A-Level Biology 2

Question 1

What is the role of haemoglobin in oxygen transport?

Accepted 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

Answer

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?

Accepted Answer

A change in the nucleotide sequence of DNA, which may alter the amino acid sequence of the encoded protein

Answer

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?

Accepted Answer

B cells produce specific antibodies that bind to antigens on pathogens, marking them for destruction (humoral immunity)

Answer

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?

Accepted Answer

A cycle in the mitochondrial matrix where acetyl CoA is oxidised, producing CO₂, reduced coenzymes (NADH, FADH₂), and ATP

Answer

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)?

Accepted Answer

The manipulation of DNA to transfer genes between organisms using restriction enzymes, ligase, and vectors

Answer

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.

GCE A-Level Practice Test

GCE A-Level Practice Test

A-Level Biology 2