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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. Reproduction - Edexcel GCSE Biology Revision Notes

    of chromosomes pair up and a chromatid from each chromosome in a homologous pair twist around each other. * The twisted section breaks off their original chromatids and rejoins onto the other chromatids and recombines their genetic material. * The point of crossing is called the chiasmata. After crossing over, the chromatid would still have the same genes but with different combination of alleles. INDEPENDENT ASSORTMENT * This is where different combination of the paternal and maternal chromosomes goes into each cell when gametes are produced.

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  2. Transpiration in Leaves Experiment

    The paper was held firmly in place by glass slides and paper clips. 2. The number of stomata on a given area of a leaf was determined by making a polystyrene replica of the leaf surface by simply spreading the polystyrene cement thing over the surface with a pin then dry peeling off this cement then observing under a microscope at medium power. 3. A transparent ruler was used to measure the diameter of the observed field. RESULTS Table showing change in mass of leaves with time in a transpiration experiment A B C Time (mins)

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  3. The Process of Osmosis and its Importance to Living Organisms.

    If blood cells, for example, are placed in contact with an isotonic solution, they will neither shrink nor swell. However, if the solution is hypertonic, the cells will lose water and shrink. A real life example of such an event occurring is the consumption of saltwater. Saltwater from the ocean is hypertonic to the cells of the human body; the drinking of ocean water dehydrates body tissues instead of quenching ones thirst. If the solution is hypotonic, for example deionised water, the cells will swell; the osmotic pressure that is developed may even be great enough to rupture the cell membrane.

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  4. Excretion and the functioning of the kidneys

    Urea is then transported by the blood from the liver to the Kidneys where it forms part of urine. The Kidney The Kidney has two main functions, it removes metabolic waste from the body through the process of excretion and it regulates the water and ion content in the blood. The excretion is of a dilute solution called urine which contains urea, mineral ions, water and other foreign chemicals from the blood. The two kidneys have a very extensive blood supply and the whole blood supply passes through the kidneys every five minutes ensuring that the waste materials don?t build up.

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  5. Intracytoplasmic Sperm Injection

    There are three parts to sperm the head, neck and tail. The head consists of a nucleus containing the highly compacted DNA, the neck maintains the connection between the sperm head and tail, the tail is like a motor it spins so the sperm can swim. For the collection of sperm it can be by means of Masturbation, or they can be surgically removed from the testis by a small incision. They would only be surgically removed in serious cases for instance a blockage that consequently means the sperm cannot be ejaculated.

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  6. Histology of Blood vessels

    The wall of the arterioles contains less elastic fibers but more smooth muscle cells than that of the aorta. Arteries carry oxygen-rich blood at high pressure, so they are tough on the outside and smooth on the inside. The arteries have three layers and the smoothness of the inner layer enables blood to flow easily with no obstacles. Arteries carry oxygen-rich blood at high pressure, so they are tough on the outside and smooth on the inside.

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  7. The major problem that occurs with organ transplantation is the shortage of organs

    However, there is always a great chance of the organ being rejected by the body. This is dangerous and can be fatal. The immune system of the body may not accept a foreign organ and recognize it as a major threat to the body (Microbiology). Many risks and complications are also involved in the surgery of transplanting the organ. Major risks such as internal bleeding, blood clots, intense pain, internal infection, allergic reactions to medications can all result in death (UC Davis Transplant Center). There has been a significant increase of organ transplants over the years as is seen in Fig 2.Fig 2 Fig 1 The are several reasons for this increase.

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  8. Should We Adhere To A Mediterranean Diet or An UK Diet In Order To Obtain A Healthy Heart?

    After many researchers and biologists proved that the Mediterranean diet was much healthier, they conducted trials and studies on many different people. A study called PREDIMED-Reus was conducted on 418 non-diabetic Spanish people. (1) They were aged 55 to 80 years old. They required a yearly oral glucose tolerance test and they were put into randomized groups. The groups were: 1. A low fat diet (Control Group) 2. A Mediterranean diet with virgin olive oil- 1 litre per week 3.

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  9. The digestion process.

    Once the food is swallowed it is pushed through the oesophagus and the gastrointestinal tract by peristalsis. The gut wall has two layers of smooth muscle, the circular layer contracts behind the bolus, it pushes the food along. Even though there is no digestion that takes place in the oesophagus, it still helps and plays a role in the system as it secretes mucus to help the food move more easily. The next stage of digestion happens in the stomach. For our cheese sandwich this is where the protein from the cheese gets digested. A human stomach is a muscular bag which is around the size of a coke can.

    • Word count: 1258

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