This focus idea is explored through:
Contrasting student and scientific views
The word energy is used every day by students in expressions like, ‘I have run out of energy’ or ‘I need some more energy’. Students’ everyday use of this term can often cause confusion for students when learning to use the correct scientific term. Most students recognise that almost all organisms need a source of energy to survive, function and reproduce. Students are strongly influenced in this area of science by the media and their everyday experiences.
Confusion around specific terms is also addressed in the focus idea
Introducing scientific language.
Students often have trouble interpreting food chains, particularly where the diagram uses arrows to represent energy exchange. Students may see the arrows as referring to a flow of matter (stuff) up a food chain. This is a problem as matter is recycled in an ecosystem but energy is not. Students also have a limited understanding of sources of energy in marine ecosystems, basing most of their understanding on their experiences of land ecosystems. Students are often very egocentric, and believe that all organisms exist solely for the benefit (or annoyance) of humans. For example, students cannot suggest a useful purpose for mosquitoes or spiders.
Research: Driver, Squires, Rushworth & Wood-Robinson (1994)
There is also a widely held conception by students that energy accumulates as one moves up through a food chain and therefore the top predator would have accrued all of the energy from the producers and the other consumers lower down in the food chain.
Students are confused about where plants get their food from and will often believe that it comes from the environment (mainly from the soil and water) rather than from plants manufacturing it themselves. This is because many students have had gardening experiences that involve watering and adding nutrients (fertilizer) to the soil. Students are usually aware that plants use carbon dioxide but are often unsure why and are confused about its involvement in the weight increase of a plant and manufacture of food.
Research: Driver, Squires, Rushworth & Wood-Robinson (1994)
Energy is transferred between organisms in food webs from producers to consumers. The energy is used by organisms to carry out complex tasks.
The vast majority of energy that exists in food webs originates from the sun and is converted (transformed) into chemical energy by the process of photosynthesis in plants. A small proportion of this chemical energy is transformed directly into heat when compounds are broken down during respiration in plants. The majority of the chemical energy stored in plants is transformed into other forms by an assortment of consumers, such as cows, rabbits, horses, sheep, caterpillars and other insects eating plants.
Some of the stored chemical energy in a producer such as grass is stored as chemical energy in the fat or protein in the first order consumers that eat the grass. This energy is available for higher order consumers. At each stage of a food chain, most of the chemical energy is converted to other forms such as heat, and does not remain within the ecosystem.
Critical teaching ideas
- The construction of diagrams with students allows them to represent and clarify their understanding of energy movement in an ecosystem and the transformations involved.
- Energy referred to in the biological sciences is the same as energy referred to in all other domains of science.
- The vast majority of energy in food webs originates from the sun.
- Energy is not recycled in ecosystems and each ecosystem requires a continuous input of energy to sustain it.
- There is some energy transformed at each level of the food chain or food web in an ecosystem.
- In an ecosystem, energy is frequently transformed from one form to another.
Explore the relationships between ideas about energy in ecosystems in the
Concept Development Maps - (Flow of Matter in Ecosystems, Flow of Energy in Ecosystems)
It is important that students are assisted to develop an understanding of the scientific terms ‘food’ and ‘nutrients’ and explore their relationship to energy and matter . The term ‘energy’ as used when working with food webs is identical to the energy that is discussed in other domains of science. A key idea to develop is that energy progresses through the food web (or food chain) from its source, the sun, undergoing repeated transformations. It is also critical to develop the idea that a food web can be complex and is made up of a number of interrelated food chains.
Practise using and build the perceived usefulness of a scientific model or idea
Students should be encouraged to observe and discuss examples of food chains where energy is transformed and matter conserved. Consider undertaking activities that help students to develop an understanding of the source of the vast majority of energy in all ecosystems and the energy transformations that take place as it progresses through the food web. Students could also undertake a number of activities that concentrate on identifying the transformations that energy must undergo as it progresses through an ecosystem.
One approach is for students to investigate the interactive ‘food webs’ website at the following link:
While attempting the tasks students can gain experience at identifying the likely positions that different organisms will have in the food webs they explore. As a follow up task, ask students to cut out pictures of organisms from magazines that are likely to be connected in the same food web or locate images on the internet (or school intranet) for them to construct a PowerPoint or Inspiration food web display. Ask students to identify and discuss the features of their food webs that have been simplified when comparing them to situations that may exist in the real world.
Promote reflection on and clarification of existing ideas
Students could examine a food web where organisms are threatened, removed or die. They could then track how the energy transformations are altered in the food chain (or food web). They can also track how sources of energy for others are changed.
Science related interactive learning objects can be found on the
FUSE Teacher Resources page.
To access the interactive learning object below, teachers must login to FUSE and search by Learning Resource ID:
Ecosystem balance – Students explore how plants and animals interact in three Tasmanian ecosystems: a dry forest, rainforest and seaweed community. They view species descriptions of the plants and animals that live there. They can increase or decrease the population of a species and compare the effects on other species within the ecosystem.
Learning Resource ID: FRZ5RA