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Teacher’s notes

• About the Science IS activities

Integrated strands

Science concept

• A food chain is a diagram used by scientists to represent a list of organisms where each one feeds on the previous one. The list always begins with a producer and finishes with a consumer.

Nature of Science Theme

Scientists’ observations are influenced by their science ideas…

Scientists may observe feeding patterns to help them understand the inter-dependence of a biological community.

DSSA Investigation Focus

Carrying out an investigation includes choosing an appropriate approach…

An investigation may include more than one approach, for example pattern seeking, modelling, and identifying and classifying.

Activity

Prior to this activity

On a field trip to the environment under study, make sure students gather:

• Samples of a variety of living things commonly found in a chosen environment (actual objects or pictures).
• Information about the living things found in the environment, and their lifestyles.

What you need

• Sets of blank cards colour-coded to represent different types of feeders (for example, green for producers, brown for decomposers, red for carnivores, yellow for herbivores).
• For field trip guidelines/activities, see Tidal Communities: Interdependence and the Effects of Change, Building Science Concepts, Book 22.

Focus

• How can we find out what eats what in this community?
• Why is it important to know what eats what in this community?
• Do scientists have a general way of showing feeding patterns?
• How can we create a pattern with the feeding information we gather?
• Will there be the same amount of food at each stage of the food chain?
• At which stage of the food chain does one living thing need the greatest amount of food?

Exploration

1. Use the information about ‘lifestyle needs’ to introduce the idea of food chains.
   Note: Make sure the students understand the conventions of showing the direction of energy flow in food chains (refer to page 4, Tidal Communities: Interdependence and the Effects of Change, Building Science Concepts, Book 22).
2. Discuss the construction of food chains starting with a producer (plants and/or seaweeds and other algae relevant to the environment type), followed by a herbivore, and so on.
3. Introduce the coloured cards to illustrate a food chain.
4. Help students use appropriately colour-coded ‘feeder’ cards to write the name of each living thing they have identified in the chosen environment.
5. Encourage them to lay out the cards in appropriate patterns to create as many (theoretical) food chains as possible.
6. Get students to use research material and their own experiences to check whether the food chains that they create could actually occur in the chosen environment. (Record any questions this raises for subsequent research.)
7. Introduce some simple scenarios for the groups or class to explore in discussing the consequences of change, for example:
   • What would happen if there were no producers?
   • What would happen if we took away most of the yellow cards (herbivores)?
   • Would it matter if we took away all the carnivores? (Students may not realise that this will impact on the needs of other things by allowing unchecked growth of populations that the carnivores usually keep down.)

Extension

• Discuss the effects of a pollutant at a specific level of the food chain.
• One example is the pollution of the sea from factory waste and mercury draining into the sea near the Japanese town of Minamata. Mercury is poisonous but some micro-organisms can absorb it without dying. Small fish take in the bacteria, then the small fish are eaten by larger fish and so on. The mercury level in the largest fish can be 50 000 times greater than in the seawater. If this fish is eaten by humans, the mercury damages the brain. This was first noticed in the 1950s and was called ‘Minamata Disease’.
• Another example could be the problem of dichlorodiphenyltrichloroethane (DDT), a pesticide used until it was banned in 1972. DDT levels can become concentrated in the same way as mercury. Plants absorb DDT, and as herbivores eat large amounts of plants to get enough energy, DDT levels are higher in herbivores than in producers, and higher in carnivores than in the herbivores. This results in higher DDT levels the further along the food chain.
• How would this process affect human health? Can we be sure about ‘safe’ levels of pollutants and some other chemicals?

Reflection

• Did using the coloured cards help you to find a pattern?
• What do all food chains start with?
• Why can’t you just construct any food chain you want?
• What do you notice about the placement of plants in a food chain?
• How would you go about building a food chain with you in it?
• What are the main things you have learned about food chains in nature?
• Scientists can’t ever see a food chain in a community but make models to show the feeding relationships. How could scientists make use of these models?