STARTER

Discussion:How can a shark

find injured prey so quickly?

DIFFUSION

LESSON OBJECTIVES

Define and describe DIFFUSION Explain what affects the RATE of

DIFFUSION To link diffusion with EXAMPLES in

BIOLOGY Respiration Digestion Leaf Cells

Maybe you can smell

your dinner cooking

when you get home... This is due

to diffusion.

Diffusion is the movement of particles from an area of HIGH concentration to an area of LOW concentration (down a concentration gradient) until there is an EQUAL spread of particles

Diffusion only occurs in fluids. Why?

Extension:Give 2 different examples of diffusion

MOVING MOLECULESIn which states are molecules able to diffuse?

Molecules in liquids and gases are constantly moving and bumping into each other. This means that they tend to spread out.

gas (e.g. steam)liquid (e.g. water)solid (e.g. ice)

The net movement of particles from an area of high concentration to an area of low concentration Due to the random movement of particles A passive process which means that no energy from respiration is needed

DIFFUSION RECAP

HIGH concentration

LOW concentration

A difference in concentration between 2 areas is called a

CONCENTRATION GRADIENT.

What effect might the gradient have on speed of diffusion?

Fast

Steep concentration gradient

Shallow concentration gradient

Rate of Diffusion

Draw both sets of diagrams, write how the rate of diffusion changes when the concentration gradient changes

Slow

FACTORS AFFECTING DIFFUSION Concentration gradient Temperature Distance particles must travel Surface area

Faster Diffusion When... Large concentration gradient Higher Temperature Short distance Larger surface area

BIOLOGICAL DIFFUSIONDissolved substances have to pass through the

partially permeable cell membrane to get into or out of a cell.

Diffusion is one of the processes that allows this to happen..

What substances are we talking

about?

WHY IS DIFFUSION IMPORTANT?

All living cells rely on diffusion to live.

They use it for:

Getting raw materials for

respiration (dissolved

substances and gases)

Removing waste products (eg. from respiration)

Plants use of photosynthesis (raw materials

in, waste products out)

Examples…

1. DIFFUSION AND BREATHINGOxygen in inhaled air diffuses through the lungs and into the bloodstream. The oxygen is then transported throughout the body.

Carbon dioxide is the waste gas produced by respiration. Carbon dioxide diffuses from body tissues into the bloodstream and is exhaled via the lungs.Where does gas exchange take place in the lungs?

CROSS-SECTION THROUGH AN ALVEOLUS

deoxygenated blood (from body

tissues)

oxygenated blood (to

body tissues)

Alveoli are the tiny air sacs at the end of the bronchioles, in which gas exchange occurs.

alveoluscapillary

red blood cell

CO2

O2

HOW ARE ALVEOLI ADAPTED?Alveoli have several adaptations that help to make gas exchange very efficient:They are very thin – only one cell thick.They are covered by a network of fine

capillaries, enabling gases to pass almost directly between the lungs and bloodstream.

They are moist, encouraging gas molecules to easily dissolve.

They have a large combined surface area, allowing large amounts of gases to be exchanged with each breath.

RESPIRATION & DIFFUSION

2. DIFFUSION AND DIGESTIONDigestion breaks down large food molecules into smaller molecules such as glucose, amino acids and fatty acids that can be easily absorbed.

Small food molecules are usually absorbed in the small intestine, diffusing across the intestine wall and into the bloodstream.

HOW IS THE SMALL INTESTINE ADAPTED?

blood vessels

capillary networkVilli

small intestine

DIFFUSION IN DIGESTIONThe small intestine has these things called villi.

The best way of explaining them, is that they look like millions of little sausages.

The villi INCREASE THE OVERALL SURFACE AREA of the small intestine, thus increasing the volume of substances which can be absorbed by diffusion.

The villi have a very GOOD BLOOD SUPPLY as each contains a capillary, which leads to the main blood supply, so when substances diffuse, they can go straight to the bloodstream.

Attached to each villi are thousands and thousands of MICROVILLI.These are exactly the same as the villi, except a lot smaller.

Again, the purpose of these is to further increase the surface area. Like before, as well, this increasing the volume of substances which can be absorbed.

So, the main points to remember are: The villi and microvilli result in a LARGE SURFACE AREA, for maximum absorption.

The villi also give a GOOD BLOOD SUPPLY to absorb the nutrients.

PHOTOSYNTHESIS & DIFFUSION

Carbon dioxide diffuses in through the stomata

Oxygen and water diffuse out of the stomata

carbon dioxide + water oxygen + glucose

During photosynthesis, the level of CO2 is low inside the leaf

This creates a big concentration gradient so CO2 diffuses into the cell

PLENARY