4. Food Chains and Energy Pyramids

Question 1

What does each species in a food chain feed on? Are there any exceptions?

Answer 1

• each species feeds on the previous one

- the exception is the producer, which makes its own food by photosynthesis

Question 2

What is the trophic level of an organism?

Answer 2

its position in the food chain

Question 3

Give some examples of trophic levels?

Answer 3

producer, primary consumer, tertiary consumer = different trophic levels

Question 4

How many trophic levels does a food chain usually have?

Answer 4

• commonly: 3 or 4

- rarely: 5+

Question 5

How can the limited length of food chains be explained?

Answer 5

by the theories of energy flow and energy loss:

• only a small proportion of biomass is passed from one trophic level to the next
• this proportion (expressed as %) is variable, but is unlikely to be more than 10%
• once the fourth/fifth trophic level is reached, too little energy remains to sustain another level

Question 6

What do energy pyramids show?

Answer 6

how much energy flows through each trophic level in a community
- they clearly demonstrate the amount of energy dropped along food chains

Question 7

How is energy shown in an energy pyramid?

Answer 7

amount of energy per square meter of area occupied by the community and per year (kJm^-2 year^-1)

Question 8

What shape are energy pyramids? Are they always this shape? Why are they this shape?

Answer 8

• pyramid shaped
• yes
• because energy is lost at each trophic level, so less remains for the next level

Question 9

Energy is lost at each successive stage of an energy pyramid. What is also lost? What does this mean?

Answer 9

biomass

- means that the energy content per gram of tissues of each successive tropic level is not lower

Question 10

How is biomass lost?

Answer 10

• when carbon compounds are broken down by cell respiration and the carbon dioxide produced is excreted
• removal of waste products of metabolism such as urea

Question 11

What type of graph is a pyramid of energy?

Answer 11

a bar chart with horizontal bars arrange symmetrically

Question 12

How should you draw an pyramid of energy?

Answer 12

• bars drawn to scale and arrange symmetrically in horizontal position
• labels should indicate trophic level with producers at the base
• helpful to put energy values alongside each bar on pyramid

Question 13

How can energy pyramids not be drawn?

Answer 13

as triangles - they do not show trophic levels accurately