AimsAims To consider how organisms vary in terms of size.To consider how organisms vary in terms of size. What are the implications of this for the What are the implications of this for the

exchange of materials.exchange of materials.

To conduct an experiment to show how size affects the To conduct an experiment to show how size affects the

rate of diffusion demonstrating safe and skilful practical rate of diffusion demonstrating safe and skilful practical

techniques.techniques.

To make observations and measurements of length, To make observations and measurements of length,

volume and time with appropriate precision.volume and time with appropriate precision.

Use your mini white boards to write down Use your mini white boards to write down the name of the smallest and the largest the name of the smallest and the largest living animal you can think of.living animal you can think of.

What do these organisms all need in order What do these organisms all need in order to survive?to survive?

Give the name of one waste substance Give the name of one waste substance that all animals must excrete?that all animals must excrete?

AmoebaAmoeba

How would you describe How would you describe it’s size and shape?it’s size and shape?

How does it exchange How does it exchange materials with it’s materials with it’s environment? Give 4 environment? Give 4 simple methods used.simple methods used.

Some multicellular organisms have evolved to Some multicellular organisms have evolved to be a particular shape eg be a particular shape eg

1. FLAT:1. FLAT:

Flatworms are small animals that live in water. They have no specialised gas exchange or circulatory systems. Explain how this organism’s shape is a good adaptation for diffusion.

Some multicellular organisms have evolved to Some multicellular organisms have evolved to be a particular shape eg be a particular shape eg

2. Long:2. Long:Earthworms are small animals that live in soil.

Explain how this organism’s is well adaptated for making exchanges with it’s environment.

TadpoleTadpole

TadpoleTadpole Initially when a tadpole is Initially when a tadpole is very smallvery small it has a it has a

large SA : Vol Ratiolarge SA : Vol Ratio. However, as a tadpole . However, as a tadpole grows in size, it’s volume and number of grows in size, it’s volume and number of cells increase. This means that it’s SA : Vol cells increase. This means that it’s SA : Vol Ratio is decreasing. The Ratio is decreasing. The tadpole develops tadpole develops EXTERNAL GILLSEXTERNAL GILLS with a large surface area with a large surface area to allow exchange of respiratory gases to to allow exchange of respiratory gases to be much more efficient.be much more efficient.

Elephant sealElephant sealHas a small SA : Vol Ratio.Has a small SA : Vol Ratio.

Large multicellular organisms have Large multicellular organisms have special internal exchange surfaces special internal exchange surfaces such as lungs.such as lungs.

Millions of Alveoli in the lungsMillions of Alveoli in the lungsprovide a MASSIVE Surface Area forprovide a MASSIVE Surface Area for

VERY efficient diffusion of gases.VERY efficient diffusion of gases.

Introduce Experiment here.Introduce Experiment here.

1 A Block10mm x 10mm x 10mm

Cut to produce 2 B Blocks

10mm x 5mm x 10mm

Cut to produce 4 C Blocks

10mm x 5mm x 5mm

Cut to produce 8 D Blocks

5mm x 5mm x 5mm

This diagram is on page 14 of your Handbook:

First cut 4 Agar Blocks dimensions: 10mm tall x 10mm wide x 10mm deep

Complete the conclusions:

The bigger the ………………………………., the shorter the……………………………………………..

The smaller the………………………………., the longer the………………………………………………

Write these conclusion statements on HB p15:

The bigger the Surface Area to Volume ratio, the shorter the time the Hydrochloric Acid took to diffuse into the agar gel and change it’s colour completely.

The smaller the Surface Area to volume ratio, the longer the time the Hydrochloric Acid took to diffuse into the agar gel and change it’s colour completely.

Surface Area : Volume Surface Area : Volume RatioRatio

Side Length = 1cm

Side Length = 10cmSurface area = (1 x 1)6 = 6cm2

Volume = 1 x 1 x 1 = 1cm3

SA / Vol Ratio = 6 : 1

6 / 1 = 6

Volume = 10 x 10 x 10 = 1000cm3

Surface area = (10 x 10)6 = 600cm2

SA / Vol Ratio = 600 : 1000

600 / 1000 = 0.6

Exchange of materialsExchange of materials Very Very small organismssmall organisms can exchange materials can exchange materials

just directly through their outer body surface as just directly through their outer body surface as they have a they have a high surface area to volume ratiohigh surface area to volume ratio..

Larger organismsLarger organisms have a have a smaller smaller

surface area : volume ratiosurface area : volume ratio, so they have to have , so they have to have special modifications of their body for efficient special modifications of their body for efficient exchange of materials with their environment.exchange of materials with their environment.

Write out and Answer these Write out and Answer these questions:questions:

What does the amount of material an organism What does the amount of material an organism needs depend on?needs depend on?

What determines the amount of material that What determines the amount of material that can be exchanged?can be exchanged?

What happens to SA:V as organism gets larger?What happens to SA:V as organism gets larger? Why is this a problem?Why is this a problem?

How do larger organisms cope with small How do larger organisms cope with small SA:V?SA:V?

Write out and Answer these Write out and Answer these questions:questions:

What does the amount of material an What does the amount of material an organism needs depend on?organism needs depend on?

The size and metabolic rate of the The size and metabolic rate of the organismorganism

What determines the amount of material What determines the amount of material that can be exchanged?that can be exchanged?

The surface area of the exchange surface The surface area of the exchange surface and the transport system of the and the transport system of the organism. Small organisms are able to organism. Small organisms are able to exchange materials directly over their exchange materials directly over their surface. surface.

What happens to SA:V as organism gets larger?What happens to SA:V as organism gets larger? It decreasesIt decreases Why is this a problem?Why is this a problem? Diffusion across the surface is not sufficient to Diffusion across the surface is not sufficient to

meets the requirements of the organism.meets the requirements of the organism. How do larger organisms cope with small How do larger organisms cope with small

SA:V?SA:V? They have specialised exchange surfaces with They have specialised exchange surfaces with

large SA:V e.g. Lungs with many alveoli in the large SA:V e.g. Lungs with many alveoli in the gas exchange systems of mammals. Or, gas exchange systems of mammals. Or, animals have a flattened shape or elongated animals have a flattened shape or elongated shape, so all cells are very close to the body shape, so all cells are very close to the body surface e.g. flatworm or earthworm.surface e.g. flatworm or earthworm.

End of first lesson.End of first lesson.

Heat exchangeHeat exchange Animals living in hot places tend to be Animals living in hot places tend to be

either either smallersmaller or or have special adaptations have special adaptations for losing excess heat such as increased for losing excess heat such as increased surface areasurface area..

Animals living in cold places tend to be Animals living in cold places tend to be larger in volumelarger in volume with a with a reduced surface reduced surface areaarea ie smaller ‘sticking out’ structures to ie smaller ‘sticking out’ structures to allow them to conserve more heat energy allow them to conserve more heat energy and reduce their heat loss.and reduce their heat loss.

Eg Penguins

Elephant sealElephant seal

ElephantElephant MouseMouse

Smaller SA : Volume Ratio Larger SA : Volume RatioSmaller SA : Volume Ratio Larger SA : Volume Ratio

Has tendency to overheat Has tendency to overheat

as conserves too much heat as conserves too much heat

energy (energy (Shows lower rate Shows lower rate

of heat loss to the of heat loss to the

environmentenvironment).).

Has tendency to lose Has tendency to lose

too much heat energy too much heat energy

to the environment.to the environment.

((Shows higher rate Shows higher rate

of heat loss to the of heat loss to the

environmentenvironment).).

Adaptations:Adaptations:ElephantElephant MouseMouse

Low level of activityLow level of activity Extremely activeExtremely active

Low metabolic rateLow metabolic rate High metabolic rateHigh metabolic rate

Sparse furSparse fur Thick furThick fur

Large SA : Vol ratio ears Large SA : Vol ratio ears with rich capillary network, with rich capillary network, are flapped to cool bloodare flapped to cool blood

Curls up into a ball shape to Curls up into a ball shape to reduce SA : Vol ratio and reduce SA : Vol ratio and prevent heat loss.prevent heat loss.

Trunk used to splash water Trunk used to splash water on back to cool body downon back to cool body down

Hibernates in Winter.Hibernates in Winter.

Assume both are relaxing as shown and environmental temperatures are the same.

They have approximately the same activity level.They have approximately the same activity level.

TASKS TO DO:TASKS TO DO:

Print out or make good notes from the ppt.Print out or make good notes from the ppt.

Read p176 to 177 of the AS textbook. Read p176 to 177 of the AS textbook.

Do the Summary Questions 1-3 from p177 Do the Summary Questions 1-3 from p177 textbook.textbook.

Read pages 40 – 41 (‘Green’ Collins AS Read pages 40 – 41 (‘Green’ Collins AS textbook) textbook)

What are the 3 mechanisms of heat What are the 3 mechanisms of heat transfer?transfer?

Why do animals tend to lose heat faster to Why do animals tend to lose heat faster to cold water than they do to cold air?cold water than they do to cold air?

Answer questions 1 and 2 from page 41.Answer questions 1 and 2 from page 41.

Recap of osmosis:Recap of osmosis:

Do Q 2 – 4 page 38 AS text bookDo Q 2 – 4 page 38 AS text book