Photosynthesis
The importance of photosynthesis needs to be appreciated by GCSE Biology students; they should relate this to the fact that photosynthetic organisms are the main producers of food and therefore biomass for life on Earth. Students should be able to describe the process of photosynthesis, including how it is an endothermic reaction. The effect of factors including temperature, light intensity and carbon dioxide concentration on the rate of photosynthesis all need to be understood and the interaction of these factors in limiting the rate of photosynthesis needs to be explained.
Students often confuse the processes of photosynthesis and respiration in plants. They have a misconception that respiration in plants is different to that in other organisms, resulting in the production of Carbon Dioxide. In teaching about photosynthesis it is important to stress that in plants both processes occur depending on conditions and that respiration in plants is the same as in all other organisms.
Some misconceptions that students have about photosynthesis may be as a result of "learning" about the process from an early age, so they often think that the sunlight absorbed by a plant is actually food and that plants "suck up" food from the soil. Students also struggle with the concept of Carbon Dioxide being used in photosynthesis as it isn't something they can see.
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 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.
Photosynthesis *suitable for home teaching*
This Catalyst article looks at the process of photosynthesis, by which plants make a range of biochemical compounds. The article explains how photosynthesis actually ties in with growth. Respiration is happening all the time in all cells in all living organisms. Taken on its own, photosynthesis adds materials to the structure of a plant and this is explored together with annotated diagrams about leaf structure.
Students could be given this article as pre-reading for a lesson and be prepared to give a two minute summary of a particular aspect of the article.
There are many ways to make use of Catalysts articles with students, a booklet outlining some of these ideas with six exemplar activities can be found at :https://www.stem.org.uk/elibrary/resource/27308
Photosynthesis *suitable for home teaching*
This film, from Twig World, journeys into the chloroplast to show how plants convert sunlight into usable chemical energy through the process of photosynthesis. The key points covered in the film are:
- Leaves are small solar-powered food factories.
- Through a process called photosynthesis they make their own food.
- Using only water, carbon dioxide and the Sun's energy they produce glucose and oxygen.
- They form the basis of the global food chain.
Students could watch this video in pairs and then be asked to identify these four key points, either from scratch or provided with a gapped handout.
Nuffield Biology Activities for GCSE
Although this is quite a dated publication there are a range of possible activities within it that could be used to support the teaching and learning of this topic. Activity B6 (page 12-teachers notes)is a straightforward worksheet on photosynthesis, this could easily be used as a self-study/homework activity. Activity B10/B11 (teachers notes page 19) is the classic factors affecting photosynthesis experiment, these sheets could be used before students complete this practical and/or as revision activity .
Measuring Photosynthesis with Cabomba
This is a reliable investigation to demonstrate photosynthesis, produced by Science and Plants for schools (SAPS). When the pond-weed Cabomba is placed in a solution of sodium hydrogen carbonate in the presence of light of appropriate intensity, it will begin to produce bubbles of oxygen-containing gas. These bubbles can be counted and the rate of bubbling can serve as an indication of the rate of photosynthesis. Cabomba is highly reliable, especially compared to Elodea, which is often used to demonstrate this process.
Investigating Factors Affecting Photosynthesis Using Leaf Discs
Another enjoyable and reliable practical activity from SAPS, allowing students to compare factors affecting photosynthesis. Possible investigations could include the rate of photosynthesis in sun and shade plants, and at different light intensities. Students punch out small discs from leaves, and float them in a syringe of sodium hydrogen carbonate solution. Once gas is evolved by photosynthesis, the leaf discs rise and fall.
Algal Balls - Photosynthesis Using Algae Wrapped in Jelly Balls
This reliable practical allows students to use algae to look at the rate of photosynthesis with quantifiable and replicable results. In this protocol, the green alga Scenedesmus quadricauda is immobilised in alginate beads. Changes in the colour of hydrogen carbonate indicator solution (also called bicarbonate indicator) can then be used to investigate the rate of photosynthesis under different environmental conditions.
Chlorophyll fluorescence
This is a straightforward and relatively simple practical investigation which allows students to see how chlorophyll can be energised and how this causes it to fluoresce. In this experiment, students can observe chlorophyll fluorescing. This is an engaging practical which is quick to set up and carry out, detailed teacher notes are also provided
The Hypothesis
This video clip explains that phytoplankton absorb carbon dioxide and can act as indicators of global warming. The video whilst interesting is not as relevant as activity D which is a standard investigation to measure the rate of photosynthesis using pond weed in varying concentrations of carbon dioxide. This investigation is clearly and concisely presented for students to follow. There are also teachers' notes available, these can be accessed by clicking onto the teacher guidance link.
Video clip on oxygen production in plants
This video clip from the BBC demonstrates a classic experiment to investigate the production of oxygen by plants through photosynthesis. Students could be asked to watch this for homework and be prepared to give a two minute summary of the video at the start of the next lesson.
Where do trees get their mass from?
This short video explores the idea that trees weigh tons, so where do they get their mass from? It would be an interesting question to pose to students as a starter activity and then they could watch the video to see how their understanding of photosynthesis should have led them to the correct answer
