Fig. 19 The cow converts some of the chemical energy in the grass to heat, motion and sound energy. The rest of the chemical energy is stored within the cow and is released when the cow is eaten.
Activity The conversion of chemical energy in food to heat energy.
Apparatus Retort stand, test tube, thermometer, mounted needle, Bunsen burner, graduated cylinder, cream cracker or a crisp.
Method 1. Place 20 cm3
water in a test tube.
2. Record the temperature of the water using a thermometer.
3. Stick the crisp onto the needle and light it with the Bunsen burner.
4. Hold the burning crisp under the test tube until it burns out.
5. Record the new temperature of the water.
Question How does the change in temperature demonstrate the conversion of chemical energy to heat energy?
Food chain A sequence of organisms where each one is eaten by the next.
176 Food sample
Mounted needle
Fig. 20 The heat energy that is released from burning the crisp is measured using a thermometer in a test tube of water.
Food chains The flow of matter and energy through ecosystems can be investigated using food chains. A food chain is a sequence of organisms where each one is eaten by the next. Each time that an organism is eaten the matter and energy it contained passes to the organism that eats it.