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
Global Challenges
Interactions between diseases, and how they spread
- 3 things to know
- Paper 8 (Biology)
Overview
How the virus that causes AIDS attacks lymphocytes and makes tuberculosis more likely, how human papillomavirus can lead to cervical cancer and how cases are reduced, how pathogens pass between people, vectors such as mosquitoes, how pathogens spread between plants and through a crop, how fast bacteria multiply, and estimating the number of infections from a sample.
What you need to know
Answer each one before you reveal it.
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Key term
Why is a figure for infected cases worked out from a sample only an estimate?
Key term
Which cells does the virus that causes AIDS attack?
Questions from this subtopic
Each one with the model answer underneath.
- 1
Which cells does the virus that causes AIDS attack?
Model answer
The white blood cells of the immune system, particularly the lymphocytes.
- 2
Explain why a person infected with the virus that causes AIDS is far more likely to develop tuberculosis.
Model answer
The virus destroys the lymphocytes, so the immune system can no longer hold the tuberculosis bacteria in check and a hidden infection becomes active disease.
- 3
What is AIDS?
Model answer
The late stage of infection at which the immune system is so badly damaged that the body can no longer fight off other infections and cancers.
- 4
Why is tuberculosis especially common in populations where infection with the AIDS virus is widespread?
Model answer
Many people already carry the bacteria without symptoms, and a damaged immune system lets those infections become active, so cases rise and spread further.
- 5
Which virus is linked to cervical cancer, and how is it passed on?
Model answer
Human papillomavirus, which is passed on by sexual contact.
- 6
Explain how infection with human papillomavirus can lead to cervical cancer.
Model answer
Some types of the virus alter the genes controlling cell division in the cells they infect, so those cells divide uncontrollably and form a tumour.
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