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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

    Cellular Structure and Function

    5 star(s)

    Figure B. shows the cells from a side-on point of view revealing the different layers of the tissue. The arrow points to the stratified squamous epithelium, the flattened top layer of cells. 1. Ciliated Columnar Epithelium Ciliated columnar epithelium is mainly located in the trachea and the upper respiratory tract. The cells are rectangular in shape and aligned tightly beside one another in columns. The primary function of the tissue is to keep mucus, which could potentially cause infection, away from the lungs.

    • Word count: 1907
  2. Marked by a teacher

    Measurement of protein solutions concentrations by biuret protein assay

    5 star(s)

    To avoid these problems, the Biuret test was developed. The Biuret reagent is made of sodium hydroxide and copper sulphate. The copper atoms of Biuret solution (CuSO4 and KOH) will react with peptide bonds, producing colour change. The blue reagent turns violet in the presence of proteins, and changes to pink when combined with short-chain polypeptides. Materials: Bovine serum albumin (BSA) Biuret reagent Spectrophotometer Test tubes Pipettes Vortex Methods: 1. A Biuret reagent, consisting of 2.25 gm sodium potassium tartrate, 0.75 gm Copper sulphate x 5 H2O, 1.25 gm potassium iodide was prepared, all dissolved in order in 100 mL 0.2 M NaOH (0.8 gm/100 mL).

    • Word count: 1343
  3. Marked by a teacher

    The Biological Importance of Water

    4 star(s)

    It has formed droplets of many water molecules ?stuck? to each other through hydrogen bonding. If water did not have a dipole, then it would spread out over the leaf in a thin layer making it much more difficult for water to get through the xylem in order to assist plant transpiration. The fact that the hydrogen bonds formed are relatively weak is significant as it allows for molecular mobility meaning processes like osmosis are a lot easier. The ability to form hydrogen bonds and its dipole nature makes water a very useful substance. For example, it is an excellent solvent meaning it can easily dissolve lots of other substances.

    • Word count: 1332
  4. Marked by a teacher

    Cellular organelles Structure and Function

    4 star(s)

    The endoplasmic reticulum is a network of folded tubules and vesicles found on the outside of the nucleus. Part of the membrane of the ER is merged with the outer membrane of the Nucleus which causes the close proximity between the organelles. The ER serves many general functions, including the facilitation of protein folding and the transport of synthesized proteins in sacs called cisternae. Many of these products are made for and exported to other organelles. The two types of endoplasmic reticulum found in eukaryotic cells, rough and smooth. These varieties are separate entities and are not joined together.

    • Word count: 1361
  5. Marked by a teacher

    How can we control the infection rates of MRSA in hospitals? issue report

    4 star(s)

    These usually involve cleaning your hands very often; even if you are a visitor you must clean your hands before and after visiting. Also, hospitals usually have a lot of alcohol based gels to clean your hands with efficiently. Staffs are told to maintain high standards of hygiene and wear disposable gloves when they have contact with open wounds. Other ways hospitals prevent MRSA spreading include: keeping the hospital as clean and dry as possible, including floors, toilets and beds.

    • Word count: 1730
  6. Marked by a teacher

    Investigate the effect of pH on Trypsin

    4 star(s)

    Thus one can predict that Trypsin will favour its native, slightly alkali environment. Egg white or egg albumen is a globular, soluble protein, which trypsin will readily break down into its constituent polypeptides. As trypsin is an endopeptidase it will break the polypeptide chain into much smaller pieces. This has the effect of reducing the opacity of the egg white. It is the effect that pH has on the action of the enzyme trypsin that is being studied in this investigation.

    • Word count: 1425
  7. Marked by a teacher

    Beetroot contains red pigments called betalains, located within the cell vacuole. Normally the pigments can't pass through membranes but they leak out when the beetroot is cooked.

    4 star(s)

    Alone, this arrangement of phospholipids would form a barrier to water and to water-soluble substances. However, other molecules are scattered among the phospholipids. These include lipids (including cholesterol in the membranes of animals), proteins and polysaccharides. The proteins in membranes are of special interest to us. This is because they have a number of important functions. Proteins function as: � Carriers for water-soluble molecules (such as glucose) � Channels for ions (such as sodium and chloride ions) � Pumps, which use energy to move water-soluble molecules and ions � Receptors, which enable hormones and nerve transmitters to bind to specific cells � Recognition sites, which identify a cell as being of a particular type �

    • Word count: 1933
  8. Marked by a teacher


    4 star(s)

    Inside the nucleus there is also a nucleolus, which shows dark on an electron microscope picture, which is the site of ribosome formation. Ribosomes are the sites of protein synthesis, where RNA is translated into protein. Protein synthesis is extremely important to cells, and so large numbers of ribosomes are found throughout cells (often numbering in the hundreds or thousands). Ribosomes exist floating freely in the cytoplasm, and also bound to the endoplasmic reticulum (ER). Figure 1 Rough endoplasmic reticulum in a mammalian cell ER bound to ribosomes is called rough ER because the ribosomes appear as black dots on the ER in electron microscope photos, giving the ER a rough texture.

    • Word count: 1510
  9. Marked by a teacher

    Enzymes in agriculture.

    4 star(s)

    Similarly the added yeast also have their enzymes and ferment maltose and other sugars during the "proving" stage to produce carbon dioxide that makes the bread rise. Literally therefore the bread making process is an ancient form of fermentation by a combination of enzymes from yeast and wheat, followed by baking. The finished product is therefore a result of dough processing, enzymatic action and cooking on a complex network of starch, protein, fibre and fats. In a large bread making operation, quality of wheat flour varies.

    • Word count: 1765
  10. Marked by a teacher

    The use of pectinase in fruit juice production

    4 star(s)

    The enzymes never actually get consumed in the process; they just increase the rate of reactions. When enzymes denature the heat starts to destroy their shape and structure. The shape of the enzyme is so important to its working that any change in the shape of the molecules will make them less effective or stop them working completely. Variables In order to create a fair test, I considered the variables that affect the activity of the enzyme, pectinase. Variables that were likely to disrupt the results were controlled, and the variables being investigated were varied accurately so that their effect could be measured precisely.

    • Word count: 1775
  11. Marked by a teacher

    The effect of temperature on the hydrolysis of starch using amylase extracted from barley.

    4 star(s)

    A disaccharide is defined as any class of carbohydrates; maltose, that yield two monosaccharides upon hydrolysis. The disaccharide sugars; maltose, lactose, and sucrose, have the empirical formula C12H22O11. When treated with enzymes, the disaccharides combine with one molecule of water and split into two molecules of monosaccharide hexose sugars, e.g. maltose splits into two molecules of glucose when treated. In order for amylase to continue working at its best, the body needs to keep within several degrees of 37 C (an optimum temperature for most enzymes), as enzymes must work in mild conditions of a cell in the body.

    • Word count: 1961
  12. Marked by a teacher

    To determine the optimum pH for two different proteolytic enzymes.

    4 star(s)

    Buffer solution is a solution which resists the change in its pH value by adding acid, base or upon dilution, so as to maintain pH values within narrow limits by absorbing or releasing hydrogen ions. It is classified as acidic buffer and alkaline buffer. Acidic buffer is a large amount of weak acid and its salt, while alkaline buffer is a large amount of weak base and its salt. pH is the negative logarithm of the H+ ion concentration. It is a measure of the acidity or basic character of a solution.

    • Word count: 1308
  13. Marked by a teacher

    The Industrial Application of Enzymes.

    4 star(s)

    The starch industry has been using enzymes too for many years in the production of 'artificial' sweeteners. Although sucrose is readily available from the harvesting of cane or beet sugar, glucose and maltose need extracting from starch by enzymic or chemical extraction. Starch is a polymer where the individual units in the polymer are glucose molecules. Enzymes that degrade starch are called amylases. During both processes, chemical (typically acid-hydrolysis) and enzymic, glycosidic bonds between these ?-glucose molecules are hydrolysed leaving only single sub-units of glucose.

    • Word count: 1711
  14. Marked by a teacher

    The Effect of Enzyme Concentration On Enzyme Activity

    4 star(s)

    Below this, an increase in temperature provides more kinetic energy to the molecules involved. The numbers of collisions between enzyme and substrate will increase so the rate will too. Above the optimum temperature, the enzymes are denatured. Bonds holding the structure together will be broken and the active site loses its shape and will no longer work. pH - as with temperature, enzymes have an optimum pH. If the pH changes much from the optimum, the chemical nature of the amino acids can change. This may result in a change in the bonds and so the tertiary structure may break down.

    • Word count: 1217
  15. Marked by a teacher

    Beetroot experiment. Aim: To investigate how the temperature affects the permeability of beetroot cells and membrane structures.

    3 star(s)

    As well as that you must tie long hair back t-shirts must be tucked with ties, as they could get caught somewhere or they might hit the liquid causing it to spill or any other accidents. Also you must wear goggles in case liquid hits your eyes. At the end of the experiment it is essential that you wash your hands. All clothing and bags should be left under the tables as this could cause people to trip and even fall on the chemicals used in this experiment causing pain to the person.

    • Word count: 1966
  16. Marked by a teacher

    Vitamin C. Core Practical. Throughout this investigation we will aim to find whether the amount of Vitamin C in various fruit juices sold at supermarkets are as high as they claim to be on the packaging.

    3 star(s)

    Vitamin C is also required for a number of metabolic reactions that without we cannot survive. Ethics behind the experiment relate to the Fair Trading Act and the treatment of consumers by the businesses that supply them, and without honesty by these companies of the content of their products, it could in extreme circumstances lead to health issues in the people using their goods. Fruits are a particularly good source of vitamin C and is why they are essential to our diet, but juices are not as good a source of vitamin C as fresh fruits due to the processes they undergo before being sold and to solely have your intake from these is not satisfactory,

    • Word count: 1147
  17. Marked by a teacher

    Beetroot experiment

    3 star(s)

    The most common molecule in the model is the phospholipids, which has a polar (hydrophilic) head and two non-polar (hydrophobic) tails. These phospholipids are aligned tail to tail so the non-polar areas form a hydrophobic region between the hydrophilic heads on the inner and outer surfaces of the membrane. This layering is termed a bilayer since an electron microscopic technique known as freeze-fracturing is able to split the bilayer. Phospholipids and glycolipids are important structural components of cell membranes. Phospholipids are modified so that a phosphate group (PO4-) replaces one of the three fatty acids normally found on a lipid.

    • Word count: 1697
  18. Marked by a teacher

    Beetroot membrane

    3 star(s)

    Variables: Independent variable - the temperature of the water in the water bath. Dependent variable - colour change in the water. The increase or decrease of water temperature would have an effect on colour change in the water. Variables which were kept constant were the diameter of the beetroot piece. Risk assessment: * Taking care when using the cork borer and knife when dividing the beetroot sections. * Boiling tubes should be handled with care, especially in the water baths. Apparatus: * One beetroot * One size 4 cork borer * White tile * Knife * Ruler * Water Baths at 0 oC, 30 oC, 40 oC, 50 oC, 60 oC, 70 oC

    • Word count: 1070
  19. Marked by a teacher

    Liver and Hydrogen Peroxide experiment

    3 star(s)

    Here are 2 graphs to show the increase of rate of reaction as enzyme and substrate concentration increase. For the purpose of this experiment the enzyme concentration will be kept constant and the variable will be the substrate concentration. Apparatus: 1dm3 10% Hydrogen peroxide - This is my substrate which I will make 6 different concentrations from. Liver (Catalase) - This is my enzyme that will be used to break down the H2O2 5x Test tubes with bungs and delivery tubes - Will be where the liver and hydrogen peroxide will react. Gas syringe - Where the gas will be collected to measure the rate of reaction.

    • Word count: 1625
  20. Marked by a teacher

    Enzyme concentration and enzyme activity. Trypsin

    3 star(s)

    Enzyme concentration: As the enzyme concentration increases the rate of the reaction increases linearly, because there are more active sites and so the reaction can proceed at a faster rate. Eventually, increasing the enzyme concentration beyond a certain point has no effect because the substrate concentration becomes the limiting factor. Hypothesis: As the enzyme-protease's concentration increases, the time taken for the breakdown of protein will decrease, meaning the rate will increase. The site of the reaction occurs in an area on the surface of the enzyme protease called the active site.

    • Word count: 1079
  21. Marked by a teacher

    biology differences in animal and plant cells

    3 star(s)

    (Toole, G & S 1984) the nucleus controls every organelle with the Cytoplasm. Within the nucleus is the Nucleolus, It is a small structure within the nucleus that forms ribosomes which then pass into the cytoplasm to produce protein (Moth.E 2003) The cell membranes is a fine membrane made of protein and lipids, it has two functions to keep the cytoplasm and the nucleus in. Plant and animal cells contain mitochondria, they are distinct organelles with two membranes, usually they are rod shaped, however they can be round, the outer membrane limit's the organelle, the inner membrane in thrown into folds or shelves that project inward, the organelles contain enzymes which convert food material into ATP (Adenosine Triphosphate)

    • Word count: 1185
  22. Marked by a teacher

    Proteins have many functions in the human body and these include transport, catalysis, protection, storage, sensitivity, structure and co-ordination.

    3 star(s)

    So this makes protein very crucial for your health. Each protein is a large complex molecule; these molecules are made up of a string of amino acids. There are 20 different amino acids that occur naturally to form proteins and they all have the same basic structure. The 20 amino acids the body needs can be linked in thousands of different ways to form thousands of different proteins, each with a unique function in the body. Both the amino acids manufactured in the liver and those derived from the breakdown of the proteins we eat are absorbed into the blood stream and taken up by the cells and tissues to build new proteins as needed.

    • Word count: 1112
  23. Marked by a teacher

    Should stem cell research be allowed?

    3 star(s)

    This means stem cells could repair diseased or damaged organs. So for example if part of a mouse's spine was removed stem cells could be put in its place and under the right conditions form the missing part of the spine. The stem cells would become spine cells. Stem cells can be extracted from adults and umbilical cords after a child is born, but are usually taken from embryos or tissue from aborted pregnancies (before the first trimester). Embryonic stem cells are of corse taken from human embryos.

    • Word count: 1110
  24. Marked by a teacher

    Investigation into how temperature affects the enzyme: Amylase.

    3 star(s)

    The second variable is PH. Each enzyme has an optimum PH, any change in temperature will affect the bonding in an enzyme & therefore, will change it's shape. In my experiment, I will not change the PH of any of my enzymes by adding or taking away substances. I know from my preliminary work that my saliva is at PH 7 and that if the PH of the starch is changed from PH 7, then the reaction will be a lot slower.

    • Word count: 1887
  25. Marked by a teacher

    The effect of enzyme concentration on enzyme activity.

    3 star(s)

    A depression on the three dimentional shaped surface of the molecule is the active site. This takes up only a fractional of the enzyme molecule so only a few of the amino acids will be directly involved in the active sites. Substrate molecules are either single or more complementary molecules that fit into the active sites. These form tempary bonds with the amino acids forming an enzyme - substrate complex. During each separate reaction products are formed which are released and enzyme concentration remains the same. The enzyme works only for a specific reation due to its uniquely shaped active site.

    • Word count: 1390

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