Osmosis

Question 1

What is Osmosis?

Answer 1

Osmosis is the net passive movement of water from dilute solution to a concentrated solution through a partially permeable membrane.

Question 2

Which of the following is required for osmosis to occur?
A) Energy from respiration
B) A partially permeable membrane
C) Carrier proteins
D) A high solute concentration on both sides of the membrane

Answer 2

Answer B

Question 3

3. In which direction does water move during osmosis?

Answer 3

From a dilute solution to a more concentrated solution

Question 4

What does “partially permeable membrane” mean?

Answer 4

It allows some molecules (like water) to pass but not others

Question 5

What happens to an animal cell placed in pure water?

Answer 5

It swells and may burst

Question 6

What happens to a plant cell placed in pure water?

Answer 6

It becomes turgid

Question 7

What happens to an animal cell placed in a concentrated salt solution?

Answer 7

It crenates (shrivels)

Question 8

What happens to a plant cell in a concentrated salt solution?

Answer 8

It becomes plasmolysed. This means the cell will become flaccid because there is no pressure on the cell wall. If more water is lost by osmosis the cell membrane pulls away from the cell wall. (plasmolysis)

Question 9

Why do plant cells not burst in pure water?

Answer 9

Because they have a strong cell wall

Question 10

What term describes the pressure of the cytoplasm pushing against the cell wall?

Answer 10

Turgor pressure

Question 11

Why does osmosis not require energy?

Answer 11

Because water moves passively down the concentration gradient

Question 12

. A red blood cell is placed in a solution with the same concentration as its cytoplasm. What will happen?

Answer 12

It will stay the same

Question 13

Why does a plant cell become plasmolysed in a concentrated solution?

Answer 13

Water leaves the cell

Question 14

What would happen to a freshwater fish if placed in seawater?

Answer 14

Its cells would lose water and shrink

Question 15

Which statement is correct about osmosis in root hair cells?
A) Water moves from the soil into the root cells
B) Water moves from the root cells into the soil
C) Water moves in both directions equally
D) Water movement depends on oxygen availability

Answer 15

Answer A

Question 16

Why do plant cells become flaccid in a concentrated solution?

Answer 16

Water moves out of the cell

Question 17

Why is osmosis important for plant cells?

Answer 17

It maintains turgor pressure, keeping the plant upright

Question 18

Which of these is an example of osmosis in the human body?

Answer 18

Water absorption in the small intestine

Question 19

If a plant wilts, what does this suggest about osmosis?

Answer 19

The plant cells have lost water due to osmosis.

Question 20

Explain the process of osmosis and its importance in plant cells.
Include:

• Definition of osmosis
• Role of water potential and concentration gradients
• How osmosis affects plant cells in different solutions (turgid, flaccid, plasmolysed)
• Importance of osmosis for plant support and function

Answer 20

Definition of osmosis: Movement of water molecules from a region of high water potential to a region of low water potential through a partially permeable membrane. (1 mark)

Water potential gradient: Water moves down the water potential gradient. (1 mark)

Effect on plant cells:

In pure water: Water enters, cell becomes turgid due to increased turgor pressure. (1 mark)

In a concentrated solution: Water leaves, cell becomes flaccid and may become plasmolysed. (1 mark)

Importance of osmosis in plants: Maintains turgor pressure, which keeps the plant upright and supports photosynthesis. (1 mark)

Link to function: Helps transport water throughout the plant via osmosis between cells. (1 mark)

Question 21

A student places a potato strip into pure water and another into a concentrated sugar solution. Describe and explain what will happen to each strip.
Include:

• The direction of water movement in both cases
• Changes in mass and length of the potato strips
• Explanation using terms like turgid, flaccid, water potential, and partially permeable membrane
• The effect of osmosis on plant tissue

Answer 21

Mark scheme:

Potato in pure water: Water moves into the cells by osmosis. (1 mark)

Effect on the potato strip: Becomes turgid, increasing in mass and length. (1 mark)

Potato in concentrated sugar solution: Water moves out of the cells by osmosis. (1 mark)

Effect on the potato strip: Becomes flaccid, decreasing in mass and length. (1 mark)

Explanation using water potential: Water moves from a high to low water potential across a partially permeable membrane. (1 mark)

Use of correct terminology: Turgid, flaccid, water potential, plasmolysis. (1 mark)

Question 22

3 Describe how osmosis is involved in water uptake by root hair cells and how this benefits the plant.
Include:

• How root hair cells absorb water from the soil
• The role of water potential in the movement of water into the roots
• How water moves through the plant via osmosis
• The importance of osmosis for photosynthesis, support, and transport

Answer 22

Mark scheme:

Water uptake process: Water moves from the soil (high water potential) into the root hair cells (lower water potential) by osmosis. (1 mark)

Partially permeable membrane: Water passes through the membrane of root hair cells. (1 mark)

Movement through the plant: Water moves cell to cell via osmosis towards the xylem. (1 mark)

Benefit to the plant: Provides water needed for photosynthesis. (1 mark)

Support and structure: Water helps maintain turgor pressure, keeping the plant upright. (1 mark)

Water transport: Helps move water up the plant through transpiration. (1 mark)