AQA AS Level Biology Paper 1, November 2020: Question 9

✅ Correct Answer

• The genetically modified plant expresses a gene from a different species (1 mark).
• This results in a new or additional protein being produced within its set/range of proteins (1 mark).

💡 Key Knowledge

The proteome is defined as the full range of proteins that a cell is able to produce at a given time. Introducing foreign DNA into tobacco plants means instructions for a novel polypeptide are transcribed and translated, expanding the organism's total proteome.

🧠 Exam Technique

Be precise with biological terminology. Examiners look for explicit references to expression of a foreign gene and the resulting production of a new/additional protein. Do not just say "it has more DNA"—focus specifically on proteins.

❌ Common Errors

Students often lose marks by confusing the genome with the proteome, or vaguely stating that "genes make cells different" without explaining that translation creates a novel protein.

✅ Correct Answer

• More/increased aquaporins or channel proteins are made (1 mark).
• This leads to increased water permeability across the membrane (1 mark).

💡 Key Knowledge

Aquaporins are specific channel proteins that facilitate the rapid diffusion of water molecules (osmosis) across biological membranes. Increased transcription leads to more mRNA, higher rates of translation, and a greater density of these channel proteins embedded in the phospholipid bilayer.

🧠 Exam Technique

Link the molecular event (transcription) directly to structural changes (more channel proteins) and functional consequences (permeability). Always explicitly mention water permeability.

❌ Common Errors

Candidates frequently forget to link transcription to translation and protein synthesis, jumping straight from gene expression to permeability without mentioning aquaporin channels.

✅ Correct Answer

Advantage (max 2 marks):

• More carbon dioxide uptake (1 mark).
• Leads to more photosynthesis, resulting in faster or greater growth (1 mark).

Disadvantage (max 2 marks):

• More water loss/transpiration (1 mark).
• Leads to less photosynthesis due to water stress/wilting/reduced metabolic reactions, or slower/less growth (1 mark).

💡 Key Knowledge

Stomata are the primary sites for gas exchange in leaves. They allow CO₂ to diffuse into the leaf for the Calvin cycle in photosynthesis, but simultaneously allow water vapour to escape via transpiration, creating a constant physiological trade-off for terrestrial plants.

🧠 Exam Technique

This is a "suggest and explain" question. You must pair a valid feature with a logical biological consequence affecting growth. Ensure your explanation connects the gas exchange point all the way through to sugar production or cellular hydration.

❌ Common Errors

Simply stating "more water loss" is insufficient for the second marking point of the disadvantage unless linked to a consequence such as plant wilting, reduced turgor, or slower growth/metabolism.