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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.

  • Marked by Teachers essays 46
  • Peer Reviewed essays 14
  1. Marked by a teacher

    Transport across plasma membranes

    4 star(s)

    This allows the cell to maintain a constant internal environment. This is more commonly known as osmosis; the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration. It is a physical, hydrophilic process in which a solvent moves, across a semi-permeable membrane separating two solutions of different concentrations. Osmosis releases energy but does not require it as it is a passive process. Diffusion is similar to this in the sense that it is also passive, meaning no energy required and it also takes place through the phospholipid bilayer.

    • Word count: 880
  2. Marked by a teacher

    The Role of Carbohydrates in Living Organisms

    4 star(s)

    be used as respiratory substrate, or is converted to starch for storage. Both of these trioses are intermediates in glycolysis, where glucose is broken down by enzymes into pyruvic and lactic acid. Pentoses such as ribose an ribulose possess five carbon atoms. Ribose or deoxyribose make up part of nucleotides and as such give structural support to nucleic acids RNA and DNA. Ribose is a constituent of hydrogen carriers such as NAD, NADP and FAD. Further more it is involved in the synthesis of coenzymes and ATP. The third type of monosaccharides is hexoses like glucose and fructose, which possess six carbon atoms.

    • Word count: 624
  3. Marked by a teacher

    A Colorimetric Method for the Estimation of Glucose in Solution.

    4 star(s)

    A clean pipette and pipette filler was used to transfer 2cm of potassium permanganate solution into each boiling tube. A stopwatch was started the exact moment the potassium permanganate was added to the acidified glucose solutions. A time was recorded, in seconds for the complete decolourisation of the potassium permanganate solutions. Results Concentration of glucose (%) Start time (seconds) Finish time (seconds) Elapsed time (seconds) 10 90 562 472 9 80 578 498 8 70 590 520 7 60 605 545 6 50 614 564 5 40 629 589 4 30 635 605 3 20 963 943 2 10 1787 1777 1 0 2486 2486 Results of Unknowns Name of Unknown Start time (seconds)

    • Word count: 930
  4. Marked by a teacher

    The transport system in plants moves water soluble molecules by vascular tissue. There are two types of vascular tissue which are Xylem and Phloem.

    3 star(s)

    Most importantly the tissues do not use any energy or transport mechanism to move the water based molecules however the water or water based substance itself has cohesive properties. The cohesive properties of water cause molecules to attract to each other and the surface tension in the vessels keeps it moving up towards the leaves. As the water on the leaves is evaporating or being used in a process it causes water to move up the plant and more water to be taken in by the root's which is also seen as an ongoing cycle.

    • Word count: 484
  5. Marked by a teacher

    Investigating and testing for reducing and non-reducing sugars

    3 star(s)

    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.

    • Word count: 855
  6. Marked by a teacher

    Importance of diffusion to living organisms

    3 star(s)

    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.

    • Word count: 946
  7. Marked by a teacher

    Reducing and non-reducing sugars tests.

    3 star(s)

    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

    • Word count: 649
  8. Marked by a teacher

    To estimate the sugar content of different fruit solutions.

    3 star(s)

    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.

    • Word count: 547
  9. Marked by a teacher

    How do different concentrations of sucrose solution effect potato tissue?

    3 star(s)

    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

    • Word count: 632
  10. Marked by a teacher

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

    3 star(s)

    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.

    • Word count: 914
  11. Marked by a teacher

    Treatment of Kidney Failure

    3 star(s)

    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.

    • Word count: 573
  12. Marked by a teacher

    Adaptations of Small Intestine for Absorption

    3 star(s)

    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.

    • Word count: 490
  13. Peer reviewed

    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
  14. Peer reviewed

    The Various Roles Played By Proteins

    3 star(s)

    Intrinsic proteins lie across the whole membrane. They help ions and molecules which are water soluble to cross the membrane at this point, therefore controlling what goes into and what comes out of the cell. Another function of proteins in the cell membrane is to 'detect signals from the outside of cells and relay them to the inside' (Phillipallan,nov 1999); these are known as receptor proteins (sometimes with sugars attached) and their job is to alter a cells behaviour to enable signal molecules like hormones to bind specifically to their own receptor.

    • Word count: 889
  15. Peer reviewed

    Types of diffusion

    3 star(s)

    Plants use osmosis to take up water into their roots because they have a large surface area and the water coming through the permeable membrane generates the pressure needed to send the water up the plant to the vital areas. Simple diffusion is a process of diffusion which does not require a special protein channel, facilitated diffusion (or facilitated transport) is a process of diffusion, a form of passive transport, where molecules diffuse across membranes, with the assistance of transport proteins.

    • Word count: 796
  16. Free essay

    Movement of Nutrients in Plants

    3 star(s)

    In some cases, the ions may enter the plant against a concentration gradient. The ions are selectively absorbed by active transport, therefore energy is used. Mineral ions are taken up by the root hairs and other surface cells in the young parts of the root. Active transport occurs across the plasma membranes of the root hairs and the cortex cells. The ions move inwards via the symplast, through plasmodesmata. Once inside the vessels and tracheids, the ions are carried up the stem, along with the water in the transpiration stream.

    • Word count: 944

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