OCR GCSE Biology B (Twenty First Century)
OCR GCSE Biology B B1.1 What is a genome and what does it do? Exam Questions
Free OCR GCSE Biology B exam questions for B1.1 What is a genome and what does it do?, with a mark scheme for every pack. Covers the genome, chromosomes, genes, DNA structure, base pairing, protein synthesis, genetic variants and how Genotype and environment shape phenotype.
B1.1 What is a genome and what does it do? exam questions
2 question packs of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About OCR GCSE Biology B B1.1 What is a genome and what does it do?
This opening topic of chapter B1, You and Your Genes, explains what the genome is and how the information in DNA is used to make proteins. You need to describe the structure of DNA, relate genes to chromosomes, and explain how a change in the base sequence can alter a protein and so the phenotype. It underpins inheritance in B1.2, gene technology in B1.3 and evolution in B6. Examiners like questions that ask you to link a genetic variant to its effect on a protein, and to explain why most characteristics depend on both genes and the environment.
What you need to know
- The genome The genome is the entire genetic material of an organism. In plants and animals it is found in the nucleus, packaged into chromosomes made of long DNA molecules.
- Genes and chromosomes A gene is a section of DNA that codes for a particular protein. Each chromosome carries many genes, and humans have 23 pairs of chromosomes in body cells.
- DNA structure DNA is a polymer made of repeating nucleotides, each with a sugar, a phosphate group and a base. Two strands twist into a double helix, held together by complementary base pairs: A with T, and C with G.
- Protein synthesis The order of bases is a code: each triplet of bases codes for one amino acid. The gene is copied into mRNA in the nucleus (transcription), then ribosomes in the cytoplasm join amino acids in the coded order to make a protein (translation).
- Genetic variants A genetic variant (mutation) is a change in the base sequence. Most have no effect, but some change the amino acid sequence, which can alter the shape and function of a protein such as an enzyme.
- Genotype and phenotype Genotype is the combination of alleles an organism has; phenotype is the observable characteristics. Most phenotypes result from many genes interacting with the environment.
Common mistakes in B1.1 What is a genome and what does it do?
- Saying a gene codes for a characteristic directly. A gene codes for a protein, and the protein affects the characteristic.
- Pairing A with C or G with T. The complementary pairs are always A with T and C with G.
- Writing that all mutations are harmful. Most genetic variants have no effect on the phenotype, and a few are beneficial.
- Confusing genome, gene and chromosome. The genome is all the DNA, a chromosome is one long DNA molecule, and a gene is a short section of it.
- Stating that proteins are made in the nucleus. The code is copied in the nucleus but proteins are assembled on ribosomes in the cytoplasm.
Try three B1.1 What is a genome and what does it do? exam-style questions
1. One strand of DNA has the base sequence ATCGGA. Write the base sequence of the complementary strand. (1 mark)
Show the mark scheme answer
TAGCCT.
2. A section of DNA contains 1200 bases on one strand. Calculate the maximum number of amino acids it could code for. (2 marks)
Show the mark scheme answer
Each amino acid is coded by three bases; 1200 / 3 = 400 amino acids.
3. Explain how a change in one base of a gene could stop an enzyme from working. (4 marks)
Show the mark scheme answer
The base sequence changes, so a triplet codes for a different amino acid; the sequence of amino acids in the protein changes; the protein folds into a different shape; the active site changes shape so the substrate no longer fits.
B1.1 What is a genome and what does it do? FAQs
What does OCR GCSE Biology B B1.1 cover?
It covers what the genome is, how DNA is structured, how genes code for proteins, and how genetic variants and the environment affect phenotype.
Which paper is B1.1 examined in?
J257 has two papers at each tier, Breadth in Biology and Depth in Biology, and content from any chapter, including B1, can be assessed on either one. Expect it to be linked to ideas about science and to other chapters.
What should I memorise for DNA questions in B1.1?
Learn the parts of a nucleotide, the base pairing rules (A with T, C with G), that three bases code for one amino acid, and the sequence from gene to protein to characteristic.
