AQA NEW

Question 1

Describe two differences between the structure of a tRNA molecule and the structure of a mRNA molecule

Answer 1

1. tRNA molecule has a clover leaf shape whereas mRNA has a linear shape
2. mRNA has codons whereas tRNA has anticodons

Question 2

Describe the difference between pre-mRNA and mature mRNA

Answer 2

Pre mRNA contains exons and introns whereas the mRNA used in translation has been spliced so exons which are non coding regions of DNA have been removed and introns have been joined together.

Question 3

Name the structure of the HIV

Answer 3

A- glycoprotein

B- capsid

Question 4

How is HIV replicated?

Answer 4

HIV attachment proteins attach to CD4 receptors on helper T cell and infects the t-cell. Reverse transcriptase produces a DNA from the HIV’s RNA and viral protein is produced. The virus particles are assembled and released from the cell.

Question 5

Why is not possible to see the identity of sub cellular structure using an optical microscope?

Answer 5

The resolution is too low because the wavelength of light is too long

Question 6

Describe the role of a named organelles in bacteria digestion

Answer 6

Lysosomes fuse with the phagosome within the cell and release hydrolytic enzymes which digest and break down the bacteria

Question 7

Magnification equation

Answer 7

Magnification= Image/ Actual

Question 8

Why are mitochondria found close to the cell surface membrane in large cells

Answer 8

Large cells have a smaller surface area to volume ratio so takes longer for oxygen to diffuse to mitochondria as diffusion distance is longer

Question 9

Describe and explain the arrangement of the genetic material shown in figure 4

Answer 9

Chromosomes have condensed and become visible and are arranged randomly because they are not attached to spindle fibres as spindles have not formed

Question 10

Name the fixed position occupied by a gene on a DNA molecule

Answer 10

Locus

Question 11

Describe how a gene is a code for the production of a polypeptide

Answer 11

The base sequence of the gene is in triplets which determines the sequence of amino acids in the primary structure of a polypeptide

Question 12

Describe how the structure of glycogen is related to its function

Answer 12

Glycogen is insoluble so does not affect the water potential of the cell it is stored in. It has a compact due to its coiled alpha helix shape so lots of glycogen can be stored in a small area. It is a polymer of glucose so is easily hydrolysed and it is highly branched so more ends for faster hydrolysis

Question 13

What type of peptidases hydrolyse the bonds within a polypeptide chain

Answer 13

Endopeptidases hydrolyse the peptide bonds within a polypeptide chain

Question 14

Give the pathway a red blood cell takes when travelling in the human circulatory system from a kidney to the lungs

Answer 14

Deoxygenated red blood cell passes through the renal vein and through the vena cava into the right atrium. It then pass through the atrioventricular valve into the right ventricle and then through the pulmonary artery into the lungs

Question 15

Identity the blood vessel seen in the figure

Answer 15

The blood vessel is a vein since it has a large lumen and a thin wall due to low pressure that blood flows at

Question 16

Describe how water from tissue fluid is returned to the circulatory system

Answer 16

Larger plasma proteins remain in the blood as they are too large to pass through fenestrations in the cell membrane. This means there is a lower water potential at the venous end of the capillary so water moves by osmosis from the tissue fluid into the capillary down the concentration gradient as osmotic pressure is greater than the hydrostatic pressure.

Question 17

Suggest how the student should use the data from plot 1 and other information provided to estimate the total number of beetle species in the meadow

Answer 17

Find the number of beetle species in plot 1 then calculate the total area of plot 1 and the total area of the meadow. Divide the area of the meadow by the total area of plot 1 and times this number by the number of species in plot 1 to estimate the total number of species

Question 18

How can the table and the presentation of data be improved

Answer 18

1. Improve the design of the table by putting the independent variable which is the name of the solution covering the egg in column1.
2. Use the same number of decimal points in the final column so 1.29 and 0.70

Question 19

Suggest and explain an advantage of carrying out this investigation at 30C rather than at 20C

Answer 19

Water has more kinetic energy so more osmosis occurs so there is a larger difference in mass in the time available

Question 20

The student concluded from the information in Table 2 that the water potential of the solution inside the egg is higher than the water potential if the vinegar

Answer 20

Water moves by osmosis down the concentration gradient from a region of higher to lower water potential, the ratio of the final to initial mass was 1.29 to zero which means water has entered the egg by osmosis so the water potential of the solution inside the egg is lower

Question 21

How would you advise the student to use her calculated ratios to determine the water potential of the eggs?

Answer 21

1. Plot the calculated ratio of the final mass to initial mass on the y axis against the dilution series of sugar concentration from 0.0 mil/dm3 to 1mol/dm3 increasing in increments of 0.1mol/dm3 which is your independent variable
2. Draw a line of best fit for the calculated ratios on the graph
3. Find the point at which the line of best fit crosses the x axis where the ratio of final to initial mass is 1:1, this is the water potential of the eggs
4. Use a table or graph to find the water potential of the eggs using the concentration found

Question 22

Identity the two organelles in kidney cells that enable the production of EPO

Answer 22

Ribosomes and Golgi Apparatus/ Vessicles

Question 23

Explain the biological advantage to athletes of injecting synthetic EPO

Answer 23

Injecting synthetic EPO increases the production of red blood cells in the athletes body, this means there is greater delivery of oxygen to tissues around the body so muscles can respire aerobically for a longer period of time

Question 24

Describe how mice injected with human synthetic EPI produce anti human EPO antibody

Answer 24

Phagocytes engulf the foreign human EPO protein, break it down an display it’s antigens on its surface. If specific t helper cell with complementary receptors binds to these antigens on the antigen presenting cells they stimulate B cells to divide rapidly by mitosis into plasma cells which release antibodies to neutralise or immobilise the pathogen making them readily identifiable to the phagocytes.

Question 25

Explain the roles of the anti human EPO and anti mouse antibody with enzyme attached in producing a positive result for EPO in the ELIZA test

Answer 25

Anti human EPO has complementary receptors to EPO and binds to EPO in playing well. Anti mouse antibody bonds to anti human antibody and when the colourless substrate of the enzyme is added the enzyme catalyses the production of the coloured substrate. If a colour change is seen then EPO is present.

Question 26

Name the group represented by COOH

Answer 26

Carboxyl Group

Question 27

Name the R group shown in figure 1

Answer 27

Alkene, is made up of only carbon and hydrogen atoms and is unsaturated

Question 28

Test for lipids

Answer 28

Add ethanol to sample, then pour solution into water, if milky white emulsion forms then lipids are present

Question 29

Give one similarity and two differences between the membrane structure shown and the fluid mosaic model

Answer 29

Similarity is that both models contain proteins Difference is that fluid mosaic model of membrane structure has proteins that vary in shape size and structure while this only has one type of protein that is uniform in size and shape Difference is that cholesterol is not present whereas it is in fluid mosaic model

Question 30

Describe and explain one feature of the alveolar epithelium that makes the epithelium well adapted as a surface for gas exchange

Answer 30

Alveolar epithelium has a one cell thickness which means there is a short diffusion pathway for oxygen to enter the capillaries

Question 31

Suggest how a reduced tidal volume affects the exchange of carbon dioxide between the blood and alveoli

Answer 31

Less carbon dioxide moves out of lungs so reduces concentration gradient between blood and alveoli so slower movement of carbon dioxide out of the blood

Question 32

In taxonomy an organism is identified by referring to the species name and the genus name. What is the term used to describe this method of naming organism?

Answer 32

Binomial system

Question 33

Define the term mutagenic agent

Answer 33

A factor that increases the rate of mutation

Question 34

Name the type of mutual ion that causes the number of chromosomes in S townsendil to produce S anglica and explain your answer.

Answer 34

Non disjunction, during meiosis the chromosomes were not separated so all the chromosomes remain in one cell

Question 35

Explain one way genetic variation within a species is increased

Answer 35

Random fusion of gametes produces new allele combinations

Question 36

Give two structure found in all prokaryotic and in all eukaryotic cells

Answer 36

1. Cell membrane | 2. Ribosomes

Question 37

Suggest why there is a faster rate of plasmid replication in cells growing in a culture with a high amino acid concentration

Answer 37

Amino acids are used in protein synthesis so more enzymes for plasmid replication

Question 38

What can you conclude about a structural difference between the plasmids and the circular DNA?

Answer 38

The circular DNA is more dense than the plasmid as the band is formed is closer to the bottom of the test tube

Question 39

What can you conclude about the effect of antibiotic X on plasmid and circular DNA replication?

Answer 39

Antibiotic X has not effect on circular DNA replication but doubles the rate of plasmid replication as the band is twice as thick in tube B

Question 40

Explain the appearance of agar in the clear area surrounding well D

Answer 40

The amylase solution has hydrolysed the breakdown of the agar as it is made of starch to maltose

Question 41

What can you conclude about the activity of amylase from the appearance of the agar surrounding well E and well F in figure 7?

Answer 41

Amylase has been denatured in E and amylase is needed for the breakdown of starch in well F as only water is present

Question 42

Describe a biochemical test the student could use with this solution to confirm the amylase had affected the starch in the clear area surrounding well D

Answer 42

Do test for reducing sugars as starch is converted into maltose which is made up of glucose. Add Benedict’s reagent and heat in a water bath at 60C if the colour changes from blue to brick red reducing sugars are present.

Question 43

The enzyme encoded by the ADF allele catalyses the breakdown of alcohol faster than the enzyme coded by the ADS allele. Suggest why.

Answer 43

The enzyme codes for by the ADS allel has a different primary protein structure so has a different tertiary structure so the shape of the active site is diffenet and enzyme substrate complexes are more likely to be formed.

Question 44

Alcohol is toxic to fruit flies. Suggest and explain why the frequency of the ADF allele changed during the 45 generations

Answer 44

Fruit flies with the ADF allele outcompetes those without as it is more likely to survive due to favourable allele. This means it is more likely to reproduce and pass on allele to offspring, over time the proportion of the population with the favourable ADF will increase as seen in figure 1 so allele frequency will increase

Question 45

Describe how ATP is formed from its component molecules

Answer 45

ATP is formed from ADP and an inorganic phosphate in an condensation reaction catalysed by ATP synthase in which water is released as a by product

Question 46

Using the figure what can you conclude about the amino acid uptake by G and H cells?

Answer 46

The rate of amino acid uptake is much faster in H cells than it is in G cells. Amino acid uptake occurs by active transport but cyanide reduces amino acid uptake so ATP production stops on membranes but ATP production continues in cytoplasm

Question 47

What can you conclude from the figure about the effect of trapping GOx and HRP inside cages?

Answer 47

There is a significant difference between the relativ activity of GOx and HRP when trapped and not trapped as the error bars do not overlap. Trapping increases the activity of the enzymes.