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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
  2. Marked by a teacher

    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
  3. Marked by a teacher

    The Effect of Substrate Concentration on Enzyme Action.

    4 star(s)

    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
  4. Marked by a teacher

    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.

    4 star(s)

    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
  5. Marked by a teacher

    Explain the link between cancer and mitosis. Describe how the chances of cancer developing in the human body may be increased.

    4 star(s)

    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
  6. Marked by a teacher

    Following the Progress of an Enzyme Controlled Reaction

    4 star(s)

    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.

    • Word count: 4626
  7. 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
  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
  9. 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
  10. 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
  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
  12. 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
  13. Peer reviewed

    The effect of drugs on the nervous system

    5 star(s)

    The PNS receives thousands of sensory inputs and transmits them to the brain via the spinal cord. The brain will then process this information, discarding around 99% of it as unimportant. After this sensory information has been processed, areas of the nervous system generate nerve impulses to organs or tissue and form a suitable response. As influences from chemicals are able to affect how the nervous system functions, it can be assumed that chemicals such as drugs are potentially able to change the way an organism functions. Whilst our knowledge of different regions of brain function and neurotransmitters within the brain is limited, explanations involving the mechanisms of drugs may be vague.

    • Word count: 923
  14. Peer reviewed

    The Function and Structure of Lipids in Living Organisms

    4 star(s)

    Fatty acids can be saturated or unsaturated depending on their carbon bonding and can be told apart easily because of their state at room temperature, ether solid or liquid. Saturated fatty acids are made up of hydrogen, oxygen and carbon, the carbon in the saturated fatty acid has single bonds and it is bonded to the maximum number of atoms that it can bond with. Because of this it is a strait chain which means that it can be closely packed with other chains which means that it is a solid at room temperature.

    • Word count: 977
  15. Peer reviewed

    Effect of enzyme concentration on rate of reaction

    4 star(s)

    The shape of the active site is determined by the 3D structure of the enzyme as aforementioned. The 3D structure is dependant the bonds in the protein molecule that are affected by the enzyme's primary structure. Enzyme work by lowering the activation energy required for a certain reaction to take place. Activation energy is the minimum energy that must be supplied (usually in the form of heat) to chemicals before a reaction can take place. Image 1: Enzyme lowers the activation energy needed for a reaction to take place3 The basic mechanism of an enzyme is that the substrate molecules bind to the enzyme to form an enzyme-substrate complex.

    • Word count: 4053
  16. Peer reviewed

    Determination of Vitamin C in food

    4 star(s)

    The titration method takes advantage of the ability of Iodine to oxidise Vitamin C. Iodine is relatively insoluble, but this can be improved by binding to iodide to form triiodide: I2 + I- <--> I3- Triiodide oxidizes vitamin C to form dehydroascorbic acid: C6H8O6 + I3- + H2O --> C6H6O6 + 3I- + 2H+ As long as vitamin C is present in the solution, the triiodide ion is converted to the iodide ion very quickly. However, when the all the vitamin C is oxidized, iodine and triiodide will be present.

    • Word count: 1478
  17. 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
  18. Peer reviewed

    Skeletal System. What is the difference between the axial and appendicular skeleton? What is the difference between ligaments and tendons? How are bones important in maintaining homeostasis?

    4 star(s)

    The human endoskeleton skeleton is a combination of cartilage and 206 bones that make up the skeletal system. It is organized into two basic units: the axial skeleton and the appendicular skeleton. The axial skeleton supports the axis or trunk of the body and includes the skull, enclosing and protecting the brain, vertebrae of the spinal column, enclosing the spinal cord and the rib cage, around the heart and lungs. It includes 80 bones.

    • Word count: 428
  19. Peer reviewed

    Cell Structure

    4 star(s)

    * Contains molecules for the light dependant stage of photosynthesis * Synthesis of ATP * Enzymes required for conversion of CO2 and water to carbohydrate * Temporary storage of carbohydrate Sacs called thylakoids formed by membranes Stroma contains enzymes plants, protists (rare kleptoplastic organisms)

    • Word count: 536
  20. Peer reviewed

    Features of Lungs & Tissues

    4 star(s)

    * Macrophages that destroy foreign material, such as bacteria. Where they are located? Type II cell is located in the alveolar epithelium. Macrophage cell is found in the pulmonary alveolus, near the pneumocytes, but separated from the wall and type I cell is located beneath the plasmalemma . Main organelles within the cell? Organelles found within the cells are as follows: Nucleus, Mitochondria, Lysosomes, Vacuole, Ribosomes and Cell membrane. Their function? Nucleus controls the cell's activity. Mitochondrion produces energy. Lysosomes is capable of breaking down all types of biological polymers-proteins, nucleic acids. Vacuole is the storage.

    • Word count: 1109
  21. Peer reviewed

    Explain how the structure of collagen and haemoglobin are related to their function.

    4 star(s)

    Furthermore, the triple helix is held together by an extensive network of hydrogen bonds. Covalent cross-links are also present within tropocollagen molecules to impart the collagen fibre with strength and rigidity. Proline with its ring structure also helps in stabilizing the rigid three-stranded collagen helix. Beside, the tropocollagen molecules are arranged in a staggered manner with each other. This confers collagen greater strength. Secondly, it is insoluble in water. This is due to the large molecular size of the tropocollagen molecule and the nature of the amino acid residues. Each of the three polypeptide chains in a collagen molecule is about 1000 amino acid residues long and they coil up into a collagen helix.

    • Word count: 612
  22. Peer reviewed

    structural differences between fibrous and globular proteins.

    4 star(s)

    (X is proline, Y is either hydroxyproline or hydroxylysine) A globular protein has a more compact structure owing to highly contorted pattern of folding, bending and twisting along polypeptide chain to give the protein a spherical 3D shape while a fibrous protein is usually formed with elongated polypeptide chains wrapped around to form multi-molecular paralleled filaments to strands. For example, haemoglobin is a tetramer made up of 4 polypeptide chains of 2?

    • Word count: 398

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