Energy flow 4.2

This topic is all about the way that energy from sunlight is trapped by photosynthesis and then passed from organism to organism in a food web.  We can call this the transfer of energy within food webs. Being able to describe the path taken by the energy as well as interpreting food web diagrams and pyramid of numbers are skills required.

Key concepts

Learn and test your biological vocabulary for 4.2 Energy flow in ecosystems using these flashcards.

Essentials

These slides summarise the essential understanding and skills in this topic. 
They contain short explanations in text and images - good revision for all students.

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Summary

Summary list for topic 4.2 Energy flow in ecosystems

  • Ecosystems get a continuous supply of energy from sunlight.
  • Photosynthesis converts light energy to chemical energy in carbon compounds, e.g. glucose.
  • Chemical energy in carbon compounds flows through food chains by means of feeding.
  • Energy released from carbon compounds by respiration is used in living organisms and is eventually converted to heat which is lost from ecosystems.
  • Living organisms cannot convert heat to other forms of energy.
  • The length of food chains is restricted by energy losses as is the biomass of higher trophic levels.
  • Biomass in terrestrial ecosystems diminishes with energy along food chains due to loss of carbon dioxide, water and other waste products, such as urea.
  • Inorganic nutrients are cycled within ecosystems and their supply is finite. This is in contrast to energy.

Skills (can you ....)

  • Show energy flow using pyramids of energy. Pyramids of energy should be drawn to scale and should be stepped, not triangular. The terms producer, first consumer and second consumer and so on should be used, rather than first trophic level, second trophic level.

Mindmaps

These diagram summaries cover the main sections of topic 4.2 Energy flow in ecosystems.
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Exam style questions

Exam style question about energy flow in ecosystems

The skill of understanding how to draw a pyramid of biomass is important in this topic.

Answer the question below on a piece of paper, then check your answer with the model answer.

Use the data in the table below to draw a pyramid of energy for the river ecosystem. [3]

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Extra exam question on food chains   - - - click the + to open it -- >

This question requires understanding of the transfer of energy between the levels of a food chain.

Answer the question on paper and then check it with the model answer.

Explain why food chains are limited in length. (4 marks)

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 Examiner hint: Explain asks for a detailed account including reasons or causes.

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Test yourself

Multiple choice questions

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Drag and drop activities

Test your ability to construct biological explanations using the drag and drop questions below.

Energy flow through ecosystems is an important concept.

Drag and drop the correct word into the box to summarise energy flow through an ecosystem.

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cannot 50% chemical producers apex detritivores next 10% basis respired light excretion heat previous predators

Primary transduce energy to chemical energy as the of the food chain.

Consumers then ingest energy at the succeeding levels of the food chain. Most of the energy consumed by an organism is and lost as . The remaining loss is due to or as undigested material (not assimilated). Only the energy present in the organism when it is consumed passes to the next level, the rest of the energy goes to and saprotrophs.

Energy flow through a food chain shows the amount of energy passing from one level of a food chain to the . Usually only about (maximum 20%) of the energy available passes from one level to the next.

Energy be recycled and is eventually lost from the ecosystem as heat .

Producers convert light to chemical energy which then passes up the food chain to eventually be lost to the ecosystem as heat.


Just for fun

If you can't see the content below please click this link to Energy flow in ecosystems card match game.

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