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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

    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
  3. 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
  4. Marked by a teacher

    Relating the structure and function of cell organelles

    5 star(s)

    The inner membrane of nucleus will break down and allow chromosomes lying freely in cytoplasm. DNA contains the genetic information and control the synthesis of protein. Each cell contains millions of ribosomes. They are very tiny, non-membrane bounded organelles made of protein and RNA which consist of two sub-units that come together during protein synthesis. Ribosomes are distributed throughout the cell. Some of them are embedded in rough endoplasmic reticulum to translate a protein secreted into it while some flows freely in the cytoplasm for making protein that stays in the cell. Fused to the nuclear membrane is the endoplasmic reticulum.

    • Word count: 968
  5. Marked by a teacher

    Investigating respiration of maggots

    5 star(s)

    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
  6. 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
  7. 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
  8. 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
  9. 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
  10. 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
  11. 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
  12. 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
  13. 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
  14. 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
  15. 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
  16. 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
  17. 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
  18. 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
  19. 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
  20. 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
  21. 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
  22. 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
  23. Marked by a teacher

    The structure and function of the ileum in relation to absorption and digestion.

    4 star(s)

    * The lining epithelium is very thin and the fluids can pass rapidly through it. The outer membrane of each epithelial cell has microvilli which increase the exposed surface of the cell by 20 times. * There is a dense network of blood capillaries in each villus for quick absorption and maintainance of the concentration of the concentration gradient. * The villi possess smooth muscle fibres that contract and relax and mix the food up and bring it into contact with the epithelial cells of the absorptive surface. * Each villus has a lacteal for the absorption of fatty acids and glycerol, most of which combine to form fats.

    • Word count: 680
  24. 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
  25. 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

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