2017 A2 Paper 1

Question 1

Molecules from which a ribosome is made

Answer 1

rRNA

Protein

Question 2

Role of ribosome in production of a polypeptide

Answer 2

mRNA binds to ribosome

Allows tRNA with anticodons to bind

Catalyses formation of peptide bond between amino acids

Moves along mRNA

Question 3

Why would mRNA have different base sequence to pre-mRNA

Answer 3

Introns in pre-mRNA

Removal of introns during splicing

Question 4

Structure of glycogen

Answer 4

Polymer of alpha glucose

Joined by glycosidic bonds

Question 5

How does glycogen act as a source of energy

Answer 5

Hydrolysed to glucose

Glucose used in respiration

Question 6

How may the cell membrane of cells be adapted to allow rapid transport of nutrients

Answer 6

Membrane folded SO large surface area

Large number of protein channels FOR facilitated diffusion

Large number of protein carriers FOR active transport

Large number of protein FOR co-transport

Question 7

Sodium ions from salt are absorbed by cells lining the gut. Some of these cells have membranes with a carrier protein called NHE3

NHE3 actively transports one sodium ion into the cell in exchange for one proton out of the cell

Use your knowledge of transport across cell membranes to suggest how NHE3 does this

Answer 7

Co-transport

Uses hydrolysis of ATP

Sodium ion and proton bind to protein

Protein changes shape to move sodium ion across the membrane

Question 8

How can an increase in salt absorption lead to tissue fluid build up

Answer 8

Higher salt results in LOWER water potential of tissue fluid

So less WATER returns to capillary by osmosis

Question 9

How do bacteria divide

Answer 9

Binary fission

Replication of circular DNA

Replication of plasmids

Division of cytoplasm to produce 2 daughter cells

Question 10

Some proteases are secreted as extracellular enzymes by bacteria

Suggest an advantage to a bacterium of secreting an extracellular protease in its natural environment

Answer 10

To digest protein

So they can absorb amino acids for growth

Question 11

What is the action of membrane bound dipeptidases and what is their importance

Answer 11

Hydrolyse peptide bonds to release amino acids

Amino acids can cross cell membrane

Question 12

How does phagocytosis of a virus lead to presentation of its antigen

Answer 12

Phagosome fuses with lysosome

Virus destroyed by lysozymes

Antigen from virus displayed on the cell membrane

Question 13

How does presentation of a virus antigen lead to the secretion of an antibody against this virus antigen

Answer 13

Helper T cells bind to the antigen

Helper T cell stimulates a specific B cell

B cell divides by mitosis

Forms plasma cells that release antibodies

Question 14

Comparisons of genetic diversity that scientists use to generate classifications

Answer 14

Base sequence of DNA

Base sequence of mRNA

Amino acid sequence of proteins

Question 15

How is insects tracheal system adapted for efficient gas exchange

Answer 15

Tracheoles have thin walls SO short diffusion distance to cells

Highly branched SO large surface area

Highly branched so short diffusion distance to cells

Tracheae provides tubes full of air so fast diffusion

Water in the end of the tracheoles that moves out during exercise SO larger surface area

Body can be moved to move air so maintains concentration gradient for oxygen

Question 16

Contrast how optical microscope and TEM work

Answer 16

TEM uses electrons AND optical use light

TEM allows for a GREATER resolution

TEM allows SMALLER ORGANELLES to be observed

Question 17

Contrast the limitations of using optical microscope and TEM

Answer 17

TEM view only dead specimen and optical can view live specimens

TEM does not show colour and optical can

TEM requires thinner specimens

TEM requires a more time consuming preparation

Question 18

How to collect and process data to investigate a variable between two populations

Answer 18

Use random samples

Use large enough sample to be representative of whole population

Indication of what was measured

Calculate a mean and standard deviation for each population

Use the t-test

Analyse whether there is a significant difference between the means of the 2 populations