2022 AS Paper 1

Question 1

Describe the mechanism for the absorption of amino acids in the ileum

Answer 1

• facilitated diffusion of amino acid into the cell
• sodium ions are actively transported from cell to blood
• this creates a sodium ion concentration gradient
• facilitated diffusion of amino acids into the blood

Question 2

Give the two types of molecule from which a ribosome is made

Answer 2

• RNA
• Protein

Question 3

Give 4 structural differences between DNA and mRNA

Answer 3

• DNA has deoxyribose, mRNA has ribose
• DNA has thymine, mRNA has uracil
• DNA is double stranded, mRNA is single stranded
• DNA has hydrogen bonds, mRNA does not

Question 4

Describe and explain 1 difference between SEM and TEM

Answer 4

• SEM is 3D, TEM is 2D
• since electrons are deflected in SEM

Question 5

Why is the resolution of an electron microscope higher than optical microscope

Answer 5

electron microscope has shorter wavelengths between its electrons

Question 6

How to determine size of a structure using a microscope

Answer 6

• measure length of structure and divide by image length of scale bar
• multiply by actual length of scale bar

Question 7

Name 2 structures found in all bacteria that aren’t found in plants

Answer 7

• circular DNA
• smaller ribosomes

Question 8

Name 2 features of HIV particles that aren’t found in bacteria

Answer 8

• reverse transcriptase
• capsid

Question 9

What can you conclude about the uptake of oxygen over the entire body of the lugworm

Answer 9

• oxygen enters via diffusion down a concentration gradient
• more oxygen is present where there are gills
• this is because gills increase SA to volume ratio

Question 10

Describe how monomers join to form the primary structure of a protein

Answer 10

condensation reaction between amino acids, forming peptide bonds, forming a sequence of amino acids

Question 11

1 similarity and 1 difference between induced fit model and lock and key theory

Answer 11

• both have a substrate which binds to active site
• induced fit changes shape for substrate to become complementary but lock and key doesn’t change shape

Question 12

State how enzymes help reactions to proceed quickly at lower temperatures

Answer 12

lower activation energy

Question 13

Explain a property of iron ions that enables these ions to carry out their role in red blood cells

Answer 13

contain haemoglobin so transport oxygen

Question 14

What is a tumour

Answer 14

abnormal cells which undergo uncontrolled mitosis

Question 15

Describe how to determine a reliable mitotic index from tissue observed using an optical microscope

Answer 15

count the cells undergoing mitosis in your field of view, divide by total number of cells in field of view, repeat many times

Question 16

Suggest why the number of E.coli cells per mm3 in each culture after 24 hours might be lower if the student hadn’t used a sterilised pipette

Answer 16

other bacteria may have been introduced and these produce toxins