A- level paper 1 june 2017 Flashcards
Give the two types of molecule from which a ribosome is made
One of RNA/ribonucleic acid(s)/nucleotide(s)/nucleic
acid(s)/rRNA/ribosomal RNA/ribosomal ribonucleic
acid
and
one of protein(s)/polypeptide(s)/amino acid(s)/
peptide(s)/ribosomal protein;
Give the two types of molecule from which a ribosome is made
One of RNA/ribonucleic acid(s)/nucleotide(s)/nucleic
acid(s)/rRNA/ribosomal RNA/ribosomal ribonucleic
acid
and
one of protein(s)/polypeptide(s)/amino acid(s)/
peptide(s)/ribosomal protein;
Describe the role of a ribosome in the production of a polypeptide. Do not include
transcription in your answer.
[3 marks]
- mRNA binds to ribosome;
- Idea of two codons/binding sites;
- (Allows) tRNA with anticodons to bind/associate;
- (Catalyses) formation of peptide bond between
amino acids (held by tRNA molecules); - Moves along (mRNA to the next
codon)/translocation described;
In a eukaryotic cell, the base sequence of the mRNA might be different from the
sequence of the pre-mRNA.
Explain why.
[2 marks]
- Introns (in pre-mRNA);
- Removal of sections of (pre-mRNA)/splicing;
- ‘Introns removed’
scores 2 marks.
In mammals, in the early stages of pregnancy, a developing embryo exchanges
substances with its mother via cells in the lining of the uterus. At this stage, there
is a high concentration of glycogen in cells lining the uterus.
Describe the structure of glycogen.
[2 marks]
1. Polysaccharide of α-glucose; OR polymer of α-glucose; 2. (Joined by) glycosidic bonds OR Branched structure;
During early pregnancy, the glycogen in the cells lining the uterus is an important
energy source for the embryo.
Suggest how glycogen acts as a source of energy.
Do not include transport across membranes in your answer.
[2 marks]
- Hydrolysed (to glucose);
2. Glucose used in respiration;
Suggest and explain two ways the cell-surface membranes of the cells lining the
uterus may be adapted to allow rapid transport of nutrients.
[2 marks]
- Membrane folded so increased/large surface
area;
OR
Membrane has increased/large surface area
for (fast) diffusion/facilitated diffusion/active
transport/co-transport; - Large number of protein channels/carriers (in
membrane) for facilitated diffusion; - Large number of protein carriers (in membrane)
for active transport; - Large number of protein (channels/carriers in
membrane) for co-transport;
Sodium ions from salt (sodium chloride) 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
(hydrogen ion) out of the cell.
Use your knowledge of transport across cell membranes to suggest how NHE3
does this.
[3 marks]
- Co-transport;
- Uses (hydrolysis of) ATP;
- Sodium ion and proton bind to the protein;
- Protein changes shape (to move sodium
The scientists carried out a statistical test to see whether the difference in the
means was significant. They calculated a P value of less than 0.05.
They concluded that Tenapanor did reduce salt absorption in the gut.
Use all the information provided and your knowledge of water potential to explain
how they reached this conclusion.
[4 marks]
- Tenapanor/(Group)B/drug causes a significant
increase;
OR
There is a significant difference with
Tenapanor/drug/between A and B; - There is a less than 0.05 probability that the
difference is due to chance; - (More salt in gut) reduces water potential in gut
(contents); - (so) less water absorbed out of gut (contents)
by osmosis
OR
Less water absorbed into cells by osmosis
OR
Water moves into the gut (contents) by
osmosis.
OR
(so) water moves out of cells by osmosis;
High absorption of salt from the diet can result in a higher than normal
concentration of salt in the blood plasma entering capillaries. This can lead to a
build-up of tissue fluid.
Explain how.
[2 marks]
- (Higher salt) results in lower water potential of
tissue fluid; - (So) less water returns to capillary by osmosis
(at venule end);
OR - (Higher salt) results in higher blood
pressure/volume; - (So) more fluid pushed/forced out (at arteriole
end) of capillary;
Bacteria are often used in industry as a source of enzymes. One reason is
because bacteria divide rapidly, producing a large number of them in a short time.
Describe how bacteria divide.
[2 marks]
- Binary fission;
- Replication of (circular) DNA;
- Division of cytoplasm to produce 2 daughter
cells; - Each with single copy of (circular) DNA;
Explain the shape of the curves at 50 °C and 60 °C.
[4 marks]
- Both denatured (by high temperature);
- Denaturation faster at 60 °C due to more
(kinetic) energy; - Breaks hydrogen/ionic bonds (between amino
acids/R groups); - Change in shape of the active site/active site no
longer complementary so fewer enzymesubstrate complexes formed/substrate does not
fit;
Some proteases are secreted as extracellular enzymes by bacteria.
Suggest one advantage to a bacterium of secreting an extracellular protease in its
natural environment.
Explain your answer.
[2 marks]
To digest protein;
2. (So) they can absorb amino acids for
growth/reproduction/protein synthesis/synthesis
of named cell component;
OR
(So) they can destroy a toxic substance/protein;
Mammals have some cells that produce extracellular proteases. They also have
cells with membrane-bound dipeptidases.
Describe the action of these membrane-bound dipeptidases and explain their
importance.
[2 marks]
- Hydrolyse (peptide bonds) to release amino
acids; - Amino acids can cross (cell) membrane;
OR
Dipeptides cannot cross (cell) membrane;
OR
Maintain concentration gradient of amino acids
for absorption;
OR
Ensure (nearly) maximum yield from protein
breakdown;
the reaction catalysed by ATP synthase. Formula
ADP + Pi → ATP + H2O
The new antibiotic is safe to use in humans because it does not inhibit the ATP
synthase found in human cells.
Suggest why human ATP synthase is not inhibited and bacterial synthase is
inhibited.
Human ATP synthase has a different tertiary
structure to bacterial ATP synthase
OR
Human ATP synthase has a different shape
active site to bacterial ATP synthase
OR
Antibiotic cannot enter human cells/mitochondria
OR
Antibiotic not complementary (to human ATP
synthase);
The scientists suggested that people newly diagnosed with this bladder infection
should be treated with both the current antibiotic and the new antibiotic.
Explain why the scientists made this suggestion.
Use information from Figure 2 and your knowledge of evolution of antibiotic
resistance in bacteria in your answer.
[3 marks]
- (From Fig 2) New/old antibiotic does not kill
all bacteria;
OR
(From Fig 2) Some bacteria are resistant to
the new/old antibiotic; - Resistant bacteria will reproduce to produce
(more) resistant bacteria; - (Use of both) one antibiotic will kill bacteria
resistant to the other antibiotic;
OR
Unlikely that bacteria are resistant to both the
new and the old antibiotic;
OR
Use of both antibiotics (likely to) kill all/most
bacteria;
Give three environmental variables that should be controlled when growing the
plants before treatment with the different sprays.
[2 marks]
1. Concentration of mineral ion/named mineral ion in soil; 2. Soil pH; 3. Temperature; 4. Light intensity/wavelength/duration; 5. Distance between seeds/plants; 6. Volume of water given; 7. CO2 concentration; 8. Humidity;
Evaluate the use of 2,4-D as a herbicide on a wheat crop that contains wild oats as
a weed. Use all the information provided.
[4 marks]
- 2,4-D causes an increase in release of ions
from wild oat cells and 2,4-D does not
affect/has little effect on the release of ions
from wheat cells; - (For wheat) Difference is less than LSD/7 so
difference is not significant;
OR
(For wild oats) Difference is more than LSD/10
so difference is significant; - Loss of ions from cells (likely to) lead to
cell/plant death/damage;
OR
Disruption of cell membrane (likely to) lead to
cell/plant death/damage; - No evidence here about death of plants as a
result of this ion loss; - No evidence here of other
ecological/environmental impact;
The scientists incubated the flasks containing the leaf discs at 26 °C and gently
shook the flasks.
Suggest one reason why the scientists ensured the temperature remained constant
and one reason why the leaf discs were shaken.
[2 marks]
Temperature ___
Shaken ___
- (Maintain temperature) so that the rate of
diffusion (of ions out of cells) remains constant
OR
(Maintain temperature) so no change in fluidity
of phospholipids/kinetic energy of
phospholipids;
OR
(Maintain temperature) so no change in
shape/structure/denaturation of membrane
proteins; - (Shaking) So all surfaces of the leaf discs are
exposed (to water)/so all submerged;
OR
To maintain diffusion/concentration gradient
(for ions out of leaf discs);
Describe how phagocytosis of a virus leads to presentation of its antigens.
[3 marks]
- Phagosome/vesicle fuses with lysosome;
- (Virus) destroyed by lysozymes/hydrolytic
enzymes; - Peptides/antigen (from virus) are displayed on
the cell membrane;
Describe how presentation of a virus antigen leads to the secretion of an antibody
against this virus antigen.
[3 marks]
- Helper T cell/TH cell binds to the antigen (on
the antigen-presenting cell/phagocyte); - This helper T/TH cell stimulates a specific B
cell; - B cell clones
OR
B cell divides by mitosis; - (Forms) plasma cells that release antibodies;
Collagen is a protein produced by cells in joints, such as the knee.
Scientists have found a virus that produces a protein very similar to human
collagen.
Suggest how the immune response to this viral protein can result in the
development of RA.
[2 marks]
- The antibody against virus (antigen) will bind
to collagen; - This results in the destruction of the (human)
cells/collagen;
What do these classifications suggest about the evolutionary relationships between these species of snake? [2 marks] Classification X \_\_\_ Classification Y\_\_\_
- (Without genetic analysis/X) mackloti and
olivaceus have a more recent common
ancestor with each other (than with papuana); - (Genetic analysis indicates/Y) papuana and
mackloti have a more recent common
ancestor with one another (than with
olivaceus);
