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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.

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. role of neural mechanism in controlling eating and satiation

The LH is activated when glucose levels fall below a certain level. This causes the individual to become hungry, and triggers the motivation to eat, along with all its accompanying behaviours such as searching for and preparing food. A further neural mechanism associated with LH activity is the secretion of a hypothalamic neurotransmitter called neuropeptide Y (NPY), which is closely associated with hunger and a reduction in physical activity. NPY is a powerful stimulant of hunger. Rats injected with NPY directly into the hypothalamus will eat excessively, and eventually become obese as the injections continue.

• Word count: 1116
2. 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
3. How is biodiversity maintained nationally and globally?

If a species has a low genetic diversity, such problems like change in climate may occur. As humans have begun to spread over the world and increase, the rate of extinction of other species has risen dramatically. For example, the giant sloth and mammals 10000-14000 years ago were animals that were hunted for food. There are two different ways of conserving biodiversity. Conservation in situ is where there are attempts to minimise human impact on the natural environment. It is possible to pass legislation to stop activities such as hunting, logging and clearing land for development and agriculture. However, it can be difficult to enforce it especially if the government is not in favour of it.

• Word count: 1016
4. Abiotic Factors Affecting Organisms - revision notes

Humidity Hygrometers may be designed for indoor or outdoor use (or both). Analog hygrometers use a moisture-sensitive material that is attached to a coil spring. The spring controls a needle on an easy-to-read circular dial. Analog hygrometers are often part of a durable, weather-resistant device that also includes a thermometer. Digital hygrometers determine the relative humidity by using a sensor to monitor an electric current that is affected by moisture levels. Relative humidity, expressed as a percent Salinity Salinity is often measured by measuring how well electricity travels through the water. This property of water is called conductivity.

• Word count: 877