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How does energy transfer through an ecosystem, and how do humans affect biodiversity?

Explain energy transfer between trophic levels and biomass calculations, the positive and negative human impacts on biodiversity, the benefits of maintaining biodiversity, food security, and indicator species.

A focused answer to Edexcel GCSE Biology 9.7B to 9.11B and 9.16B, covering energy transfer and biomass efficiency between trophic levels, human impacts on biodiversity, conservation, food security and indicator species.

Generated by Claude Opus 4.810 min answer

Reviewed by: AI editorial process; not yet individually human-reviewed

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  1. What this dot point is asking
  2. Energy transfer and trophic levels
  3. Biomass efficiency calculations
  4. Human impact on biodiversity
  5. Food security and indicator species
  6. Try this

What this dot point is asking

Edexcel statements 9.7B to 9.11B and 9.16B (mostly Biology only) want you to explain energy transfer between trophic levels and do biomass efficiency calculations, describe the positive and negative human impacts on biodiversity, explain the benefits of maintaining biodiversity, describe factors affecting food security, and explain the use of indicator species to assess pollution.

Energy transfer and trophic levels

This loss is why food chains rarely have more than four or five levels: there is not enough energy left to support another level.

Biomass efficiency calculations

Human impact on biodiversity

Humans affect biodiversity in both directions:

  • Negative impacts: deforestation and habitat destruction remove where organisms live; pollution of air, water and land harms organisms; overhunting and overfishing reduce species; and farming over large areas reduces variety.
  • Positive impacts (conservation): reforestation and replanting, setting up protected areas and nature reserves, breeding programmes for endangered species, and reducing pollution all help maintain biodiversity.

The benefits of maintaining biodiversity include protecting food supplies and resources, keeping ecosystems stable, supporting tourism, and preserving species that may have future medical or economic value.

Food security and indicator species

Food security means having enough safe, affordable food for a population. It is affected by biological factors such as a rising human population, changing diets, new pests and pathogens, the cost of farming inputs, and environmental change such as drought.

Indicator species are organisms whose presence or absence shows the level of pollution. For example, certain lichens and mayfly larvae only survive in clean air or water, so finding them indicates low pollution, while their absence (or the presence of pollution-tolerant species) indicates higher pollution. Indicator species give a quick biological measure of environmental quality.

Try this

Q1. State two reasons why energy is lost between trophic levels. [2 marks]

  • Cue. Any two of: respiration releasing heat, waste (faeces and urine), and uneaten parts of the organism.

Q2. Give one way humans reduce biodiversity and one way they can protect it. [2 marks]

  • Cue. Reduce: deforestation, pollution or overhunting. Protect: reforestation, conservation areas, or reducing pollution.

Exam-style practice questions

Practice questions written in the style of Pearson Edexcel exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

Edexcel 20193 marksA producer contains 50000 kJ of energy. The primary consumers that eat it contain 4000 kJ. Calculate the percentage of energy transferred to the primary consumers, and explain why it is low.
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A 3-mark question rewards the percentage calculation and a reason for the loss.

Percentage transferred =energy in consumersenergy in producers×100=400050 000×100=8%= \dfrac{\text{energy in consumers}}{\text{energy in producers}} \times 100 = \dfrac{4000}{50\,000} \times 100 = 8\%.

The percentage is low because energy is lost between trophic levels: it is used in respiration (and released as heat to the surroundings), lost in waste materials (faeces and urine), and some parts of the producer are not eaten.

Markers reward the correct percentage (8%8\%) and at least two reasons for energy loss (respiration or heat, and waste or uneaten parts). Forgetting that respiration releases heat is a common gap.

Edexcel 20214 marksExplain two ways humans can have a negative impact on biodiversity and one way biodiversity can be protected.
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A 4-mark question rewards negative impacts and a protective measure.

Negative impacts: deforestation and habitat destruction remove the places organisms live, reducing biodiversity; pollution (of air, water or land) harms or kills organisms; and overhunting or overfishing reduces species numbers.

Protection: biodiversity can be protected by conservation measures such as reforestation, setting up protected areas and nature reserves, breeding programmes for endangered species, and reducing pollution.

Markers reward two distinct negative impacts and one valid protective measure. Repeating the same impact in different words, or giving a measure that does not protect biodiversity, loses marks.

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