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21 exam-style questions with model answers, plus 28 quick multi-choice questions — every question on the site for this standard, grouped by the 7 pages of notes they come from.
Write a full answer before you reveal the model one — that comparison is where the marks come from. Every block links back to the notes that teach it.
Name the three parts of a nucleotide, and state two differences between DNA and RNA.
Explain the difference between the coding strand and the template strand of DNA, and explain why the mRNA sequence matches the coding strand.
Discuss why the specific complementary base pairing rules of DNA are essential, considering what would happen to gene expression if bases could pair in any combination.
Define the terms triplet, codon and anticodon, and state what is meant by saying the genetic code is degenerate.
Explain why the genetic code must be read in groups of three bases rather than one or two, and explain one advantage of the code being degenerate.
Two mutations occur in the same gene. Mutation A changes a base but the polypeptide is unchanged. Mutation B changes a single base and the polypeptide produced is much shorter than normal. Discuss the likely nature of each mutation, and evaluate which is more likely to affect the organism's phenotype.
State where transcription and translation each take place, and name the molecule produced by each.
Explain why the cell makes an mRNA copy of a gene rather than using the DNA directly at the ribosome.
All the cells in a plant contain identical DNA, yet a leaf cell and a root cell produce different proteins. Discuss how this is possible, and explain the significance for the organism.
State the relationship between a gene and a polypeptide, and give one example each of a structural protein and a catalytic protein.
Explain how the sequence of bases in a gene determines the function of the protein it codes for.
A single base substitution in a gene changes one amino acid in the protein it codes for. In one patient this has no noticeable effect; in another, a different single-amino-acid change causes severe illness. Discuss why the consequences differ so much.
Define a metabolic pathway, and state the relationship between genes and the enzymes in it.
Explain how a mutation in a single gene can change an organism's phenotype, using a metabolic pathway in your answer.
A metabolic pathway converts P to Q to R. Two individuals lack pigment R. One accumulates large amounts of P; the other accumulates large amounts of Q. Both have the same phenotype. Discuss what this reveals, and evaluate whether phenotype alone is sufficient to identify a genetic condition.
Define a mutation and a mutagen, and give two examples of mutagens.
Explain why a deletion of one base is usually far more damaging to a protein than a substitution of one base.
A person's skin cells accumulate mutations from UV exposure over many years. Discuss the possible consequences, and explain why these mutations cannot be passed to their children while a change in skin colour from tanning also cannot.
Give one example of an environmental factor changing an organism's phenotype, and state what happens to the genotype.
A Himalayan rabbit has white body fur and dark ears, nose, tail and feet. Explain how this happens, given that every cell in the rabbit has the same genotype.
Identical twins are separated at birth and raised in different countries with very different diets and climates. As adults they differ in height, skin tone and muscle mass. Discuss what this reveals about the relationship between genotype, environment and phenotype, and evaluate what conclusions can and cannot be drawn.