Energy for biological processes - ATP, photosynthesis and respiration
All organisms need energy. Life depends on the transfer of energy. ATP is an important source of energy for biological processes. Energy is transferred from molecules such as glucose, to an intermediate energy source, ATP.
ATP is a reservoir of potential chemical energy and acts as a common intermediate in metabolism, linking energy requiring and energy yielding reactions. A level biologists need to know the structure of ATP, its uses and its role in biological processes.
In photosynthesis energy is transferred to ATP in the light-dependent stage and the ATP is utilised during synthesis in the light-independent stage. Students should know in detail the chemical process of photosynthesis. This topic often proves very challenging for students and they can easily become confused, making simple mistakes such as pigments absorb light rather than absord light energy.
In cellular respiration, glycolysis takes place in the cytoplasm and the remaining steps in the mitochondria. ATP synthesis is associated with the electron transfer chain in the membranes of mitochondria. Students need to be able to explain the process of glycolysis, with the resulting production of ATP and reduced NAD. They then need to be able to describe and explain the remaining steps, in terms of the link reaction, Krebs cycle and electron transport chain.
Whilst this list provides a source of information and ideas for experimental work, it is important to note that recommendations can date very quickly. Do NOT follow suggestions which conflict with current advice from CLEAPSS, SSERC or other recent safety guides. eLibrary users are responsible for ensuring that any activity, including practical work, which they carry out is consistent with current regulations related to Health and Safety and that they carry an appropriate risk assessment. Further information is provided in our Health and Safety guidance.
Algal Balls - Photosynthesis Using Algae Wrapped in Jelly Balls
This protocol is very reliable and allows students to look at the rate of photosynthesis with quantifiable and replicable results.
The green algae Scenedesmus quadricauda is immobilised in alginate beads. Changes in the colour of hydrogen carbonate indicator solution can then be used to investigate the rate of photosynthesis under different environmental conditions.
For quantitative data, the indicator can be removed from the bottles of algal balls, placed into cuvettes, and the absorbance measured using a colorimeter.
Students will also enjoy making their own algal balls.
A-level set practicals: factors affecting rates of photosynthesis
This updated version of the SAPS algal balls resource is designed to support the use of practicals across 2015 A-level biology specifications.
Students measure the rate of photosynthesis in comparison to the rate of respiration. Because of this, it is possible to determine the light intensity at which the photosynthesising material is using the same quantity of carbon dioxide in photosynthesis as it is producing in respiration (the light compensation point).
This practical provides the opportunity for skills development in
- the use of appropriate instrumentation (a colorimeter) to record quantitative measurements
- the safe and ethical use of organisms to measure plant responses to changing conditions
- the use of computer modelling, or a data logger to collect data, or the use of software to process data
- immobilisation of organic material (in this case algae but the technique is often used for enzymes as well)
- the use of a smart phone as a lux meter (optional)
- graphical skills (including plotting graphs with lines of best fit and reading off intercept points).
The Respiration of Higher Plants
This resource is one of the many in-depth topic booklets available in the Institute of Biology series. It provides an account of the biochemistry of respiration in higher plants. The booklet is quite unusual in dealing with respiration of higher plants specifically, as although basic respiratory processes are the same, plants do exhibit biochemical idiosyncrasies.
The whole booklet would make interesting reading for teachers who need to refresh their subject knowledge on the topic of respiration before delivering it to students.
Photosynthesis *suitable for home teaching*
This article from the Catalysts magazine provides a good overview of the process of photosynthesis, but does not go into the biochemical reactions involved.
The article includes some excellent illustrations of plant and leaf structure showing how this is linked to the processes of photosynthesis and respiration within plants.
This article could be used at the start of a topic on photosynthesis to recap with students their knowledge and understanding from Key stage Four.
It could then be used later on in the topic as a template for an article where students are asked to write about the process of photosynthesis, to include information on how energy is transferred to ATP in the light dependent stage and ATP is utilised during synthesis in the light-independent stage
Measuring Photosynthesis with Cabomba
In this investigation from Science & Plants for Schools (SAPS), students are able to measure photosynthesis using Cabomba.
Cabomba is widely available and is an alternative to using Elodea. Cabomba is highly reliable, especially compared to Elodea.
The protocol for this investigation is relatively straightforward, and with A level students it would therefore be possible to alter variables to compare results and relate this to the limiting factors involved in photosynthesis. This investigation could consider different light concentrations (students will need to think about heat from the lamps), different wavelengths of light by use of coloured filters, and the effect of temperature.
It would also be possible to link sensors and data loggers to this investigation.
Advanced investigation of the light dependent reaction in photosynthesis
This investigation is a good way to test A level biologists understanding of the link between the light-dependent and light-independent reactions in photosynthesis. Without a clear understanding of the link between these reactions students will struggle to interpret the results.
The protocol for this investigation is also challenging and will test the practical abilities of many students, but it is worth doing.
The resource also very helpfully includes a set of results for students to interpret should the results from their own investigation not be as expected. They can compare their results against the provided results and evaluate any possible sources of error.
Respiration Changes During Fruit Ripening and Storage
In this investigation from Science & Plants for Schools (SAPS), students are asked to consider how respiration changes during the fruit ripening and storage process.
This investigation provides two different protocols, one of which students could alter to investigate a range of variables.
In the first protocol the respiratory activity in tissue slices of fruit are investigated by using tetrazolium chloride (TTC), which produces a red colour in respiring tissues. This is a straightforward observation activity however students could be asked to alter the protocol to consider one or more of the following:
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Does the rate of respiration vary during the ripening process?
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Does the temperature of storage affect the rate of respiration?
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Does the skin affect the exchange of gases between a fruit or vegetable and the atmosphere?
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Does an infected fruit or vegetable have a higher respiratory rate than a healthy one?
The second protocol in this investigation entitled Measuring carbon dioxide (from respiration) using baryta water involves using a titration, following the absorption of carbon dioxide by barium hydroxide solution.
Measuring Respiratory Quotient
This investigation using a respirometer provides a quantitative method of exploring metabolism. There are alternative investigations available, which will give a rate of respiration, but this investigation provides a suitable level of challenge for A level. In this investigation students will be able to calculate the respiratory quotient.
There is a downloadable student sheet for this investigation (scroll to the bottom of the page) which does include some useful post experimental questions (remember to remove the last page which gives the answers).
Respirometer questions are popular in exams at A level (as well as GCSE), so this would be a very useful investigation for students to have completed.
As with any respirometer investigation if the respiring material used are invertebrates, it is very important to handle these organisms carefully.
A-level set practicals: TLC of plant photosynthetic pigments
This resource, from SAPS, supports the use of practicals across 2015 A-level biology specifications.
Students conduct Thin Layer Chromatography (TLC) individually or in pairs to separate and identify the photosynthetic pigments from plant material within half an hour. This simple method has been designed to produce good separation of photosynthetic pigments using solvents that are suitable for use in a school biology laboratory. By using grass from a school lawn or playing field, students can see the variety of different molecules that can be separated from a plant that they are all very familiar with.
These resources and this practical allow students to develop their understanding of photosynthetic pigments and how chromatography separates molecules. By taking simple distance measurements from the chromatogram for calculating Rf values, this practical provides a good opportunity to introduce the concept of percentage error. It provides students with the opportunity to develop (and demonstrate) their skills of taking quantitative measurements as well as their ability to consider variables that need to be controlled.
Materials include:
- Tested materials to support the A-level practical endorsement (CPAC)
- Support materials for teachers and technicians
- Student worksheet to help provide evidence for meeting the practical skills requirements
- Student revision materials to help prepare for exams