Osmosis

Question 1

What is osmosis?

Answer 1

Osmosis is a special type of diffusion that involves the random movement of water molecules. It is the movement of water across a selectively permeable membrane from and area of high water concentration to an area of low water concentration.

Question 2

What happens to a plant cell when water is lost by osmosis

Answer 2

A plant cell will become plasmolysed if it loses too much water by osmosis. This means the cytoplasm pulls away from the cell wall as the contents of the cell shrinks.

Question 3

What happens to a plant cell when it gains water by osmosis

Answer 3

Plant cells have a strong hard rigid cell wall on the outside of the membrane. This stops the cell bursting but causes the vacuole to increase in size. This pressure of water inside the cell cause it to become turgid. Instead of a skeleton plants are supported by the turgor pressure in cells.

Question 4

What is transpiration

Answer 4

The evaporation of water from mesophyll cells followed by diffusion through air spaces and stomata.

Question 5

What happens to an animal cell if too much water exits by osmosis

Answer 5

Water will move out through the cell membrane. If more water continues to leave the cell it will shrink and become crinkly, this is called crenation.

Question 6

What happens if too much water enters an animal cell due to osmosis

Answer 6

If water continues to enter the cell it will eventually burst. This is called lysis. This happens as animal cells are not surrounded by an inelastic cell wall.

Question 7

What causes plants to wilt

Answer 7

If water is lost by osmosis the cell membrane will not push against the cell wall losing the cells rigid structure. This causes the plant to wilt and the cell to be known as flaccid

Question 8

What is the continuous movement of water in a plant called?

Answer 8

The transpiration stream.

Question 9

What 4 reasons explain the importance of the transpiration stream?

Answer 9

1. It supplies the water to the leaves to be used as one of the raw materials for photosynthesis
2. The movement of water also transports minerals through the root and up to the stem to the leaves.
3. As water passed through the plant it will enter cells by osmosis to provide support through turgor.
4. Providing water for the actual process of transpiration itself

Question 10

How does light affect transpiration rate

Answer 10

In bright light transpiration increases. The stomata open wider to allow more carbon dioxide into the leaf for photosynthesis. Because the stomata open wider more water will leave through the space by transpiration.

Question 11

How does temperature affect transpiration

Answer 11

Transpiration is faster in higher temperatures. Evaporation and diffusion are faster at higher temperatures

Question 12

How does wind affect transpiration

Answer 12

Transpiration is faster in windy conditions. Water vapour is removed quickly by air movement, speeding up diffusion of more water water vapour out of the leaf.

Question 13

How does humidity affect transpiration

Answer 13

Transpiration is slower in humid conditions. Diffusion of water vapour out of the leaf slows down if the leaf is already surrounded by moist air.

Question 14

What is the method for the water uptake potometer experiment?

Answer 14

Collect apparatus, ensure potometer is filled and contains no air bubbles, take a section of laurel plant and cut the bottom cm or so from the shoot.
Insert the cut end into the potometer ensuring it is a tight fit and use Vaseline to create an air tight seal.
Remove the apparatus from the water and turn the valve to allow the water to move through the capillary tube.