Osmosis

Question 1

Define solvent

Answer 1

A liquid where other substances are dissolved in, usually water

Question 2

Define solute

Answer 2

A substance that can be dissolved in a solvent

Question 3

Define solution

Answer 3

A mixture created by dissolving one substance in another

Question 4

Define dilute

Answer 4

A solution that contains more solvent than solute

Question 5

Define concentrated

Answer 5

A solution that contains more solute than solvent

Question 6

Define permeable

Answer 6

Allows substances, particularly liquids and gases, to pass through

Question 7

Define water potential

Answer 7

A measure of the tendency of water molecules to diffused from one area to another (kPa)

Question 8

As you increase the concentration of a solution, what happens to the water potential. Explain why

Answer 8

Decreases, because there is a greater proportion of solute to solvent

Question 9

What is the water potential of distilled water

Answer 9

0kPa

Question 10

What type of liquid has negative water potential

Answer 10

Water with dissolved solutes

Question 11

What are the standard conditions of temperature and pressure

Answer 11

25°C and 100kPa

Question 12

Why does pure water have a water potential of 0kPa

Answer 12

It contains no solutes within it

Question 13

The more negative the water potential of a solution is..

Answer 13

There are more solutes within the solution

Question 14

Define osmosis

Answer 14

The passive net movement of water from a region of high water potential, to a lower water potential, through a selectively permeable membrane

Question 15

Why can’t water move through the membrane directly

Answer 15

It’s polar, therefore it is not a lipid-soluble molecule

Question 16

What does water pass through instead

Answer 16

A type of channel protein called aquaporin

Question 17

Therefore what type of diffusion does this make osmosis. Explain why

Answer 17

Facilitated diffusion because it uses a protein, whereas simple diffusion passes straight through the membrane

Question 18

State the factors that decrease the rate of osmosis

Answer 18

• Decrease in SA
• Decrease in temperature
• Increase in diffusion distance
• Decrease in water potential gradient
• Reduction in the permeability of the membrane/ fewer aquaporin proteins in the membrane

Question 19

When would the net rate of water movement be 0

Answer 19

When equilibrium is reached (water potential is equal on both sides)

Question 20

Describe what happens in a hypotonic solution

Answer 20

Water moves into the cell via osmosis, as the cell has a lower water potential

Question 21

Describe what happens in a hypertonic solution

Answer 21

Water moves out the cell via osmosis, as solution has a lower water potential

Question 22

Describe what happens in an isotonic solution

Answer 22

No net movement of water as the water potential inside and outside are equal

Question 23

Describe What happens when a red blood cell is placed in pure water

Answer 23

It will absorb water because it has a lower water potential

Question 24

Describe what happens when RBC are placed in a hypotonic soltion

Answer 24

Water will enter the RBC via osmosis, because it has a lower water potential

Question 25

Describe what happens when RBC are placed in a hypertonic soltion

Answer 25

Water will leave the cell via osmosis, and the cell will shrink and become shrivelled

Question 26

Where are RBCs kept to prevent haemolysis or shrinking.
Explain why

Answer 26

RBCs are kept within our blood plasma, which has the same water potential as the RBCs (isotonic)

Question 27

Describe what happens when a plant cell is placed in a hypotonic solution

Answer 27

As the water moves into the cell, the vacuole expands and exerts pressure on the cell wall. This pressure makes the cell turgid.

Question 28

Why does the animal cell burst, but not the plant cell, when it’s placed in a hypotonic solution

Answer 28

The cell wall provides structure and strength

Question 29

Describe what protoplast refers to

Answer 29

Outer cell surface membrane, nucleus, cytoplasm, and inner vacuole membrane

Question 30

Describe what happens when a plan cell is placed in a hypertonic solution

Answer 30

The volume of the cell decreases as water leaves via osmosis. When the protoplast no longer presses on the cell wall, this is called incipient (about to be) plasmolysis.

Question 31

^ Describe what happens when there is a further loss of water

Answer 31

If there is a further loss of water will cause the cell contents to shrink further and the cell membrane pulls away from the cell wall as the cytoplasm shrinks (plasmolysed).

Question 32

If a potato core is allowed to dehydrate by sitting in open air, what would happen to the water potential and the concentration of the potato cells? Explain your answer

Answer 32

The water potential of the cells would decrease, whereas their
concentration would increase. This is because water has been lost through evaporation

Question 33

The cells in plant roots pump mineral ions into their cytoplasm from the soil. Explain how this would allow the cells to also take up water

Answer 33

The concentration of the plant root cells increases, therefore their water potential decreases. As the water potential of the cells decreases, water will move into the root cells via osmosis down the water potential gradient

Question 34

This plant hasn’t been watered and so has wilted. Use your knowledge of osmosis to explain why

Answer 34

• As the plant wasn’t watered, the water potential in the soil was lower than that of the plant cells
• Water left the plant cells down the water potential gradient via osmosis
• This caused the cytoplasm to shrink, and the cell membrane pulls away from the cell wall
  The plant cells become plasmolysed and so are flaccid
• The plant therefore is no longer rigid and cannot stand upright

Question 35

What happens if you put salt on slugs? Why?

Answer 35

• The salt lowers the external water
  potential of the slug
• Water leaves the slug via osmosis * This causes the cells of the slug to undergo cytolysis, and the slug shrivels up
• The slug no longer has enough water to carry out metabolic reactions such as hydrolysis and consequently the slug dies