Key term
Edexcel GCSE Biology 1BI0
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 calculationsFood tests and the energy in foodDiffusion, osmosis and active transportOsmosis in potatoes and percentage change in mass
Cells and Control
Topic overviewMitosis and the cell cycleWhy mitosis matters: growth, repair and cancerGrowth, differentiation and percentile chartsStem cells and their use in medicineThe structure and function of the brainInvestigating and treating the brainNeurones, receptors and the reflex arcThe structure and function of the eyeEye defects and how they are corrected
Genetics
Topic overviewAsexual and sexual reproductionMeiosis and the formation of gametesDNA structure, genes and the genomeExtracting DNA from fruitProtein synthesis: transcription and translationGenetic variants in coding and non-coding DNAMendel's work and the inheritance of blood groupsAlleles, genotype and phenotypeMonohybrid crosses and sex determinationProbability and ratios from genetic crossesSex-linked disordersCauses of variation: genes and environmentThe Human Genome ProjectGenetic variation and the effects of mutation
Natural Selection and Genetic Modification
Topic overviewDarwin, Wallace and the theory of evolutionNatural selection and antibiotic resistanceFossil evidence for human evolutionStone tool evidence for human evolutionThe pentadactyl limb and the three domainsSelective breedingTissue cultureGenetic engineering and modern agricultureThe stages of genetic engineeringBenefits and risks of GM organisms
Health, Disease and the Development of Medicines
Topic overviewHealth, disease and susceptibilityPathogens and common infectionsHow pathogens spread, and the virus life cycleSexually transmitted infectionsHow plants defend themselves and how plant disease is detectedPhysical barriers and chemical defencesThe immune system, immunisation and herd immunityAntibiotics and developing new medicinesAseptic technique in culturing microorganismsTesting antiseptics and antibiotics on bacterial culturesMonoclonal antibodiesLifestyle factors and non-communicable diseaseTreatments for cardiovascular disease
Plant Structures and Their Functions
Topic overviewPhotosynthesis as an endothermic reactionLimiting factors in photosynthesisLight intensity and the rate of photosynthesisRoot hair cells, xylem and phloemTranspiration and translocationLeaf structure for photosynthesis and gas exchangeFactors affecting the rate of transpirationPlant adaptations to extreme environmentsPlant hormones and their commercial uses
Animal Coordination, Control and Homeostasis
Topic overviewHormones, endocrine glands and homeostasisAdrenalin, thyroxine and negative feedbackThe menstrual cycle and its hormonesHormonal and barrier contraceptionAssisted reproductive technology and IVFHomeostasis and thermoregulationControlling blood glucose, and type 1 diabetesType 2 diabetes and body massThe urinary system and the production of ureaThe nephron, filtration and the effect of ADHTreating kidney failure: dialysis and transplants
Exchange and Transport in Animals
Topic overviewWhy multicellular organisms need exchange surfacesAlveoli and gas exchangeRate of diffusion and Fick's lawThe 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
Topic overviewLevels of organisation and interdependenceAbiotic and biotic factors in a communityParasitism and mutualismSampling with quadrats and transectsEstimating population size from field dataEnergy transfer between trophic levelsHuman impact on ecosystems and biodiversityFood securityThe carbon cycleThe water and nitrogen cyclesIndicator species and pollutionFactors affecting the rate of decompositionCalculating the rate of decay
Genetics
Sex-linked disorders
- 3 things to know
- Paper 1
Overview
Sex-linked disorders carried on the X chromosome such as red-green colour blindness, why males are affected more often, female carriers, why fathers cannot pass the allele to their sons, the chances from a carrier mother's cross, and how a daughter can be affected.
What you need to know
Answer each one before you reveal it.
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Key term
Explain why males are affected by sex-linked recessive disorders far more often than females.
Numbers
A carrier mother and an unaffected father have children. What percentage of their sons are expected to be affected?
Questions from this subtopic
Each one with the model answer underneath.
- 1
On which chromosome is the faulty allele for a sex-linked disorder usually carried?
Model answer
It is usually carried on the X chromosome.
- 2
Name one disorder in humans that is inherited in a sex-linked way.
Model answer
Red-green colour blindness is one example.
- 3
Explain why males are affected by sex-linked recessive disorders far more often than females.
Model answer
A male has only one X chromosome, so a single faulty allele has no matching normal allele to mask it.
- 4
What is meant by a female carrier of a sex-linked disorder?
Model answer
She has the faulty allele on one X chromosome and a normal allele on the other, so she is unaffected but can pass it on.
- 5
Explain why a father with a sex-linked disorder cannot pass the faulty allele to his sons.
Model answer
He passes his Y chromosome to his sons, and the faulty allele is on his X chromosome.
- 6
A carrier mother and an unaffected father have children. What percentage of their sons are expected to be affected?
Model answer
50% of their sons are expected to be affected.
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