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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

    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. 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

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