Biology 5 – Exam technique & past-paper fixes

Enzyme and substrate shape?

"Complementary". Never "same shape", "fits" or "matches"

Energy from ATP or respiration?

"Released". Never "made", "produced" or "created"

Version of a gene?

"Allele". Writing "gene" is penalised

Enzyme–substrate complex?

Write it in full. "E-S" and "ESC" are not credited

DNA and RNA bases?

Full names: adenine, thymine, cytosine, guanine, uracil. Letters alone score nothing

Oxygen and haemoglobin?

Oxygen "binds", not "bonds"

Water potential abbreviation?

Ψ, or write it in full. "WP" is ignored

Measured quantity?

Volume, mass or concentration. "Amount" is not accepted

Antibody's binding region?

Antigen-binding site. Never "active site"

Overlapping SD ranges?

No significant difference; the difference is probably due to chance. Never "the results are significant"

What enzymes do?

Lower activation energy. "Provide an alternative pathway" scores nothing

Features of all bacteria?

Murein cell wall, circular DNA not associated with proteins, smaller ribosomes, no membrane-bound organelles. Plasmids, flagella and capsule are only sometimes present

Why viruses are non-living?

Not cells / no cell-surface membrane; no metabolism

Microvilli?

Increase surface area, so faster absorption/diffusion. Not "thin walls"

Bile salts?

Emulsify lipids into small droplets, giving a larger surface area for lipase. They do not digest

Fatty acids into ileum cells?

Simple diffusion, carried there by micelles. Not facilitated diffusion

Tumour?

A mass of cells formed by uncontrolled mitosis

Interphase?

Part of the cell cycle, not mitosis; DNA replicates

Herd immunity?

Enough of the population vaccinated to reduce the spread of the pathogen

Natural selection chain?

Mutation gives new allele → those with it more likely to survive → reproduce, passing on allele → allele frequency increases over generations

Proteome?

The full range of proteins a cell can produce

Gene?

A base sequence of DNA coding for the amino acid sequence of a polypeptide, or for a functional RNA

Homologous chromosomes vs sister chromatids?

Homologous: two separate chromosomes, one from each parent, with the same genes at the same loci (alleles may differ). Sister chromatids: two identical copies of one chromosome, joined at the centromere

Evidence from a photo that a cell is in mitosis?

Chromosomes visible because they have condensed; each chromosome is two chromatids because DNA has replicated; not in homologous pairs (that would suggest meiosis)

Cells in a solution with a higher water potential than the cytoplasm?

Water enters the cytoplasm by osmosis, so the cell swells (chromosomes spread apart). Water does not move into the nucleus

Percentage change?

(new − original) ÷ original × 100. Always divide by the ORIGINAL (starting) value

"Calculate the increase" from a graph?

Subtract the starting value from the final value before doing anything else

Reading a value off a graph?

Find the exact tick on the x-axis, go straight up to the line, across to the y-axis, and count small squares. Check the scale of one small square first

Uncertainty of a length measured with a ruler (1 mm graduations)?

±1 mm (two readings, each ±0.5 mm). Percentage error = uncertainty ÷ measurement × 100

±2 SD bars on a graph?

If the bars overlap, the difference is not significant (may be due to chance); if they don't overlap, it is significant

Plotting an oxygen dissociation curve?

Linear axes, plot points to within half a small square, draw an S-shaped (sigmoid) curve that levels off just below 100%

Dissociation curve further right (e.g. mouse vs horse)?

Lower affinity for oxygen, so it unloads O₂ more readily to respiring tissues; supports a higher respiration/metabolic rate

Why a mouse has a higher metabolic rate than a horse?

Smaller, so larger SA:V; loses more heat per gram; faster respiration releases heat to replace it. Never "generates heat"

Something binds to an enzyme and changes its activity?

Binding alters the tertiary structure → active site changes shape → more (or fewer) E–S complexes form

Non-competitive inhibitor answer?

Start with: binds at a site other than the active site (allosteric site); then tertiary structure changes, active site no longer complementary, fewer E–S complexes

Respiratory inhibitor and active transport?

Less ATP made, so less ATP hydrolysed, so less active transport. Write "less ATP", never "lack of energy"

Proton pump (X) inhibited; H⁺ still leaves by co-transport (Y)?

Fewer H⁺ pumped in, H⁺ concentration inside falls, pH increases

Increased gene expression?

More transcription of the gene, so more of the protein (e.g. carrier proteins) is made. It is not a mutation

How is an enzyme phosphorylated?

ATP hydrolysed to ADP + Pi; the phosphate attaches to the enzyme

Scientists breed only plants with a trait?

Artificial selection: selected plants pass on their alleles, so the allele frequency increases (say "frequency", not "number" or "prominence")

Antivenom made from venom of many snakes of one species?

Snakes of one species may have different alleles, so different forms of the toxin; several different antibodies are produced

Why antivenom is passive immunity, not active?

Antibodies bind the toxin, causing agglutination/destruction straight away; active immunity would be too slow

B cells after clonal selection become?

Plasma cells (secrete antibodies) and memory cells. Never phagocytes. Memory cells do not make antibodies; on reinfection they divide into plasma cells

Small first dose then larger second dose of antigen?

First dose small so the animal isn't harmed; second dose triggers the secondary response: much more antibody, made faster

Tube leading into alveoli seen at low magnification?

Bronchiole. Capillaries are far too small to see as tubes at ×40

Improving data collection for a biodiversity study?

Count individuals of each species (so index of diversity can be calculated); sample more sites/years (more representative); sample more often (more points). Each needs a reason

Two species share a genus name, a third doesn't?

The two in the same genus are more closely related to each other than to the third (more recent common ancestor). Name them and compare

"Do the data support the conclusion?"

Give evidence for AND against each conclusion, quote figures, and note what wasn't measured (e.g. index of diversity)

Transpiration rises in the morning, dips around midday?

Higher temperature gives water molecules more kinetic energy (more evaporation); stomata open after sunrise; some stomata close at midday, so the rate dips

Test whether root cells have a lower water potential than sea water?

Blot dry and weigh; leave in sea water for a set time; blot dry and reweigh; mass increase means water entered by osmosis, so the cells have a lower water potential

Drug stops cytokinesis?

Cells contain two nuclei (stuck at telophase); the cytoplasm/membrane doesn't divide

A list with one wrong item?

The wrong item cancels the right ones (list rule). Only write points you're sure of

Comparing two organisms or conditions?

Name both and make every point comparative ("larger", "more", "than")