Explain inefficient energy transfer
Energy transfer between trophic levels is often inefficient because some material is not consumed or assimilated and organisms transfer energy to the environment.
Exam scope and assessment notes
Mapped to the named 0973 section using teaching from the corresponding single-science course. A 0973-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade. This qualification reports two grades on the 9–1 scale; confirm the entry route for your zone and exam series.
Before you begin
- Read energy-transfer arrows and distinguish energy from matter in the 19.1 Energy flow pathway.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which combination explains why less energy reaches the next trophic level?
What you will learn
- Explain why energy available to the next level is reduced
- Distinguish energy flow from matter recycling
Track what happens to food energy
Not all biomass at one trophic level is eaten by organisms at the next: parts may be inedible, die or remain uneaten. Some eaten material is not digested and leaves as waste. Of the energy assimilated, organisms use some in respiration and other life processes; energy is transferred to the environment, including as heat.
These routes explain why less energy is available to the next trophic level. Energy is not destroyed. “Lost” in an ecological explanation means transferred out of the food-chain pathway to the environment or remaining in material that is not passed on.
Do not turn the explanation into a universal percentage
The proportion transferred varies with organisms and conditions. Unless a question supplies data, explain the pathways qualitatively rather than inventing a fixed efficiency. Nutrients in matter may be recycled; energy flows through organisms and eventually to the environment.
Use the evidence in a question to calculate an efficiency if values are supplied, and state the calculation basis. Without values, identify the biological reasons for the transfer being less than complete.
Sources for this lesson
Pause and explain
What does “energy lost from a food chain” mean in this context?
Worked example
A caterpillar eats a leaf, but a bird later receives only some of the leaf’s stored energy. Give two reasons why transfer is incomplete.
Show the worked solution
- Some leaf material may not be eaten or digested.
- The caterpillar uses energy in respiration and transfers some to the environment.
Answer Some leaf material is not eaten or assimilated, and energy is used in respiration and transferred to the environment, including as heat.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
A fox eats a rabbit but receives only part of the rabbit’s energy. Give two biological reasons.
Give me a hint
Consider consumption, assimilation and life processes.
Compare my reasoning
- Some rabbit parts may not be eaten or digested.
- The rabbit’s stored energy is also used by the rabbit before it is eaten; the fox uses assimilated energy in respiration.
Some material may be uneaten or undigested, and energy in the rabbit has been used in life processes; the fox also transfers energy to its environment through respiration and activity.
Look for these in your work
- More than one pathway named
- Energy not described as destroyed
A student writes “90% of energy is lost at every trophic level” without data. What is the problem with the statement?
Give me a hint
Distinguish a qualitative syllabus explanation from a measured value.
Compare my reasoning
- Transfer efficiency varies.
- A percentage requires specific data and a stated calculation basis.
The statement gives an unsupported fixed percentage. Explain uneaten, undigested and life-process routes qualitatively unless the question provides data for a calculation.
Look for these in your work
- Unsupported figure identified
- Valid explanation offered
Explain why nutrients can be recycled while energy is not recycled through the same loop.
Give me a hint
Compare matter and energy pathways.
Compare my reasoning
- Matter can be rearranged in decomposition and taken up again.
- Energy is transferred and eventually to the environment.
Decomposition can release nutrients that producers reuse, whereas energy flows through organisms and eventually transfers to the environment; it is not recycled as nutrients are.
Look for these in your work
- Matter pathway explained
- Energy pathway distinguished
Common mistakes
- Saying energy is destroyed
- Giving an unsupported percentage for transfer
- Confusing nutrient recycling with energy flow
What can you explain now?
Which combination explains why less energy reaches the next trophic level?
Compare with the explanation
Uneaten or undigested material and energy used in life processes
Both reduce energy available to the next level.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Name two reasons why energy transfer between trophic levels is often inefficient and explain what “lost” means.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.