AS Biology unit 2 Biological molecules questsion and answers

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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 charges on each atom.
[Total 3 marks]
2.
+ hydrogen bond
+
H H
O -
O
-
H H
+
+
1 hydrogen bond represented as,
horizontal / vertical, dashed line between O on one molecule and H on the adjacent
molecule;
DO NOT CREDIT if >1 H bond is drawn between the same
two molecules
2 hydrogen / H, bond label (on any drawn bond between 2 molecules);
3 (delta positive) + on each drawn H
and (delta negative) (2) ­ on each drawn O;
if both molecules drawn, + and ­ on all atoms.
ACCEPT d (lower case) for
[3]
Swakeleys School 1

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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 for ions such as nitrates (NO3­)
· a large quantity of energy is required to raise the temperature of water by 1 °C.…read more

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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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P1 (ice less dense because) molecules spread out;
P2 molecules form, crystal structure / lattice / AW;
P3 ice forms insulating layer / clearly described;
e.g.…read more

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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 / metabolic rate
S8 gases remain soluble;
Award once in any section
H hydrogen bonds;
DO NOT CREDIT if in incorrect context
(e.g.…read more

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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
O
HO O S
C
N N
H H H H
PABA sulfonamide
(i) Diagrams X, Y and Z represent these enzyme molecules and their active sites.…read more

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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.…read more

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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 inhibitor
sulfonamide.…read more

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Total 5 marks]
10.…read more

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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 groups in cysteine.
group letter
carboxyl
R group
amine group
[3]
(ii) The primary structure of a protein consists of a chain of amino acids.…read more

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