GCSE Biology: Food Chains, Biomass and Food Security

Why are there so few top predators, and why does it take far more land to produce meat than to produce the same mass of crops? This material answers those questions through the ecology content on trophic levels, pyramids of biomass and food production. Most of it belongs to separate GCSE Biology (for example, the AQA sections on trophic levels, pyramids of biomass, transfer of biomass, decomposition and food production), and it builds on the food chains and cycles covered in the general ecology material of this category.

You start by numbering the trophic levels in a food chain — producers at level 1, then primary, secondary and tertiary consumers, with the apex predator at the top — and by describing how decomposers secrete enzymes into their surroundings and absorb the small soluble molecules produced. You then look at pyramids of biomass: why level 1 always sits at the bottom, and why a pyramid of biomass keeps its shape even where a pyramid of numbers would not, such as a single oak tree feeding thousands of insects.

The central skill is calculating the efficiency of biomass transfer: biomass at the higher level divided by biomass at the lower level, multiplied by 100. The questions give you the figures and ask for answers to the right number of significant figures, alongside the two reference values examiners expect you to know — producers transfer about 1% of the incident light energy for photosynthesis, and only about 10% of biomass passes from one level to the next. You explain where the rest goes: material egested as faeces, carbon dioxide and water lost in respiration, water and urea lost in urine, and glucose used up in respiration. From there you can explain why food chains rarely have more than four or five levels.

The final part turns to food. You look at how temperature, water and oxygen affect the rate of decay, how compost and biogas are produced, what food security means and what threatens it, how intensive farming reduces energy transfer from animals to the environment and why some people object to it, how net size controls and fishing quotas protect fish stocks, and how biotechnology contributes, from mycoprotein made from the fungus Fusarium to GM crops such as golden rice.

Four formats are offered. The quiz has twelve questions with explanations and worked calculations. The flashcards cover the key terms, from trophic level and apex predator to fishing quota and biogas. The printable written sheet has eight longer questions — efficiency calculations from a pyramid, explanations of biomass loss, an evaluation of intensive farming and a compost investigation — to complete by hand and photograph for feedback. The oral exam lets you talk through the topic with an examiner who asks one question at a time and gives short feedback at the end.

All numerical data in the questions are illustrative.

• Assign organisms in a food chain to numbered trophic levels and identify the apex predator
• Describe how decomposers feed and how temperature, water and oxygen affect the rate of decay
• Explain the shape of pyramids of biomass and how biomass is lost between trophic levels
• Calculate the efficiency of biomass transfer as a percentage to a given number of significant figures
• Describe threats to food security and evaluate intensive farming and sustainable fishing methods
• Describe how mycoprotein and GM crops can help feed a growing population

Practice material written by Zestly, based on the DfE GCSE biology subject content and exam-board specification content for separate Biology (for example, AQA GCSE Biology 8461: trophic levels; pyramids of biomass; transfer of biomass; decomposition; food production). All data in the questions are illustrative.