Energy flow

Question 1

Pyramids of Numbers and Biomass

Answer 1

• Pyramids of numbers and pyramids of biomass can both be used to represent feeding relationships between organisms in a food chain.
• Pyramids of biomass show the dry mass of living material at each stage of a food chain.

Question 2

They may look different to pyramids of numbers if:

Answer 2

• producers are very large
• a small parasite lives on a large animal.

Question 3

Although pyramids of biomass are a better way of representing trophic level they are difficult to construct. This is because:

Answer 3

• Some organisms feed on organisms from different trophic levels.
• Measuring dry mass is difficult as it involes removing all the water from an organism, which will kill it.

Question 4

As energy flows along the food chain some is used in growth. However, at each trophic level much of the energy transferred into others, less useful forms, such as:

Answer 4

• Heat from respiration
• Egestion
• Excretion.

Question 5

Why is the material lost at each stage not wasted?

Answer 5

Most of the waste is used by decomposers that can then start another food chain.

Question 6

Why are there not long food chains?

Answer 6

Because each trophic level ‘loses’ up to 90 % of the available energy, an animal at the end of a long food chain does not have much food available to it.

Question 7

The efficiency of energy transfer can be calculated between trophic levels:

Answer 7

= energy used for growth/energy input