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Plants use osmosis to prevent wilting.

Unit 3 - Osmosis

GCSE Biology shows how osmosis moves water across partially permeable membranes, affecting animal and plant cells in different external solutions.

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Fascinating Fact:

In animal cells, if the surrounding solution is too dilute, water enters by osmosis. The cell may swell and burst because it does not have a cell wall to resist the pressure.

In GCSE Biology, osmosis is studied as the movement of water across partially permeable membranes. You compare what happens to animal and plant cells in concentrated and dilute solutions and link this to real-life examples such as red blood cells and plant roots.

Key Terms

Osmosis: The diffusion of water from a dilute solution to a more concentrated solution through a partially permeable membrane.
Partially permeable membrane: A barrier that allows some molecules, such as water, to pass through but not larger solute particles.
Hypertonic solution: A solution with a higher solute concentration than inside a cell, which can cause the cell to lose water by osmosis.

Frequently Asked Questions (click to see answers)

What is osmosis in GCSE Biology?

In GCSE Biology, osmosis is defined as the diffusion of water from a dilute solution to a more concentrated solution through a partially permeable membrane, such as a cell surface membrane.

How is osmosis different from diffusion?

Diffusion can involve many types of particles moving down a concentration gradient, while osmosis specifically describes the movement of water through a partially permeable membrane between solutions of different concentrations.

What happens to plant cells in pure water and concentrated solution?

In pure water, plant cells gain water and become turgid because the cell wall stops them bursting. In a concentrated solution, they lose water, the cytoplasm shrinks and the cell becomes plasmolysed.

Try These Related Quizzes

1 .

Plants use osmosis to prevent...

respiration

photosynthesis

wilting

excretion

Plant cells become flaccid when they are short of water. Osmosis makes them turgid once more

2 .

Osmosis takes place in this important structure.

Alveolus

Villus

Nephron

Artery

Water is reabsorbed by osmosis in the nephrons of the kidneys, keeping the blood plasma at the right concentration to avoid the lysis (bursting) of the red blood cells in particular

3 .

Why is osmosis not the same thing as diffusion?

A partially permeable membrane is needed for osmosis

A partially permeable membrane is needed for diffusion

Osmosis involves oxygen only

Diffusion involves water only

True diffusion occurs when two substances are in direct contact with one another, here they are physically separated by the partially permeable membrane

4 .

Water molecules move...

down the concentration gradient

along the concentration gradient

against the concentration gradient

nowhere

Along the gradient is always marked as incorrect in exams

5 .

Osmosis is the movement of which molecules?

Oxygen

Hydrogen

Any

Water

Osmosis is only about water molecules

6 .

In living organisms, the partially permeable membrane is the...

nucleus

cell membrane

chloroplast

bacterium

This contains the cytoplasm and when there is a concentration gradient between the outside of the cell and the cytoplasm, osmosis occurs, restoring the equilibrium

7 .

Potato cylinders are put into a strong sugar solution. After an hour they are...

bigger

smaller

the same

sweet potato

Water leaves the potato cells by osmosis, so the potato cylinders shrink in size due to water loss

8 .

Dilute means...

a little solute and a lot of water

a lot of solute and little water

concentrated

the same

Dilute means weak and watery. A small amount of solute, e.g. salt, dissolved in a lot of water

9 .

Water molecules move from...

dilute to a more dilute solution

dilute to a more concentrated solution

concentrated to a more dilute solution

concentrated to a less concentrated solution

It is a special case of diffusion as it involves a movement of only water particles from a higher concentration to a lower concentration across a partially permeable membrane

10 .

Osmosis takes place in which of the following?

Roots

Hair

Soil

The atmosphere

Water is taken up by root hair cells from the soil as there is a concentration gradient from soil to the root hair cell

You can find more about this topic by visiting BBC Bitesize - Osmosis and plant transport (CCEA)

Author: Donna Davidson (GCSE Biology Teacher & Examiner, Quiz Writer)