Osmosis

Question 1

What is osmosis?

Answer 1

Osmosis is a special type of diffusion by which water molecules are transported across a partially permeable membrane.

Question 2

What does solute mean?

Answer 2

The dissolved substance in a solution

Question 3

Solvent

Answer 3

A substance (usually a liquid), capable of dissolving another substance.

Question 4

What is a solution?

Answer 4

A solution is the state of being dissolved

Question 5

What is the word used to describe how much solute there is in something?

Answer 5

Concentration

Question 6

What is the word used to describe the amount of water in something?

Answer 6

Water potential

Question 7

What is water potential ?

Answer 7

Water potential is the potential of water molecules to diffuse out form one place to another.

Question 8

What is the relationship between the amount of water and water potential?

Answer 8

The MORE water there is
The higher the WATER POTENTIAL
And the more freely molecules can move

Question 9

What is the symbol of water potential?

Answer 9

Psi

kPa

Question 10

What is the value of pure water’s water potential?

Answer 10

Pure water has the highest water potential but has a value of 0 kPa

Question 11

What happens to the value of water potential when there are dissolved molecules (solutes) present?

Answer 11

When dissolved molecules (solutes) are present this lowers the water potential so the value becomes negative

Question 12

What is the definition for osmosis?

Answer 12

OSMOSIS IS THE NET MOVEMENT OF WATER MOLECULES FROM A REGION OF HIGH WATER POTENTIAL TO A REGION OF LOW WATER POTENTIAL (more negative)
ACROSS A PARTIALLY PERMEABLE MEMBRANE,
DOWN A CONCENTRATION GRADIENT.

Question 13

How does water move across a membrane?

Answer 13

• fits between phospholipids or can go through the phospholipid bilayer
• can go via protein channels known as AQUAPORINS

Question 14

How is osmosis in animal and plant cells studied?

Answer 14

Osmosis in animal and plant cells is studied by placing them in different solutions

Question 15

What is a HYPOTONIC solution?

Answer 15

If the solution has a HIGHER water potential than inside the cell, we say its a HYPOTONIC SOLUTION

Question 16

What is a HYPERTONIC solution?

Answer 16

If the solution has a LOWER water potential than the solution inside the cell, we say it’s HYPERTONIC SOLUTION

Question 17

What is an ISOTONIC solution?

Answer 17

If the solution has the same water potential as the solution inside the cell, it’s an ISOTONIC SOLUTION.

Question 18

Osmosis in plant cell is different, explain why?

Answer 18

Because plant cells not only have a cell membrane but also have a cell wall.

Question 19

What is the role of the cell wall?

Answer 19

The cell wall holds the cell firm

Preventing the cell from bursting

Question 20

What would happen if a plant cell was placed in a HYPOTONIC solution?

Answer 20

Water would move into –> the cell
By osmosis.
This is because the cell has a LOWER WATER POTENTIAL (more negative than the surrounding solution)
Water would then move D O W N a WATER POTENTIAL GRADIENT
From HIGH to LOW water potential
The plant cell becomes TURGID

Question 21

When a plant cell becomes turgid what happened to the cell membrane?

Answer 21

The cell membrane gets pushed right up against the cell wall

Question 22

Why would a turgid plant cell not burst?

Answer 22

The plant cell would not burst because the cell wall provides strength/withstands internal pressure
It limits the uptake of water

Question 23

What would happen to a pants cell in a ISOTONIC solution >?

Answer 23

In this case the water potential inside the cell is the same as the water potential outside the cell
There is NO overall net movement of water
Therefore the cell membrane is not placed right up to the cell wall

Question 24

What would happen to a plant cell placed in a HYPERTONIC solution?

Answer 24

Water would move OUT OF the cell
By osmosis
This is because the cell has higher (less negative) water potential than the surrounding solution
Water would then be moved down a water potential gradient from high to low water potential
The plant cell can be described as PLASMOLYSED

Question 25

What happens to the cell membrane when a plant cell is plasmolysed?

Answer 25

The cell membrane gets pulled away from the cell wall

Question 26

Why can’t animal cells withstand the uptake of too much water without bursting?

Answer 26

Animal cells lack a CELL WALL and therefore are unable to withstand the uptake of too much water without bursting.

Question 27

What happens when an animal cell is placed in a hypotonic solution?

Answer 27

CELLS CYTOPLASM has a lower water potential than distilled water
Water moves into cells down a water potential gradient
From high water potential to low water potential
Via osmosis
Cell surface membrane of blood cell is weak so bursts - as it cannot withstand pressure
The red blood cell is therefore HAEMOLYSED

Question 28

What happens to an animal cell in an ISOTONIC solution?

Answer 28

Here the water potential inside the cell is the same as the water potential outside the cell
There’s no overall net movement of water
THE CELL IS INTACT

Question 29

What happens to a cell in a hypertonic solution?

Answer 29

The cells CYTOPLASM has a higher water potential than the surrounding solution
Water moves out of the cells down a water potential gradient - from high water potential to low water potential
Via osmosis
The red blood cells shrink and appear wrinkled
The red blood cell is CRENATED