2020 AS Paper 1

Question 1

Describe a biochemical test to prove the presence of a non-reducing sugar

Answer 1

• heat with acid and neutralise
• add benedicts reagent
• brick red if non-reducing sugars are present

Question 2

Explain the arrangement of phospholipids in a cell-surface membrane

Answer 2

• arranged in a bilayer
• hydrophobic head points away from water and hydrophilic tail points towards water

Question 3

Describe how an ester bond is formed in a phospholipid molecule

Answer 3

a glycerol undergoes a condensation reaction with 3 fatty acids

Question 4

State and explain a property of water that helps to prevent temperature increase in a cell

Answer 4

• high specific heat capacity
• buffers changes in temperature

Question 5

Describe how a phagocyte destroys a pathogen present in the blood

Answer 5

• phagocyte binds to antigen on the pathogen and engulfs it
• this forms a vesicle which fuses with a lysosome
• the enzymes released digest the pathogen

Question 6

Give 2 types of cell, other than pathogens, that can stimulate an immune response

Answer 6

• tumour cells
• cells from any transplants

Question 7

Role of the disulfide bridge in forming the quaternary structure of an antibody

Answer 7

joins two polypeptides

Question 8

Outline the role of organelles in the production, transport and release of proteins from eukaryotic cells

Answer 8

• ribosomes produce protein
• mitochondria releases ATP for protein synthesis
• golgi apparatus packages and modifies the proteins
• the proteins are transported through vesicles

Question 9

Suggest why a nucleus is not visible in the figure

Answer 9

the nucleus isn’t stained

Question 10

Name organelles S and T

Answer 10

S = vacuole (very small)
T = chloroplast (thylakoids present)

Question 11

Give an advantage of using TEM over SEM

Answer 11

higher resolution

Question 12

Describe and explain the mechanism which causes lungs to fill with air

Answer 12

• external intercostal muscles contract, diaphragm contracts
• volume increases and pressure decreases
• air moves down a pressure gradient

Question 13

Why did the scientist use haematoxylin over iodine

Answer 13

• since there’s no starch present on the lung tissue
• the nucleus becomes visible

Question 14

Describe how mRNA is produced from an exposed template strand of DNA

Answer 14

• free nucleotides bind to complementary base pairs
• phosphodiester bonds form due to the action of RNA polymerase

Question 15

Define the term exon

Answer 15

nucleotide sequence which codes for a sequence of amino acids

Question 16

Describe binary fission in bacteria

Answer 16

circular DNA replicates, plasmids then replicate and the cytoplasm divides

Question 17

Suggest and explain how 2 environmental factors can be changed to increase the growth rate of cells

Answer 17

• increase temperature, particles have more kinetic energy so increased enzyme activity
• increase oxygen concentration, increases respiration