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AS and A Level: Energy, Respiration & the Environment

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Things to remember when planning an A level experiment

  1. 1 Write your procedure/method as a series of numbered steps. This helps the reader to follow your procedure easily. Describe precisely how you plan to control all control variables. Explain why it is necessary to control these variables in terms of how they could impact on the results.
  2. 2 Include all volumes, weights, concentrations, times, temperatures etc ensuring that you specify SI units. The method needs to provide all relevant details, so that another A-level student could complete the experiment to obtain data.
  3. 3 Use the results of a trial experiment to explain your reasons for selecting specific equipment, volumes, times, independent variable ranges, concentrations, pH, etc.
  4. 4 Clearly state the statistics test you plan to use to analyse your data. To look for:
    a) Statistically significant relationships between the independent and dependent variables use Spearman’s rank.
    b) Statistically significant differences between two categories use t-tests for normally distributed data or a Mann Witney U for non-normally distributed data.
  5. 5 Ensure that you state the range you plan to investigate and the number of times you will repeat the experiment clearly. Make sure that you include an independent variable range of at least 7 if you plan to use Spearman’s rank (eg. 7 different temperatures or concentrations) or at least 6 repeats if you plan to use the Mann Witney U test for difference.

Helpful hints for ecological sampling

  1. 1 Systematic sampling along a transect is used to investigate species distribution along an environmental gradient. For example if you are investigating the effect of water depth on seaweed growth as you move further up a rocky shore, you would use a transect and sample systematically at specified intervals (eg 2 Metres).
  2. 2 Random sampling is used to investigate the abundance of species in two distinct areas. For example the growth of daisies in mowed and un-mowed areas of a park.
  3. 3 Quadrats are used for both systematic and random sampling to ensure that species are counted within a defined and controlled area.
  4. 4 Random coordinates are generated and used to sample un-biased areas of each plot during random sampling.
  5. 5 The data from systematic sampling is analysed for correlation using Spearman’s rank. The data from random sampling is analysed for significant difference using a t-test (if the data is normally distributed) or Manny Whitney U.

Respiration and ATP facts

  1. 1 Energy cannot be produced, it is transferred. Conversely ATP is produced when energy is transferred from glucose during respiration.
  2. 2 The energy stored in ATP is released after ATP is hydrolysed to ADP and Pi. Some energy is required for ATP hydrolysis, but when bonds form between Pi and water more energy is released than is required for the initial hydrolysis of ATP, i.e. the reaction is exergonic.
  3. 3 Glycolysis is the first step in both aerobic and anaerobic respiration. Glycolysis occurs in the cell cytoplasm and yields 2 ATP molecules by substrate level phosphorylation. Glycolysis is the only source of ATP in anaerobic respiration.
  4. 4 The link reaction, Kreb’s cycle and electron transfer stages of respiration occur in the mitochondria and depend on oxygen as a terminal electron acceptor. In the absence of oxygen these aerobic stages cannot take place.
  5. 5 In aerobic respiration the majority of ATP is produced as a consequence of electron transfer. Each reduced NAD molecule donates electrons to the electron transfer chain, and 3 ATP molecules are generated as a consequence. Each reduced FAD molecule that donates electrons leads to the generation of 2 ATP molecules. During glycolysis, the link reaction and the Kreb’s cycle a total of 10 reduced NAD and 2 reduced FAD are produced, leading to the generation of approximately 34 ATP molecules following electron transfer.

  • Marked by Teachers essays 42
  • Peer Reviewed essays 15
  1. Aim: To see how productivity of algae and Elodea changes with depth in a simulated lake.

    Fill each bottle with pond water and add a strand of Elodea. Secure the correct number of OHP films around each labeled bottle. Use the elastic bands to hold them in position. Take care not to cover the Elodea. Cover the dark bottles in aluminum foil. Measure the DO in mg/l in each bottle and record in a table ? these are the initial readings. Record each bottle three times after stirring the probe gently for 10 seconds. Place each bottle on its side under the light array.

    • Word count: 942

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