A-Level A-Level Biology 1 — Questions and Answers
Question 1: What is the role of ATP in cellular processes?
- Long-term energy storage only
- The universal energy currency that transfers energy between exergonic and endergonic reactions in cells (Correct answer)
- The structural component of cell membranes
- The enzyme that catalyses glycolysis
Correct answer: The universal energy currency that transfers energy between exergonic and endergonic reactions in cells
ATP (adenosine triphosphate) is the universal cellular energy currency. It is synthesised in respiration (exergonic) and hydrolysed to ADP + Pi (endergonic reactions), releasing energy for cellular work such as active transport, muscle contraction, and synthesis.
Question 2: What is the difference between a gene and an allele?
- They are the same thing
- A gene is a section of DNA coding for a polypeptide; an allele is a variant form of that gene at the same locus (Correct answer)
- An allele is a chromosome; a gene is a protein
- Genes are only found in plants; alleles are in animals
Correct answer: A gene is a section of DNA coding for a polypeptide; an allele is a variant form of that gene at the same locus
A gene is a specific sequence of DNA at a locus coding for a polypeptide (or functional RNA). An allele is one of the alternative versions of a gene. For example, the gene for eye colour has alleles for blue, brown, green, etc.
Question 3: What is the fluid mosaic model of the cell membrane?
- A model showing a rigid, impermeable barrier
- A model describing the membrane as a phospholipid bilayer with mobile proteins embedded in it (Correct answer)
- A model for the nuclear envelope only
- A model describing the cytoskeleton
Correct answer: A model describing the membrane as a phospholipid bilayer with mobile proteins embedded in it
The fluid mosaic model (Singer & Nicolson, 1972) describes the plasma membrane as a phospholipid bilayer in which proteins are embedded and can move laterally (fluid), forming a mosaic pattern. Cholesterol adds stability.
Question 4: What is the process of transcription in protein synthesis?
- Building a polypeptide from tRNA at a ribosome
- Copying a section of DNA into mRNA in the nucleus (Correct answer)
- Replicating DNA before cell division
- Activating amino acids for translation
Correct answer: Copying a section of DNA into mRNA in the nucleus
Transcription occurs in the nucleus: RNA polymerase binds to the promoter region of a gene, unwinds the DNA, and synthesises a complementary mRNA strand using the template strand. The mRNA then leaves via nuclear pores.
Question 5: What is codominance in genetics?
- When one allele completely masks another
- When both alleles in a heterozygote are fully expressed, producing a phenotype distinct from either homozygote (Correct answer)
- When recessive alleles skip a generation
- When genes are on the X chromosome
Correct answer: When both alleles in a heterozygote are fully expressed, producing a phenotype distinct from either homozygote
Codominance occurs when both alleles in a heterozygote are expressed fully and simultaneously. Neither is dominant over the other. Example: AB blood type — both Iᴬ and Iᴮ alleles are expressed equally.
Question 6: What is the role of the mitochondrion in aerobic respiration?
- Producing ATP by photosynthesis
- The site of the Krebs cycle and oxidative phosphorylation, producing the majority of ATP per glucose molecule (Correct answer)
- Storing glucose as glycogen
- Synthesising proteins from mRNA
Correct answer: The site of the Krebs cycle and oxidative phosphorylation, producing the majority of ATP per glucose molecule
Mitochondria are the site of aerobic respiration's latter stages: the link reaction and Krebs cycle (matrix) and oxidative phosphorylation/ETC (inner membrane). They produce ~34 ATP per glucose (vs. 2 from glycolysis).
A-Level A-Level Biology 1
What is the role of ATP in cellular processes?