AQA A Level Biology Mock Paper 1 Q&A

Describe the structure of glycogen (2)

1. polysaccharide of alpha glucose 2. joined by glycosidic bonds

Give the 2 types of molecule from which a ribosome is made (2)

1. ribosomal Proteins 2. ribosomal RNA

The scientists incubated the flasks containing the leaf discs at 26C 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)

1. temperature - so rate of diffusion remains constant 2. shaking - so all surfaces of the leaf discs are exposed

Suggest one advantage to a bacterium of secreting an extracellular protease in its natural environment (2)

1. to digest protein 2. so they can absorb amino acids for protein synthesis

In a eukaryotic cell, the base sequence of the mRNA might be different from the sequence of the pre-mRNA. Explain why (2)

1. introns in pre-mRNA 2. splicing

Explain how the presence of gills adapts the damselfly to its way of life (2)

1. larvae have higher respiration rate 2. so use more oxygen

Explain 3 ways in which an insects tracheal system is adapted for efficient gas exchange (3)

1. tracheoles have thin walls so short diffusion pathway 2. large number of tracheoles so large surface area 3. tracheae provide tubes full of air so fast diffusion

Contrast how an optical microscope and a transmission electron microscope work and contrast the limitations of their use when studying cells (6)

1. TEM uses electrons and optical use light 2. TEM allows a greater resolution 3. with TEM smaller organelles can be observed 4. TEM view only dead/dehydrated specimens and optical can view live specimens 5. TEM does not show colour and optical can 6. TEM requires thinner specimens 7. TEM requires a more complex/time consuming preparation 8. TEM focuses using magnets and optical uses glass lenses

Describe how bacteria divide (2)

1. binary fission 2. replication of circular DNA 3. division of cytoplasm to produce 2 daughter cells 4. each with single copy of circular DNA

Complete the complementary base sequence of DNA strand from which pre-mRNA may be transcribed: ACGCAUUAU (1)

TGCGTAATA

Give 3 environmental variables that should be controlled when growing the plants before treatment with the different sprays (2)

1. carbon dioxide concentration 2. light intensity 3. temperature

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 promo (hydrogen ion) out of the cell. Use your knowledge of transport across cell membranes to suggest how NHE3 does this (3)

1. co-transport 2. uses hydrolysis of ATP 3. sodium ion and proton bind to the protein 4. protein changes shape

State 3 comparisons of genetic diversity that the scientists used in order to generate classifications based on other comparisons of genetic characteristics (3)

1. comparison of DNA sequence 2. base sequence of mRNA 3. amino acid sequence

Suggest ways to improve a scientific drawing (2)

1. dont shade 2. no sketching, only single lines 3. dont cross labelling lines 4. add measurement or scale 5. label more features

Describe how presentation of a virus antigen leads to secretion of an antibody against this virus antigen (3)

1. helper T cells bind to the antigen 2. this stimulates a specific B cell 3. B cell clones

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)

1. higher salt results in lower water potential of tissue fluid 2. so less water returns to capillary by osmosis at venue end

Suggest why human ATP synthase is not inhibited and bacterial synthase is inhibited (1)

1. human ATP synthase has a different shape active site to bacterial ATP synthase

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)

1. hydrolyse peptide bonds to release amino acids 2. amino acids can cross cell membrane

Suggest how glycogen acts as a source of energy (2)

1. hydrolysed to glucose 2. glucose is used in respiration

Describe the role of a ribosome in the production of a polypeptide. Do not include transcription in your answer (3)

1. mRNA binds to ribosome 2. allows tRNA with anticodons to bind 3. catalyses formation of polypeptide bond between amino acids

Suggest and explain two ways the cell0surface membranes of the cells lining the uterus may be adapted to allow rapid transport of nutrients (2)

1. membrane folded so increased surface area 2. larger number of protein channels for facilitated diffusion 3. large number of protein carriers for active transport 4. large number of protein for co-transport

Describe how phagocytosis of a virus leads to presentation of its antigens (3)

1. phagosome guess with lysosome 2. virus destroyed by lysozymes 3. peptides from virus are displayed on the cell membrane