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
,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
, ✔✔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
3
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
,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
, ✔✔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
3
