Biology (9700) Past Papers & Revision Resources

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1 mm = 1000 µm; 1 µm = 1000 nm.

Example: 0.004 mm = 4 µm = 4000 nm, a typical bacterium.

Sense-check: bacteria 1 to 5 µm, most eukaryotic cells tens of µm.

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Peptide bonds hold only primary structure.

Example: an α-helix is held by hydrogen bonds between backbone C=O and N-H.

Each hydrogen bond is weak; among R-group bonds, disulfide is strongest.

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Benedict's detects any reducing sugar: glucose, fructose or maltose.

Example: pure sucrose stays blue.

Boil with dilute HCl, neutralise, retest: a new or stronger colour means non-reducing sugar.

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Cytoplasm and rough ER: 80S ribosomes.

Mitochondria and chloroplasts: 70S ribosomes and small circular double-stranded DNA, like bacteria.

Example: a leaf cell has both ribosome types.

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Only pressure differences move valves.

Example: ventricle 9 kPa, aorta 10 kPa, so the semilunar valve stays shut.

The valve opens once ventricular pressure passes 10 kPa.

Arteries never pump.

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Pathogens cause disease; vectors carry pathogens.

Malaria: pathogen Plasmodium, a protoctist, carried by female Anopheles mosquitoes.

TB is a disease, caused by bacteria such as Mycobacterium tuberculosis.

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Loading: pumped-out H⁺ re-enters companion cells via cotransporters, bringing sucrose.

Flow: osmosis raises hydrostatic pressure in leaf sieve tubes.

Sap moves by mass flow towards lower pressure in the roots.

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A vaccine's antigens give artificial active immunity, with long-lived memory cells.

Injected antibodies, such as antivenom, give artificial passive immunity.

It works at once but fades, with no memory cells.

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Compare water potentials, never water concentrations.

Pure water is 0 kPa; solutes make it more negative.

Example: a −300 kPa cell in a −500 kPa solution loses water by osmosis.

Fix

Water evaporates from mesophyll cell walls into air spaces.

Water vapour then diffuses out through stomata.

Cohesion: hydrogen bonds between water molecules.

Adhesion: water hydrogen-bonds to cellulose in xylem walls.

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RNA has uracil: template strand TACGGT gives RNA AUGCCA.

Phosphodiester bonds join nucleotides along a strand.

In eukaryotes, removing introns from the primary transcript and joining exons gives mRNA.

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Rise: more substrate, more enzyme-substrate complexes.

Plateau: all active sites occupied, so enzyme concentration limits.

Example: doubling enzyme concentration doubles Vmax.

Product against time flattens when substrate is used up.

Fix

Charge or polarity, not size: the hydrophobic core blocks K⁺ and amino acids.

Facilitated diffusion: down a gradient via channel or carrier proteins, no ATP.

Non-polar O₂ diffuses straight through.

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Plan: tissue outlines in proportion, no cells, no shading.

Example: an artery plan outlines the lumen and wall layers.

Cells: thin unbroken lines that join, plant walls as double lines.

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Calibrate each objective: stage micrometer length ÷ eyepiece divisions.

Example: 25 µm per division at ×4, 10 µm at ×10.

Scale bar: 25 mm (25,000 µm) labelled 100 µm gives ×250.

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

Example: 'light intensity / lux' above 200, 400, 600.

One precision per column: by-eye timings in whole seconds, such as 47, not 47.38.

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Independent variable goes on the x-axis.

Example: 1, 2, 5 and 10 min sit at true positions, not equal gaps.

Draw the line only between your first and last points.

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Name the step that was hard to judge or control.

Example: 'the water-bath cooled from 30 °C to 26 °C during each run'.

Matching improvement: a thermostatically controlled water-bath.

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Call them populations until reproductively isolated.

Allopatric: a geographical barrier, e.g. a new river, stops gene flow.

Sympatric: same area, but insects mating on different host plants stop interbreeding.

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Reverse transcriptase uses mRNA as a template to build cDNA.

Example: mRNA AUGUUC gives cDNA TACAAG.

DNA polymerase then makes it double-stranded.

RNA polymerase binds the promoter.

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Key: ${\mathrm{X^B}}$ normal vision, ${\mathrm{X^b}}$ colour blindness, no allele on ${\mathrm{Y}}$

Cross: ${\mathrm{X^BX^b} \times \mathrm{X^BY}}$

Offspring: 2 normal females ${\mathrm{X^BX^B}}$ ${\mathrm{X^BX^b}}$ 1 normal male ${\mathrm{X^BY}}$ 1 colour-blind male ${\mathrm{X^bY}}$

Fix

Reduced NAD's hydrogen atoms split into H⁺ and e⁻.

Energy released by electrons, never 'produced', pumps H⁺ into the intermembrane space.

H⁺ diffuses back through ATP synthase: ADP + Pi → ATP.

Fix

Na⁺ diffuses in via voltage-gated channels, depolarising the membrane to +30 mV.

K⁺ diffuses out to repolarise.

ATP drives the Na⁺/K⁺ pump, not depolarisation: 3 Na⁺ out, 2 K⁺ in.

Fix

Crossing over swaps alleles between non-sister chromatids in prophase I.

Example: chromatids AB and ab give recombinants Ab and aB.

Independent assortment: homologous pairs orient randomly at metaphase I.

Fix

Mutations are random; selection never causes them.

Example: one bacterium already carries a penicillin-resistance allele.

Penicillin kills the rest; the survivor's offspring spread the allele.

Bacteria become resistant, never immune.

Fix

Carotene passes absorbed light energy, not light, to the reaction centre.

Chemiosmosis: H⁺ is pumped from stroma into thylakoid space.

It diffuses back through ATP synthase, making ATP.

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Write 'mean', not 'average'.

Run at least three replicates at every value of the independent variable.

Example: five concentrations × three replicates = 15 runs and five means.

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Use the p = 0.05 column.

Example: rs = −0.84 for 7 pairs, so row 7 gives critical value 0.786.

Ignore the sign: 0.84 > 0.786, so reject the null hypothesis.

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Give points for and against, with values and units.

Example: 'fertiliser increases plant height'.

For: mean height 31 cm treated, 24 cm untreated.

Against: one species only, no t-test.

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Measure 'volume of gas / cm³', not 'amount'.

Standardised variables stay constant.

A control removes only the factor you are testing.

Example: 2 cm³ water replaces 2 cm³ fungicide solution.

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Give volumes of stock and distilled water for every concentration.

Proportional: 6 cm³ of 5% stock + 4 cm³ distilled water gives 3%.

Serial: each step dilutes the previous one.

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Link the hazard, the harm and a matching precaution.

Example: a 75 °C water-bath can scald your hands.

Precaution: lift tubes out with a test-tube holder.

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Match the hypothesis to the test.

For a t-test: no significant difference between mean tomato masses of two varieties.

Spearman's: no significant correlation between soil pH and plant height.

Fix

Overlapping 95% CI bars: no significant difference.

Example: 95% CIs 12 ± 2 and 17 ± 2 do not overlap (14 < 15), so significant.

Non-overlapping SE or SD bars only suggest significance.