question 16

How is water transported from the roots of a plant to its leaves?

Answer 16

Through xylem vessels.

Question 17

How does humidity affect the rate of transpiration?

Answer 17

If the air is very humid (this means it contains a lot of water vapour) then it can accept very little more from plants, this causes the rate of transpiration to slow down. When the air is dry the rate of transpiration will be much greater.

Question 18

How does temperature affect the rate of transpiration?

Answer 18

Warm air can hold more water vapour than cold air. This means that transpiration has the potential to take place more rapidly in warm air compared to cold air. Also, if leaves are warmer due to the heat they absorb from the sun or other sources, evaporation will take place more rapidly, this causes the rate of transpiration to speed up.

Question 19

How does water move up the xylem?

Answer 19

Attractive forces between water molecules results in cohesion (this is where the water molecules stick together).

Question 20

What is translocation?

Answer 20

The movement of sucrose and amino acids in the phloem, from regions of production (the source) to regions of storage or to regions where they are used in respiration or growth (the sink).

Question 21

How can some regions of a plant act as a source and as a sink at different times during the life of a plant?

Answer 21

When a bud containing new leaves is forming it would require nutrients, however, once that bud has burst and the leaves start photosynthesising it could begin to act as a source and produce and send sugars and amino acids to other parts of the plant which do not photosynthesise. Also storage organs which act as sinks can become sources.