past paper questions

Question 1

explain how the action of protein kinase can switch a target protein from inactive to active

Answer 1

the kinase phosphorylates the target protein, causing it to change conformation

Question 2

explain the importance of a system being able to return the target protein to its active state

Answer 2

it allows the target protein to respond again

Question 3

name the process where the binding of oxygen to one subunit of haemoglobin alters the affinity of the remaining subunits

Answer 3

cooperative binding

Question 4

tissues with higher metabolic rates require more oxygen. these tissues produce more carbon dioxide, which dissolves in tissue fluids to form carbonic acid. what impact does this have on the release of oxygen?

Answer 4

the acid means there is a lower pH, which means there is a lower affinity for binding to oxygen in haemoglobin, so there is a greater release of oxygen

Question 5

explain the term cooperativity in binding in relation to oxygen binding to haemoglobin

Answer 5

Binding (to one subunit of one
oxygen) makes the binding of
other oxygen more likely

Question 6

Explain why the rate of uptake by GLUT transporters levels off at high
glucose concentrations

Answer 6

most binding sites on the glut transporters are filled

Question 7

name a purpose of the sodium potassium pump

Answer 7

generates an ion concentration gradient for maintenance of resting potential in cells and neurons

Question 8

a decrease in the activity of glucose symport proteins in the cells lining the small intestine could be caused by an increase in the…

Answer 8

sodium ion concentration in the cells

Question 9

describe the mechanism by which a hydrophobic signalling molecule causes an effect within the target cell

Answer 9

• diffuses through the cell membrane
• binds to receptor which switches off transcription / binds to a transcription factor

Question 10

how can a signalling molecule have different effects on different tissues

Answer 10

they have different transduction pathways and may have different responses to receptor binding

Question 11

what is a peptide hormone an example of

Answer 11

a hydrophilic extracellular signalling molecule

Question 12

why is there not a rapid increase in the transport of glucose into muscle and fat cells via glut4 in individuals with type 2 diabetes

Answer 12

the insulin receptors lose sensitivity, and the glut4 is not recruited and transported to the membrane from intracellular stores

Question 13

explain why rod cells can function in low light intensity

Answer 13

higher degree of amplification

Question 14

explain the importance of potassium channels in nerve transmission

Answer 14

ions flow out of the cell in opposite direction. this returns it to the resting membrane potential

Question 15

rod cells are more sensitive than cone cells at low light intensities. how is this sensitivity achieved?

Answer 15

high degree of amplification

Question 16

in cone cells, the light sensitive molecule retinal combines with a membrane protein to form photoreceptor proteins. name this membrane protein

Answer 16

opsin

Question 17

name the additional wavelength range to which organisms are sensitive

Answer 17

UV

Question 18

name the light sensitive molecule in animals that combines with the protein opsin to form photoreceptors of the eye

Answer 18

retinal

Question 19

describe the role of bacteriorhodopsin in archaea

Answer 19

absorbs light to pump protons to generate a potential difference

Question 20

describe the structure of spindle fibres and explain their role in the movement of chromosomes during cell division

Answer 20

cell division requires remodelling of the cytoskeleton.
spindle fibres are made of microtubules - hollow cylinders made of tubulin
they attach to chromosomes kintechores in the centromere region. they radiate from the MTOC
the spindle fibres contract and shorten and separate chromatids

Question 21

name the globular protein of which microtubules are composed

Answer 21

tubulin

Question 22

name the structure from which microtubules radiate

Answer 22

the microtubule organizing centre

Question 23

state the cause of cell death during apoptosis

Answer 23

destruction of the cell by digestive enzymes / caspases

Question 24

describe the action of caspases in cell destruction

Answer 24

they are proteases and digest proteins

Question 25

Cholera is a disease caused by the bacterium Vibrio cholerae. It causes severe watery diarrhoea, which can lead to dehydration and even death. The bacterium produces cholera toxin which interferes with the control of the CFTR protein channel by constantly activating a kinase enzyme. describe the reaction catalysed by a kinase enzyme

Answer 25

phosphorylation

Question 26

Cholera is a disease caused by the bacterium Vibrio cholerae. It causes severe watery diarrhoea, which can lead to dehydration and even death. The bacterium produces cholera toxin which interferes with the control of the CFTR protein channel by constantly activating a kinase enzyme. Explain how the production of cholera toxin by Vibrio cholerae can lead to more water being drawn out of the epithelial cells

Answer 26

constantly activated kinase leads to constant phosphorylation of CFTR. the ion channels is always open, so there is an increased movement of the chlorine ions out of the cell.

Question 27

alpha helices in proteins are stabilised by

Answer 27

hydrogen bonds

Question 28

what impact does an increase in temperature have on the delivery of oxygen to cells

Answer 28

the affinity of haemoglobin decreases, resulting in an increase delivery to cells

Question 29

state the cause of death in apoptosis

Answer 29

destruction of the cell by proteases

Question 30

what are factors that can increase transmission of parasites

Answer 30

- inadequate sanitation - contaminated drinking water - high abundance of parasites - overcrowding of hosts

Question 31

how does patchiness arise during the development of tortoisehell cats

Answer 31

in each cell, one of two of the X chromosome inactivates, meaning only the allele on the active X chromosome is expressed. this inactivation is random in each cell, and as the cells multiply they form patches, where the dominant allele is expressed in some cells, and recessive is expressed in others.

Question 32

state the term used to describe an individual able to produce gametes that differ in their sex chromosomes

Answer 32

heterogametic

Question 33

suggest one reason why controlling parasitic disease with drug treatment has proved to be so difficult

Answer 33

drugs toxic to parasites also toxic to human cells

Question 34

describe how complementary shape and chemistry of an enzyme and its substrate are essential to an enzymes function

Answer 34

induced fit. lowers activation energy.

Question 35

describe the role of caspases in apoptosis

Answer 35

they are proteases that destroy the cell and activate other enzymes like DNAase

Question 36

a vital stain...

Answer 36

only stains dead cells

Question 37

what would decrease haemoglobins affinity for oxygen

Answer 37

an increase in temperature and a decrease in pH

Question 38

how do black grouse mate

Answer 38

polygamy

Question 39

would improved vector control be an appropriate measure to reduce parasitic infections

Answer 39

no

Question 40

describe the mechanism by which a steroid hormone causes an effect in a target cell

Answer 40

diffuses through the cell membrane and binds to a transcription factor

Question 41

how is protein electrophoresis used to separate proteins

Answer 41

charge separates proteins in the gel on the basis of size shape and charge

Question 42

how can antibodies be used to detect the presence of proteins

Answer 42

antibody labelled by fluorescence, and this detects if the antibody has bound to the protein, showing its presence

Question 43

suggest one reason why counting latrines is an appropriate indirect sampling technique for water voles

Answer 43

species may be elusive

Question 44

describe how an environmental factor can influence the sex ration of offspring in reptiles

Answer 44

temperature of egg incubation

Question 45

explain why males are more likely to be affected by diabetes insipidus than females

Answer 45

males lack the homologous alleles on the Y chromosome so the recessive allele is always expressed.

Question 46

with reference to the red queen hypothesis, discuss the importance of sexual reproduction in defence against parasites

Answer 46

parasites benefit at the expense of the host. the host and the parasite coevolve. in coevolution, a change in the traits of one species acts as a selection pressure on the other species. RQ hypthesis states that species have to adapt to avoid extinction. so hosts that are better able to tolerate parasites have greater fitness and survive. sexual reproduction generates genetic variation which provides these raw materials for genetic variation.

Question 47

explain what is meant by horizontal gene transfer

Answer 47

transfer of genetic material outwith reproduction/ within the same generation

Question 48

what are the different protein locations within the cell

Answer 48

- polar r groups are mostly at the surface of a soluble protein - soluble proteins are found in the cytoplasm - membrane proteins are integral or peripheral. - some integral proteins are transmembrane, such as channels and transporters. - the peripheral proteins have hydrophilic r groups interacting with hydrophilic heads of the phospholipids - the membrane has hydrophobic and hydrophilic regions

Question 49

what are the different types of transporter proteins

Answer 49

channels and pumps are transmembrane proteins that control ion concentration and maintain concentration gradients. different cells have different channels movement through channels is passive transporter proteins change conformation to transport the molecules across the membrane this conformational change requires phosphorylation by ATP an example of a pump is the sodium potasium pump which generations ion gradients for glucose symport.

Question 50

how do ligand gated channels open

Answer 50

by the binding of a signal molecule

Question 51

how do voltage gated channels open

Answer 51

by changes in ion concentration

Question 52

in animal rod cells rhodopsin absorbs a photon of light intiating the following cell events

Answer 52

activation of hundreds of g protein molecules activation of thousands of molecules of an enzyme sufficient product formation is triggered nerve impulse is generated

Question 53

what is the benefit to the parasite if its vector lives longer

Answer 53

allows more time for reproduction

Question 54

state an advantage of using an in vivo trial

Answer 54

allows the overall effect of a drug to be observed

Question 55

why would a placebo group be included in a trial

Answer 55

to provide results in the absence of the drug

Question 56

describe an ethical issue associated with in vivo

Answer 56

right to withdraw and justification of research. informed consent.

Question 57

name the type of cell that undergoes meiosis

Answer 57

gamete mother cell

Question 58

explain the importance of potassium channels in nerve transmission

Answer 58

potassium ions flow out of the cell and return the cell to resting membrane potential.

Question 59

name the level of protein structure describing several connected polypeptide units

Answer 59

quaternary

Question 60

suggest why invasive populations are found to be composed of only parthonogenic females

Answer 60

parasite density is low

Question 61

what is a retrovirus

Answer 61

one that inserts its genome into the host genome

Question 62

if the interactions between the phospholipids on the membrane are disrupted, how could this then lead to cell death

Answer 62

would allow leakage of material in and out of th cell, which could be severe enough to lead to the lysis of the cell

Question 63

describe the chemical reaction that ATPase catalyse

Answer 63

hydrolysis

Question 64

why may something be moving into a cell against its concentration gradient

Answer 64

because the effect of the electrical potential difference is greater than that of the concentration gradient

Question 65

how can vaccinations lead to herd immunity

Answer 65

non vaccinated people are also protected

Question 66

what is meant by morphology

Answer 66

the form and structure of an organism or part of an organism

Question 67

other than morphology, what else can be used to construct a phylogenetic tree

Answer 67

protein structure