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
Organism Level Systems
Tropisms, auxin and the roles of plant hormones
- 3 things to know
- Paper 1
Overview
Tropisms, phototropism and gravitropism, where auxin is made and how its uneven spread bends shoots towards light and roots downwards, the processes plant hormones control, and why controlling germination and shedding leaves before winter helps a plant.
What you need to know
Answer each one before you reveal it.
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Key term
What are phototropism and gravitropism?
Evaluation
Why is it an advantage to a plant for its shoots to grow towards the light?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is a tropism?
Model answer
A growth response of a plant in which the direction of growth is set by the direction of the stimulus.
- 2
What are phototropism and gravitropism?
Model answer
Phototropism is a plant's growth response to light and gravitropism is its growth response to gravity.
- 3
Where is auxin made in a growing shoot?
Model answer
In the tip of the shoot.
- 4
Explain how the unequal distribution of auxin makes a shoot bend towards light coming from one side.
Model answer
Auxin moves to the shaded side, where it makes the cells elongate more than those on the lit side, so that side grows longer and the shoot bends towards the light.
- 5
Why is it an advantage to a plant for its shoots to grow towards the light?
Model answer
The leaves receive more light, so the plant can photosynthesise faster and grow better.
- 6
Explain why a root grows downwards when a seed germinates on its side.
Model answer
Auxin collects on the lower side of the root, where it slows down cell elongation, so the upper side grows faster and the root curves downwards.
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