Unit 3 – Food and Ecology

This unit looks at energy flow in nature, how much energy is available in different foods, and the energy costs involved in some modern food production processes.  The background reading introduces the concepts tested in:

Activity 1 - Investigation of stored energy in food
Activity 1 Datasheet
Activity 2 - “Energy costs” of food products
Activity 2 Datasheet

Background – An introduction to energy in food

Remember that energy is the ability to do work? Well think how much work your body must do to keep you alive an healthy. It takes energy to allow you to move, think, dance… it even takes energy for you to sleep because your body keeps all your systems working while you rest.

Where does this energy come from?

• All energy comes first and foremost from the sun. Remember the law of conservation of energy? “Energy cannot be created or destroyed, it can only change from one form to another". This means that the energy going into an ecosystem from the sun is the only energy available to drive and support all living things which are there.
• Green plants, algae and some micro-organisms trap a small amount of the sun’s energy when it hits earth. They do this by photosynthesis. This means plants can make their own food by changing light energy to chemical energy.
• Animals, including humans, cannot make their own food so they must eat plants and vegetables and also other animals to get their energy. Animals release the energy from food by respiration. The relationships between organisms and their food sources can be demonstrated by food chains and food webs. A food web represents energy flow in ecosystem.

How is energy stored in food?
Different foods have different amounts of energy stored in them.  The energy food you’re your body likes most is carbohydrates.  Starch and sugar are types of carbohydrates, so foods such as bread would contain lots of energy.  There is also lots of energy in fat, but this is released more slowly into the body and too much is not very good for you.  To get energy from food, your body breaks down carbohydrates to the simple sugar glucose.