bio transport in plants

chapter 7 of O level biology 5090

what does the xylem do? [2]

It transports water and mineral ions from the roots to the stem and leaves. It also provides support to the plant.

what does the pholem do?

It transports food (amino acids and sucrose) made by the plant from photosynthesising leaves to non-photosynthesising parts of the plant(roots and stem).

what is the structure of the xylem vessels like? [3]

xylem tissues have no cell contents and the cells are joined end to end, with no cross-walls, to form a continuous tube. The walls are strengthened with a substance known as lignin.

what is transpiration?

It is the loss of water vapour from the leaves.

Describe the term “transpiration pull”.

Wtaer molecules are joined together by forces of attraction called cohesion. A transpiration pull draws up a column of water molecules up the xylem vessels. As the water evaportaes at the leaf and diffuses out of the stomata, more water is drawn up the plant from the roots.

How does humidity affect transpiration rate?

As himidity increases, transpiration rate decreases. Humid air contains a high concentration of water vapour; this reduces the diffusion gradient between the inside of the leaf and outside air, so less water vapour diffuses out of the leaf.

How does light intensity affect transpiration rate?

As light intensity increases, transpiration rate increases. Increased light intensity increases the rate of photosynthesis, so the stomata open to allow gas exchange. When this happens water vapour diffuses out of the stomata.

what is translocation?

The movement of sucrose and amino acids in the phloem, from sources to sinks.

How does temperature affect transpiration rate?

As temperature increases, transpiration rate increases. When temperatures are high, water vapour molecules have more kinetic energy and move around faster. So they are more likely to move out of the stomata by diffusion.

How does wind speed affect transpiration rate?

As wind speed increases, transpiration rate increases. When it's windy, water molecules that diffuse out fot he stomata are carried away quickly. This creates a concentration gradient and more vapour diffuses out of the leaf.

wilting

If water is lost by transpiration quicker than it can be replaced, wilting occurs.

cells lose water > no longer turgid > plant tissues become floppy> plant loses firmness