Osmosis

Question 1

What is the definition of osmosis?

Answer 1

The movement of WATER molecules from an area of high concentration to an area of low concentration through a selectively permeable membrane

Question 2

Describe what a cell would look like if it was turgid

Answer 2

The cell would be filled with water which pushes the membrane against the cell wall

Question 3

What is the role of the plant cell wall?

Answer 3

Prevents too much water from entering stops the cell from bursting. This ensures the plant stays upright giving the plant support

Question 4

Explain why a plant cell would become turgid

Answer 4

• This occurs if there is a higher concentration of water outside the cell than inside the cell
  -Water moves into the cell

Question 5

What does plasmolysed mean?

Answer 5

When the cell loses too much water and causes it to shrink in size

Question 6

What would a plasmolysed cell look like?

Answer 6

The cell membrane would pull away from the cell wall and the vacuole would shrink in size

Question 7

Why can red blood cells burst if too much water enters them?

Answer 7

As they do not have a cell wall and cannot limit the volume of water that enters

Question 8

What is the key word when a red blood cell fills with water and eventually bursts?

Answer 8

Cell lysis

Question 9

What piece of equipment measures the rate of water uptake?

Answer 9

A potometer

Question 10

Describe how you would set up a bubble potometer

Answer 10

• Water is taken up by the shoot and it evaporates from the leaves
  -As water evaporates the bubble will moves towards the shoot
• This allows us to calculate the rate of water uptake (distance the bubbles moves / time)
  -The reservoir (or syringe) allows us to rest the practical and repeat it again

Question 11

What is water used for in a plant?

Answer 11

photosynthesis, support (turgor) or transport

Question 12

What is the definition of transpiration?

Answer 12

The evaporation of water from the mesophyll cells, followed by the diffusion through the air spaces and out of the stomata

Question 13

What factors increase transpiration?

Answer 13

increased wind speed, increased temperature and decreased humidity

Question 14

Explain why plants close their stomata in the dark

Answer 14

To reduce water lost from the plant by transpiration

Question 15

Why does a warmer temperature speed up transpiration?

Answer 15

The water molecules have more kinetic energy so they evaporate faster

Question 16

Why does a higher wind speed, speed up transpiration?

Answer 16

The wind moves the evaporating water away from the stomata faster. This creates a steeper concentration gradient of moisture.

Question 17

Why does transpiration slow in periods of darkness?

Answer 17

Plants close their stomata in the darkness which reduces water loss

Question 18

What will happen to the number of stomata as the surface area of the leave increases? How does that affect transpiration?

Answer 18

The number of stomata will increase and therefore the rate of transpiration will be higher

Question 19

Explain why higher levels of humidity slows down the rate of transpiration.

Answer 19

Humid conditions slow down the evaporation of water molecules. Therefore, there is a decrease in the moisture concentration gradient between the leaf and the air.

Question 20

How do you calculate the rate of transpiration in the mass potometer?

Answer 20

Distance bubble moves / time

Question 21

How do you calculate % change in mass in the osmosis potato cylinder practical

Answer 21

Change / initial mass x 100

Question 22

How could you work out the concentration of the potato cylinder?

Answer 22

This is the concentration which causes 0% change in mass. There is no net movement of water

Question 23

Why does increased humidity slow the rate of transpiration?

Answer 23

There is a less steep concentration gradient

Question 24

What is the term for a plant cell that has lost lots of water?

Answer 24

Plasmolysed

Question 25

What is the term for a plant cell that has gained lots of water?

Answer 25

Turgid

Question 26

Where does water diffuse out of the leaf?

Answer 26

Stomata

Question 27

What happens to the stomata at night and why?

Answer 27

Stomata close to stop water being lost by transpiration