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
Genes, Inheritance and Selection
Sex determination, multiple genes and Mendel's work
- 3 things to know
- Paper 2
Overview
The X and Y chromosomes and which parent decides a child's sex, the Punnett square for the cross, characteristics controlled by many genes, and Mendel's pea crosses and their late acceptance.
What you need to know
Answer each one before you reveal it.
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Key term
Which pair of chromosomes determines sex in humans?
Key term
What sex chromosomes does a human female have, and what sex chromosomes does a human male have?
Questions from this subtopic
Each one with the model answer underneath.
- 1
Which pair of chromosomes determines sex in humans?
Model answer
The sex chromosomes, which are the twenty-third pair.
- 2
What sex chromosomes does a human female have, and what sex chromosomes does a human male have?
Model answer
A female has two X chromosomes, XX, and a male has one X and one Y, XY.
- 3
Which parent determines the sex of a human child, and why?
Model answer
The father, because all of the mother's eggs carry an X chromosome while his sperm carry either an X or a Y.
- 4
In a cross between an XX mother and an XY father, what proportion of the children is expected to be male?
Model answer
One half of them, which is 50%.
- 5
A Punnett square is drawn for a cross between an XX mother and an XY father. What four combinations fill the four boxes?
Model answer
XX, XX, XY and XY.
- 6
What sex chromosome does every human egg cell carry, and what can a sperm cell carry?
Model answer
Every egg carries an X chromosome, while a sperm carries either an X or a Y.
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