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Delivery guides are designed to represent a body of knowledge about teaching a particular topic and contain:
- Content: A clear outline of the content covered by the delivery guide;
- Thinking Conceptually: Expert guidance on the key concepts involved, common difficulties students may have, approaches to teaching that can help students understand these concepts and how this topic links conceptually to other areas of the subject;
- Thinking Contextually: A range of suggested teaching activities using a variety of themes so that different activities can be selected which best suit particular classes, learning styles or teaching approaches.
In Section B1.3, learners investigated two important cellular reactions that provide cells with the resources necessary to maintain life. This section will look at the reaction necessary to provide one of the reactants needed for cellular respiration.
B1.4a describe photosynthetic organisms as the main producers of food and therefore biomass for life on Earth
B1.4b describe the process of photosynthesis including:
– reactants and products, two-stage process, location of the reaction (in the chloroplasts)
B1.4c describe photosynthesis as an endothermic reaction
B1.4d describe experiments to investigate photosynthesis
B1.4e explain the effect of temperature, light intensity and carbon dioxide concentration on the rate of photosynthesis
B1.4f explain the interaction of these factors in limiting the rate of photosynthesis
Life on Earth is dependent on photosynthesis, in which green plants and algae trap light from the Sun to fix carbon dioxide and combine it with hydrogen from water to make organic compounds and oxygen.
Underlying knowledge and understanding
Learners should have an understanding that plants make carbohydrates in their leaves by photosynthesis, and be able to recall word summaries for photosynthesis.
Common misconceptions or difficulties learners may have
Learners may have a fairly unscientific idea of plant nutrition, often thinking that plants suck it (‘food’) up from the soil through the roots. However, this may be because they believe water is food for plants and this is compounded by the everyday description of fertilisers as ‘plant food’ leading to frequent confusion.
Learners have problems realising that one of the raw materials for photosynthesis is the ‘invisible’ gas carbon dioxide. It may be necessary to convince pupils that carbon dioxide does have mass.
Some learners think that the sunlight absorbed is food. Somewhere in their education they may have been told that plants make their food using sunlight and from this they seem to think that light is converted into food. It will be beneficial if learners can understand that sunlight ‘energy’ gets stored into the internal energy of the bonds of the carbohydrates formed.
Learners find it confusing when text books make inconsistent references to the products of photosynthesis, such as ‘food’ ‘starch’ ‘sugar’ and ‘glucose’ If they can understand that all of these are terms which can be applied to the products of photosynthesis, they are less likely to be confused.
Conceptual links to other areas of the specification - useful ways to approach this topic to set students up for topics later in the course
Photosynthesis is a reaction found in producer organisms. It is specifically covered in the topic ‘Ecosystems’ where it is considered in terms of application to abiotic factors affecting communities and in an understanding of pyramids of biomass.
In the topic ‘Feeding the Human Race’ consideration of the key factors involved in photosynthesis will need to be applied to factors affecting food security and possible agricultural solutions. There will be many other areas where an understanding of photosynthesis will underpin the reasons for other biological processes.
A very quick, easy method to demonstrate an endothermic reaction.
- 25ml citric acid solution
- 15g baking soda
- polystyrene cup
- stiffing rod
1. Pour the citric acid solution in a polystyrene cup. Use a thermometer or other temperature probe to record the initial temperature.
2. Stir in the baking soda (sodium bicarbonate). Monitor the change in temperature over time.
The reaction is:
H3C6H5O7(aq) + 3NaHCO3(s) → 3CO2(g) + 3H2O(l) + Na3C6H5O7(aq)
3. When you have completed your demonstration or experiment, wash the cup out in a sink.
4. Extension activities could include varying the concentration of the citric acid solution or the quantity of sodium bicarbonate. An endothermic is a reaction that requires energy to be added to the system to enable it to proceed. The intake of energy may be observed as a decrease in temperature as the reaction proceeds. Once the reaction is complete, the temperature of the mixture will return to room temperature.
The activity could be introduced by demonstrating or learners actually making a ‘bath bomb’ such as can be found at Cool Science GIFS. This kind of endothermic reaction can then be seen in the context of photosynthesis.
Approaches to teaching the content
A link to Section B1.3 can be made with 'Demonstrating an endothermic reaction', demonstrating the type of reaction that requires energy to be added to the system for the reaction to proceed. Here 'Demonstrating an endothermic reaction' will allow learners to practically measure the temperature changes in an easily managed endothermic reaction.
Learners should have the opportunity to gain investigative skills that will be used throughout the specification through 'Pupil-led photosynthesis investigation'. This will allow learners to plan and manage an investigation to make sure that it is:
If practical resources, or time, are limited then there are a number of interactive online software (such as those identified in 'Pupil-led photosynthesis investigation') that can provide an opportunity to reinforce learning of investigative skills. Learners have the facility to manipulate structures in 3D in order to change variables and measure the effect on photosynthesis.
The idea of this activity is to get learners to examine their misconceptions about photosynthesis (Activity sheet 1 or PowerPoint presentation plus cards 1A - 1D).
It is an activity that gets learners to engage with historical evidence of photosynthesis and the approach could easily be applied to the evidence provided by other historical scientists, such as Priestley's experiment using Cabomba to collect oxygen or Ingenhousz's experiment to show mass gain.
The information covers the historical work done by Jean Baptiste van Helmont in the 16th century. After reading an extract from van Helmont's diary, learners discuss his interpretations. Four typical student responses to van Helmont's experiment are given in the speech bubbles.
Learners are given cards (A-D) as stimulus to talk in structured groups about each of the statements and examine data and pictures of more recent experiments. They summarise their thoughts and feedback to the rest of the class. Throughout the discussion it is important to introduce and reinforce the idea that an increase in mass (biomass) is good evidence that photosynthesis has taken place and carbon dioxide from the air contributes to this.
Details of this activity, and many more designed to overcome misconceptions associated with photosynthesis, can be found at SAPS.
In this practical, learners use algae to look at the rate of photosynthesis. Since algae are tiny and are difficult to work with directly in the water, the first part of the practical involves ‘immobilising’ the algae as algal balls. This effectively traps large numbers of algal cells in ‘jelly like’ balls made of sodium alginate. Sodium alginate is not harmful to the algae, and they will continue to photosynthesise once immobilised.
A video showing how to make ‘algal balls’ and subsequent experiments that can be done is found on YouTube.
Further details of the experiment can be found at Science and Plants for Schools (SAPS).
The ‘algal balls’ learners made earlier, details found above, can be used to promote investigative skills in providing reliable and easily managed photosynthetic material. Alternatively, Cabomba species of pondweed can be used.
A framework for learners to plan, carry out and evaluate their own investigation into factors affecting photosynthesis and to develop their investigative skills can be found at TES Teaching Resources.
If practical resources and equipment are limited there are several proprietary software packages that allow investigations of factors affecting photosynthesis to be carried out interactively. One example can be found at Focus Educational.
The Focus suite of interactive science resources available as an online version compatible with iPads, Android tablets, Windows and Mac. This suite has a Science Apps Pack that allows learners access to a range of interactive resources that they can access on tablets and computers both in school and at home. A free online resource can be found at Syngenta.
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