Use Living pollen
Use Dead pollen
When the British botanist Robert Brown looked through a microscope at small grains of pollen in water he saw some pollen which behaved in a strange fashion. In the square you see what the pollen was doing.
That happens when the pollen is dead?
What happens when the temperature is changed?
Using the idea of molecules write an explanation of why the pollen moves in the strange manner.
Do you think any small particles will also behave in this fashion when they are in a fluid?