Pearson Edexcel · International A-Level

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Supports de cours · Biologie A-Level (19)

Fiches d'exercices · Biologie A-Level (44)

Diaporamas de présentation · Biologie A-Level (19)

Unités de cours et objectifs d'apprentissage

Ces leçons abordent des objectifs de cours sélectionnés. Vérifiez les lacunes restantes en couverture ; ce matériel ne constitue pas un programme d'entraînement complet.

Leçons →Pratique du vocabulaire →

1 · Molecules, Diet, Transport and Health

Breakdown of large food molecules.
Absorption moves soluble products into blood or lymph. Thin exchange surfaces and a large surface area shorten diffusion paths and increase transfer. Enzyme activity and transport are different processes.
Use Benedict reagent with controlled heating for reducing sugars, iodine for starch, Biuret reagent for protein, and the ethanol emulsion test for lipids. Keep ethanol away from flames. Use positive and negative controls.
Net water movement through a partially permeable membrane.
Use percentage change to compare samples with different initial masses. A zero percentage change estimates a solution concentration with no net water movement. This is an estimate from a trend, not proof that water molecules stop moving.
Use equal-length cylinders from similar tissue, fixed solution volume, temperature and immersion time. Blot each cylinder in the same way before weighing. Repeat each concentration and plot mean percentage change against concentration.
Formation of RNA using a DNA template.
A codon comprises three bases. The genetic code is degenerate: more than one codon can specify the same amino acid. A substitution can therefore be silent, while insertions or deletions can shift the reading frame.
Keep DNA template, coding DNA and mRNA distinct. State the strand used and write sequences in the required direction. Use a codon table for mRNA, not an unexplained DNA triplet.

digestion: Décomposition des grandes molécules alimentaires
absorption: Transport des produits solubles vers le corps
osmose: Mouvement net de l'eau à travers une membrane partiellement perméable
variable de contrôle: Un facteur maintenu constant pour une comparaison équitable
transcription: Formation d'ARN à partir d'un brin d'ADN
traduction: Formation d'un polypeptide à partir d'une séquence d'ARNm

2 · Cells, Development, Biodiversity and Conservation

Image length divided by actual length.
A scale bar provides a known real distance in the same image. Convert the image length and real length to the same unit before dividing. Magnification is a ratio and has no unit.
Focus a prepared slide at low power first. Move to a higher power and use fine focus. Make a clear line drawing, label structures with straight lines, and record the scale rather than shading the image.
A variant of a gene.
In a simple monohybrid cross Aa × Aa, gametes carry A or a. Combining independent gametes gives AA, Aa, Aa and aa. The predicted probabilities describe many possible fertilizations, not a fixed order of children.
Write parental genotypes and gametes before making the grid. State the inheritance model and phenotype key. Use a pedigree to check consistency with a model; do not infer certainty from a small family alone.
A defined area used for sampling.
Estimate total abundance by multiplying mean density by area, with consistent units. This assumes sampled areas represent the habitat. Patchiness and too few samples widen uncertainty.
Choose coordinates with random numbers before visiting the patches. Record quadrat area and counting rules. For a transect, use fixed distances and measure a relevant abiotic variable. Do not damage habitats or sample unsafe locations.

organite: Longueur de l'image divisée par la longueur réelle
résolution: Capacité à distinguer deux points proches
allèle: Une variante d'un gène
génotype: Les allèles que porte un organisme
quadrat: Une zone définie utilisée pour l'échantillonnage
population: Organismes d'une même espèce dans une zone définie

3 · Practical Skills in Biology I

A biological catalyst.
Measure rate using product formed per unit time or a fixed endpoint. For an endpoint test, 1/time is a rate proxy if the same amount of product or substrate change defines the endpoint each time.
For starch digestion, equilibrate enzyme and starch in a water bath, control pH with buffer, mix measured volumes, and test samples with iodine at fixed intervals. Use a clean spot for each test. Do not put iodine into the reaction mixture.
A quantified limitation on a measured result.
For a product or quotient, adding fractional uncertainties is a common maximum-uncertainty approximation. For a difference, add absolute uncertainties. A nonzero intercept can reveal an offset or an incomplete model.
Show units on axes and choose a sensible scale. Plot uncertainty bars where justified, draw a best-fit line rather than joining every point, and estimate steepest and shallowest plausible gradients when the course method calls for them.

enzyme: Un catalyseur biologique
dénaturation: Une modification structurale qui altère la fonction
une incertitude: Une limite quantifiée sur un résultat mesuré
erreur systématique: Un biais de mesure constant

4 · Energy, Environment, Microbiology and Immunity

A factor whose shortage restricts rate.
Change only one factor when testing a limiting factor. At low light, extra light may increase rate. At a plateau, the changed factor is no longer the main limit in that range; the graph alone does not identify which other factor is limiting.
Measure collected gas volume over a fixed time instead of assuming all bubbles have the same volume. Control temperature, plant size and carbon dioxide supply. Allow the plant to adjust before each reading and repeat.
A defined area used for sampling.
Estimate total abundance by multiplying mean density by area, with consistent units. This assumes sampled areas represent the habitat. Patchiness and too few samples widen uncertainty.
Choose coordinates with random numbers before visiting the patches. Record quadrat area and counting rules. For a transect, use fixed distances and measure a relevant abiotic variable. Do not damage habitats or sample unsafe locations.
An agent that causes disease.
After vaccination, memory cells can support a faster secondary response. Antibiotic resistance arises through heritable variation and selection; an individual bacterium does not choose to become resistant because it needs to survive.
Use published infection data to compare rates per equal population size. Distinguish prevalence at a time from new cases over a period. In school, use safe simulations or approved cultures rather than collecting unknown pathogens.

facteur limitant: Un facteur dont le manque limite le taux
photosynthèse: Formation de glucides pilotée par la lumière
quadrat: Une zone définie utilisée pour l'échantillonnage
population: Organismes d'une même espèce dans une zone définie
pathogène: Un agent qui provoque une maladie
potentiel hydrique: Une structure reconnue par une réponse immunitaire spécifique

5 · Respiration, Internal Environment, Coordination and Gene Technology

Cell reactions that transfer energy from substrates.
Anaerobic processes allow ATP production when oxygen supply cannot support the required aerobic rate, but give less ATP per glucose. In humans lactate can accumulate; yeast can produce ethanol and carbon dioxide.
A respirometer can measure oxygen uptake when carbon dioxide is absorbed. Control temperature with a water bath and use a comparison containing inert material. Keep absorbent separated from organisms and follow the school risk assessment.
Maintenance of suitable internal conditions.
When blood glucose is high, insulin helps increase glucose uptake and storage as glycogen. When it is low, glucagon supports release of glucose from stores. These responses are coordinated, not identical effects of two hormones.
Interpret a time graph by identifying the initial disturbance, the response and the return toward the normal range. Mark the delay before a response. Do not assume a graph shows an instantaneous correction.
Formation of RNA using a DNA template.
A codon comprises three bases. The genetic code is degenerate: more than one codon can specify the same amino acid. A substitution can therefore be silent, while insertions or deletions can shift the reading frame.
Keep DNA template, coding DNA and mRNA distinct. State the strand used and write sequences in the required direction. Use a codon table for mRNA, not an unexplained DNA triplet.

respiration: Réactions cellulaires qui transfèrent l'énergie à partir des substrats
ATP: Une molécule qui couple les transferts d'énergie dans les cellules
homéostasie: Maintien de conditions internes appropriées
rétroaction négative: Une réponse opposant au changement initial
transcription: Formation d'ARN à partir d'un brin d'ADN
traduction: Formation d'un polypeptide à partir d'une séquence d'ARNm

6 · Practical Skills in Biology II

A defined area used for sampling.
Estimate total abundance by multiplying mean density by area, with consistent units. This assumes sampled areas represent the habitat. Patchiness and too few samples widen uncertainty.
Choose coordinates with random numbers before visiting the patches. Record quadrat area and counting rules. For a transect, use fixed distances and measure a relevant abiotic variable. Do not damage habitats or sample unsafe locations.
A quantified limitation on a measured result.
For a product or quotient, adding fractional uncertainties is a common maximum-uncertainty approximation. For a difference, add absolute uncertainties. A nonzero intercept can reveal an offset or an incomplete model.
Show units on axes and choose a sensible scale. Plot uncertainty bars where justified, draw a best-fit line rather than joining every point, and estimate steepest and shallowest plausible gradients when the course method calls for them.

quadrat: Une zone définie utilisée pour l'échantillonnage
population: Organismes d'une même espèce dans une zone définie
une incertitude: Une limite quantifiée sur un résultat mesuré
erreur systématique: Un biais de mesure constant

Préparation à cette qualification

Six separately assessed units; IAS uses Units 1–3, IAL uses Units 1–6.
Units 3 and 6 are written practical-skills examinations based on experimental experience; they are not a Cambridge hands-on practical paper.
Retain core-practical numbering from the acquired specification. Unit weights, marks and times are in the assessment evidence manifest.

Couverture pédagogique encore nécessaire

Complete cardiovascular, diet-risk, membrane, protein and gene-expression statements remain.
Complete reproduction/development, plant structure, biodiversity and conservation statements remain.
All specified AS core practicals and written design/analysis objectives need full mapping.
Complete energy flow, environmental data, immunity and forensics statements remain.
Full muscle/renal/neural/gene technology statements and the session-specific scientific article remain.
Full A2 practical planning/statistics/evaluation objective coverage remains.

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