Download An Introduction to Diffusion and Osmosis

An Introduction to Diffusion and Osmosis – Worksheet
Why do your fingers go wrinkly in the bath? How do moths find a mate in the dead of night? Why
doesn’t jam go off in the cupboard? Plants and animals are always transferring chemicals from one
place to another. In this activity you will investigate two of the ways they do this and discover the
answers to these questions.
1.
Figure 1 shows some red particles moving inside a box. They represent the particles of a gas.
Describe the way the particles of a gas move. In your answer you should use the words random,
collide and direction.
2.
Figure 2 shows the same number of particles in Fig. 1 except most particles start out on one side of
the box. Explain why after a while, Figure 2 resembles Fig. 1. In your answer you should refer to
the concentration of the particles on either side of the box
3.
You can smell food when molecules from the food enter your nose.
a) By referring to your answers in questions 1 and 2 above explain how the molecules get from the food
to your nose
b) Would the smell be stronger or weaker if you were stood down wind of the food? Explain your
answer.
c) Why are some foods like coffee or fried onions easier to smell?
4. Copy and complete the sentence:
Diffusion is the _______ movement of particles from a _____ concentration to a _____ concentration
until they are spread out ________.
5.
a)
b)
c)
Moths emit chemicals called pheromones to attract a mate.
Which process is responsible for the distribution of these chemicals through the air?
If a moth detects pheromones, how might it work out which direction they are coming from?
What would be the advantage of a moth releasing the pheromones on a night when
there was little wind?
6. The diagram shows a typical cell. The cell membrane has tiny pores in it.
Cell wall
Pore
Cytoplasm
Nucleus
Small molecules, like water, can get through the pores. However large molecules, like starch cannot.
Because some molecules can get through the membrane and some cannot, scientists say the
membrane is semi-permeable.
Figure 4 shows a semi-permeable membrane with
water molecules moving on either side of it. Notice
that sometimes water molecules pass through the
pores in the membrane. They represent a solute,
say starch, dissolved in a solvent, water. At the start
there is the same number of water particles on each
side of the membrane.
a) Which side (left or right) contains starch solution
with the highest concentration?
Explain your answer.
b) Predict what will happen after a while
c) What happens to the number of water particles
on the right hand side?
d) What happens to the number of water particles
on the left hand side
e) What happens to the concentration of the
solution on the right hand side?
f) What happens to the concentration of the
solution on the left hand side?
g) Explain why the concentrations of solution on
either side of the semi-permeable membrane
change?
h) Copy and complete the sentence:
Osmosis is the passage of ______ molecules from a ____ concentrated solution to a ______
concentrated solution through a ______________
8. The roots of a plant have root hair cells which absorb water from the
soil. The picture shows a root hair cell. The concentration of the solution
inside the cell is higher than the concentration of the solution in the soil.
a) Explain why water moves from the soil into the root hair cell.
b) Suggest why root hair cells are long and thin?
9.
When you take a bath the cells in the skin of your fingers are immersed in water.
a) Which is the stronger solution: the solution inside you skin cells or the bath water?
b) Your skin cells have a semi-permeable membrane. Does osmosis cause water to pass from the
cells in your fingers into the bath, or from the bath into the cells in your finger?
c) What will happen to the size of the skin cells in your fingers?
d) Suggest why your fingers go wrinkly in the bath.
e) Would your fingers go more or less wrinkly in the sea? Explain your answer.
10. Jam is a very strong solution of sugar. By contrast the cytoplasm in a microbe is a much weaker
solution.
a) The cell wall of a microbe is made up of a semi-permeable membrane. Would water flow from
the microbe to the jam, or from the jam to the microbe by osmosis?
b) Suggest a reason why microbes find it difficult to survive in jam.