A-Level Biology 2 — Questions and Answers
Question 1: What is the role of haemoglobin in oxygen transport?
- It digests food in the blood
- It binds reversibly to oxygen in the lungs and releases it at body tissues, with cooperative binding shown by the sigmoidal oxygen dissociation curve (Correct answer)
- It fights infections
- It clots blood at wound sites
Correct answer: It binds reversibly to oxygen in the lungs and releases it at body tissues, with cooperative binding shown by the sigmoidal oxygen dissociation curve
Haemoglobin is a quaternary protein in red blood cells that binds O₂ cooperatively — binding of the first O₂ increases affinity for subsequent O₂ molecules. It loads O₂ at the lungs (high pO₂) and unloads at tissues (low pO₂).
Question 2: What is a gene mutation?
- A change in chromosome number
- A change in the nucleotide sequence of DNA, which may alter the amino acid sequence of the encoded protein (Correct answer)
- A change in the organism's appearance only
- A change that always causes disease
Correct answer: A change in the nucleotide sequence of DNA, which may alter the amino acid sequence of the encoded protein
A gene mutation involves changes to the DNA base sequence — substitutions, insertions, or deletions. These may be silent, missense, or nonsense, with varying effects on the protein produced.
Question 3: What is the immune response involving B lymphocytes?
- B cells directly kill infected cells
- B cells produce specific antibodies that bind to antigens on pathogens, marking them for destruction (humoral immunity) (Correct answer)
- B cells produce enzymes
- B cells form the skin barrier
Correct answer: B cells produce specific antibodies that bind to antigens on pathogens, marking them for destruction (humoral immunity)
B lymphocytes, when activated by antigens, differentiate into plasma cells that produce large quantities of specific antibodies. These antibodies neutralise pathogens, opsonise them for phagocytosis, or activate complement.
Question 4: What is the Krebs cycle and where does it occur?
- A cycle in the nucleus that copies DNA
- A cycle in the mitochondrial matrix where acetyl CoA is oxidised, producing CO₂, reduced coenzymes (NADH, FADH₂), and ATP (Correct answer)
- A cycle in the cell membrane
- A cycle that occurs only in plants
Correct answer: A cycle in the mitochondrial matrix where acetyl CoA is oxidised, producing CO₂, reduced coenzymes (NADH, FADH₂), and ATP
The Krebs cycle occurs in the mitochondrial matrix. Acetyl CoA (from pyruvate) enters the cycle, is oxidised to CO₂, and generates NADH, FADH₂ (for the electron transport chain), and a small amount of ATP.
Question 5: What is genetic engineering (recombinant DNA technology)?
- Selective breeding of organisms
- The manipulation of DNA to transfer genes between organisms using restriction enzymes, ligase, and vectors (Correct answer)
- Cloning entire organisms
- Natural gene transfer between species
Correct answer: The manipulation of DNA to transfer genes between organisms using restriction enzymes, ligase, and vectors
Genetic engineering involves cutting DNA with restriction enzymes, inserting desired genes into vectors (e.g., plasmids), and introducing them into host organisms to produce useful proteins like insulin.
Question 6: What is the significance of the Bohr effect in oxygen transport?
- It increases oxygen binding at tissues
- A decrease in pH (increased CO₂) reduces haemoglobin's oxygen affinity, promoting oxygen release at actively respiring tissues (Correct answer)
- It only occurs at high altitudes
- It increases blood pressure
Correct answer: A decrease in pH (increased CO₂) reduces haemoglobin's oxygen affinity, promoting oxygen release at actively respiring tissues
The Bohr effect explains how increased CO₂ and decreased pH at metabolically active tissues shift the oxygen dissociation curve to the right, facilitating oxygen unloading where it is most needed.
A-Level Biology 2
What is the role of haemoglobin in oxygen transport?