Why do it?

There are numerous research papers documenting the alternative frameworks that students and teachers have to explain everyday phenomena. (More) Rosalind Driver and others (1994) wrote a very useful book compiling the alternative frameworks which some students have concerning secondary science topics.

Misconceptions is now also an integral part of the KS3 strategy, as there is general consensus that unless teachers are aware of these prior ideas then there will not be the progression in the understanding of the students. Some of these alternative views are very resistant to teaching and it is also possible for the student to hold two different views simultaneously, the alternative and the scientifically accepted one.

Pupils have common misconceptions about the topic plant nutrition; these are useful as they can be directly addressed if the teacher is aware of them.

Students ideas and understanding of plant nutrition

Most pupils have an understanding of how plants make their food by KS3, some of these understandings are scientifically acceptable and some are not. A large amount of research has been carried out on children’s ideas about plant nutrition over the last three decades.

The conceptual demands of the photosynthesis topic were succinctly put by Arnold and Simpson as quoted in Driver (1994 p30); Pupils having to understand that:

‘an element, carbon (which is solid in pure form), is present in carbon dioxide (which is a colourless gas in the air) and that this gas is converted by a green plant into sugar (a solid, but in solution) when hydrogen (a gas) from water (a liquid) is added using light energy which is consequently converted to chemical energy.’

They put also forward the idea that the necessary concepts of gas, food and energy are not fully understood by pupils; therefore, the pupil’s ability to correctly understand the process of photosynthesis is prejudiced.

Studies showed that pupils think ‘that the plants take in organic food substances (such as starch, sugar or protein) from the soil and thought that the plant has multiple sources of food’ (Driver et al 1994). A number of 10 – 19 year old pupils in a survey thought that the soil in a plant pot decrease in mass as a plant photosynthesised (Driver et al 1994).. In Bell’s review (1985), she notes that most of the studies carried out on children’s understanding concluded ‘that plants get their food from the environment, most specifically the soil and that the roots are the organs of feeding.’

Why do pupils find photosynthesis so difficult?

Intrinsic to the students understanding of photosynthesis is their understanding of the word ‘food’ as understood by scientists, as opposed to the everyday usage. As was said by Bell (1985),it is possibly not photosynthesis that the pupils find hard but that it is compounded by the language problem in that words such as food and energy have different meanings in school and everyday science so this is where the problem lies.

Barker and Carr (1989a) described how a majority of textbooks and teaching schemes advocated using a guided discovery approach to teaching photosynthesis. Most textbooks described experiments that involved altering the environmental conditions of the plant and subsequent testing of a leaf for starch. They commented that their research showed this method did not enable the pupils to view photosynthesis as a carbohydrate producing process. This research showed that the chemical tests performed did not actually mean anything to many pupils, some thought that ‘plants produce food by mixing chlorophyll with iodine to make a black substance called starch’. They subsequently developed a teaching scheme that concentrated on photosynthesis as being a carbohydrate producing process called ‘Where does the wood come from’.

As previously mentioned it has been found that pupil’s alternative frameworks of how plants make their food are very resistant to teaching. Anderson and Smith in their 1987 study found that most fifth graders studied thought that plants got their food from the environment. The pupils were subsequently taught about photosynthesis using the traditional textbook-based approach. After eight weeks of teaching, 90% of the pupils still thought that plants take in their food from the environment (Glynn, Yeany & Britton 1991). Therefore, it can be seen that it is important to take the prior ideas of pupils and try to teach with the aim of changing pupils alternative frameworks into scientifically accepted concepts.