2025 AQA AS Biology 7401/1 Paper 1 – Question Paper and Mark Scheme (Merged) | June 2023, Exams of Biology

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2025 AQA AS Biology 7401/1 Paper 1 – Question Paper and

Mark Scheme (Merged) | June 2023 Verified Exam, Correct

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Material

Describe the induced-fit model of enzyme action - ✔✔✔ANSWER-- active site not complementary to/does not fit substrate

• Shape of active site changes as enzyme- substrate complex forms
• Distorting bonds (in substrate leading to reaction)
• The human cell then makes a complementary strand to the HIV DNA. The complementary strand is made in the same way as a new complementary strand is made during semi-conservative replication of human DNA. Describe how the complementary strand of HIV DNA is made. - ✔✔✔ANSWER-- there are complementary nucleotides/bases pair
• DNA polymerase used
• Nucleotides join together (to form new strand)/phosphodiester bonds form;

Contrast the structures of DNA and mRNA molecules to give three differences. - ✔✔✔ANSWER-- DNA is double stranded/double helix and mRNA single-stranded;

• DNA (very) long and RNA short; -Thymine/T in DNA and uracil/U in RNA;
• Deoxyribose in DNA and ribose in RNA;

Describe the difference between the structure of a triglyceride molecule and the - ✔✔✔ANSWER-In phospholipid, one fatty acid replaced by a phosphate

Give two ways in which the hydrolysis of ATP is used in cells. - ✔✔✔ANSWER-- To provide energy for other reactions/named process;

• To add phosphate to other substances and make them more reactive/change their shape

What is the evidence from Figure 2 that a scanning electron microscope was used to take this photograph? - ✔✔✔ANSWER-(Can see) 3D image

name the part of the mitochondrion labelled X in Figure 2 - ✔✔✔ANSWER-Crista/cristae

Y is a protein. One function of Y is to transport cellulose molecules across the phospholipid bilayer. Using information from Figure 3, describe the other function of Y. - ✔✔✔ANSWER-- (Y is) an enzyme/has active site/forms ES complex;

• That makes cellulose

In the cell wall, bonds hold the cellulose molecules together side by side. Name that bond - ✔✔✔ANSWER-Hydrogen

Name the products of the hydrolysis of sucrose. - ✔✔✔ANSWER- glucose and fructose

Describe how giving this vaccine leads to production of antibody against HPV - ✔✔✔ANSWER-- Vaccine contains HPV antigen

• Displayed on antigen-presenting cells
• Specific helper T cell (detects antigen and) stimulates specific B cell
• B cell divides to give plasma cells
• B cell/plasma cell produces antibody

Suggest why the development of a monopolar mitotic spindle would prevent successful mitosis - ✔✔✔ANSWER-- No separation of chromosomes

• chromosomes all go to one pole of cell
• one daughter cell gets no chromosomes or chromatids;

Describe what happens in the hydrolysis - ✔✔✔ANSWER-- Peptide bond broken

• Using water

Many people with Alzheimer's disease have mutations that decrease α- secretase production or increase β-secretase production (lines 8-9). Use the information provided to explain how these mutations can lead to Alzheimer's disease. - ✔✔✔ANSWER-- Mutations prevent production of enzyme

• (Increase in β-secretase) leads to more β-amyloid production
• (Leads to) more/greater plaque formation

One possible type of drug for treating Alzheimer's disease is a competitive inhibitor of β-secretase (lines 10-11).

• Compare (base sequences of) (m)RNA

Chromosomes line up on the equator of the mitotic spindle in the... - ✔✔✔ANSWER-Metaphase