1.4 Diffusion in cells
Summary: If someone starts cooking, you will probably smell the food before you see it. The movement of the smell is a scientific process. The same process moves substances into and out of cells. Tags: science oxford-science student-book-7 biology Created: 2026-05-19 Last Updated: 2026-05-19
After this topic, you will be able to:
Think back
- What is a specialized cell?
- Which type of plant cell takes in water from the soil?
- What equipment is used to look at cells?
Key idea Diffusion is when particles move from a place of high concentration to a place of low concentration.
Key words diffusion, particle, concentration, glucose, oxygen, carbon dioxide, vacuole
If someone starts cooking, you will probably smell the food before you see it. The movement of the smell is a scientific process. The same process moves substances into and out of cells.
What is diffusion?
Diffusion is the movement of particles from a place where they are at a high concentration to a place where they are at a low concentration. The concentration of a substance means the number of particles of that substance present in a volume, or space.
Someone burns toast. Particles that make up the smell of burnt toast move from a place of high concentration (the kitchen) to one of low concentration (the rest of the house). At first, you may only be able to smell the burnt toast in the kitchen. Later, you may be able to smell the burnt toast in the living room. Diffusion continues until the concentration of particles is the same everywhere. You can see this example in Figure 1.
Figure 1This diagram shows how you smell burnt toast in another room. Full text alternative to the content
Literacy skills Imagine you work for a company that produces and sells air fresheners. A customer is interested in buying an air freshener. They want to know how they work. Write a reply to the customer. Explain simply how air fresheners make a room smell nice. Use what you know about diffusion.
Diffusion in body cells
All the cells inside your body need glucose and oxygen for Respiration. Glucose enters the body through the food you eat. It moves by diffusion from an area of higher concentration inside the small intestine to an area of lower concentration in the blood. Oxygen enters the body when it is breathed into your lungs. It moves by diffusion from an area of higher concentration inside the lungs to an area of lower concentration in the blood. These substances are carried around your body in your blood, and then passed on to the cells that need them.
Carbon dioxide is a waste product made inside cells during respiration. This substance moves by diffusion out of the cells into the blood. It is carried around your body in your blood to your lungs, and then breathed out.
A Name a gas that moves into a body cell. Name a gas that moves out of a body cell.
Diffusion in plant cells
Plant cells need carbon dioxide and water (from the air and soil) for Photosynthesis. Carbon dioxide enters a leaf by diffusion, through tiny holes on the bottom of the leaf. Water enters the roots by diffusion. Figure 2 shows how water diffuses into the plant through the root hair cells. The water Molecules move from the soil (high water concentration) into the root hair cell (low water concentration).
Figure 2Water diffuses into the plant through the root hair cells. It then travels from the root hair cells to other cells in the plant by diffusion.
Why do plants wilt?
If plants are not watered regularly, they will wilt and eventually die. Inside the cells, water fills up the vacuole. This pushes out against the cell wall and makes the cell firm. This helps the plant stand up straight. If the plant does not have enough water, the vacuole gets smaller and the cells become soft. This causes the plant to wilt. You can see a wilted plant in Figure 3.
Figure 3If a plant does not have enough water, it will wilt. Full text alternative to the content
B Name the process that causes water to move out of the vacuole.
Stretch zone
- Copy and complete the sentences. Substances move from an area where they are at a blank concentration to an area where they are at a blank concentration. This process is called blank.
- Various substances move into and out of cells. Name one substance, used for respiration, that moves into body cells.Name one substance, used for photosynthesis, that moves into plant cells.
Stretch zone
- Explain why oxygen moves into your body cells from the blood.