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National 5 Biology Unit 3 Revision Questions and Answers | Latest Version | 2025/2026 | Correct & Verified
What is the role of DNA in living organisms?✔✔To store genetic information that controls cell functions and traits
What does a gene code for?✔✔A specific protein or a part of a protein
What are the two main stages of protein synthesis?✔✔Transcription and translation
What is the difference between mitosis and meiosis?✔✔Mitosis results in two identical daughter cells, while meiosis results in four genetically diverse gametes
What are chromosomes made of?✔✔DNA and proteins 1 / 3
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What is the genetic material found in the nucleus of a cell?✔✔Chromosomes, which are made up of DNA
What does the term "homozygous" mean?✔✔An organism has two identical alleles for a particular gene
What is the genotype of a heterozygous organism?✔✔Two different alleles for a particular gene, such as Aa
What is the phenotypic ratio in a monohybrid cross of two heterozygous parents?✔✔1:2:1 (1 homozygous dominant, 2 heterozygous, 1 homozygous recessive)
What is the purpose of meiosis in sexually reproducing organisms?✔✔To produce gametes (sperm and eggs) with half the number of chromosomes as the parent cell
What does a Punnett square represent? 2 / 3
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✔✔The possible genetic outcomes of a cross between two organisms
What is the difference between dominant and recessive alleles?✔✔Dominant alleles are expressed in the phenotype if present, while recessive alleles are only expressed if both alleles are recessive
What is the function of ribosomes in protein synthesis?✔✔Ribosomes are the site where proteins are assembled from amino acids
What is a codon?✔✔A sequence of three nucleotides on mRNA that codes for a specific amino acid
How does a mutation affect an organism?✔✔A mutation can change the genetic code, potentially affecting the protein produced and the organism’s traits
What are sex chromosomes?✔✔Chromosomes that determine an organism’s sex, typically X and Y in humans
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