1. Surfaces for Exchange

2. Exchange In groups – discuss what is meant by the word “exchange” – Apply the word exchange to a biological concept – Exchange takes place over surfaces Write down features of a good exchange surface Which processes are used in the exchange of substances Where does exchange occur in organisms and what is exchanged?

3. Learning Outcomes Explain, in terms of surface area:volume ratio, why multicellular organisms need specialised exchange surfaces and single-celled organisms do not. Explain the need for transport systems in multicellular organisms in terms of size, level of activity and surface area to volume ratio.

4. What do you need to know? Adaptations for gas exchange allow an increase in body size. Small animals exchange gases across their general body surface. Comparison of amoeba, flatworm and earthworm.

5. Gas Exchange All living things take gases from their environment and return gases to it. Organisms which respire aerobically take in oxygen and give out carbon dioxide Photosynthesizing plants take in carbon dioxide and give out oxygen. Many Organisms have specialized surfaces through which this gas exchange occurs.

6. Size, Surface area and gas exchange Organisms – oxygen in, carbon dioxide out Exchange of gases takes place via diffusion The part where this happens is the gas exchange Surface.

7. Size, Surface area and gas exchange The amount of oxygen needed by an organism is determined by: The amount of living cells The rate they need to respire Requirement of oxygen is related to volume of an organism and the rate depends on the surface area. Note: make sure you understand Fick’s Law from BY1

8. Which organism has the highest volume?

9. Which has the most surface available for gas exchange?

10. Small organisms e.g. Amoeba Amoeba has a very high surface area to volume ratio Small organisms get all the oxygen they need by diffusion through their body surface.

11. Large Organisms e.g. Elephant The surface area to volume ratio is much smaller The external surface area of the body is not large enough for diffusion of oxygen through it to take place rapidly enough to supply cells with the oxygen it needs.

12. For Example These usually have ‘extra’ surfaces that are designed for gas exchange For example: the human lungs

13. Progress Question Very small organisms such as the amoeba do not have specialised gas exchange systems. Mammals are large, multicellular organisms and have a complex gas exchange system. Explain why the mammal needs such a system when an amoeba does not.

14. Progress Question - suggestions Why do we need gas exchange? – Oxygen is needed for respiration – Body needs to get rid of waste carbon dioxide. How do simple animals take in the oxygen they need? – Diffusion through the surface membranes e.g. amoeba or flatworm

15. Gas Exchange surfaces They are designed so that… – Large surface area – Thin as possible – Create a high gas gradient for greater diffusion – Often have a transport system that takes gases to and from the gas exchange site

16. Why do larger animals need specialised exchange surfaces?

17. Why do some organisms need specialised exchange surfaces? 1)More active so require more food and oxygen for respiration. 2)Warm blooded – need more respiration to keep warm. 3)Large organism, small surface area: volume – surface area is not big enough to supply all the oxygen.

18. Gas Exchange Problems For Land organisms Problem 1.cells need to be exposed to air in order for the oxygen to diffuse into the organism. 2.Terrestrial organisms bodies are made of a high percentage of water. 3.When living cells are exposed to the air, water molecules evaporate and the cell dehydrates

19. This problem is combatted in different ways You need to know: How the flatworm is adapted to the problem How the earthworm is adapted to the problem The insects gas exchange system The humans gas exchange system

20. Flatworm

21. Simple animals that lack specialized exchange surfaces have flattened, tubular, or thin shaped body plans, which are the most efficient for gas exchange. Flatworms use their outer surfaces as gas exchange surfaces. They exchange gases exclusively by diffusion through their body surface. This is only possible because all cells are localized relatively near to the exterior since gases diffuse cell by cell

22. Earthworm Earthworms have a series of thin-walled blood vessels known as capillaries. Gas exchange occurs at capillaries located throughout the body as well as those in the respiratory surface.

23. Earthworm Adaptation 1.Cells on surface for gas exchange 2.Live in moist conditions to prevent water loss 1.e.g. Live in damp soil to reduce moisture 3.Slimy covering reducing evaporation

24. Humans Gas exchange surfaces inside the body – this reduces water loss Air is brought inside the body to make contact with the gas exchange surface Water proof coating on the outside of the body Breathing system to allow high rate of exchange of gas

25. Insect Tubes called trachea penetrate inside the body carrying air to every tissue.

26. Insect Many terrestrial animals have their respiratory surfaces inside the body and connected to the outside by a series of tubes. Tracheae are these tubes that carry air directly to cells for gas exchange. Spiracles are openings at the body surface that lead to tracheae that branch into smaller tubes known as tracheoles. Body movements or contractions speed up the rate of diffusion of gases from tracheae into body cells.

27. Essay Question Describe how gas exchange occurs in different organisms. Include 3 different organisms and how gas exchange varies between them. [10]

28. Task Read your partners essay question In a different colour underline where you think they will get a mark

29. Markscheme A.Oxygen into the organism B.Carbon dioxide out of the organism C.Plants opposite direction D.Diffusion E.The more living cells the more oxygen is needed F.Increased surface area increases rate of diffusion

30. Markscheme G. Amoeba have high surface area to volume ratio H. Amoeba obtain oxygen by diffusion I. Amoeba is a single cell organism J. Humans have lungs K. Gas exchange surface is inside the body L. Larger body/volume M. Needs more oxygen for respiration

31. Markscheme O. Insects have trachea P. Tubes allow gas exchange inside the body R. Comparison between organisms (up to 3 marks)