Aims 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 rate of diffusion demonstrating safe and skilful practical techniques. To conduct an experiment to show how size affects the rate of diffusion demonstrating safe and skilful practical techniques. To make observations and measurements of length, volume and time with appropriate precision. To make observations and measurements of length, volume and time with appropriate precision.

Use your mini white boards to write down the name of the smallest and the largest living animal you can think of. Use your mini white boards to write down the name of the smallest and the largest living animal you can think of. What do these organisms all need in order to survive? What do these organisms all need in order to survive? Give the name of one waste substance that all animals must excrete? Give the name of one waste substance that all animals must excrete?

Amoeba

How would you describe it’s size and shape? How would you describe it’s size and shape? How does it exchange materials with it’s environment? Give 4 simple methods used. How does it exchange materials with it’s environment? Give 4 simple methods used.

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

Tadpole

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

Elephant seal Has a small SA : Vol Ratio.

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

Millions of Alveoli in the lungs provide a MASSIVE Surface Area for VERY efficient diffusion of gases.

Introduce Experiment here.

1 A Block 10mm 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 Ratio Side Length = 1cm Side Length = 10cm Surface area = (1 x 1)6 = 6cm 2 Volume = 1 x 1 x 1 = 1cm 3 SA / Vol Ratio = 6 : 1 6 / 1 = 6 Volume = 10 x 10 x 10 = 1000cm 3 Surface area = (10 x 10)6 = 600cm 2 SA / Vol Ratio = 600 : / 1000 = 0.6

Exchange of materials Very small organisms can exchange materials just directly through their outer body surface as they have a high surface area to volume ratio. Very small organisms can exchange materials just directly through their outer body surface as they have a high surface area to volume ratio. Larger organisms have a smaller Larger organisms have a smaller surface area : volume ratio, so they have to have special modifications of their body for efficient exchange of materials with their environment. surface area : volume ratio, so they have to have special modifications of their body for efficient exchange of materials with their environment.

Write out and Answer these questions: What does the amount of material an organism needs depend on? What does the amount of material an organism needs depend on? What determines the amount of material that can be exchanged? What determines the amount of material that 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 SA:V? How do larger organisms cope with small SA:V?

Write out and Answer these questions: What does the amount of material an organism needs depend on? What does the amount of material an organism needs depend on? The size and metabolic rate of the organism The size and metabolic rate of the organism What determines the amount of material that can be exchanged? What determines the amount of material that can be exchanged? The surface area of the exchange surface and the transport system of the organism. Small organisms are able to exchange materials directly over their surface. The surface area of the exchange surface and the transport system of the organism. Small organisms are able to exchange materials directly over their surface.

What happens to SA:V as organism gets larger? What happens to SA:V as organism gets larger? It decreases It decreases Why is this a problem? Why is this a problem? Diffusion across the surface is not sufficient to meets the requirements of the organism. Diffusion across the surface is not sufficient to meets the requirements of the organism. How do larger organisms cope with small SA:V? How do larger organisms cope with small SA:V? They have specialised exchange surfaces with large SA:V e.g. Lungs with many alveoli in the gas exchange systems of mammals. Or, animals have a flattened shape or elongated shape, so all cells are very close to the body surface e.g. flatworm or earthworm. They have specialised exchange surfaces with large SA:V e.g. Lungs with many alveoli in the gas exchange systems of mammals. Or, animals have a flattened shape or elongated shape, so all cells are very close to the body surface e.g. flatworm or earthworm.

End of first lesson. End of first lesson.

Heat exchange Animals living in hot places tend to be either smaller or have special adaptations for losing excess heat such as increased surface area. Animals living in hot places tend to be either smaller or have special adaptations for losing excess heat such as increased surface area. Animals living in cold places tend to be larger in volume with a reduced surface area ie smaller ‘sticking out’ structures to allow them to conserve more heat energy and reduce their heat loss. Animals living in cold places tend to be larger in volume with a reduced surface area ie smaller ‘sticking out’ structures to allow them to conserve more heat energy and reduce their heat loss.

Eg Penguins

Elephant seal

Elephant Mouse Smaller SA : Volume Ratio Larger SA : Volume Ratio Has tendency to overheat as conserves too much heat energy (Shows lower rate of heat loss to the environment). Has tendency to lose too much heat energy to the environment. (Shows higher rate of heat loss to the environment).

Adaptations: ElephantMouse Low level of activity Extremely active Low metabolic rate High metabolic rate Sparse fur Thick fur Large SA : Vol ratio ears with rich capillary network, are flapped to cool blood Curls up into a ball shape to reduce SA : Vol ratio and prevent heat loss. Trunk used to splash water on back to cool body down 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: 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 textbook. Do the Summary Questions 1-3 from p177 textbook.

Read pages 40 – 41 (‘Green’ Collins AS textbook) Read pages 40 – 41 (‘Green’ Collins AS textbook) What are the 3 mechanisms of heat transfer? What are the 3 mechanisms of heat transfer? Why do animals tend to lose heat faster to cold water than they do to cold air? Why do animals tend to lose heat faster to 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: Do Q 2 – 4 page 38 AS text book