Biology AS Paper 2022

Question 1

Describe the mechanism for the absorption of amino acids in the ileum (4 marks)

Answer 1

1. facilitated diffusion of amino acids into cell when high concentration in lumen
2. co-transport
3. Na+ active transport from cell to blood
4. Na+ diffusion gradient established
5. facilitated diffusion of amino acids into blood

Question 2

Which of these are hydrolysed in the ileum and a product of this hydrolysis is found in micelles?
A. maltose
B. triglyceride
C. nucleotide
D. cellulose
E. amino acid
(1 mark)

Answer 2

triglyceride

Question 3

Which is formed by a condensation reaction between two a-glucose molecules?
A. maltose
B. triglyceride
C. nucleotide
D. cellulose
E. amino acid
(1 mark)

Answer 3

maltose

Question 4

Which is formed by the action of DNA polymerase?
A. maltose
B. triglyceride
C. nucleotide
D. cellulose
E. amino acid
(1 mark)

Answer 4

nucleotide

Question 5

Which gives a positive result in an emulsion test?
A. maltose
B. triglyceride
C. nucleotide
D. cellulose
E. amino acid
(1 mark)

Answer 5

triglyceride

Question 6

Give two types of molecules from which a ribosome is made
(2 marks)

Answer 6

rRNA
protein

Question 7

Give four structural differences between a DNA molecule and an mRNA
(4 marks)

Answer 7

double helix/stranded : single helix/stranded
deoxyribose : ribose
long : short
thymine : uracil

Question 8

Explain why the resolution of an image obtained using an electron microscope is higher than the resolution of an image obtained using an optical microscope
(1mark)

Answer 8

wavelength of light rays is longer than that of electrons

Question 9

How can a student determine the size of the structure?
(2 marks)

Answer 9

measure length of cell using ruler (cm)
divide image size by magnification to find actual size
convert answer from cm->nm by x10,000

Question 10

Name two structures found in all bacteria that are NOT found in plant cells
(2 marks)

Answer 10

circular DNA
murrain cell wall

Question 11

Name two features of HIV particles that are NOT found in bacteria
(2 marks)

Answer 11

reverse transcriptase
capsid

Question 12

Describe how monomers join to form the primary structure of a protein
(3 marks)

Answer 12

monomers of proteins are amino acids
amino acids form peptide bonds with other amino acids in a condensation reaction which involves the removal of water
creates a sequence of amino acids- the primary structure of a protein

Question 13

Describe one similarity and one difference between the induced fit model of enzyme action and the lock and key model of enzyme action
(2 marks)

Answer 13

similarity: both result in formation of enzyme-substrate complex
difference: lock and key- substrate exactly complementary to active site of enzyme
induced fit- substrate not exactly complementary to active site, active site alters shape to bind with substrate

Question 14

State how enzymes help reactions to proceed quickly at lower temperatures
(1 mark)

Answer 14

enzyme acts as biological catalyst which provide an alternative pathway of lower activation energy

Question 15

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

Answer 15

iron ions polar as they are charged (Fe2+) so associate with oxygen to form oxyhaemoglobin

Question 16

What is a tumour?
(2 marks)

Answer 16

mass of cells produced from uncontrolled mitotic division

Question 17

Describe how you would determine a reliable mitotic index from tissue observed with an optical microscope
(3 marks)

Answer 17

count number of cells undergoing mitosis in field of view
divide by total number of cells in field view
repeat process many times

Question 18

Suggest why the number of E.coli cells per mm3 in each culture after 24 hours might be lower if the student had NOT used a sterilised pipette. Explain why
(2 marks)

Answer 18

bacteria other than E.coli in culture
competition for nutrients
E.coli may be outcompeted
less nutrients for E.coli, less division, less E.coli cells

Question 19

Describe how composition of blood in pulmonary artery of foetus is different from composition of blood in pulmonary artery of mother
Give one reason for this difference
(2 marks)

Answer 19

fetal blood has more oxygen
gas exchange occurs in placenta

Question 20

Explain how a foetus is protected against pathogens that infect its mother during pregnancy
(3 marks)

Answer 20

antibodies from mother complementary to antigens crossing placenta
binding between antibodies and antigens forms antibody-antigen complex
provides passive immunity in foetus

Question 21

Suggest how vaccinating as many babies as possible protects UK population against pathogens in measles
(1 mark)

Answer 21

measles a virus
vaccinations achieve herd immunity
reduces transmission

Question 22

Suggest how vaccinating as many babies as possible protects UK population against pathogens in tetanus
(1 mark)

Answer 22

tetanus is a bacteria
no herd immunity
only protects individual

Question 23

Suggest why there has been a recent increase in the number of children catching measles
(1 mark)

Answer 23

virus has mutated