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AS and A Level: Molecules & Cells

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  1. 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
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    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
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    The Effect of Substrate Concentration on Enzyme Action.

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    To retard 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
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    My task is to describe how the cell structure of different cells is related to their function. I am going to carry out my task by researching different cells such as animal, plant, nerve cells etc.

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    They function as an "antennae" of the neurone and are covered by thousands of synapses. These cells are linked to one another by electrical impulses and because of their long straight shape are able to transfer information around the nervous system quickly and uninterrupted. Red Blood cell Red blood cells perform the most important blood duty. A single drop of blood contains millions of red blood cells, which are constantly travelling through the body delivering oxygen and removing waste. If they weren't, everything in the body would slowly die.

    • Word count: 859
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    Explain the link between cancer and mitosis. Describe how the chances of cancer developing in the human body may be increased.

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    The problem is cased by mutations or abnormal activation of the genes which control cell division. We can say that a gene has been mutated if there is a change in one of the bases; for example, one base turns (e.g. adenine) into another base (e.g. thymine). This can lead to uncontrolled cell division. When genes are abnormal (or have been mutated) they are called oncogenes (onkos means tumour), about a hundred of which have been discovered. Cancerous cells will divide uncontrollably and repeatedly forming clones of genetically identical cells.

    • Word count: 726
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    Following the Progress of an Enzyme Controlled Reaction

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    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.

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    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
  8. 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
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    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
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    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
  11. Marked by a teacher

    Cellular Respiration and the Role of Mitochondria

    4 star(s)

    The first stage, glycolysis is the anaerobic catabolism of glucose, it occurs in almost all cells. The process uses glucose and co-enzyme NAD (Nicotinamide Adenine Dinucleotide), and yields 2 molecules of Pyruvic acid, as below C6H12O6 + 2NAD+ -> 2C3H4O3 + 2NADH + 2H+ The free energy stored in 2 molecules of pyruvic acid is somewhat less than that in the original glucose molecule. Some of this difference is captured in 2 molecules of ATP. The Krebs Cycle then decarboxylates the pyruvic acid resulting in a 2-carbon fragment of acetate. This 2-carbon fragment is coupled to a molecule of oxaloacetic acid , this results in a molecule of citric acid (the process is also known as the citric acid cycle)

    • Word count: 750
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    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
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    The Process of Protein Synthesis

    3 star(s)

    * tRNA pulls the amino acids into the rRNA (ribosome) and adds them to the polypeptide protein chain. * When the ribosome reaches one of the three codons for which there is no matching tRNA, the ribosome falls off and the synthesized protein is released. * mRNA (messenger RNA) is the only type of RNA that carries protein-building information * The mRNA takes the message to synthesize protein from the DNA in the nucleus; the mRNA carries the codons e.g. the A, U, G, and C codons. * mRNA is the one strand and it goes through the ribosome, it contains the codons that tells the tRNA which peptides to add.

    • Word count: 2030
  14. Marked by a teacher

    The aim of this activity is to investigate the effect of a reduction in enzyme concentration on the rate of reaction, in this case the breakdown of protein by protease enzymes.

    3 star(s)

    Risk Assessment: In this experiment there were not a lot of risk assessment that was dangerous to both my lab partner and I. The main risk assessments were to tie our hair back, we had to make sure that we didn't spill any of the chemical on the floor has this could be dangerous. Apparatus To carry out this experiment, the following apparatus are needed: * Trypsin * Milk powder * Standard laboratory glassware and apparatus * Stop clock * Colorimeter * Thermometer Reliability To be reliable, measurements should also be accurate.

    • Word count: 890
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    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
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    Investigation to determine the effect of different brands of mouthwashes on microbes

    3 star(s)

    4 6.29 mm 4.79 mm 5.81 mm 1.90 mm 5 6.45 mm 4.42 mm 5.39 mm 2.64 mm Average 6.5975 mm 4.635 mm 5.3925 mm 2.074 mm Order of Zone of Clearance of Microbial Decay (Highest to Lowest) 1. Mouthwash A - Colgate Plax 2. Mouthwash C - Listerine 3. Mouthwash B - Dentyl Active 4. Mouthwash D - Superdrug Figures 1 to 3 show photographs of some of the results I collected from the pilot investigation. You can clearly see that different brands of mouthwash had different effects on the microbes as some destroyed them more than others and this is shown by a ring of clearance around each sample of mouthwash on the filter paper.

    • Word count: 765
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    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
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    Observing Mitosis. The purpose of this experiment is to prepare a slide of actively dividing plant tissue and to observe stages of the cell cycle in living tissue.

    3 star(s)

    We put these roots into some acetic alcohol which is a fixative, so it stops and helps preserve the cells. Then we removed them and put them in ice cold water and then dried them on filter paper. After this we put the root tips in the pre-heated hydrochloric acid, this will dissolve the calcium pectate but leave the cell walls unharmed. So it breaks up tissue without damaging the cell.

    • Word count: 430
  19. 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
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    Core practical(Why does the colour leak out of cooked beetroot?)

    3 star(s)

    * We took nine test tubes and labelled them from A-I. And we placed 6 cm3 of water in each tube with the help of pipette. * We put nine cylinders of beet root tissues into a beaker of 150 cm3 of water. * We put a beaker on a Bunsen burner and took some water and heated the water and then put a thermometer in to the beaker. * We put beet root in to the hot water for two minutes and noted the temperature.

    • Word count: 599
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    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
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    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
  23. 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
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    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
  25. 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

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