Plants and water

Question 1

What is the water potential for distilled water?

Answer 1

0

Question 2

What is the water potential measuring and what does it determine?

Answer 2

The chemical energy found in a water molecule which determines how that water molecule moves

Question 3

What does Ψ stand for?

Answer 3

The total chemical potential for a water molecule

Question 4

What is the formula for Ψ

Answer 4

Ψs + Ψp + Ψm = Ψ

Question 5

What does Ψs stand for?

Answer 5

Solute potential - water moves by osmosis in response to the presence of solutes

Question 6

What does Ψp stand for?

Answer 6

Pressure potential - Water moves due to hydrostatic pressure

Question 7

What does Ψm stand for?

Answer 7

Matric potential

Question 8

Why does Ψs always have a negative value?

Answer 8

Water always moves from a positive water potential to a negative water potential

Question 9

What determines whether the value of Ψp has a negative or positive value?

Answer 9

If the water is being sucked then the atmospheric pressure is less than 1 so gives a negative value.
If the water is being pushed the atmospheric pressure is more than one so gives a positive value.

Question 10

How do plants suck water from the soil and how is this linked to irrigated crops?

Answer 10

Plants must make the water potential in their cells lower than that of the soil to be able to move the water towards a more negative water potential. Crop plants are made to have a lower water potential so the maximum amount of water can be taken up by the plant for better growth

Question 11

What happens to a plant cell if dropped into a concentrated solution?

Answer 11

The water potential of the cell will become more negative because water will leave the cell making the Ψs more negative because the concentration of solutes increases which causes plasmolysis.

Question 12

What is plasmolysis?

Answer 12

The plasmodesmata that holds plant cells together is broken down and the living matter inside the cell shrivels and condenses in the centre of the cell which causes the plant to die

Question 13

What happens if a plant cell is dropped into a diluted solution?

Answer 13

The water potential becomes less negative and moves towards the value of 0. This is because the plant cell gains water so solutes become less concentrated which makes the value of Ψs less negative but increases the value of Ψp so the cells become turgid.

Question 14

What is the importance of plant cells being in a turgid state and why are plant cells turgid?

Answer 14

Plant sells must be turgid so the plant has a structure as it’s made up of hydrostatic bricks. This is because plants sit in a diluted solution at all times

Question 15

Why don’t plant cells burst when there is a build up of pressure?

Answer 15

Because the negative Ψs value and positive Ψp value cancel each other out so the movement of water stops

Question 16

What does Ψp also control?

Answer 16

Controls the opening and closing of stomatal guard cells which regulate the loss of water and intake of carbon dioxide

Question 17

Describe transpiration in a tree

Answer 17

The root cells have a low water potential that moves water from the soil up into the roots. The xylem tubes in a tree are always full of water so evaporation takes place at the top of the tree because the atmosphere has a more negative water potential than the water in the xylem. This process allows the water to be drawn up the xylem tubes and transported to the rest of the tree.

Question 18

Why does transpiration work?

Answer 18

Because water is polar and has a high tensile strength