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Page 1

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1. The figure below represents a water molecule.


H


O



H




Water molecules are polar. As a result, they attract each other.

Draw a second water molecule on the figure above.

Your drawing should show:

· the bond(s) between the two molecules
· the name of the bond
· the…

Page 2

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3. Ponds provide a very stable environment for aquatic organisms.

Three properties of water that contribute to this stability are as follows:

· the density of water decreases as the temperature falls below 4 °C so ice floats
on the top of the pond
· it acts as a solvent…

Page 3

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Explain how these three properties help organisms survive in the pond.

In your answer you should make clear the links between the behaviour of the water
molecules and the survival of the organisms.

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Page 4

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4. ice floats
P1 (ice less dense because) molecules spread out;
P2 molecules form, crystal structure / lattice / AW;
P3 ice forms insulating layer / clearly described;
e.g. acts as a barrier to the cold
P4 water (below ice), does not freeze / still liquid / remains water /…

Page 5

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S6 temperature does not change much / small variation in temperature;
could refer to organisms or surrounding water
ACCEPT stays cool in summer / stays warm in winter
DO NOT CREDIT constant alone
S7 effect of temperature on, enzymes / metabolic rate;
ACCEPT any reference to temperature affecting enzyme
activity…

Page 6

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7. The enzyme DHPS is involved in the production of folic acid in bacteria.

· The substrate for DHPS is a molecule known as PABA.

· The enzyme DHPS is inhibited by the drug sulfonamide.

The figure below shows the structure of PABA and that of sulfonamide.

H H
N…

Page 7

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(ii) Using the information in the figure above, explain why sulfonamide acts as a
competitive inhibitor of DHPS.

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[3]
[Total 4 marks]




8. (i) X;
1



(ii) 1 substrate / PABA, and, inhibitor / sulfonamide, similar shape;
ACCEPT similar structure DO NOT CREDIT…

Page 8

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9. The figure below shows the effect of increasing the concentration of the substrate
(PABA) on the rate of reaction.

· Curve A shows the rate of reaction without the presence of the competitive
inhibitor sulfonamide.
· Curve B shows the rate of reaction in the presence of the competitive…

Page 9

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(ii) with inhibitor.

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[2]
[Total 5 marks]




10. (i) without inhibitor
1 more, PABA / substrate, molecules enter active site:
ACCEPT more successful collisions between substrate and
active site
2 more, enzyme substrate complexes / ESCs, formed;
3 at low concentration not all active sites…

Page 10

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11. (a) Amino acids are the basic building blocks for proteins. The figure below shows
the amino acid cysteine.

M
CH2 SH


H OH
J N C C
L
H O


H
K



(i) Complete the table by selecting the letter, J, K, L or M, that represents the
following…

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