2. What are the benefits of eating plants?
Your friend is at university and has phoned you to complain that all she can afford to eat is beans on toast.
How could you make her feel better about her diet?
What are the energy arguments for eating a plant-based diet?

3. An 800 g loaf of bread costs £0.80.
A luxury item?
How can the costs of these food items be compared fairly?
Photo credits: © 2007 Jupiterimages Corporation
A 400 g steak costs £4.00.
An 800 g loaf of bread costs £0.80.
This equals £1.00 per 100 g.
This equals £0.10 per 100 g.
Why is meat more expensive than bread?

4. How energy efficient is it to eat meat?
Food chains can be used to understand why some foods cost more than others. Which of these chains is the most efficient?
The first food chain is the most efficient because it contains fewest trophic levels, so less energy will be lost.

5. Is eating meat less energy efficient?
Cattle and other livestock are fed grain and cereals. Would it be more energy efficient if humans ate the plant crops instead?
If a one-acre field of corn is used to feed cows, it can support one person.
If the same area is used to feed humans directly, it can support 10 people.
Why is so much energy lost?

6. Energy loss in food chains
Teacher notes
This activity provides illustrated information about how energy is lost in food chains. It could be used as an introduction to this topic or for revision purposes.

7. Why do some animals need more energy?
Mammals and birds are able to regulate their body temperature. This has many advantages but it uses lots of energy.
Other animals, such as snakes, lizards and fish, are unable to regulate their body temperature, so need less energy.
Photo credit: © 2007 Jupiterimages Corporation
Would it be more energy efficient to farm snakes for food than chickens?

8. How do you calculate efficiency?
Energy efficiency can be calculated using the following equation: =
efficiency
energy used for growth (input)
energy supplied (output)
For example, if grass receives 1,000,000 kJ of energy from the Sun and uses 20,000 kJ of energy for growth, then:
20,000 kJ
efficiency =
1,000,000 kJ
= = 2%

9. Energy efficiency calculations
Teacher notes
This calculation activity could be used as a plenary exercise to check students’ ability to calculate energy efficiency in food chains.

10. What is a primary producer?
What is a secondary consumer?
What is a primary consumer?
State the formula to calculate the efficiency.