Diffusion

States of Matter

You will remember from science that matter exists in different forms depending on the amount of energy the atoms have

We only need to know about liquids, solids and gases

When molecules are in a liquid or in a gas they move and get mixed together

This is important in living organisms Let’s look at the States of matter:

This is what they look like in a container:

Kinetic energy is the energy of

movement

Remember that in the solid the molecules only vibrate – they have low kinetic energy

In a liquid the molecules have more kinetic energy and kind of roll over each other

In a gas the molecules have a lot of kinetic energy and move randomly in any direction

If you have internet click on this animation which shows the different states. You will need to look at water and increase the pressure on the one axis

If we opened a bottle of a type of gas what would happen? The blue is the air particles:

Using a diffusion tube

Litmus paper tells us what the pH of something is; that is if it is acidic or alkali

For the experiment with ammonia we will use red litmus paper

It should change to blue when ammonia is present (because it is alkali)

This is the experiment we will set up

The results:

Cotton wool soaked in ammonia

Litmus paper

Direction of diffusion of ammonia gas

Potassium permanganate molecules mix with the water moleculesThe purple colour slowly spreads throughout the water: this is diffusion

Diffusion in Living Organisms

Living organisms rely on diffusion to move substances in and out of cells and organs

This only works when there is a diffusion gradient: when you look at the examples think about how the diffusion gradient is kept as steep as possible

Diffusion in the lungs

we need oxygen in our bodies for respiration

This oxygen is used in cells to make energy by respiration

Carbon dioxide is a product of respiration that we must get rid of!

We take oxygen in and expel carbon dioxide in the lungs

The lungs are a system of branching tubes that end in many small structures called alveoliThese are surrounded by blood vessels

Look at how gases move in/out of alveoliHow do you think we keep the oxygen content in the alveoli high even though oxygen is moving into the blood constantly?

Gaseous Exchange in a Leaf

Leaves need carbon dioxide for photosynthesis

The carbon dioxide has to go into the palisade cells at the top of the leaf

Oxygen is a product of photosynthesis; this must move out of the palisade cells

Let’s look at a leaf in section first

Can you see the Palisade cells? The green dots are chloroplasts where photosynthesis takes place. They are also found in spongy mesophyll cellsNote the stomata which are openings through which gases can pass

This picture shows how oxygen and carbon dioxide move in and out of the leafTo get in and out of cells they must diffuse across the membraneThe cells have large air spaces to allow gases to move around

Diffusion in the small intestine

When you eat your food is digested, or broken down, into small molecules

These can now diffuse out of the gut and into the blood – this is called absorption

This happens in a place called the ileum in the small intestine

To increase the surface area for absorption the ileum has tiny projections called villi:

This is what villi look likeLook at the scale bar to get an idea of how small they are - there are 1000µm in 1mm

This is what a villus looks like insideNote the thin layer of cells around it – this makes the distance for diffusion shorterAlso see there is a capillary with blood flowing through to take up digested food and move it away

The lacteal also absorbs some digested food – we will learn more about all of tis later this year