A-Level A-Level Biology

Question 1

What is the role of ATP in cellular processes?

Accepted Answer

The universal energy currency that transfers energy between exergonic and endergonic reactions in cells

Answer

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?

Accepted 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

Answer

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?

Accepted Answer

A model describing the membrane as a phospholipid bilayer with mobile proteins embedded in it

Answer

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?

Accepted Answer

Copying a section of DNA into mRNA in the nucleus

Answer

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?

Accepted Answer

When both alleles in a heterozygote are fully expressed, producing a phenotype distinct from either homozygote

Answer

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.

A-Level Revision Practice Test

A-Level Revision Practice Test

A-Level A-Level Biology