Key term
OCR GCSE Combined Science Biology J250
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 mutationsHaploid, diploid and meiosisSingle gene inheritance and Punnett squaresSex determination and characteristics controlled by many genesVariation within a population, and classificationNatural selection and evolutionEvidence for evolution from fossils and antibiotic resistance
Global Challenges
Topic overviewField investigations, and human impact on ecosystemsMaintaining biodiversity, monitoring conservation and ecotourismSelective breeding and genetic engineeringHealth, disease, and types of diseaseInteractions between diseases, and how they spreadReducing the spread of disease, and named examplesWhite 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 arcHormonal coordination, thyroxine and adrenalineHormones in reproduction and the menstrual cycleContraception and treating infertilityHomeostasis and control systems in the bodyInsulin and glucagon in blood sugar controlType 1 and type 2 diabetes
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
Scaling Up
Diffusion, osmosis and active transport
- 3 things to know
- Paper 7 (Biology)
Overview
What diffusion is and why it needs no energy, osmosis and water potential, a plant cell in salt solution, and active transport against a gradient in root hairs and the gut.
What you need to know
Answer each one before you reveal it.
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Key term
In terms of water potential, in which direction does water move between two solutions?
Key term
Which has the higher water potential, pure water or a concentrated sugar solution?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is diffusion?
Model answer
It is the net movement of particles from where they are more concentrated to where they are less concentrated, down a concentration gradient.
- 2
Does a cell have to use energy from respiration to move a substance in by diffusion?
Model answer
No, diffusion is a passive process driven by the random movement of the particles themselves.
- 3
Name one substance that diffuses into a respiring cell and one that diffuses out of it.
Model answer
Oxygen diffuses in and carbon dioxide diffuses out.
- 4
What is osmosis?
Model answer
It is the movement of water across a partially permeable membrane, from a dilute solution to a more concentrated one.
- 5
In terms of water potential, in which direction does water move between two solutions?
Model answer
Water moves from the solution with the higher water potential to the solution with the lower water potential.
- 6
Which has the higher water potential, pure water or a concentrated sugar solution?
Model answer
Pure water, because dissolving sugar in water lowers its water potential.
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