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AS and A Level: Molecules & Cells

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  1. effect of different concentration of H2O2

    This because each enzyme has an active site this is a cleft in the enzyme surface where substrate molecules can bind. The substrate molecule has to be the correct shape for the enzymes active site or otherwise it will not fit. This is the lock and key hypothesis. If the substrate does not fit to the active site it tells you that it is not the specific enzyme for the active site. Fisher's lock and key hypothesis above (diagram from Biological Science)

    • Word count: 5812
  2. Plan an investigation to determine which part of a pineapple fruit " stem, flesh or leaves " has the highest concentration of bromelain.

    Bromelain There is no side effect but for the people who are allergic to bromelain might be aware. It also irritates if contact with the skin or eyes. Should not eat the fruit. Wash it immediately after contact with the enzyme. Prediction: I predict that stem has more concentration of Bromelain because stem part is tougher than the fruit so that means that they must have a lot of enzyme stored inside. The leaves containing the chlorophyll attracts the sunlight to make photosynthesis which is then transported to other part through the stem so that means that more are stored in the stem and the Bromelain is tougher and heavier so that means that more juice so more Bromelain.

    • Word count: 2602
  3. What is the effect of substrate concentration on the rate of reaction?

    explosion) Enzymes are biological catalysts. Enzymes are special protein that speeds up a reaction without being used up. There are lots of different type of Enzymes but the one I' am going to investigate is the Catalyse and it's job is to breakdown the Hydrogen Peroxide (H?O?) to form Water (H?O) and Oxygen (O?) in this experiment. Enzymes work by decreasing the Activation energy needed for a reaction to occur, so the smaller the Activation energy is the less job for the catalyse. Hydrogen Peroxide is toxic to cells so the catalyse protect the cells from getting toxic thus it breakdown the H?O?

    • Word count: 2714
  4. Enzyme Concentration Practical

    Then I added 5ml of 5% protease solution - there are plenty of enzymes to collide as the concentration is strong and it will make the experiment fast.Next I have placed in a water bath at 37�C for 2-3 minutes - 37� is the temperature at which human enzymes work best and 2-3 minutes are not enough for the enzymes to digest the whole jelly. I then pour the mixture through a filter funnel, timing how long it takes.

    • Word count: 857
  5. Investigating the water potential of potato discs in different concentrations of sucrose solution

    Plant cells continue to swell until they are prevented from swelling anymore by the cell wall. At this point the plant is turgid which basically means swollen and hard. This turgid state is very important to plants as it allows them to elongate and absorb more sunlight. When plants are placed in concentrated sugar/salt solutions they lose water by osmosis. This is because the water potential in the plant is now greater then in the solution. As a result water moves from an area of high water potential inside the plant to an area of lower water potential in the solution. As a result of this a process called plasmolysis will occur.

    • Word count: 564
  6. Factors That Encourage and Limit the Growth of Microorganisms

    Oxygen Concentration Bacteria vary in their requirements for oxygen, depending on the nature of their metabolism. Aerobes are bacteria that are capable of growing in the presence of oxygen; anaerobes are bacteria that do no require oxygen for growth. Within this, are obligate anaerobes that die in the presence of O2; facultative anaerobes such as E. coli which grow much better in the presence of O2 but can grow anaerobically; aerotolerant anaerobes that ignore the presence of O2 and grow equally well with or without; and microaerophilic bacteria that are damaged by normal atmospheric conditions, and only survive in areas of very low concentrations of O2.

    • Word count: 969
  7. Investigation Of Water Potential

    Equipment: * Borer * Potatoes * Scalpel * Ruler * Sucrose Solutions (0.1, 0.2, 0.3, 0.4, 0.5, 0.6 molar) * Distilled Water * Boiling tube * Boiling tube rack Fig.1 Method: * The equipment was set up for quick and efficient use (see fig.1) * The borer was used to extract 7 cores from the potatoes. * These 7 cores were then measured accurately and marked at 30mm in length * The cores were then cut accurately with the scalpel to 30mm in length * Then 20ml of distilled water was put into one boiling tube * Each concentration of sucrose solution was put into a separate boiling tube.

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  8. Increasing obesity in children

    Whitaker et al (1997) have tried to define the odds of children who are obese remaining obese in adults, in comparison to those children who are not obese. They found out: The risk of being obese as an adult if obese when a pre-school child is 2-3 times greater that for those who were not obese as pre-school children. For those obese as primary school children, it is 5-15 fold. For those obese as adolescents, it is > 15 fold.

    • Word count: 1378
  9. The structure and function of Mitochondria and Chloroplast

    This is a very efficient process for using food energy to make ATP. One of the benefits of "aerobic exercise" is that it improves your body's ability to make ATP rapidly using the respiration process. All living cells have mitochondria. Hair cells and outer skin cells are dead cells and no longer actively producing ATP, but all cells have the same structure. Some cells have more mitochondria than others. Your fat cells have many mitochondria because they store a lot of energy. Muscle cells have many mitochondria, which allows them to respond quickly to the need for doing work.

    • Word count: 1202
  10. Investigation to see what effect the changing the concentration of calcium ions has on the rate of coagulation of milk by Rennin.

    This can be done by adding 1cm� sodium citrate solutions to the milk. If I want to increase the increase the concentration of calcium ions then I can simply add calcium chloride solution into the milk which shall provide me with the calcium ions. In this investigation my independent variable will be the calcium ion, whose concentration I shall change. The dependant variable will the rate of coagulation, or the time it takes for the flecks of curd to appear.

    • Word count: 1001
  11. An investigation into the effect of lipase concentration on the rate of lipid digestion in milk, in the presence and absence of bile salts.

    Bile salts are derivatives of cholesterol, and consist mostly of sodium glycochlolate, and sodium taurocholate. 1 2 In an enzyme controlled reaction such as that of lipid digestion in milk, an increased enzyme concentration will lead to an increased rate of reaction. This is thanks to the fact that, when more enzyme molecules are present, there is a greater chance of the substrate (the lipid) colliding with the enzyme to form an enzyme-substrate complex. When an enzyme-substrate complex is formed, the shape of the substrate is altered slightly by interactions with the R-groups in the amino acids of the active site of the enzyme.

    • Word count: 2158
  12. Tests for carbohydrates practical

    which is colourless. When the Benedict's reagent is added to test tube 1 (glucose) and heated it produces a copper oxide precipitate, this is because glucose is a reducing sugar due to it being able to change Cu 2+ to Cu+ forming the copper oxide precipitate. The colour of copper oxide is a rusty brown/red colour (final colour). In test tube 2 when Benedict's reagent is added the colour is blue also. It does not reduce the copper sulphate as the bonds between the fructose and glucose have not been broken and therefore sucrose remains to be sucrose and therefore not a reducing sugar.

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  13. Enzyme concentration and activity

    If there is extra heat energy, it will take a shorter time, so the point will be lower. Random Size of piece of egg Cut all pieces to the same size More protein present will increase the overall time. A larger egg piece would take a longer time, so the point would be higher. Random How cooked the egg is Cook all of the egg white in one batch If the egg white is undercooked it will already be partially clear, the apparent rate of reaction will be faster.

    • Word count: 927
  14. The Strength of Plant Fibres

    When plants reach maturity the fibre cells are dead, only supporting the plant stems and roots. Fibres are one of the main components of sclerenchyma tissue, along with other cells, which produce the gritty texture in pears. Longitudinal section and cross section of a fibre cell: The lumen inside a mature, dead fibre cells is very small when viewed in cross section. Fibres are removed from the stems by retting, which has various ways. These include field retting and water retting. The fibre may also be removed practically, by just removing it using the hand. This is the cheapest and quickest method, with no produced harmful waste.

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  15. Free essay

    What is Homeostasis?

    This is called thermoregulation. When the temperature of the surrounding environment increases the internal environment must be decreased. To do this the arterioles dilate (vasodilation) so that more blood flows through the capillaries next to the skins surface. This means more heat can be released through the skin as the blood is closer to the upper dermis of the skin and escapes by radiation. The sweat glands secrete sweat which can evaporate from the skin and so takes heat away from the skin and the skin cools down as the water in sweat needs heat energy in order to evaporate.

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  16. beetroot cells

    Precautions When carrying out an experiment, safety precautions must be thought about to ensure the safety of the pupil. * Hot water can be extremely dangerous and cause serious damage to skin especially as we will be working with temperatures around 85oC. * Safety goggles should be used to protect eyes when heating water as near boiling water could scold and blind. * Hair should be tied up and lose items of clothing should be tucked away or removed in case they catch fire when heating the water. * Only hold the borers when in use because they are sharp and you could easily cut yourself.

    • Word count: 923
  17. The use of antibiotics has advantages and disadvantages. Discuss.

    The extreme effectiveness of antibiotics in destroying harmful bacteria is such a big advantage in using antibiotics, but the chance that one bacterium may have the resistance gene means resistance can be a huge problem. But in contrast it has been found that the effectiveness of antibiotics can help many in their fight against cancer, with the use of chemotherapy. Since 1940s antibiotics have saved millions of lives, they can kill bacteria by preventing its peptidoglycans from synthesising, making the cell burst.

    • Word count: 1087
  18. Liver and its role

    The Liver has got more than one function in the body. One of the most important is the production and secretion of bile, which can aid digestion of fats and then absorption may occur. When substances such as phospholipids, cholesterol, water, and bilirubin are absorbed from the intestine they are being transported to liver (via hepatic portal vein) where they are being converted into bile. Bile is transported to the gall bladder (storage) via many lobules. When the bile is needed, it will diffuse into the small intestine to digest lipids.

    • Word count: 6225
  19. A2 coursework- The effects of bile salts on digestion of fat

    * 6ml of Lipase- 2ml of lipase will be added to each of the 3 different food stuffs. Lipase acts as the enzyme will breaks down fats. * 2ml of egg- egg is a food stuff that will be tested and 2ml was what we agreed to use as it would show a pH change every 2minutes * 2ml of cream- cream is a food stuff that will be tested and 2ml was what we agreed to use as it would show a pH change every 2minutes * 2ml of milk- milk is a food stuff that will be tested and 2ml was what we agreed to use as it would show a pH change every 2minutes * 100% concentrated bile salt- bile salt will be used to emulsify the food stuff.

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  20. Cost effectiveness of mainstream bench cleaners against generic supermarket cleaners on the number of bacterial colonies killed

    C difficile is transmitted through poor surface hygiene and improper cleaning. Carried from surfaces when hands are not washed after use of the lavatory c difficile can get into foods and then into the human body. The C difficile spores cannot be destroyed by alcohol cleaners. Surfaces must be cleaned with bleach. MRSA does not pose a threat to the health of the public but has become prevalent in hospitals and in particular to vulnerable or debilitated patients. These include patients in intensive care units, burns units, surgical and orthopaedic wards because of its resistance to antibiotics (beta-lactams).

    • Word count: 6215
  21. stem cells research essay

    For a large number of years scientist have worked on particular areas involving adult stem cells and embryonic stem cells. Embryonic stem cells are pluripotent, derived from the inner mass of an early stage blastocyst (embryo). Due to their plasticity and unrestricted ability to self-renewal they are ideal for various therapies, regenerative medicine and tissue replacement after injury [4]. Adult stem cells are also known as somatic cells that can differentiate throughout the body, they have the ability to divide and produce all cell types of the major organs, and unlike embryonic stem cells they do not need a destructed embryo [4].

    • Word count: 1581
  22. the rate of reaction of the enzyme Pancreozymin

    Therefore, based on this graph, we can say that the optimum temperature for the enzyme Pancreozymin is 40�C as it has to highest rate of reaction at 49.0%. Discussion: Enzymes are biological catalysts and speed up chemical reactions by reducing the activation energy required to break the bonds in the reactants in order to form the new products. All enzymes are globular proteins, each with a specific three- dimensional tertiary structure that determines its function. Enzymes are usually specific to the substance- or substrate- they work with and so the shape of the enzyme's active site- where the substrate binds - has to be complementary to the shape of the substrate.

    • Word count: 1082
  23. The effect of Temperature on the rate of Enzyme Activity.

    Between 44 and 49�C there is a sharp increase from 9.2 to 13.9/s-1 x1000. Furthermore, between 49 and 60�C the rate decreases at an even greater rate as indicated by the steepness of the graph at these points where the rate decreased from 13.9/s-1 x1000 to 0/s-1 x1000. Conclusion: The graph shows that the highest rate at which the milk protein is solidified by the rennin is 13.9/s-1 x1000 and this occurred when the thermostatically controlled water bath was set at 49�C. Therefore, based on this graph, we can say that the optimum temperature for the enzyme rennin is 49�C.

    • Word count: 1787
  24. the rate of reaction of amylase as measured by the breakdown of starch into glucose

    Starch is easily hydrolysed into soluble glucose by amylase enzyme. Enzymes are biological catalysts and speed up chemical reactions by reducing the activation energy required to break the bonds in the reactants in order to form the new products. All enzymes are globular proteins, each with a specific three- dimensional tertiary structure that determines its function. Enzymes are usually specific to the substrate they work with and so the shape of the enzyme's active site where the substrate binds has to be complementary to the shape of the substrate.

    • Word count: 1173
  25. The effect of enzyme concentration on the rate of reaction of the enzyme catalase.

    As the concentration of enzyme-catalase- increases, the rate of reaction increases, therefore more oxygen gas is produced at a quicker rate. Discussion Enzymes are globular proteins and have a specific tertiary structure determines by the arrangements of the amino acids and the ionic and hydrogen bonds present. Due to this specific structure, enzymes can only bind to specific substrates and this binding occurs at the active site. Once an enzyme has bound to its substrate, an enzyme-substrate complex is formed, after which the enzyme is released along with the new product.

    • Word count: 1559

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