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AS and A Level: Exchange, Transport & Reproduction

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Five tips on presenting and analysing data from core practicals

  1. 1 Raw data should be presented in a table with clear headings. All table column and row headings should contain units and readings should all be recorded to the same decimal place.
  2. 2 Raw data should be processed to provide descriptive statistics such as the mean and standard deviation.
  3. 3 Present data using the relevant graph type. Ensure that you add error bars showing either standard deviation or standard error.
  4. 4 When describing trends and patterns, manipulate data to calculate the size of key changes. For example, absorbance increases by 0.09 absorbance units between 10◦C and 40 ◦C. Preferably express the change as a percentage increase or decrease. Do not simply quote points, eg at 10 ◦C absorbance was 0.01 and at 40 ◦C it had gone up to 0.1 absorbance units.
  5. 5 Discuss each phase of the graph. For example if there is a slow increase, followed by a rapid increase, and then the graph levels off and shows a decrease, discuss these four key phases. Do not give detailed descriptions of each small fluctuation. The trends and patterns are the important things.

Meiosis and Mitosis facts

  1. 1 Meiosis generates gametes/sex cells, whereas mitosis is for growth/repair and generates daughter cells identical to the parent cell.
  2. 2 During Meiosis chromosome number is halved producing haploid gametes with a single copy of each chromosome. During Mitosis chromosome number is maintained producing diploid daughter cells with maternal and paternal copies of each chromosome, i.e. homologous chromosome pairs.
  3. 3 Before mitosis and meiosis all chromosomes are copied as part of interphase. At the end of interphase there are two identical copies of every maternal chromosome and every paternal chromosome, so chromosome number has doubled (i.e. at the end of interphase a human cell contains 46 x 2 = 92 chromosomes). The identical copies of chromosomes are referred to as sister chromatids and they are joined by a centromere.
  4. 4 In meiosis, genetic variation is generated by crossing over during prophase 1, and independent chromosome assortment at metaphase 1 and metaphase 2. During crossing over maternal and paternal chromosomes cross each other, and break at points known as chiasma. Maternal and paternal alleles below the chiasma change places so that the paternal chromosome contains maternal alleles and vice-versa. During metaphase 1 and 2, maternal and paternal chromosomes align randomly on one side of the equator. As the maternal and paternal chromosomes can align on either side, different potential chromosome combinations can occur.
  5. 5 The events in metaphase, anaphase and telophase are identical in both mitosis and meiosis 1 and 2. In mitosis a single division occurs, whereas in meiosis cells undergo 2 meiotic divisions.
    a) During meiosis 1, maternal and paternal sister chromatids are separated so that 1 cell contains both maternal sister chromatids of a pair and the other contains both paternal sister chromatids.
    b) During the second meiotic division, sister chromatids are separated. The gametes that result contain only 1 chromosome from each pair, i.e. they are haploid.

How to evaluate experimental methods

  1. 1 When evaluating the reliability of experimental methods, always consider whether all variables other than the independent variable have been adequately controlled. If a variable cannot be controlled has it been monitored to establish any effect it might have?
  2. 2 All experiments must be repeated to establish reliability. Has the experiment been repeated at least three times? Preferably you should repeat it more than 3 times.
  3. 3 What does the standard deviation suggest about the spread of the data? If the mean is 5, but the standard deviation is 3, readings vary from the mean considerably. This suggests that the mean does not represent the actual readings.
  4. 4 How precise are the measurements? If a balance used to measure change in mass only measures to 0.1 g then the reading could be 0.12 g, 0.15g, or 0.18g etc.
  5. 5 How accurate are the readings? If equipment is re-used for different repeats for example, cross contamination could affect the accuracy of subsequent readings. If tubes are shaken different amounts, different volumes of gas could be released. Consider all potential sources of error and discuss how the procedure could be improved to reduce these sources of inaccuracy.

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  1. Marked by a teacher

    Compare and Contrast the Transport System of a Mammal and a Plant

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    A slower blood flow is desired when going to the lungs to allow more time for gas exchange and prevent damage on lung tissues. Blood never leave the vessels during transport so that a quicker blood flow rate can be obtained and this also allows vasoconstriction or vasodilatation to occur. The Transport System of Plants: Plants also require a regular supply of oxygen and nutrients, yet their requirements differ from those of animals in several ways. Instead of oxygen, carbon dioxide is required for photosynthesis while oxygen is the waste product.

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    Properties of Water

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    Its properties as a solvent depend on the fact that it is a polar molecule. A polar molecule is one which has an unevenly distributed charge. Water is made up of 2 oxygen atoms and one hydrogen atom. Oxygen has a bigger nucleus and because of this, the oxygen attracts electrons more strongly ten oxygen. Therefore, oxygen is slightly negative and hydrogen is slightly positive. Water's polarity is also caused by its shape. Instead of being a straight line (180�), the angle between the two hydrogen atoms is 105�: It can also act as an ionic substance because of this property.

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    Daphnia experiment - Does caffeine affect heart rate?

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    They mature in just a few days, so it does not take long to grow a culture of test organisms. They possess fairly transparent bodies which make observation on heart rate in daphnia fairly observable. Foster, in the journal of Biological education (1997) provides a method using a stroboscope to freeze the motion. Use of the stroboscope may overcome the problems of counting faster heart rates. However, we would not recommend this method. Positioning the light sources of the strobe is tricky.

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    Daphnia experiment - Does caffeine affect heart rate?

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    The more caffeine present in the bloodstream, the faster the heart rate. Equipment * Culture of Daphnia (water fleas) * Cavity slides * Pipette * Distilled water * Caffeine tablets * Cotton wool * Standard glass wear (beakers, measuring cylinders) * Stop clock * Paper towels * Microscope Procedure 1. Using 6 beakers, label and set up the following solutions using the correct volumes: - % Weight per volume 50ml (Total volume) Caffeine solution (ml) Water pond (ml) 0.5 5 5 0.4 4 6 0.3 3 7 0.2 2 8 0.1 1 9 0.0 0 10 2.

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    Beetroot pigments

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    Therefore, this means the molecules must be lipid soluble and non-polar, and the beetroot molecules are not. However, facilitated diffusion is the movement of molecules through a membrane by protein channels, and since transport proteins have hydrophilic interior, hydrophilic molecules are able to pass. Facilitated diffusion is the movement of molecules or ions from a region of high concentration to a region low concentration. This results in the molecules travelling down the concentration gradient until equilibrium is reached; where the molecules or ions are evenly distributed. Diffusion is a passive process and it does not require metabolic energy. Diffusion can occur from one part of a fluid to another or across a membrane separating two fluid regions.

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    Investigating and testing for reducing and non-reducing sugars

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    Apparatus List: * Beaker * Test tube rack * Test tubes * Samples of sugar solutions * Syringe * Pipette * Benedict's solution * Hot water available * Hydrochloric acid, HCL * Sodium hydrogen carbonate, NaHCO3 * Universal indicator paper Theory: Benedict's solution is often used as a general test for detecting reducing sugars. If the saccharide is a reducing sugar, it will reduce the copper (II) ions to copper (I) oxide, and form a yellow-red precipitate. However, some saccharides need to be split and neutralised in order to detect their reducing sugars.

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    What is Type 1 diabetes

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    The hospital healthcare team dietitian, general practitioner and diabetic nurse are all on hand to give advice and guidance. Ways to help yourself Keep an eye on any signs indicating either high or low glucose levels. Learn how to measure glucose levels and do it regularly. The most important piece of equipment is the home blood glucose meter, which enables you to measure your blood glucose levels and control your insulin dose. Try to follow the diabetic diet as rigorously as possible.

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    Investigating how changing the concentration of sucrose, affects the time it takes for a reaction to take place with Sucrase

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    This is shown through the diagram below. As can be seen, there is a point at which the rate of reaction becomes constant, and no longer increases. This is because of the way in which the substrate interacts with the enzyme to form the end products. The diagram above shows that the substrates interact with the enzymes at a specific location. This location is known as the active site. Each enzyme molecule has one active site, and this is where the substrate will attach itself, and the reaction will take place.

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    Importance of diffusion to living organisms

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    In this type of diffusion, a hydrophobic molecule moved into the hydrophobic region of the membrane without getting rejected. A key feature is that it does not need a carrier protein to take place. An example of simple diffusion is osmosis. Facilitated diffusion on the other hand is dependant on carrier proteins to transport it across the membrane. Diffusion is essential for many organisms as it is a feature of a number of processes which control and supply vital substances to the body in order for basic survival. A few of these are discussed below. Gas exchange is one of these processes.

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    Reducing and non-reducing sugars tests.

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    REDUCING sugar * Using new samples of the solutions, add 2cm of dilute hydrochloric acid * Boil the test tubes over a Bunsen burner passing it through a blue flame so it doesn't reach boiling point to rapidly * Once the solutions are bubbling remove from Bunsen burner * Neutralise the solutions by adding small amounts of NaHCO until it stops fizzing * Test the pH using litmus paper to make sure that the solutions are neutral * Using the same solutions carry out the test for NON-REDUCING sugars Results: REDUCING sugars test: SOLUTION COLOUR AFTER REDUCING SUGARS TEST A

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    This is an experiment to find out what factors affect osmosis in potato chips.

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    Measuring Cylinder- To measure out the amount of solution accurately 15. Calculator- To calculate the percentage mass change Diagram showing how some of the apparatus will be used. Measurements We are going to weigh the potato chips before they are put in the varied sucrose solution and then after and calculate the total percentage mass change. I feel that the accuracy of the investigation and the simplicity would be jeopardised if we chose just to try and get the weight of the potato chips the same before putting them in the solution and then getting a weight difference after.

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    Investigation to Calculate the Water Potential of Potato Tissue.

    3 star(s)

    Table 1: Mass difference of potato tissue in varying concentration of Sucrose solution. Boiling tube Concentration of Sucrose (aq) Initial weight of potato (g) Final weight of potato (g) Mass gain (g) % Mass gain 1 0 3.08 3.30 0.20 6.5 2 0.25 3.10 3.14 0.04 1.3 3 0.5 3.07 2.94 -0.13 -4.2 4 0.75 3.09 2.91 -0.18 -5.8 5 1.0 3.04 2.75 -0.29 -9.5 With the above table using the concentration of sucrose concentration against the percentage mass gain, a graph was plotted. The second graph plotted with the use of a table showing solute potentials of given sucrose solutions at 20 �C.

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    To estimate the sugar content of different fruit solutions.

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    I expect to find that lemon will have the least sugar content and the melon to have the most. I predict that Melon juice would have the a more red precipitate colour solution followed by grape juice with a slight brownish yellow precipitate, then will be lemon juice with the lightest colour of these precipitate. Method: In order for this experiment to work we had to be extremely accurate with measurements. This is why we chose to use a graduated pipette and a different one each time.

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    Investigating osmosis in plant tissue.

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    We have done an experiment to try and investigate osmosis further; we performed an experiment with visking tubing and a glucose solution. We filled up a visking tubing with water, and weighed it, we then placed the visking tubing inside a glucose solution that had a very low water concentration. After approximately twenty minutes we took the visking tubing out of the glucose solution and weighed it again, it had lost weight. This proves our theory that osmosis can only move along the concentration gradient.

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    How do different concentrations of sucrose solution effect potato tissue?

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    Therefore water will travel in or out of the potatoes cell though its partial permeable membrane. Concentrations I will be using the following suitable concentrations of Sucrose Solution for my experiment. 9, 0.25, 0.50, 1.00, 1.50, 2.00 Apparatus List * 15 Boiling Tubes * All Sucrose solutions as stated above * Stop Watch * 5 Pipettes * 3 Test Tube Racks * Distilled Water * Top Pan Balance * Potato Borer * Ruler Diagram 25 cm3 of Solution 1 cm length of tissue Leave for 15 minutes for it to change length and mass Preliminary Method * I will firstly

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    Write an essay on the functions of proteins in plants and animals

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    In this structure the folding and coiling of the chain is irregular. This causes the types of bonding between the amino acid residues to vary. The quaternary structure consists of more than one polypeptide chain this structure is found in haemoglobin. The bonding between different groups in this case can vary depending upon the functional groups present. If hydrogen and oxygen bind to another hydrogen and oxygen of another R group the hydrogen bonding is present. If not then ionic bonding occurs. If the amino acid residues contain sulphur then disulphide bridges are formed.

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    Treatment of Kidney Failure

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    In this way the imbalance in the body can be corrected. Peritoneal Dialysis What is Peritoneal Dialysis? Peritoneal dialysis is a form of dialysis that occurs inside the body. Dialysis solution will flow into the peritoneal (abdominal) cavity through a silastic catheter. The peritoneal membrane (petrionuem) acts as a filter. Waste products and excess water pass from the body through the membrane into the dialysis solution. When the filtering process is completed, the waste filled solution is to be drained from the peritoneal cavity into a bag and is then discarded.

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    Adaptations of Small Intestine for Absorption

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    called villi covering the whole internal surface of the small intestine. (Each square millimemtre of surface has about 20-40 villi and there are about 5 million in the ileum.) Each villus bears even smaller projections, microvilli. The villi & microvilli further increase surface area for absorption. Villi contain network of blood capillaries & lacteals for transporting digested, absorbed food away. One-cell thick epithelium. The digested food can easily cross the wall to reach the capillaries & lacteals. *There are intestinal glands between bases of villi.

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    Blood structure and function in the body.

    Plasma is mainly made up from water; nearly %90-%92 is water. This is a straw coloured fluid. Plasma contains dissolved substances including electrolytes for example: sodium, chlorine and potassium. Albumin, globulin and fibrinogen are the protein of blood plasma. Hormones are also in the blood plasma. Red blood cells also named as erythrocytes. Red blood cells sometimes may be immature and they do have nucleus but in general, the mature ones do not have any nucleus. This gives them ability to carry more oxygen.

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    The comparison of antibacterial properties of herbal products and standard antibiotics

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    * Broad spectrum antibiotics- these are used to destroy a large range of bacteria. * Narrow spectrum bacteria- these are specific, and are only effective against minimal numbers of bacteria. This investigation will entail the use of penicillin and streptomycin, which are both narrow spectrum antibiotics. Penicillin, being the first discovered antibiotic, has a mode of action that involves interference with the formation of small peptide chains cross-linking in the peptidoglycan; the main wall polymer within bacteria during cell wall synthesis.

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    "An investigation into the Respiration of Carbohydrate Substrates by Yeast."

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    According to the Collision theory however, in order for a reaction to take place a certain level of energy, called the activation energy, must be reached. This energy needs to be reached by the particles colliding in the right way and fast enough, so a reaction can take place. By giving the particles more energy it encourages more to collide therefore the activation energy can be reached and a reaction can happen. The kinetic theory explains the effect of temperature, volume and pressure on the number of collisions.

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    Can heart disease be prevented?

    4 star(s)

    This deposit is also known as atheromatous plague or an atheroma. Rheumatic heart disease used to be one of the most serious heart diseases in both children and adolescence as it involves damage to the entire heart and its membranes.It is a complication of rheumatic fever and usually occurs after attacks of rheumatic fever. (1) This condition has been greatly reduced with the widespread use of an antibiotic effective against the streptococcal bacterium which causes rheumatic fever. There are three main types of congenital defects.

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    Difference in number of Stomata in different leaves

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    3- Add nail varnish to the bottom of the leaf 4- Wait for the nail varnish to dry, you can place it on a warm object to dry it quicker but it should no be placed on a hot object as it can affect the leaf. 5- Once the nail varnish is dry put tape on in and then remove the tape, making sure the nail varnish sticks to the tape. 6- Stick the tape on the microscopic slide 7- Count the number of stomata in your marked areas 8- Add the results to a table (see Table1)

    • Word count: 1540
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    The Importance and Biological Functions of Carbohydrates.

    4 star(s)

    The carbohydrate in milk is lactose and it is formed from Glucose and galactose. Important polysaccharides include Starch, Glycogen and Cellulose. They are all made up from Glucose but have different functions. Starch is the main store of carbohydrates on plants, Glycogen is the main store in animals and Cellulose is important for plant cell walls. All have the formula C H O but they are structurally different. This gives them different properties. Glucose exists in two different forms, ? and ?. The carbons are numbered as shown. Carbon number one has a hydroxyl group that can be in the up position or the down position. ? is in the down position and ?

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    The Heart, Structure and Function

    3 star(s)

    Unlike other muscles, it never fatigues. However it does not tolerate lack of oxygen or nutrients and soon dies if its supply of blood is cut off. The heart is divided into a left side and a right side by the septum. The septum becomes rigid just before the heart contracts, so that it functions as a fulcrum for the action of the heart muscle. Each side of the heart has 2 chambers: an atrium which receives blood from the veins and a ventricle which pumps blood into arteries.

    • Word count: 533

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