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Cell Structure Revision Notes

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Introduction

´╗┐Cell Structure Revision Notes Structure of a typical plant cell: * Contains cytoplasm and a nucleus. Rough and smooth ER found in the cytoplasm, along with Golgi. Mitochondria produce ATP * Nucleus is surrounded by a double membrane * Organelles in the cytoplasm are surrounded by one membrane Plant cell wall: * Cell wall gives strength and support- made up of insoluble cellulose * In cellulose, the monomer units are beta glucose and held together by 1,4 bonds, where one monomer has to be turned around so the bonding can take place * This linking of beta glucose molecules means that the hydroxyl groups stick out on both sides of the molecule * This means hydrogen bonds can form between the partially positively charged hydrogen atoms of the hydroxyl groups and the negatively charged oxygen atoms in other areas of the glucose molecules * This is known as cross linking and it holds neighbouring chains firmly together * In the cell wall, cellulose molecules form microfibrils, which are laid down in layers held together by a matrix. * Contains a middle lamella which is made of pectin which helps hold adjacent cells together * Plasmodesmata are involved in cell to cell transport. Both cell walls are absent, lined with membrane and have a cytoplasm filled channel with ER extending through * Pits are also involved in cell to cell transport. ...read more.

Middle

properties of cellulose and plant fibres: * Properties of cellulose, as microfibrils, produce rope that does not stretch, but is flexible and has great strength * Lignified plant fibres are very resistant to chemical and enzyme breakdown. This property makes plant fibres, such as wood, a good choice as building material Plant fibres, starch and sustainability * Fossil fuels are not sustainable as they are non-renewable resources * Both starch and plant fibres are renewable resources as they come from plants and more can be produced the next growing season * Starch can be processed into bioplastic to replace oil based plastics whilst plant fibres can be used for rope * Both can be burned to release heat energy Transpiration: * Loss of water vapour from the surface of the plant, mainly from the leaves * Once in the leaves, water moves out by osmosis from the xylem into the veins of the leaves into the mesophyll cells * Water evaporates from the cellulose walls of the spongy mesophyll cells into the air spaces * The water vapour moves through open stomata into the external air along a diffusion gradient The uptake of water by plants: * In the vacuolar pathway, water moves by osmosis across the vacuoles of the cells of the root system. The water moves down a concentration gradient from the soil solution to the xylem * In the symplast pathway, water moves down the concentration gradient from the root hair cells to the xylem. ...read more.

Conclusion

Contemporary drug testing protocols: * Placebo: name given to tablet/treatment that appears identical in all ways to the drug but is chemically inactive * Double blind trial: patients are randomly divided into 2 groups. One group receives the drug, and the other receives the placebo. Neither the patients nor the people recording the changes in the patients know who has received the drug or who has received the placebo. This reduces the chance of bias * Three phase testing: * Phase 1: a few healthy people used with a range of doses to check drug is safe and that it behaves in the manner predicted by animal tests * Phase 2: 100-300 patients with the condition to check it is patient safe and to check that it works on the condition as anticipated * Phase 3: 1000-3000 patients used, and normally involves a double blind trial. Used to collect as much data as possible including effectiveness compared to placebo or standard treatment and frequency of any side effects Modern day testing vs Withering: * Similarities: both isolated a possible drug/treatment and both initially tested on a small number of patients and then a larger group of patients * Differences: only modern tests test on animals before phase 1 and only modern tests on healthy people first. Only modern day trials have double blind trials. ...read more.

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