• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

AS and A Level: Molecules & Cells

Browse by

Currently browsing by:

Meet our team of inspirational teachers

find out about the team

Get help from 80+ teachers and hundreds of thousands of student written documents

  • Marked by Teachers essays 108
  • Peer Reviewed essays 26
  1. Marked by a teacher

    Investigate the effect of temperature on dehydrogenase activity in yeast. At which temperature is tetrazolium chloride (TTC) discoloured most rapidly?

    4 star(s)

    I will be observing the speed at which the colour changes with the redox indicator that I am using, tetrazolium chloride (TTC). This indicator is an artificial hydrogen acceptor; when oxidised is colourless, but when reduced it forms red, insoluble compounds called formazans. The compound ... NH2 - N=CH - N=NH ...Is called a formazans. Enzymes of the dehydrogenase class can be revealed I their location because they convert tetrazolium salts in solution to coloured, insoluble formazans. TTC can be used to show the presence of active dehydrogenase enzymes by a change in colour.

    • Word count: 2293
  2. Marked by a teacher

    Investigating the breakdown of hydrogen peroxide using celery tissue to supply the enzyme catalyst

    4 star(s)

    This can also be related to the collision theory. If the H202 is made more concentrated it means there are more particles of reactant between the water molecules, which makes collisions between the important particles more likely. This reaction is called a 'catabolic' reaction. This is a 'breaking down' reaction, where the enzyme combines with the substance for a short time, and then two substances are produced. Hydrogen peroxide is a chemical found in our liver, with the presence of enzymes in our body the catalyst help the decomposition of the H202 and accelerates it, so water and oxygen are produced faster.

    • Word count: 2343
  3. Marked by a teacher

    An investigation into the effect of Hydrogen Peroxide concentration on Yeast Catalyse activity

    4 star(s)

    The enzyme ends up unchanged by the process, ready to repeat it many times. Hypothesis Several ideas as to the likely outcome of the investigation can be drawn from this model of the enzymes working. Firstly, the reaction depends on H2O2 molecules actually coming into contact with the active sites of the enzyme. The chances of this occurring will be affected by the proportion of enzyme to substrate to water- both the stock H2O2 and yeast cells are supplied in aqueous solution, the H2O2 at a concentration of 32moldm-3 and the yeast at 2gdm-3.

    • Word count: 2328
  4. Marked by a teacher

    Vitamin C content of fruit juices

    3 star(s)

    This is because vitamin C is required in the synthesis of collagen which is an important protein in blood vessels, skin, tendons and ligaments. Vitamin C also plays an important role in the healing of wound and the repair and maintenance of cartilage, bones and teeth. Not only that, vitamin C is also a strong antioxidant. Antioxidants are nutrients that block some of the damage caused by free radicals, which are by-products that result when our bodies transform food into energy.

    • Word count: 2861
  5. Marked by a teacher

    An investigation to see how different sugars affect the growth and respiration of yeast.

    3 star(s)

    Prediction I predict that glucose will allow yeast to produce the most respiration. This is because it is a monosaccharide Fair Test Whilst doing the experiments, it is necessary to have minimal errors. By this, each experiment must be done fairly. To make each experiment fair it is important to make sure: * The same quantities are used throughout all the experiments. * Separate syringes are used for the methylene blue, sugars and yeast; this is to avoid any contaminations. * Repeat each experiment to gain an average set of results. * The same equipment must be used * The time be used in the same units throughout the experiments Safety It is important to ensure: * All equipment is used safely and correctly.

    • Word count: 2677
  6. Marked by a teacher

    Biology Coursework Investigation

    3 star(s)

    I found this out through the preliminary work. As the pH of an enzyme increases (becomes less acidic) the enzyme activity increases until there is an optimum pH. As pH increases further (becomes more alkaline) the activity decreases. At very low pH and very high pH, the enzyme is denatured and does not work. - The type of enzyme (input variable)- The type of enzyme you use is also very significant to your results. This is due to the fact that different types of enzymes have different optimum temperatures and therefore are denatured at different temperatures.

    • Word count: 2640
  7. Marked by a teacher

    Effect of different temperatures on the permeability of beetroot cell membrane.

    3 star(s)

    therefore there is a positive significant correlation between the two values. Group 2 Site Temp (�C) Rank R1 Absorbance (Arbitrary units) Rank R2 D (R1-R2) D2 1 25 1 0.26 2 -1 1 2 35 2 0.34 3 -1 1 3 45 3 0.21 1 2 4 4 55 4 0.63 4 0 0 5 65 5 2 6 -1 1 6 75 6 2 6 0 0 7 85 7 2 6 1 1 0 8 From using the formula the rs was 0.85, which is over the critical value (0.79)

    • Word count: 2077
  8. Marked by a teacher

    The effect of temperature on catalase activity

    3 star(s)

    For this reason few cells can tolerate temperatures higher than approximately 45�C. Enzymes are specific in the reactions they catalyse, much more so than inorganic Catalysts. Normally, a given enzyme will Catalyse only one reaction, or type of reaction. The enzyme has an active site that helps it to recognise its substrate in a very specific way. Just like a key only fits into a specific lock, each enzyme has its own specific lock; each enzyme has its own specific substrate. This is called the lock and key theory. The enzymes never actually get consumed in the process; they just increase the rate of reactions.

    • Word count: 2724
  9. Marked by a teacher

    Investigation of factors affecting the enzyme Amylase.

    3 star(s)

    Therefore I have developed two similar experiments (one for each factor I am investigating). To investigate the pH effects on the enzyme amylase activity. 1. Pour amylase solution into a test tube to a depth of 2cm. 2. Half fill another test tube with a 4% starch solution. 3. With a pipette, place a drop of iodine into each dimple in a dimple tray. 4. With a glass rod lift a drop of the starch solution from the first test tube and mix it with the first drop of iodine in the first dimple in the tray. A blue/black colour should develop; this will be used as the control. 5. Rinse the glass rod.

    • Word count: 2074
  10. Marked by a teacher

    I am going to investigate the ability of Pepsin on Gelatin. I aim to investigate the effect of temperature on the rate of action of Pepsin on Gelatin.

    3 star(s)

    The volume of the pepsin was chosen to be 20ml. Variables * The volume of pepsin that is used * The amount of filmstrip that is used * Temperature of the pepsin * The concentration of the pepsin solution that is used * The apparatus that is used. * The method that is used. * Quality of film * pH of pepsin The variable will be temperature. This will be measured with a thermometer. The following non-variable parameters will be used (determined by preliminary work) - 20ml of pepsin 2cm by 2cm of filmstrip 2% solution of pepsin Black and white film The student has elected to perform the following

    • Word count: 2080
  11. Marked by a teacher

    The effect of amylase concentration on the breakdown of starch

    3 star(s)

    Because the thing I am trying to test in the effect of the concentration of the enzyme, the only thing that I should be changing in each experiment is the concentration of the enzyme and nothing else. This will make all of the tests identical (apart from the enzymes concentration) which means the experiment should be accurate and fair. Because of this any differences in the results of my experiment I will be able to put down to the concentration of the enzyme.

    • Word count: 2298
  12. Peer reviewed

    Compare the structures of a cell to those of a city. Although vast differences in size, organization and infrastructures seem alike, the cell and the city may share a lot in common.

    4 star(s)

    A denser region inside the nucleus is called the nucleolus which is the site of RNA and ribosomal synthesis. Surrounding the nucleus is a nuclear envelope which contains many pores allowing it to communicate with the cytosol by permitting the passage of large molecules. (5) Analytically, in a city the control centre is the city hall, where a Mayor works and along with the elected party runs the whole city, creating rules and legislation, administering public policies and regulating industries.

    • Word count: 2191
  13. Peer reviewed

    Transport across membranes How do substances cross into and out of cells.

    3 star(s)

    It is the cell membrane which ultimately defines the boundaries of all cells and protects it from environmental changes. The membrane provides numerous functions for a cell, they exhibit protective qualities as they control and prevent and regulate the passing of molecules within to and out of cells. The transport and exchange across cell membranes is an essential and continuous feature of the life of all cells. The intake of new materials and the expulsion of waste must all occur through the cell membrane. The cell membrane acts as a selective barrier between the inside of the cell and the external fluid/molecules.

    • Word count: 2313
  14. Peer reviewed

    Measuring Vitamin C content in different substances

    3 star(s)

    the juice), > Test tubes (To contain the solutions), > Stopwatch (To measure the time for the DCPIP to turn colourless), > Glass rod (To stir the contents of the test tube to ensure that it is distributed evenly), > Test tube rack (They are needed to hold the quantity of test tubes used to accommodate the solutions) Method: 1. Measure out 15cm� of Vitamin C solution and pour into a test tube. Measure out 1cm� of DCPIP, pour it into test tube with the Vitamin C solution and stir it evenly with the glass rod.

    • Word count: 2250
  15. Peer reviewed

    "An investigation to find out the optimum temperature for the activity of Lipase".

    3 star(s)

    I expect as the temperature is lowered the rate of reaction will be slower and that at the higher temperatures the rate of reaction will be decrease as the enzyme becomes denatured. * METHOD MATERIALS USED: Electric Kettle, 250ml Beaker, 10 Boiling tubes, 2 Boiling tube racks, Milk, Sodium Carbonate, Phenolphthalein, Spirit Thermometer, 5% Lipase. PROCEDURE: STEP 1: We mixed 5cm� of milk with 7cm� of Sodium Carbonate and added 6 drops of phenolphthalein into each of 5 boiling tubes.

    • Word count: 2210

Marked by a teacher

This document has been marked by one of our great teachers. You can read the full teachers notes when you download the document.

Peer reviewed

This document has been reviewed by one of our specialist student essay reviewing squad. Read the full review on the document page.

Peer reviewed

This document has been reviewed by one of our specialist student document reviewing squad. Read the full review under the document preview on this page.