Download Section B

Suggested Answers to F.6 Mid-year Examination Final Revision Exercise
Section A
1.
2.
3.
Similarities:
- Both synthesise ATP
- Both involve ATPase / ATP synthetase
- Both take place on / across membranes
- Both involve a series of electron carriers
- Both involve electron flow.
(a)
-
peristalsis / move the content of intestine
mechanical digestion
(b)
(i)
(ii)
(a)
Water enters A by osmosis
since A has a negative water potential.
The entry of water builds up a (hydrostatic) pressure in A.
increase surface area for absorption
provide energy for active uptake of digested foods.
The amount of water enter B is less
as it has a less negative water potential,
The pressure in A is larger than that in B.
Max. 3
2
1
1
5
This pushes the content of A through the glass tubing to B.
(b)
No.
Because temperature fall affects respiration.
The model does not require energy supply from respiration.
2
OR Yes.
Because cooling lowers viscosity of sugar solution,
which therefore flows more slowly.
4.
(a)
(b)
5.
(a)
(b)
-
time taken to complete trace decreases
number of errors decreases
no further significant improvement made after 7 attempts
max. 2
-
Does not test hypothesis
Sample size too small
Age / gender not considered
Not random or right-handed / left-handed not considered
Period of practice not considered
Same time needed between attempts from both groups
Any 3
3x1
The substrate may be attached to the enzyme by hydrophobic interactions, hydrogen bonds and
ionic forces.
In addition, the substrate also disturbs the shape of the enzyme, causing it to assume a new
configuration that lowers the activation energy required / induced fit.
This induced fit helps hold the substrate closer to the enzyme.
3
The precise position of these amino acids is due to the exact sequence of amino acids that form
a polypeptide helix, which folds into a compact structure.
The folding of the amino acid chains enables those amino acids to be brought closer to form the
active site.
Hydrogen bonds, disulphide bridges, hydrophobic interactions and ionic forces help maintain
this tertiary structure.
3
Section B
6.
(a)
(i)
Mean for plants: 35.6, 38.4, 21.8
Mean for animals: 46.5, 39.25, 10.25
(ii)
The statement is incorrect.
Pigs / chicken have less than 50% saturated fatty acids.
The mean of saturated fatty acid for animal is less than 50%.
Cocoa / coconut are high in saturated fatty acids.
Although the mean saturated fatty acid content of the animals is higher than that of the
plants by 10.9%,
there is only a small sample of data / there is great variation in both groups.
All the animals are land vertebrates / homoeotherms.
There is no fish / invertebrate / not representative of animals.
1
1
Any 6
6x½
Butter is not a storage material.
(iii)
7.
Rape has highest proportion of linolenic acid / essential amino acid.
It has half as much / less saturated fatty acid as olive oil [or it has more polyunsaturates
than olive oil]
Polyunsaturates lower cholesterol / polyunsaturates raise high density lipoprotein levels /
polyunsaturates lower low density lipoprotein levels
and thus lowering the chance for cardiovascular diseases.
Any 3
3x1
(b)
glycerol
1
(c)
must be present in the diet
cannot be synthesized in the body.
2
(a)






(b)
(c)
Mass / concentration of yeast
Temperature
Size / surface area of beads
Volume of solution
pH
Oxygen concentration
Yeast respires / ferments
using glucose
and produce carbon dioxide
and decrease the density of the beads
Rise faster as concentration increases from 2 up to 6%.
Because glucose is a respiratory substrate.
The time required levels off above 6%,
because glucose cannot enter the cells any faster / other factors limited the rate.
(d)
Maltose is a disaccharide,
thus rate of entry is slower.
Any 3
3x1
4x½
any 3
3x1
3
It needs to be hydrolysed before it can be used in respiration.
(e)
-
Continuous production (if the beads are contained in a column).
Enzymes can be recovered / re-use
Products will not be contamined with enzymes
Less affected by high temperatures / extremes of pH
any 2
2x1
8.
(a)
(i)
CO2 concentration
Even with decrease in temperature photosynthesis increased when CO 2 concentration
increased.
OR
Increased temperature raised rate by 1 unit but increasing CO2 concentration increases rate
by 2.8 units.
OR
When CO2 concentration is increased the effect on photosynthesis is greater than when the
temperature is increased.
OR
Difference in rate of photosynthesis from 0.01% at 25C to 0.1% at 25C is greater than
difference between 0.1% at 15C to 0.1% at 25C.
(ii) Curve below 0.01% CO2,. 25C.
Starts at zero, levels off and continues to 60 kilolux.
(iii) Decrease in CO2 with time.
OR
Increase in oxygen with time.
OR
Number of bubbles of oxygen with time.
OR
Rate of CO2 uptake
OR
Change in CO2 / O2 with time
OR
Rate of O2 released / evolved
(b)
-
(c)
Increases/ accumulates / rises
Because RuBP no longer combines / reacts with CO2
OR
GP is still being converted to RuBP
1
Any 1
1
1
1
½, ½
Transmitted / passes through leaf
Reflected
2
1
1
Section C
9.
(a)
-
absorb solar energy and converted into chemical energy
release oxygen from photolysis of water
production of ATP
as the high energy electron release its extra energy through electron transport chain
NADP+ receive electron and proton
to form NADPH+H+
ATP and NADPH+H+ are used in light-independent reaction
to convert PGA into TP
any 7
7
The process of adding inorganic phosphate to ADP to synthesise ATP
and takes place in the electron transport system during aerobic respiration.
During this process, the hydrogen atoms that are passed along the respiratory chain split into
protons and electrons.
The electrons pass from carrier to carrier through the electron transport system,
and provide the energy required for the phosphorylation.
6
oxidative phosphorylation
in cristae / mitochondrion
energy comes from chemicals / food
product is not required for subsequent reactions
3
-
(b)
(c)
photophosphorylation
in thylakoid / chloroplast
energy comes from solar energy
product is used for subsequent reactions
10.
(a)



(b)
the pigment possess by red algae can absorb green light (1), green light has higher
penetration power, can reach deep water (1)
blue and red light are utilized by photosynthetic green plants at the surface of water (1),
leaving very little to reach deep water (1)
red light has low penetration power, cannot reach deep water (1)
At any given moment, a biochemical process (e.g. photosynthesis) which involves a series of
reactions, will be limited by the slowest reaction in the series.
This slowest reaction is determined by the factor which is in shortest supply / which is nearest
its minimum value.
This factor is called the limiting factor.
For example, photosynthetic dark reactions are dependent on the production of NADPH 2 and
ATP from light reaction.
At low light intensity, the rate at which these are produced is too slow to allow dark reactions to
proceed at maximum rate, the light is then becoming the “limiting factor”.
When light is no longer limiting, both temperature and carbon dioxide concentration can
become limiting factors.
(c)
Chemosynthesis
In photosynthesis sunlight is used as the source of energy and chlorophyll or some other closely
related pigment is used for trapping the light energy.
In chemosynthesis energy is derived from the oxidation of compounds.
11.
(a)
(b)
(c)
(d)
12.
2
2
3
-
Structure
one glycerol molecule
two hydrophobic fatty acids chains
a hydrophilic polar phosphate group
-
3 phosphate groups
a pentose sugar
an organic base (adenine)
-
short term storage of energy
breaking of the final phosphodiester bond
between the two terminal phosphates
release significant amount of energy
3, 2
-
four polypeptide chains
a prosthetic group (haem)
iron inside each haem group
-
combines with oxygen to form
oxyhaemoglobin
to carry oxygen in alveoli and release
oxygen at tissue
3, 2
-
amylose & amylopectin
polymers of -glucose
unbranched spiral (amylose) & branched
spiral (amylopectin)
-
-
-
Function
important part of the membrane structure
forming a bilayer with partial permeability
(max. 4)
photosynthetic product
storage carbohydrate in green plants
3, 2
3, 2
As reactions in the Krebs cycle proceeds (½), malate concentration will increase (½). Malate is
structurally similar to succinate , hence will compete with succinate (½) for binding to the active site
on succinate dehydrogenase (½) / malate is a competitive inhibitor (1). This slows down the reactions
max. 4
in the Krebs cycle (½). Malate concentration is in turn lowered (½). Inhibition is removed (½),
reaction rate in the Krebs cycle increases again (½).
[Bonus : negative feedback (B - ½)]
Section D
13. Nitrate  Plant protein:
The nitrogen atom in nitrate is absorbed by diffusion or active transport into the root of a plant (e.g.,
grass) through the root hair.
Description of structure and function of root hair cells.
It is then translocated within the plant through the xylem tissue.
Description of the structure and function of xylem tissue.
The nitrates are converted into various amino acids through a series of chemical reactions.
5
Description of Krebs cycle and production of amino acids.
The amino acids are combined in a controlled manner with the help of rough endoplasmic reticulum
under the instructions from the nucleus.
Plant protein  Amino acids in ileum:
The cattle ingested the grass.
It is then grinded by the premolars and the molars before swallowing.
Description of the dentition and characteristics of teeth.
The cellulose is digested in the rumen and reticulum by microorganisms there.
Description on the characteristics ruminant digestion.
The food is then regurgitated and re-chewed.
Now the food bypass the first two chambers and enters to the omasum and the abomasum where the
gastric enzyme, protease, digested the proteins into peptides.
10
Description of the digestion in stomach.
Pancreatic proteases and intestinal proteases finished the digestion of proteins into simple amino
acids.
Description of the digestion in small intestine.
Amino acids  Protein in stomach wall:
The digested amino acids are absorbed into the blood capillaries through the villi and microvilli.
Description of the structure and function of small intestine in relation with absorption of food.
The blood is collected to the liver by the hepatic portal vein.
It is further transported to the stomach through the general circulation.
Description of circulation system.
5
After entered a cell of the stomach wall, it is then combined with other amino acids to form protein in
the same way as it had been in the plant cell.
organization and presentation
14.
(1)
(2)
max. 15
5
Compartmentalization
to safeguard cell and organelle function / keep cell shape
1
½
Forms boundary of individual cells, i.e., plasma membrane and boundary of organelles like
nucleus, mitochondria, chloroplasts.
Brief mention of function of membrane in compartmentalization in any one example.
½
1
membrane integrity due to arrangement of phospholipids and proteins.
illustration of membrane structure and composition with a diagram (accurate drawing of
phospholipid bilayer and proteins, labelling of phospholipid, protein)
1
Control exchange
between two sides of membrane by selective permeability
any one example.
e.g., nutrient absorption in microvilli (plasma membrane) of small intestine, ion uptake in
plant root, active absorption of glucose in kidney tubules, calcium pump, establish
electrochemical gradient for nerve impulse conduction.
½
½
1
–
–
–
phospholipid bilayer
permeable to fat-soluble substances
channel proteins
permeable to small particles
carrier proteins
for facilitated passage of specific solutes and active transport
2
½
½
½
½
½
½
6
–
(3)
-
(5)
(6)
membrane proteins can be single enzymes or aggregated to form multi-enzyme
complexes
foldings
to increase area for such reactions.
6
1
1
1
½
½
Recognition of stimuli
any one example
e.g., insulin / hormone receptors in (liver) cells, light receptors in rod cells, antigen
receptors in white blood cells, neurotransmitter receptors in post-synaptic membranes)
1
1
- membrane glycoproteins / glycolipids as recognition sites
1
Cell and organelle identity
any one example
e.g., antigens on RBC in relation to blood group
1
1
Endocytosis
any one example
e.g., phagocytosis in Amoeba / phagocytic WBC, cell uptake of cholesterol by pinocytosis
½
1
Exocytosis
any one example
e.g., glandular secretions, release of particulate wastes from cells, synaptic vesicles release
neurotransmitter
½
1
-
(7)
½
½
Site of membrane-bound enzymatic reactions
any one example.
e.g., electron transport system at cristae of mitochondria, light reactions at thylakoids of
chloroplasts
-
(4)
presence of pores at nuclear membrane
controls passage of substances into and out of the nucleus
4
3
2
fluidity of membrane
due to phospholipid / cholesterol
½
½
Myelin sheath insulates against “cross-talk” between adjacent axons
- electrical resistance due to high lipid composition in membrane
4
1
1
2
max. 15
5
organization and presentation
15. (a) Energy source
Mitochondria
- potential / chemical energy in food (½)
Chloroplasts
- light energy (½) / sun / photon
Process energy
- release energy by breaking down food (1), in - capture energy by photophosphorylation (½)
Krebs cycle (½)
to build up food (½) in photosynthesis (½)
- hydrogen is removed from intermediates of
Krebs cycle (1) forming NADH (½)
- electron from NADH passes along the
electron transport chain (1) where members of
the chain undergo oxidation-reduction reactions
releasing energy (1) to build up ATP (½) from
ADP (½). This is oxidative phosphorylation
(½),
- after absorption of light (½) chlorophyll is
excited (½), release excited electron (½), to a
chain of electron carriers (½),
oxidation-reduction process of carriers release
energy (1) used to synthesize ATP (½) from
ADP (½), NADPH is also formed (½),
ATP and NADPH carrying the energy (1) are
used in the dark reaction to synthesize
carbohydrate (1) / hexose starch, thus
chloroplast converts light energy to potential /
chemical energy stored in food (½)
1
3
6
6
Both make ATP involving electron transport chain (1).
1
(c) Inter-relationship between mitochondria and chloroplast
(1)
(2)
(3)
(4)
The two organelles bridge the flow of biological energy (1).
Light energy from the sun, together with CO2 and water are processed in the
chloroplast in photosynthesis (2) to form carbohydrate.
The carbohydrate with stored energy and O2 formed in chloroplast are eventually
taken up and processed by the mitochondria (2). ATP is liberated (1).
Products of cellular respiration, i.e. CO2 and water are utilized in chloroplast as raw
materials of photosynthesis (2).
organization and presentation
16.
(a)
General points:
- amino acids
- formation of the peptide bond and polypeptides
- primary, secondary, teritary and quanternay structure
- fibrous and globular proteins
- conjugated proteins
8
max. 15
5
4
Enzymes:
- illustrated with specific examples in metabolic pathways
- structure of enzymes and function (active site)
- induced fit model
4
Structural proteins:
- membrane proteins
- chromsomal proteins
- cytoskeleton
2
Hormones:
- insulin
- glucagon
- ADH
- receptors and function in target organ
2
Transport:
- channel proteins
- protein pumps
- haemoglobin
- myoglobin
4
Contractile proteins:
- actin
- myosin
- their roles in muscle contraction
- spindle fiber
4
Body defence:
- antibodies
- structures – function
- fibrinogen – blood cloting
3
Contents:
Style of presentation:
Max. 15
Max. 5