A membrane is selectively-permeable if some substances can move through it but others cannot.

All substances are made up of particles that are too small for us to see.

Diffusion is the net movement of particles of a substance down a concentration gradient.

A concentration gradient is a difference in the concentration of particles from one area to another.

Net movement is the overall movement of particles from one area to another.

Diffusion through a selectively-permeable membrane: practical

Science

Pupils will learn about absorption of small molecules from food in the digestive system.

Pupils learned about muscles and that they have roles in organ systems.

Physical activity and equipment requiring safe use

Particles of iodine can only move through holes in the membrane because they are ...

Particles of starch are too {{}} to move though holes in the membrane.

Particles of iodine move through the membrane into the tubing due to diffusion down a {{}} gradient.

Because particles of iodine can move through the membrane but particles of starch cannot, the membrane is described as {{}}-permeable.

Alex: “It will be yellow or pale brown.”

Andeep: “It will still be colourless.”

The diagram shows the experiment at the start. Who correctly predicts what the liquid **inside** the tubing will look like after 10 minutes?

iodine diffused into the tubing from the edges to the middle

The diagram shows the experiment after 10 minutes. Match each observation to the correct explanation for it.

What is the name of the structure labelled A in the diagram of an animal cell?

It controls what can enter and leave the cell.

What is the job of the cell membrane in an animal cell?

The cell membrane has lots of small {{}} in it.

Jacob: “The cell breathed the oxygen particles in.”

Aisha: “The particles diffused through the cell membrane.”

Lucas: “The cell sucked them in from the blood.”

Sofia: “The cell is fully permeable to all particles, including oxygen.”

Who correctly explains how the particles of oxygen got into the cell?

can move through the cell membrane in both directions.

will only move through the membrane from inside the cell to outside the cell.

will only move through the membrane from outside the cell to inside the cell. 

The {{}} movement of carbon dioxide particles will be from inside to outside.