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AS and A Level: Molecules & Cells

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  • Marked by Teachers essays 108
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  1. Marked by a teacher

    Analysing the vitamin C content in different fruit juices

    5 star(s)

    We get what we need, instead, from food. Besides, man is one of the few mammals unable to manufacture ascorbic acid in his liver. Excess vitamin C is eliminated through urine once the body has used up what it needs. Therefore, it is important to consume adequate quantities of fruits and vegetables containing vitamin C on a daily basis. Vitamin C plays important role in the body in many aspects, including : boosting the immune system, healing cuts and wounds, promoting healthy teeth and gums, protecting body against lifestyle diseases, improving eye?s health and enhancing the absorption of fundamental iron and zinc.

    • Word count: 3700
  2. Marked by a teacher

    Investigating respiration of maggots

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    After several minutes I will close both the three-way tap and the screw-clip and make a note of the position of the manometer fluid. I will then begin the stopwatch and record how far the fluid has travelled after 1-minute time intervals. 9. Once I have carried out the experiment I will open the screw-clip and the three-way tap to allow the fluid to return back to normal. I will then repeat the experiment twice to allow for any anomalous results.

    • Word count: 5209
  3. Marked by a teacher

    Find out if enzymes work faster or slower at different temperatures.

    5 star(s)

    In the body enzymes are used in many ways. Enzymes are produced in the small intestine, pancreas, mouth, stomach and in white blood cells. In the stomach, small intestine, and mouth, the enzymes produced are to aid the digestion (breakdown) of food. The neutrase that we are using is also used in the digestive system being extracted from a bacterium (Baccilus Subtilis). There are two types of white blood cell, one type (the phagocyte) has a 3 - lobed nucleus and will engulf any bacteria in a vacuole and then release enzymes to effectively digest them inside the vacuole.

    • Word count: 5814
  4. Marked by a teacher

    Investigating the effect of enzyme concentration on the activity of cellulase.

    5 star(s)

    is plotted against enzyme concentration. Cellulose is found in wall paper paste and makes it viscous. The enzyme cellulase breaks down cellulose reducing the viscosity of the wall paper paste. This reduced viscosity can be measured by timing how long the paste solution takes to drain through a syringe barrel when different concentrations of the enzyme are added. From carrying out this experiment the result that would be expected would be as the concentration of enzyme increases the time taken for the wall paper paste to drain will decrease i.e.

    • Word count: 4527
  5. Marked by a teacher

    The Effect Of Temperature on the Respiration Of Yeast.

    5 star(s)

    s****l reproduction of yeast only occurs in the yeast colonies occasionally. The genetic mixing that occurs in meiosis and the random fusion of haploid cells, results in genetic variation in the offspring. Respiration: - Yeast respires aerobically and anerobically. In this experiment the yeast is bubbled to make it oxygenated therefore the experiment will be aerobic for about 20 minutes before it will switch to anerobic respiration. Aerobic respiration: - C16H12O6 + 6O2 6CO2 + 6H2O Glucose + Oxygen Carbon + Water Dioxide Anerobic respiration: - C16H12O6 Alcohol + 6CO2 Glucose Carbon Dioxide Enzymes and TTC: - Enzymes have a big role in the anaerobic respiration of yeast.

    • Word count: 6179
  6. Marked by a teacher

    Beetroot Experiment. The purpose of this experiment is to determine the effect of temperature on the permeability of cell membranes

    4 star(s)

    Figure 2 shows the complex structure that is the plasma membrane. The image shows the arrangement of membrane proteins present within the phospholipid bilayer2 The plasma membrane is a complex and important structure whose major function is to determine which substances enter and leave the cell. Each protein channel will only let a specific molecule through, this is essential for controlling what goes in and out of the cell. Cytoplasm How would temperature affect the membrane? The purpose of the cell plasma membrane is to selectively control the movement of substances in and out of the cell.

    • Word count: 3524
  7. Marked by a teacher

    effect of concentration of copper sulphate on the action of amylase to break down starch.

    4 star(s)

    Copper sulphate Copper sulphate has the formula CuSO4 and is commonly used to control fungus diseases [17], both in agriculture and medicine. According to the Turkish Journal of Zoology (source 16), copper sulphate can inhibit the activity of amylase by 5%. Enzymes- Alpha Amylase Enzymes are biological catalyst, and a catalyst is substance which speeds ups a chemical reaction but remains unchanged itself at the end. [71] Enzymes are biological catalyst because they are globular protein molecules that are made by living cells to speed up reactions inside a living organism.

    • Word count: 8508
  8. Marked by a teacher

    The effects of Hydrogen Peroxide concentration on the activity of Potato Catalase

    4 star(s)

    Enzymes are long chains of amino acids, folded to produce a three-dimensional shape [2]. These folded chains of amino acids are specific to a certain enzyme. The structure of an enzyme can be described by four main structures. Primary structure A large number of Amino Acids join together (via peptide bonds) to form a polypeptide chain. From the 20 different kinds of amino acids available to link together, the primary structure is the number, type and sequence of these amino acids within the polypeptide chain sequence [1].

    • Word count: 4036
  9. Marked by a teacher

    Factors effecting enzyme activity

    4 star(s)

    Hydrogen peroxide is a by-product of fatty acid oxidation. White blood cells produce hydrogen peroxide to kill bacteria. Enzymes are used to speed up biochemical reactions by lowering the energy level necessary to initiate the reactions. Catalase's function is to catalyse the decomposition of hydrogen peroxide to water and oxygen. It is necessary to remove hydrogen peroxide, which is toxic, and a product of metabolism. The equation for this is, H202 --> H20 + O2 Balanced: 2H2O2 --> 2H2O + O2 But why do chemical reactions occur and why do rates of reactions differ? There is a simple answer to this, the collision theory.

    • Word count: 5094
  10. Marked by a teacher

    How does the concentration of enzymes affect the breakdown of starch by a-amylase in biological washing powders?

    4 star(s)

    This is the main reason why enzymes are used in washing powders. The enzyme I will be focusing on is ?-amylase, which is an enzyme present in biological washing powders that breaks down starch deposits in food stains into maltose, which is then further broken down into glucose sub-units. I however, am only looking at the initial breakdown of the starch by ?-amylase into maltose. Aim: The aim of my investigation is to investigate the effect that changing enzyme concentration has on the breakdown of starch (i.e.

    • Word count: 12799
  11. Marked by a teacher

    Investigate the effect of copper sulphate on pepsin activity.

    4 star(s)

    An enzyme works in a similar way, using what is called a 'lock and key' mechanism. This process is illustrated below. This 'lock and key' mechanism means that a particular enzyme will only catalyse a particular reaction, as different substrate molecules have different shapes and cannot all fit into one type of enzyme. This is why different enzymes are needed to catalyse different reactions. This is called enzyme specificity. Pepsin, like all other enzymes, is affected by temperature and pH. The general trend with enzymes and temperature is that the higher the temperature, the faster the enzymes can catalyse reactions, up until a certain temperature, where the rate of reactions begins to slow down, and eventually, when the temperature gets too high, the enzymes stop working.

    • Word count: 3300
  12. Marked by a teacher

    The effect of temperature on the enzyme Catalase.

    4 star(s)

    When heating the test tubes, measuring the froth or transporting the test tubes around I need to make sure that I don't shake or tip the test tubes to much as this could effect the froth produced. Method - For this experiment I will need some Catalase enzyme which can be found in potatoes. Also I will need some hydrogen peroxide (2H2O2). I will be using a ratio of 2:1 because I found that in my preliminary investigation this was best. 2 being Catalase and 1 hydrogen peroxide. So I will need 2ml of Catalase and 1ml of hydrogen peroxide.

    • Word count: 3769
  13. Marked by a teacher

    Investigating the effect of temperature on the movement of pigment through beetroot cell membranes.

    4 star(s)

    Preliminary Experiment: EQUIPMENT- * Beetroot:5 x 2mm discs/ sample * Beakers 400cm� * Distilled water * Thermometers * 10cm� syringe * 3 sample tubes and lids * Access to colorimeter BEETROOT PREPARATION- Cylinders of beetroot obtained with a No. 6 borer and cut into 2mm discs which are washed for several hours in running water to rinse away any pigment released when the cells were cut open during preparation. METHOD- 1. Heat 200cm� of distilled water to 75?C. 2. Whilst water is heating place 10 cm� of distilled water (at room temperature)

    • Word count: 4655
  14. Marked by a teacher

    The Effect of Substrate Concentration on Enzyme Action.

    4 star(s)

    To r****d the decomposition of the peroxide into water and oxygen, organic substances, such as acetanilide, are added to the solutions, and they are kept in dark bottles at low temperature. The substrate that shall be used in this experiment is hydrogen peroxide. (2) Enzymes can be builders or breakers. Breakers are enzymes, which break down large molecules. Builders are enzymes, which build up large molecules from small ones. In a chemical reaction energy is required to break chemical bonds so that new bonds can be formed.

    • Word count: 3673
  15. Marked by a teacher

    Following the Progress of an Enzyme Controlled Reaction

    4 star(s)

    The Amylase is most efficient at an optimum rate at pH 7 in the mouth this is neutral. Amylase, any member of a class of enzymes that catalyze the hydrolysis (splitting of a compound by addition of a water molecule) of starch into smaller carbohydrate molecules such as maltose (a molecule composed of two glucose molecules). Two categories of Amylases, denoted alpha and beta, differ in the way they attack the bonds of the starch molecules. Alpha-Amylase is widespread among living organisms. In the digestive systems of humans and many other mammals, an alpha-Amylase called ptyalin is produced by the salivary glands, whereas the pancreas into the small intestine secretes pancreatic Amylase.

    • Word count: 4626
  16. Marked by a teacher

    How Does the pH of a Solution Affect the Rate of Starch Digestion By Diastase

    3 star(s)

    When I was at the preliminary stage of my experimental procedures I used a data logger that contained a pH meter that could only give me approximate values of the pH's that I was measuring. It could not tell me what the exact pH is or any decimal places. I later then used a more accurate data logger that could measure pH's accurately to 2 decimal places in my actual experiment. I also changed the time that took my samples at; I started off taking a sample every 60 seconds where I changed this measurement to 30 seconds when I did my actual experiment.

    • Word count: 3062
  17. Marked by a teacher

    Beetroot Practical Write up

    3 star(s)

    Diffusion or Facilitated diffusion (Passive transport): By diffusion the ions and molecules move spontaneously across their concentration gradient (from a region of higher to a region of lower concentration). Small, polar, hydrophilic molecules, like oxygen, and water, can pass through cell membranes by diffusion. Where as larger hydrophilic molecules, like glucose, can pass through the cell membrane by facilitated diffusion. In all cases of facilitated diffusion through channels, the channels are selective. Meaning that the structure of the protein admits only certain types of molecules through (hydrophilic pores).

    • Word count: 5905
  18. Marked by a teacher

    The effect of temperature on the permeability of beetroot membrane

    3 star(s)

    Therefore as the cell membrane becomes broken down by heat the contents of the vacuole will be released. As a result the red betalain pigments will be released and their distinctive red colouring will be visible. As I am going to be using different levels of heat shock treatment the amount of betalain released should be relative. Therefore the greater the heat the more betalain released so the redder the sample will be. This is because at greater heat intensities there will be more kinetic energy so the breakdown of the membrane will be faster and much greater.

    • Word count: 3105
  19. Marked by a teacher

    The Effect of Ethanol Concentration on the Permeability of Beetroot Cell Membranes to Betalain

    3 star(s)

    11. Repeat 10. for each concentration, in between each concentration ensure the boiling tube is cleaned and dried before and after pouring solution into it. 12. Repeat 10. and 11. two times, take average for each concentration of ethanol. My results from my preliminary experiment were as follows: Ethanol Concentration / % Transmission of Blue Light / % 1st Reading 2nd Reading Average 0 72 73 72.5 10 53 48 50.5 20 40 40 40.0 30 17 17 17.0 40 24 15 19.5 50 27 13 20.0 60 20 19 19.5 70 26 20 23.0 80 23 20 21.5 From my

    • Word count: 3988
  20. Marked by a teacher


    3 star(s)

    * My results are the first set of results * The anomalous results are in bold italics. ANALYSIS, EVIDENCE AND CONCLUSION Mean of class calculated to give more reliable data for conclusion and to use it to produce graph and standard deviation. Looking at the result table and the graph produced from the results obtained form this experiment; it shows that as temperature increases, the percentage transmission decreases. This tells us that temperature does affect the membrane, resulting in more leakage of the red pigment.

    • Word count: 3800
  21. Marked by a teacher

    effect of temperature on beetroot pigment through membrane

    3 star(s)

    There will also be the same number of disks per boiling tube, 3 disks, to increase the surface area. Origin of Beetroot: The beetroot have to be of the same sort and source in order to make it a fair test. Ideally, I would use one, organic beetroot for all of the experiments. Organic beetroot tend to be juicier and richer in colour, however they are expensive. Therefore, I will be using beetroot from the local grocers, knowing that the beetroot have been grown in the same conditions and are the same species. Clean Glassware: This is essential for when placing test tubes into the colorimeter as a stain on the test tube can read a false reading, making my results unreliable.

    • Word count: 3426
  22. Marked by a teacher

    Cell Biology and Genetics

    3 star(s)

    In other words allowing what would be very long DNA molecules to fit into the cell's nucleous tiny space. These chromosomes provide a very important function for the cell. They carry the strands of DNA and proteins for the cells functionality. DNA's function to the cell is that it carries the code for the proteins controlling which proteins are made therefore controlling the cells activity. Ribosome's are very small organelles found in the cytoplasm and on the endoplasmic reticulum. They are structured into two parts, a large and small subunit which fit together and work as one. Their job is to synthesise proteins needed for the cell to function.

    • Word count: 3398
  23. Marked by a teacher

    Enzymes - investigate how the substrate concentration (H2O2) affects the activity of catalase on hydrogen peroxide.

    3 star(s)

    This theory of how enzymes work Is known as the lock and key theory. A substrate Lock and key theory (Biology 1, 2002) molecule is a 'key', and binds to the active site of an enzyme, a 'lock'. The induced fit theory is another theory of how enzymes work. The active site of an enzyme is a cavity of a particular shape, and initially the active site is not the correct shape in which to fit the substrate. As the substrate approaches the active site changes and this results in it being a perfect fit.

    • Word count: 6008
  24. Marked by a teacher

    How does the pH affect the activity of amylase

    3 star(s)

    The buffer solution must also be kept at the same volume as the starch and amylase, but obviously the pH would be different. Apparatus 0.5% starch Solution - this is used for the experiment as it is the substrate that the enzyme will be breaking down 0.1% Amylase solution - we need the amylase, as this is the enzyme that is used in the experiment to breakdown the starch Water Bath at 37�C - this is used to keep the temperature constant throughout the experiment, at times the room temp can be different.

    • Word count: 3845
  25. Marked by a teacher

    An investigation to examine the effects of temperature on membrane stability in beetroot, by assessing the degree of pigment leakage.

    3 star(s)

    The bilayer is impermeable to ions and large polar molecules due to the hydrophobic regions within the phospholipids bilayer. However, specialised proteins within the bilayer, allow movement of these substances. It is selectively permeable and controls what enters and exits the cell. It does this by the proteins that are in it, however small lipid molecules, non-polar molecules and small water molecules can enter and exit the cell straight across the membrane through the phospholipids. This is due to the properties and size of the molecules, which enable them to do so.

    • Word count: 9415

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