Key term
Edexcel GCSE Combined Science Biology 1SC0
Key Concepts in Biology
Topic overviewEukaryotic and prokaryotic cellsSpecialised cells and their adaptationsMicroscopes and magnification calculationsSize, scale and units in cell biologyEnzyme action and denaturationFactors affecting enzyme activityEnzymes in synthesis and digestion, and rate calculationsDiffusion, osmosis and active transportOsmosis in potatoes and percentage change in mass
Cells and Control
Genetics
Topic overviewMeiosis and the formation of gametesDNA structure, genes and the genomeExtracting DNA from fruitAlleles, genotype and phenotypeMonohybrid crosses and sex determinationProbability and ratios from genetic crossesCauses of variation: genes and environmentThe Human Genome ProjectGenetic variation and the effects of mutation
Natural Selection and Genetic Modification
Health, Disease and the Development of Medicines
Topic overviewHealth, disease and susceptibilityPathogens and common infectionsHow pathogens spread, and the virus life cycleSexually transmitted infectionsPhysical barriers and chemical defencesThe immune system, immunisation and herd immunityAntibiotics and developing new medicinesLifestyle factors and non-communicable diseaseTreatments for cardiovascular disease
Plant Structures and Their Functions
Animal Coordination, Control and Homeostasis
Exchange and Transport in Animals
Topic overviewWhy multicellular organisms need exchange surfacesAlveoli and gas exchangeThe blood and its componentsArteries, veins and capillariesThe heart and the circulatory systemCellular respiration as an exothermic reactionAerobic and anaerobic respiration comparedInvestigating the rate of respirationCardiac output, stroke volume and heart rate
Ecosystems and Material Cycles
Plant Structures and Their Functions
Limiting factors in photosynthesis
- 3 things to know
- Paper 2
Overview
What a limiting factor is, how light intensity, temperature and carbon dioxide concentration each affect the rate of photosynthesis, why the rate levels off in bright light and falls above about 45 °C, what limits a warm, brightly lit greenhouse, and what a flat section of a rate graph shows.
What you need to know
Answer each one before you reveal it.
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Key term
Explain why the rate of photosynthesis stops rising when light intensity is increased beyond a certain point.
Key term
Explain why the rate of photosynthesis increases when temperature rises from 10 °C to 25 °C.
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is meant by a limiting factor?
Model answer
A limiting factor is a condition in short supply that holds back the rate of a process even when every other condition is plentiful.
- 2
Describe the effect of increasing light intensity on the rate of photosynthesis when the light is dim.
Model answer
The rate rises steadily as light intensity rises, because more light energy is available to be absorbed.
- 3
Explain why the rate of photosynthesis stops rising when light intensity is increased beyond a certain point.
Model answer
Light is no longer the factor in shortest supply, so something else such as carbon dioxide concentration or temperature is holding the rate back.
- 4
Explain why the rate of photosynthesis increases when temperature rises from 10 °C to 25 °C.
Model answer
The enzymes and reacting molecules gain kinetic energy, so they collide more often and react more quickly.
- 5
Explain why the rate of photosynthesis falls sharply above about 45 °C.
Model answer
The enzymes controlling photosynthesis denature, so their active sites change shape and can no longer catalyse the reactions.
- 6
Describe the effect of increasing carbon dioxide concentration on the rate of photosynthesis.
Model answer
The rate increases as carbon dioxide rises, then levels off once a different factor becomes the one in shortest supply.
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