B2.2.5

Question 1

Transpiration definition

Answer 1

Transpiration is the loss of water from a plant’s leaves, the water lost must be replaced, by uptake through the roots.

Question 2

Transpiration stream definition

Answer 2

The constant flow of water from the roots, through the xylem and out of the leaves is called the transpiration stream.

Question 3

How does the transpiration stream start

Answer 3

Water diffuses from the soil into the root hairs by osmosis. Before the water can enter a xylem vessel, it must travel from cell to cell, until it reaches the centre of the root. Once inside the xylem, the water can be transported through the plant.

Question 4

What is the transpiration stream steps

Answer 4

1) Water moves into the roots from the soil by osmosis. It replaces the water constantly moving up the stem.
2) Water moves up from the roots into the stem
3) Water moves up through the stem and into the leaves to replace the water lost by evaporation.
4) Water is lost from the leaves by evaporation due to open stomata.

Question 5

How is water lost from leaves

Answer 5

The stomata on the surface of the leaves allows carbon dioxide to diffuse in for photosynthesis. Guard cells allow the stomata open and close. While the stomata are open, water evaporates from cells inside the leaf into the leaf’s air space. This creates a concentration gradient between the air inside the leaf and the surrounding air. Water vapour then diffuses out of the leaf (high concentration of water vapour) into the area (low concentration of water vapour).

Question 6

How does water move up the plant

Answer 6

The loss of water in the leaves reduces pressure in the xylem vessels in the leaf. As the pressure at the top decreases water moves up the tube from high pressure at the bottom to lower pressure at the top.
To prevent uncontrollable water loss, the upper surface of many leaves is covered in a waxy waterproof layer. Most water is found on the underside of the life.
If a plant looses water faster than it takes it in, it may wilt. The leaves collapse and droop. Reducing surface area available for evaporation. The stomata close and prevents water loss.