Biology (9700) Past Papers & Revision Resources

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1 mm is 1000 µm and 1 µm is 1000 nm.

Sense-check answers: bacteria are 1 to 5 µm, ribosomes about 25 nm, most eukaryotic cells tens of µm.

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Peptide bonds form the primary structure.

Hydrogen bonds between backbone C=O and N-H groups give α-helices and β-sheets.

R-group interactions hold tertiary and quaternary shape; covalent disulfide bonds are strongest.

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Benedict's shows reducing sugars as a group: glucose, fructose, maltose.

Sucrose stays negative until you hydrolyse it with acid, neutralise and retest; a stronger result then reveals non-reducing sugar.

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80S ribosomes sit in the cytoplasm and on rough ER.

Mitochondria and chloroplasts, like prokaryotes, have 70S ribosomes and small circular DNA.

Prokaryotic DNA is circular yet double-stranded.

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Valves respond only to pressure differences.

Atrioventricular valves shut once ventricular pressure exceeds atrial pressure; semilunar valves open only once it exceeds pressure in the aorta or pulmonary artery.

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The pathogen causes the disease; a vector transmits the pathogen between hosts.

Malaria: the protoctist Plasmodium, carried by female Anopheles mosquitoes.

TB: bacteria such as Mycobacterium tuberculosis.

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Loading: companion cells pump H+ out; H+ returns via cotransporters with sucrose, which enters sieve tubes through plasmodesmata.

Flow: osmosis builds a hydrostatic pressure gradient, driving mass flow to sinks.

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A vaccine contains antigens, giving artificial active immunity: memory cells provide long-term protection.

Injected antibodies give artificial passive immunity: immediate but short-lived, with no memory cells.

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Water moves by osmosis from higher (less negative) to lower (more negative) water potential through a partially permeable membrane.

Adding solute lowers water potential; pure water is zero.

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Water evaporates from mesophyll cell walls; the vapour then diffuses out through stomata.

Cohesion is hydrogen bonding between water molecules; adhesion is water bonding to cellulose in xylem walls.

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RNA has uracil, not thymine.

Phosphodiester bonds link nucleotides.

In eukaryotes, the primary transcript is complementary to the transcribed (template) strand; removing introns and joining exons gives mRNA.

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Rate against substrate concentration: at the plateau, all active sites are occupied, so enzyme concentration is limiting.

Product against time: substrate ran out, or heat or pH denatured the enzyme.

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Ions are charged, so the hydrophobic core blocks them; they pass through channel or carrier proteins.

Facilitated diffusion is passive, down a gradient.

Non-polar, lipid-soluble molecules diffuse straight through.

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A plan shows tissue outlines only, in the right proportions.

For cells, use a sharp pencil and thin continuous lines that join exactly; draw plant cell walls as double lines.

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Recalibrate for each objective: divide a known stage micrometer length by the number of eyepiece divisions covering it.

For scale bars, magnification = measured bar length ÷ length it represents.

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Head each column 'quantity / unit' and enter numbers only.

Use one precision per column that suits the measurement, such as whole seconds when timing a colour change by eye.

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Put the independent variable on the x-axis with a linear scale using over half the grid.

Draw the line only across your data, and show how you read off values.

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Name the real difficulty, such as judging when a colour change is complete.

Pair it with a matching improvement: colour standards, a colorimeter, or a water bath for constant temperature.

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Separated groups stay one species until reproductively isolated.

Allopatric needs a geographical barrier; sympatric needs ecological or behavioural separation.

Without gene flow, different selection pressures shift each population's allele frequencies.

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Reverse transcriptase makes single-stranded cDNA using mRNA as a template; DNA polymerase then makes it double-stranded.

RNA polymerase binds the promoter to start transcription.

Taq is a heat-stable DNA polymerase.

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Define every symbol in a key.

X-linked alleles go as superscripts on X only; Y lacks that locus.

Give each offspring genotype its phenotype, and label the ratio with phenotypes.

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Energy is released, never made.

Hydrogen atoms split into protons and electrons; energy from electrons pumps protons from matrix to intermembrane space, and they diffuse back through ATP synthase.

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Na+ diffuses in through voltage-gated channels, depolarising the membrane; K+ then diffuses out.

ATP powers the Na+/K+ pump, three Na+ out for two K+ in, maintaining the resting potential.

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Crossing over exchanges lengths of non-sister chromatids between homologous chromosomes in prophase I, creating new allele combinations.

Independent assortment is the random orientation of homologous pairs at metaphase I.

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Mutations arise randomly.

Selection pressure favours individuals already carrying an advantageous allele; they are likelier to survive and reproduce, passing it on, so the allele's frequency rises over generations.

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Thylakoid pigments absorb light energy, passing it to a reaction centre.

Chemiosmosis in the thylakoids makes ATP, which stays in the chloroplast with reduced NADP to drive the Calvin cycle.

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Write 'mean', not 'average'.

Run at least three replicates at each value of the independent variable and calculate a separate mean for each value: six values, six means.

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Use the p = 0.05 column.

Check the heading: correlation tables usually go by number of pairs, not degrees of freedom.

Ignore any minus sign; above critical, reject the null hypothesis.

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Give points for and against, quoting values with units.

Was significance tested?

Does the conclusion go beyond the species, sites or range tested?

Could another factor explain the pattern?

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Name measurable quantities with units, like 'volume of gas / cm³'.

Standardised variables stay constant.

A control swaps only the tested agent for an equal volume of its solvent, usually water.

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Tabulate exact volumes of stock and distilled water for each concentration.

Serial dilution: each step comes from the previous one.

Proportional dilution: each comes straight from stock.

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Link three parts: the hazard, the harm it could cause, and a precaution that fits.

For example, enzyme solutions can trigger allergies, so avoid skin contact and wear gloves.

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Match it to the test. t-test: no significant difference between the two means.

Chi-squared: no significant difference between observed and expected.

Spearman's or Pearson's: no significant correlation.

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Non-overlapping 95% confidence intervals suggest a significant difference; overlapping ones give no evidence of one.

Standard deviation shows spread only.

Confirm with a t-test, and avoid 'prove'.