Key term
OCR GCSE Biology A J247
Cell Level Systems
Topic overviewMicroscopy, and sub-cellular structuresDNA structure: polymer, double helix and nucleotidesEnzyme action, and investigating enzymesCellular respiration as an exothermic processAerobic and anaerobic respiration comparedSynthesis and breakdown of carbohydrates, proteins and lipidsPhotosynthesis: producers and the processPhotosynthesis as endothermic, and investigating itLimiting factors in photosynthesis
Community Level Systems
Genes, Inheritance and Selection
Topic overviewGenetic terms, and the genomeGenome, environment and mutationsAsexual and sexual reproduction comparedHaploid, diploid and meiosisSingle gene inheritance and Punnett squaresSex determination, multiple genes and Mendel's workVariation within a population, and classificationNatural selection and evolutionEvidence for evolution, and the work of Darwin and Wallace
Global Challenges
Topic overviewField investigations, and human impact on ecosystemsMaintaining biodiversity, monitoring conservation and ecotourismFood security, agricultural and biotechnological solutionsSelective breeding and genetic engineeringHealth, disease, and types of diseaseInteractions between diseases, and how they spreadReducing the spread of disease, and named examplesPhysical and chemical plant defencesWhite blood cells, antibodies and plateletsNon-specific defences and the immune systemVaccines, medicines and aseptic techniqueDeveloping new medicines, and non-communicable diseaseTreating cardiovascular disease, and lifestyle factorsCancer, and the use of stem cells in medicineGene technology in medicine, and the human genome
Organism Level Systems
Topic overviewThe nervous system and coordinated responsesThe reflex arcThe eye and its common defectsThe structure and function of the brainHormones and the endocrine glandsHormones in reproduction and the menstrual cycleMethods of contraceptionTropisms, auxin and the roles of plant hormonesHomeostasis, and the skin in temperature controlInsulin and the control of blood glucoseType 1 and type 2 diabetesOsmotic changes in body fluids, and the kidneysKidney structure and the parts of the tubule
Scaling Up
Topic overviewDiffusion, osmosis and active transportMitosis, the cell cycle and cell differentiationStem cells in animals and meristems in plantsSurface area to volume ratio and exchange surfacesThe circulatory system, the heart and blood vesselsRed blood cells and plasmaRoot hair cells, transpiration and translocationXylem and phloemFactors affecting water uptake, and the potometer
Community Level Systems
Pyramids of biomass and the efficiency of transfer
- 3 things to know
- Paper 2
Overview
What biomass is, what a pyramid of biomass shows, why biomass is lost through egestion, excretion and respiration, calculating the efficiency of a transfer, and why food chains stay short.
What you need to know
Answer each one before you reveal it.
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Key term
What is biomass?
Key term
What does a pyramid of biomass show?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is biomass?
Model answer
The mass of living material present in an organism or in a trophic level, usually measured as dry mass.
- 2
What does a pyramid of biomass show?
Model answer
The mass of living material at each trophic level of a food chain, shown as bars drawn to scale in feeding order.
- 3
Explain why a pyramid of biomass is widest at the bottom.
Model answer
The producers hold the most biomass, and biomass is lost at every transfer, so each level above holds less than the one below it.
- 4
Name three ways in which biomass is lost between one trophic level and the next.
Model answer
Egestion, excretion and respiration.
- 5
What is egestion, and how does it lose biomass from a food chain?
Model answer
It is the passing out of undigested food as faeces, so that material is never built into the animal's body.
- 6
What is excretion, and how does it lose biomass from a food chain?
Model answer
It is the removal of waste products made in the body, such as urea, which carries material out of the organism.
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