Topic Four (1.4): Diffusion
Objectives
By the end of this topic, you should be able to:
- describe factors that affect the rate of diffusion.
Retrieval starter question
- Why does breathing rate increase during exercise?
Introduction
In this topic, you will learn how gases move in and out of cells. Diffusion is the random movement of particles. Many different particles move in and out of cells, including oxygen, carbon dioxide and nutrients.
Working through your course book
Reactivate activity - optional
Before applying your knowledge to new concepts in this topic, you can check your understanding of previous concepts. If you want to check your understanding and reactivate your knowledge, please complete this reactivate activity:
- Read ‘Movement in and out of cells’ on page 20 in your Activate 3 coursebook and answer the reactivate your knowledge questions at the top of page 28.
Apply your knowledge
You are now ready to apply your knowledge of diffusion and extend your learning. Particles will move at random from a high concentration to a low concentration. Oxygen will diffuse from air sacs into the blood and carbon dioxide will diffuse from the blood into the air sacs. This takes place due to respiration in our cells - as we saw in Topic 3. Diffusion can happen more quickly or more slowly depending on many factors. The rate of diffusion can be affected by concentration, surface area and temperature.
- Read pages 28-29 in your Activate 3 coursebook.
- Watch the video below about diffusion and the factors affecting the rate of diffusion and make notes on each of the three factors:
Osmosis is a special type of diffusion. It is the movement of water molecules from an area of high concentration to an area of low concentration across a partially permeable membrane.
Water moves into root hair cells from the soil by osmosis. Water moves from a high concentration in the soil through the cell membrane to the cytoplasm of the cell, where water is in a low concentration.
Watch this video about osmosis - it says ‘GCSE’, but it contains an excellent diagram representing osmosis:
- Answer the Summary question on page 29 in your Activate 3 coursebook.
- Download and keep the knowledge organiser poster for this chapter:
DOWNLOAD & KEEP - B3 Chapter 1 - Cells Knowledge organiser (Kerboodle) [Not available on sample course]
- Also, keep a copy of this glossary of all of the key words for this first chapter on cells:
DOWNLOAD & KEEP - B3 Chapter 1 Glossary (Kerboodle) [Not available on sample course]
Support activities for this topic
You can watch the video below from Activate 1 to help you to understand unicellular organisms and diffusion:
Extension activities for this topic
We can study the effects of osmosis in potato cells. Potato cells contain dilute solutions of sugar, minerals and water. When potato cells are placed into dilute water, the concentration of water outside the cell is higher than inside the cell. Water will move into the cell across the membrane by osmosis. If the potato cell was placed into a concentrated sugar solution, the water concentration inside the cell would be higher. This would result in water leaving the cell. This could change the mass of the potato cell.
WATCH - Effects of osmosis in potato cells (Twig) [Not available on sample course]
- Extension question - a potato cylinder was placed into a solution for 24 hours and then removed and weighed. The mass did not change. Why did the mass stay the same?
- Complete Chapter 1 Summary Questions 1-5 on page 35 in your Activate 3 coursebook.
Check your answers
CHECK - Topic question answers - Module One (Kerboodle) [Not available on sample course]
CHECK - Student Book Answers – B3 Chapter 1 (Kerboodle) [Not available on sample course]