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Mineral ions enter the plant by active transport through the roots.

Unit 3 - Exchange Surface and Diffusion

GCSE Biology explains how substances move by diffusion and how specialised exchange surfaces help living organisms take in what they need and remove waste efficiently.

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Fascinating Fact:

Single-celled organisms rely on diffusion across their cell surface for gas exchange and nutrient uptake. Their small size means distances for diffusion are very short.

In GCSE Biology, exchange surfaces and diffusion are studied to show how gases and dissolved substances move in and out of cells. You learn how thin, moist, well-supplied surfaces make this transfer more efficient in living organisms.

Key Terms

Diffusion: The net movement of particles from an area of higher concentration to an area of lower concentration, down a concentration gradient.
Exchange surface: A specialised area of a body or organ where substances such as gases or dissolved food move between the blood and the environment.
Concentration gradient: The difference in concentration between two areas, which affects how quickly diffusion takes place.

Frequently Asked Questions (click to see answers)

What is diffusion in GCSE Biology?

In GCSE Biology, diffusion is defined as the net movement of particles from a region of higher concentration to a region of lower concentration, as a result of random movement of particles.

Why do larger organisms need specialised exchange surfaces?

Larger organisms need specialised exchange surfaces because they have a smaller surface area compared to their volume. Simple diffusion across the outer surface is too slow to supply all their cells.

What factors affect the rate of diffusion?

The rate of diffusion is increased by a larger concentration gradient, a higher temperature, a shorter diffusion distance and a greater surface area for particles to move across.

Try These Related Quizzes

1 .

Carbon dioxide enters plants mainly through the...

roots

leaves

flowers

stem

Leaves are thin and flat which helps to make gaseous exchange more efficient.

2 .

Diffusion is faster across an exchange surface if the concentration gradient is...

less

increased

the same

moved

Think of it like a hill. If a hill is steeper (has a greater gradient), an object will roll down it better

3 .

These are found in large numbers in the lining of the small intestine.

Alveoli

Ville

Villi

Arteries

These create a very large surface area within the small intestine

4 .

Exchange surfaces are generally involved in the...

transfer of materials across a membrane

removal of waste

uptake of nutrients

respiration

This happens where there is a difference in concentration (a concentration gradient) of the materials being exchanged on the two sides of the membrane

5 .

Alveoli are found in the...

gills

lungs

liver

brain

They are also known as air sacs

6 .

Within leaves, the gases enter and leave through specialised pores called...

stomata

stoma

holes

gaps

These are found on the underside of the leaves

7 .

Exchange surfaces are usually very...

thin

thick

wide

tall

If the structure is thin, materials get through more quickly

8 .

During gaseous exchange, which two gases are involved?

Oxygen and hydrogen

Nitrogen and oxygen

Carbon dioxide and oxygen

Ammonia and oxygen

Oxygen is taken in and carbon dioxide is given out. Plants do the opposite during photosynthesis.

9 .

In animals, uptake of materials is quicker if there is a rich network of...

capillaries

villi

lungs

arteries

Lungs, gills and the villi all have a dense capillary network which takes up the materials quickly, thus maintaining a steep concentration gradient for maximal uptake

10 .

Mineral ions enter the plant by active transport through the...

stem

leaves

roots

flowers

Mineral ions, such as nitrate ions, enter the plant through specialised cells in the roots called root hair cells. These have a lot of mitochondria to supply the energy required for the active transport of the mineral ions

You can find more about this topic by visiting BBC Bitesize - Diffusion (CCEA)

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