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 ID: 1000332
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1. Surfaces for Exchange
2. ExchangeIn groupsdiscuss what is meant by the word “exchange”Apply the word exchange to a biological conceptExchange takes place over surfacesWrite down features of a good exchange surfaceWhich processes are used in the exchange of substancesWhere does exchange occur in organisms and what is exchanged?
3. Learning OutcomesExplain, 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 ExchangeAll living things take gases from their environment and return gases to it.Organisms which respire aerobically take in oxygen and give out carbon dioxidePhotosynthesizing 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 exchangeOrganisms – oxygen in, carbon dioxide outExchange of gases takes place via diffusionThe part where this happens is the gas exchangeSurface.
7. Size, Surface area and gas exchangeThe amount of oxygen needed by an organism is determined by:The amount of living cellsThe rate they need to respireRequirement 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. AmoebaAmoeba has a very high surface area to volume ratioSmall organisms get all the oxygen they need by diffusion through their body surface.
11. Large Organisms e.g. ElephantThe surface area to volume ratio is much smallerThe 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 QuestionVery 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 - suggestionsWhy do we need gas exchange?Oxygen is needed for respirationBody 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 surfacesThey are designed so that…Large surface areaThin as possibleCreate a high gas gradient for greater diffusionOften 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?More active so require more food and oxygen for respiration.Warm blooded – need more respiration to keep warm.Large organism, small surface area: volume – surface area is not big enough to supply all the oxygen.
18. Gas Exchange Problems For Land organismsProblem cells need to be exposed to air in order for the oxygen to diffuse into the organism.Terrestrial organisms bodies are made of a high percentage of water.When living cells are exposed to the air, water molecules evaporate and the cell dehydrates
19. This problem is combatted in different waysYou need to know:How the flatworm is adapted to the problemHow the earthworm is adapted to the problemThe insects gas exchange systemThe humans gas exchange system
20. Flatworm
21. FlatwormSimple 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. EarthwormEarthworms 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 AdaptationCells on surface for gas exchangeLive in moist conditions to prevent water losse.g. Live in damp soil to reduce moistureSlimy covering reducing evaporation
24. HumansGas exchange surfaces inside the body – this reduces water lossAir is brought inside the body to make contact with the gas exchange surface Water proof coating on the outside of the bodyBreathing system to allow high rate of exchange of gas
25. InsectTubes called trachea penetrate inside the body carrying air to every tissue.
26. InsectMany 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 QuestionDescribe 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 questionIn a different colour underline where you think they will get a mark
29. MarkschemeOxygen into the organismCarbon dioxide out of the organismPlants opposite directionDiffusionThe more living cells the more oxygen is neededIncreased surface area increases rate of diffusion
30. MarkschemeG. Amoeba have high surface area to volume ratioH. Amoeba obtain oxygen by diffusionI. Amoeba is a single cell organismJ. Humans have lungsK. Gas exchange surface is inside the bodyL. Larger body/volumeM. Needs more oxygen for respiration
31. MarkschemeO. Insects have tracheaP. Tubes allow gas exchange inside the bodyR. Comparison between organisms (up to 3 marks)