past paper Qs

Question 1

give two types of molecule from which a ribosome is made

Answer 1

RNA and amino acids/ribosomal protein

Question 2

in a eukaryotic cell, the base sequence of the mRNA might be different from the sequence of pre-mRNA - why?

Answer 2

introns are found in pre-mRNA only

splicing , sections of pre-mRNA are removed

Question 3

during pregnancy, cells lining the uterus are an important source of energy for the embryo.

suggest how glycogen acts as a source of energy.

Answer 3

glycogen is hydrolysed (into glucose)

this glucose is then used in respiration

Question 4

how does an enzyme affect a reaction?

(describe a typical enzyme graph)

Answer 4

an enzyme increases the rate of reaction , by lowering the activation energy - this increase is often non-linear

Question 5

explain the importance of DNA replication during the development of a zygote into a blastocyst

Answer 5

zygote divides multiple times by mitosis
making identical copies of DNA (all cells will be diploid)
so when mitochondria divides, they will have a copy of the DNA

Question 6

Describe how macrophages present antigens to t-helper cells.

Answer 6

the macrophage engulfs the pathogen
presents antigens on MHC markers
these are complementary to the t-helper cell’s receptors

Question 7

How much peptidoglycan cell wall does gram negative bacteria have?

Answer 7

thin layer

Question 8

What type of toxins does salmonella produce?

Answer 8

endotoxins

Question 9

outline the differences between endotoxins and exotoxins

Answer 9

endotoxins:
produced by gram negative bacteria
lipopolysaccharides
released from dead bacteria

exotoxins:
gram negative and positive bacteria
proteins
released from living bacteria
affect is later

Question 10

explain the importance of the phosphate group of lipids found in the cell membrane

Answer 10

phosphate group is polar
it can interact with aqueous environment
otherwise lipids will not form bilayer

Question 11

what route does a symplastic / apoplastic pathway take?

Answer 11

symplastic - through cell’s cytoplasm

apoplastic- through cell walls

Question 12

describe the structure of a ribosome

Answer 12

made from protein + RNA

made from two subunits

Question 13

explain why using antibiotics only when needed will reduce antibiotic resistance

Answer 13

because antibiotics act as a selection pressure for resistant bacteria

Question 14

how is tissue fluid formed?

Answer 14

high hydrostatic pressure forces plasma/fluid out of the capillaries

Question 15

describe what happens to the tissue fluid that is not reabsorbed into the blood capillary

Answer 15

it enters the lymphatic system (becomes lymph)

lymph is taken to subclavian veins/blood

taken to different parts of the body to be broken down

Question 16

What organism causes malaria ?

Answer 16

Plasmodium falciparum

Question 17

name methods of controlling malaria and possible implications

Answer 17

repellant

insecticide (kill mosquitos)

avoid stagnant water (inconvenient/difficult to get water that’s not stagnant near home/work)

Question 18

explain the importance of vaccinating as many people as possible against a disease

Answer 18

helps create herd immunity
fewer people will become infected, preventing those who can’t get immune through vaccination (e.g due to allergy/intolerance)

Question 19

what classification of virus is ebola?

Answer 19

RNA enveloped

Question 20

what classification of virus is lambda phage?

Answer 20

DNA non-enveloped

Question 21

what classification of virus is TMV

Answer 21

RNA non-enveloped

Question 22

what happens inside cells once they have taken up a virus?

Answer 22

the cell reproduces, producing viral RNA
viral protein made
assembly of virus and new virus particles

Question 23

are the following bonds found in carbohydrate, lipid, both or neither:

covalent
ester
hydrogen

Answer 23

covalent - carbohydrate and lipid
ester-lipid only
hydrogen-carbohydrate only

Question 24

why can lipids only be respired in aerobic conditions?

Answer 24

in anaerobic conditions
pyruvate would be used to reoxidise NADH , so no Krebs cycle
the final electron acceptor oxygen would not be there

Question 25

describe how you could identify different bacteria present in a sample from the body

Answer 25

get a sample of (named area)

use selective media to grow bacteria

grow bacteria on media containing different antibiotics

DNA profiling /gram staining/colony shape,size

Question 26

explain how cells that metabolise glycogen to lactic acid can inhibit the growth of pathogenic bacteria

Answer 26

lactic acid is toxic to cells and stops bacteria reproducing- lowers pH which denatures enzymes of pathogenic bacteria

grow on skin cells, preventing pathogenic bacteria from doing so

use glycogen so less available for bacteria

Question 27

explain how a blood clot can cause a heart attack

Answer 27

blockage due to clot means oxygen can’t reach the cells in the heart

this prevents aerobic respiration , the heart muscle can’t contract, the cells die

Question 28

explain what is meant by ‘myogenic’

Answer 28

myogenic means stimulation is generated from within the muscle , resulting in depolarisation

Question 29

explain how and EEG can be used to calculate a person’s heartrate

Answer 29

shows electrical activity of the heart

can identify time for one heartbreak using P wave / QRS complex / T wave

count number of peaks in set time

beats/time

Question 30

explain why a carbon dioxide concentration of 5% causes a change in heartrate

Answer 30

concentration of carbon dioxide increases in alveoli ( conc gradient increased)

conc of carbon dioxide in blood increases - this is detected by chemoreceptors in medulla
(medulla is a cardiac control centre)
more impulses sent to SAN
SAN rate increases
heart rate will increase

Question 31

explain why someone who has high blood pressure is at a significantly higher risk of developing CVD

Answer 31

damage to endothelium
inflammatory response
atheroma
stops blood flow, blood clot forms
this means loss of elasticity and narrowing of lumen

positive feedback- further increase in blood pressure