A-Level Biology

Question 1

What is the role of ATP in cellular processes as studied in Singapore A-Level Biology?

Accepted Answer

It is the universal energy currency of cells, providing immediate energy for cellular activities

Answer

ATP (adenosine triphosphate) is the immediate energy source for cellular processes. It releases energy when the terminal phosphate bond is hydrolysed to form ADP and inorganic phosphate.

Question 2

What is the structure of DNA according to the Watson-Crick model?

Accepted Answer

A double helix with antiparallel strands connected by complementary base pairing (A-T, G-C) through hydrogen bonds

Answer

DNA is a double helix with two antiparallel polynucleotide strands. Adenine pairs with thymine (2 hydrogen bonds) and guanine pairs with cytosine (3 hydrogen bonds). The sugar-phosphate backbone is on the outside.

Question 3

What is the difference between mitosis and meiosis?

Accepted Answer

Mitosis produces 2 identical diploid cells; meiosis produces 4 genetically different haploid cells

Answer

Mitosis produces two genetically identical diploid daughter cells (for growth and repair). Meiosis produces four genetically different haploid cells (gametes) through two divisions and introduces genetic variation.

Question 4

What is the lock-and-key model of enzyme action?

Accepted Answer

The substrate fits precisely into the enzyme's active site, like a key fitting a lock, forming an enzyme-substrate complex

Answer

In the lock-and-key model, the enzyme's active site has a fixed complementary shape to the substrate. The substrate fits precisely, forming an enzyme-substrate complex for the reaction to occur.

Question 5

What is natural selection as described in the Singapore A-Level Biology syllabus?

Accepted Answer

The process by which organisms with favourable inherited traits are more likely to survive and reproduce, passing those traits to offspring

Answer

Natural selection is the mechanism of evolution where environmental pressures favour organisms with advantageous traits. These organisms are more likely to survive, reproduce, and pass on their beneficial alleles.

GCE A-Level Practice Test

GCE A-Level Practice Test

A-Level Biology