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REVISION 1 (54 Marks)
IB Standard level Biology Dulwich College Shanghai
Topic 3: Chemistry of Life
3.1
3.1.1
3.1.2
3.1.3
3.1.4
3.1.5
3.1.6
3.2
3.2.1
3.2.2
3.2.3
3.2.4
3.2.5
3.2.6
3.2.7
Chemical elements and water
State that the most frequently occurring chemical elements in living things are carbon,
hydrogen, oxygen and nitrogen.
State that a variety of other elements are needed by living organisms, including sulphur,
calcium, phosphorus, iron and sodium.
State one role for each of the elements in 3.1.2.
Draw and label a diagram showing the structure of water molecules to show their polarity
and hydrogen bond formation.
Outline the thermal, cohesive and solvent properties of water.
Explain the relationship between the properties of water and its uses in living organisms as
a coolant, medium for metabolic reactions and transport medium.
Carbohydrates, Lipids and Proteins
Distinguish between organic and inorganic compounds.
Identify amino acids, glucose, ribose and fatty acids from diagrams showing their structure.
List three examples of each of monosaccharides, disaccharides and polysaccharides.
State one function of glucose, lactose and glycogen in animals and of fructose, sucrose and
cellulose in plants.
Outline the role of condensation and hydrolysis in the relationships between
monosaccharides, disaccharides and polysaccharides; between fatty acids, glycerol and
triglycerides; and between amino acids and polypeptides.
State three functions of lipids
Compare the use of carbohydrates and lipids in energy storage.
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Paper 1
Multiple Choice (8 Marks)
1.
Which of the following reactions occurs when a dipeptide is formed from amino acids?
A.
Hydrolysis
B.
Denaturation
C.
Condensation
D.
Oxidation
2.
The diagram below shows a channel protein in a membrane. Which parts of the surface
of the protein would be composed of polar amino acids.
A.
B.
C.
D.
3.
I and II only
II and III only
III and IV only
I and IV only
Which is the structure of glycerol? A
A.
H
H
H
H
C
C
C
B.
H
H
OH OH OH
C.
H
H
H
C
C
D.
H
H
OH OH
4.
Which molecule is a monosaccharide?
A.
Ribose
B.
Glycogen
C.
Amylase
D.
Glycerol
2
H
H
H
C
C
C
H
H
OH
H
H
C
C
H
OH
H
H
5.
Which of the following diagrams is the structure of ribose? A
A.
O
HOH 2C
H
C.
H
C
C
OH
OH
C
OH
D.
OH
H
OH
C
OH
O
H
H
C
OH
H
C
C
H
OH
HOH2 C
C
C
H
H
OH
O
HOH 2C
CH 2OH
C
C
C
H
B.
H
OH
O
H
C
C
CH 2OH
H
H
C
C
C
H
OH
H
H
OH
6.
In which part of the digestive system is most water re-absorbed?
A.
The kidneys
B.
The stomach
C.
The small intestine
D.
The large intestine
7.
What is one role of the element phosphorus?
A.
It forms part of the structure of amino acids.
B.
It forms part of the structure of fatty acids.
C.
It forms part of the structure of ribose.
D.
It forms part of the structure of nucleotides.
8.
Carbon, hydrogen, nitrogen and sulphur are elements found in living cells. Which is the
least common?
A.
Carbon
B.
Hydrogen
C.
Nitrogen
D.
Sulphur
3
Paper 2
Section A
Data Analysis (8 marks)
1.
Diatoms are unicellular algae which live as plankton in fresh water and oceans.
Biochemists investigated two species of diatom, Thalassiosira oceanica which lives in
the open ocean where the water is clear and Thalassiosira weissflogii which lives in
coastal waters where the water is often cloudy. Iron is an important part of a number
of molecules involved in photosynthesis. Iron however is often deficient in the waters
of the open ocean. The scientists investigated the amount of iron present in the cells of
the diatoms when they were grown at different intensities of light, in both high and low
iron conditions.
Thalassiosira oceanica
Thalassiosira weissflogii
1000
Key:
high iron conditions
800
low iron conditions
Iron
concentration
in cells /
mol dmΠ3
600
400
200
0
(a)
100
200
300 0
100
Light intensity / relative units
200
300
Compare the iron concentrations in the cells of T. oceanica and T. weissflogii under high
iron conditions.
(2)
under low light intensity T. weissflogii has more iron in its cells / T. oceanica
has less iron in its cells than T. weissflogii;
between light intensities of 75 and 250 units iron concentrations decrease in
T. oceanica but increase in T. weissflogii;
under high light intensity slightly more iron concentration in T. weissflogii;
between 25 and 75 units iron concentration in T. oceanica increases but
decreases in T. weissflogii;
(b)
Suggest a reason for the response of T. weissflogii to low light intensities.
(2)
in low light intensity the concentration of iron in the cells increases
(or vice versa) (this is mainly true for both high and low levels of iron);
this increase in cellular iron could be due to increased numbers of chloroplasts
/ an increase in photosynthesis / an increase in the concentration of photosynthetic
molecules when light is limiting;
this could be due to the cells being in / adapting to cloudy water;
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When the growth of these two species was compared in the two iron conditions it was
found that the growth of T. oceanica was not affected by low iron concentrations but
the growth of T. weissflogii was reduced by about 20%.
(c)
Explain how T. oceanica is adapted to oceanic waters.
oceanic waters are deficient in iron;
T. oceanica requires less iron for photosynthesis;
oceanic waters are clear so light levels are high;
T. oceanica can photosynthesise at its highest rates;
(d)
Predict what would be the effect on the populations of these diatoms if atmospheric
pollution reduced light intensities over the oceans.
(1)
T. oceanica populations would diminish
Paper 2
Section A
Short Structured (17 Marks)
1.
List four functions of proteins, giving an example of each.
Name of function and named protein must both be correct for the mark.
storage – zeatin (in corn seeds) / casein (in milk);
transport – hemoglobin / lipoproteins (in blood);
hormones – insulin / growth hormone / TSH / FSH / LH;
receptors – hormone receptor / neurotransmitter receptor /
receptor in chemoreceptor cell;
movement – actin / myosin;
defence – antibodies / immunoglobin;
enzymes – catalase / RuBP carboxylase;
structure – collagen / keratin / tubulin / fibroin;
electron carriers – cytochromes;
pigments – opsin
active transport – sodium pumps / calcium pumps;
facilitated diffusion – sodium channels / aquaporins;
Mark first four functions only. Allow other named examples.
2.
Explain the significance of secondary structure to the structure of a protein.
held together by hydrogen bonds;
between CO and NH groups;
(α-helix for) structure of fibrous proteins / keratin;
one of four levels of structure;
provides stability of structure;
a-helix;
b-sheet;
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(3)
(4)
(3)
3.
Explain the significance of polar and non-polar amino acids within the cell.
(3)
polar amino acids are hydrophilic and non-polar amino acid are hydrophobic;
position of polar and non-polar amino acids determine protein shape / function / location;
(in channel proteins) hydrophilic amino acids line the channels and allow transport of ions /
polar substances;
non-polar amino acids are in contact / embedded within the lipid membrane;
polar amino acids on the surface proteins make them water soluble;
non-polar in the centre of water-soluble proteins
stabilize the structure;
Accept any of the above points if clearly explained using a suitably labeled diagram.
4.
Draw the structure of a fatty acid.
(1)
O
CH 3 (CH 2)n COOH / CH 3
(CH 2 )n
C
OH
5.
Outline how monosaccharides are converted into polysaccharides.
condensation;
involves the removal of water to join monosaccharides together / equation to show this;
catalysed by enzymes;
consists of many monosaccharides linked (glycosidic) to make polysaccharide;
6.
Many elements are necessary to form biochemicals required by living organisms. For each
element below, state the name of one molecule containing the element and state the function
of the molecule.
(4)
Fe examples:
hemoglobin;
transports oxygen (in the blood);
myoglobin;
store of oxygen in muscle;
cytochromes / ferredoxin;
electron carrier;
(do not accept avoids anemia)
P examples:
ATP / ADP;
energy storage and release;
DNA / RNA / nucleotides;
genetic (hereditary) material;
phospholipids
structural component of membrane
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(2)
Section B
Extended Response (21 Marks)
1.
Outline the production of a dipeptide by a condensation reaction. Include the structure of a
generalized dipeptide in your answer.
(5)
carboxyl / COOH group of one amino acid reacts with amine / NH 2 group of another;
water / H2O is eliminated;
These steps can be shown diagrammatically, eg
peptide / covalent bond is produced;
diagram of dipeptide, with peptide bond shown [2 max];
eg
Award [1] if the two amino acids forming the dipeptide are shown correctly. The radicals can
be shown as R or H. Award the second mark if the C-N bond is labelled as peptide bond or
dipeptide bond. The label can include the H bonded to the N and the O double bonded to the
C.
2.
Distinguish between fibrous and globular proteins, giving one example of each.
Award [1] for each of the following pairs up to [3 max].
fibrous
globular
repetitive amino-acid sequences vs.
irregular amino acid sequences;
long and narrow / long strands
vs.
rounded / spherical / ball shaped;
support / structural functions
vs.
metabolic / other functions;
(mostly) insoluble in water
vs.
(mostly) soluble in water;
Award [1 max] for example of fibrous proteins.
collagen;
myosin;
(a)–keratin;
fibroin / elastin / silk protein in insects and spiders;
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(5)
Reject fibrinogen.
Award [1 max] for example of globular proteins.
catalyses / other named enzyme;
hemoglobin / myoglobin;
insulin / other peptide hormone;
immunoglobulin / other globular protein;
Reject examples of fibrous and globular proteins apart from the first named examples.
3.
Outline the use of carbohydrates and lipids in energy storage.
lipids have more / twice the energy content
per unit mass of carbohydrates;
energy stored as glycogen in animals / fungus;
glycogen / carbohydrates used for short-term energy storage;
glycogen converted to glucose when energy is required;
energy stored as starch in plants;
lipids / triglycerides used for long-term energy storage;
triglycerides converted to fatty acids and
glycerol (when energy is required);
triglycerides broken down to yield acetyl CoA;
(5)
4.
Describe the significance of water to living organisms.
Features and their significance may include:
surface tension – allows some organisms (eg insects) to move on water’s surface;
polarity / capillarity / adhesion – helps plants transport water;
transparency – allows plants to photosynthesise in water / allows animals to see;
(excellent) solvent – capable of dissolving substances for transport in organisms;
(excellent) thermal properties (high heat of vaporization) – excellent coolant;
ice floats – lakes / oceans do not freeze, allowing life under the ice;
buoyancy – supports organisms;
structure – turgor in plant cells / hydrostatic skeleton;
habitat – place for aquatic organisms to live;
involved in chemical reactions in organisms;
Each feature or property must be related to living organisms in order to receive a mark.
(6)
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