8 Transport in plants

Question 1

Xylem

Answer 1

Transporting water and dissolved mineral ions from the roots, through the stem and to the leaves

Providing support for the plant and helping to keep it upright.

A substance called lignin gives xylem thick walls for support.

Xylem cells form long continuous tubes from the root to the leaves.

Question 2

Lignin

Answer 2

A substance in xylem walls that makes them strong.

Question 3

Phloem

Answer 3

Transporting sucrose
Transporting amino acids.

Question 4

Positions in parts of a plant of the Xylem and Phloem

Answer 4

Xylem and phloem are located in vascular bundles in different positions, depending on the part of the plant.
In roots
In stems
In leaves

Question 5

Xylem structure

Answer 5

They have no nucleus like other cells.
This allows greater space for transporting water. As we saw in the previous section, their walls are thickened by a substance called lignin.
Xylem therefore provides support for the plant.

Question 6

Root hair cells

Answer 6

Type of cell in plant roots that has a large surface area for the absorption of water and mineral ions from the soil.

Question 7

Pathway of water from the roots to the leaves

Answer 7

Root hair cells on the surface of a root
Root cortex cells inside the root
Xylem vessels from the roots, through the stem and into mesophyll cells in the leaf.
Soil → root hair cells → root cortex cells → xylem → mesophyll cells

Question 8

Root cortex cells

Answer 8

Type of cell in a plant roots that surround xylem and phloem.

Question 9

Transpiration

Answer 9

Water is transported in plants from the roots to the leaves through the xylem vessels by osmosis. Two things happen when it gets there:

Evaporation at the surfaces of the spongy mesophyll cells (the cells found between the upper epidermis and the lower epidermis of the leaf) to form water vapour.

The loss of water vapour from the leaf by diffusion through the stomata.

Question 10

The transpiration rate is affected by variations in temperature and wind speed:

Answer 10

An increase in temperature results in a high rate of transpiration. The higher temperature increases evaporation and this cools the plant.

Wind is moving air. It sweeps away water vapour from the surface of leaves surface. The faster the wind speed the more evaporation from the leaves.

Question 11

Transpiration pull

Answer 11

A suction force that draws water in xylem upwards, from the roots to the leaves.

The forces of attraction between water molecules causes them to form a continuous column in the xylem.

Transpiration pull results from evaporation of water from mesophyll cells in the leaves.

Question 12

Effect of number of stomata on transpiration

Answer 12

The larger the leaf surface area, the more stomata and the higher the rate of water lost through transpiration

Question 13

Wilting

Answer 13

Stems and leaves of young plants rely on the turgidity of their cells to remain upright and rigid.

If plant cells rate of transpiration is greater than the rate at which water is absorbed through the root hair cells, the cells become flaccid.

Flaccid cells lose their rigidity and the stems and leaves wilt.

Question 14

Translocation

Answer 14

The movement of sucrose and amino acids in phloem. They move from a source (where they are produced) to a sink (where they are stored or used in respiration or growth).

Question 15

The movement of water and ions in the xylem

Answer 15

In xylem, the direction of movement is always from the roots to the leaves.

Question 16

The movement of substances in phloem

Answer 16

In phloem, the direction of movement depends on the circumstances.

Question 17

In a plant, a sink can be

Answer 17

A region of storage
A region of use in respiration or growth.

Question 18

Translocation involves the movement of substances in this direction

Answer 18

Source → sink

The same part of a plant may act as a source at one time in the life of the plant, but may act as a sink at a different time in its life.