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Revision 7. Cells a) Below is a drawing of a cell membrane. Name the structures labeled A and B. b) Describe the function of the i) A ii) B c) Cell membranes.

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Presentation on theme: "Revision 7. Cells a) Below is a drawing of a cell membrane. Name the structures labeled A and B. b) Describe the function of the i) A ii) B c) Cell membranes."— Presentation transcript:

1 Revision 7

2 Cells a) Below is a drawing of a cell membrane. Name the structures labeled A and B. b) Describe the function of the i) A ii) B c) Cell membranes are differentially or semi-permeable. Define differentially or semi-permeable. d) Explain the difference between passive and active transport. Give examples of each. A B

3 Cells a) Below is a drawing of a cell membrane. Name the structures labeled A and B. b) Describe the function of the i) A – waterproof, flexible layer, that lets in small particles ii) B – provides channels for larger particles (facilitated diffusions), acts as pumps (active transport), acts as receptor sites c) Cell membranes are differentially or semi-permeable. Define differentially or semi-permeable. Allows some substances through, but not others. d) Explain the difference between passive and active transport. Give examples of each. Passive – no energy required, eg osmosis, diffusion, substances move along a concentration gradient - from areas of high concentration, to areas of low concentration. Active – energy required, eg active transport, ion pumps, endocytosis, exocytosis, substances can move against a concentration gradient - from areas of low concentration, to areas of high concentration. A B A = phospholipid B = protein

4 Cells 2 after 30 minutes in salt water after 30 minutes in distilled water Plant cell Animal cell Sketch the appearance of each of the following cells & explain the changes that occur:

5 Cells 2 after 30 minutes in salt water after 30 minutes in distilled water Plant cell Animal cell Sketch the appearance of each of the following cells & explain the changes that occur: Plasmolysis Water moves out by osmosis Vacuole shrinks, cell membrane pulls away from cell wall Water moves out by osmosis Cell membrane wrinkles as cytoplasm shrinks Turgor pressure Water moves in by osmosis Vacuole swells, cell membrane pushes up against cell wall. Cell may bulge, but resists bursting because of cell wall Water moves in by osmosis Cytoplasm swells, cell membrane bulges, and then may burst because of increased pressure

6 Extended answer 2005 36d In what ways are urban and agricultural ecosystems similar in their inputs, outputs, amount of recycling of matter and stability? In what ways do they differ? What problems might arise if human population growth is concentrated in urban ecosystems?

7 Extended answer 2005 36d In what ways are urban and agricultural ecosystems similar in their inputs, outputs, amount of recycling of matter and stability? In what ways do they differ? What problems might arise if human population growth is concentrated in urban ecosystems? 2 marks per row in the table to a maximum of 8 marks Similarities/differences Similarites Urban Agricultural Inputs –high matter fossil fuels fossil fuels, fertilizers, sunlight Outputs – high pollution, rubbish, heat produce, pollution Recycling – low Stability – low waste accumulation environmental degradation Differences Inputs Increasing Can be reduced - sustainable practice Outputs Increasing Can be reduced - sustainable practice PROBLEMS OF CONTINUED URBANISATION Increased destruction of natural ecosystems (reduced habitat/ biodiversity) Increased pollution – affects natural ecosystems (water/atmospheric pollution) Depletion of resources – minerals, fossil fuels, lower water table Climate change Urban ecosystems depend on agricultural ecosystems 1 mark for each line, maximum 4 marks Maximum 10 marks total

8 Extended answer 2002 37(b) Ichthyosaurs are extinct marine animals that appear remarkably similar to a modem marine animal, the dolphin. However, ichthyosaurs were reptiles, related to snakes and lizards while dolphins are mammals related to dogs, cats and humans. Explain how two animals from such very different groups could have evolved to look so similar.

9 Extended answer 2002 37(b) Ichthyosaurs are extinct marine animals that appear remarkably similar to a modem marine animal, the dolphin. However, ichthyosaurs were reptiles, related to snakes and lizards while dolphins are mammals related to dogs, cats and humans. Explain how two animals from such very different groups could have evolved to look so similar. Similarities arise by convergent evolution where different / unrelated taxa evolve to look similar in response to similar selection pressures. Example other than dolphins & ichthyosaurs Natural selection works in populations showing variation causing differential survival rates and differential reproduction rates. Results in changes to gene frequencies Sources of variation: Crossing over Mutation Independent assortment Random recombination / fertilization Selection pressure caused by aquatic environment / predatory nature results in streamlining fins rapid locomotion large mouth for prey capture


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