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Section 2 Energetics
2.1 Photosynthesis
Q: Explain the importance of photosynthetic organisms as producers
A: Energy start food chain by convert light E to chemical E in food
=> comsumers depend on them for energy + continuous flow of E into ecosystem
Material turn inorganic substances to organic substances
=> complete carbon cycle + maintain equilibrium of CO2 & O2
-> 2.1.1 Site of photosynthesis
Q: Describe the adaptive features of leaves to photosynthesis
A: Thin left blade Shorten distance for diffusion of CO2 as raw material, easy penetration of light
Flat shape Large surface area to volume ratio => facilitate diffusion
Broad Increase surface area for absorbing more light as source of energy and CO2 as raw material
Vein Vascular bundle transport water as raw material
Support leaf in proper position for absorbing more light
Epidermis Single layer, transparent => light penetrate into leaf easily
Stomata Control gaseous exchange and water loss by opening and closing stomata
Palisade mesophyll cells Closely packed, with dense chloroplasts => absorb max light from above
Spongy mesophyll cells Loosely packed, provide intercellular air spaces
=> facilitate gaseous exchange for water vapour, O2 and CO2
Morphology
外表
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Q: Relate the structure of chloroplast to its functions in photosynthesis
A: 1) lamella hold chlorophyll in suitable position => trap max. sunlight
2) thylakoid stacking arrangement
=> provide large surface area without using too many space
for attachment of chlorophyll
3) stroma contain enzyme => reduction of CO2 in Calvin cycle
* thylakoid + granum -> lamella
Q: Relate absorption spectra of chlorophyll pigments to action spectrum of photosynthesis
A: absorption spectrum
Relative absorbance of diff. λ of light by photosynthetic pigments
Action spectrum
Relative amount of photosynthesis go at diff. λ of light
=> Higher rate of photosynthesis take place at red & blue end
because relative absorbance of red & blue light highest
=> light absorbed used as energy source for photosynthesis
-> 2.1.2 Photochemical rxns
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Q: Outline the main steps of photochemical rxns (light rxn)
A: 1) e- in chlorophyll excited by light energy
2) E from excited e- used to synthesize ATP
3) photolysis of water using light energy produce H+ for reduction of NADP, O2 gas is released
Flow chart:
Q: Explain the importance of photochemical rxns
A: NADPH => provide e- for reduction of 3C acid to TP in dark rxn
Q: Outline the principle of photophosphorylation
A: e- in chlorophyll excited by light energy => e- pass along chain of e- carriers
=> E released => ADP is phosphorylated => ATP formed
*Q: Outline the principle of formation of NADPH
A: e- excited by light energy => e- accepted by H+ produced by photolysis of H2O and H formed
=>
H reduce NADP to NADPH
Q: Relate biochemical pathways of photosynthesis to their sites in cells
A: Light rxn – photochemical rxn take place in the thylakoid of chloroplast
Dark rxn – carbon fixation take place in the stroma of chloroplast
-> 2.1.3 Carbon fixation
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Q: Outline the main steps of carbon fixation (dark rxn)
A: according to Calvin cycle, CO2 accepted by 5C cpd to give 2 3C acid (need enzyme)
=> in presence of ATP, 3C acid reduced by NADPH to triose phosphate (TP)
=>
some TP combine to form hexose phosphate which is then metabolized to sucrose and starch
+ some TP used to regenerate 5C cpd as CO2 acceptor
+ some TP used to make lipids and amino acids
Flow chart:
Q: Point out the dependence of this process to the photochemical rxns
A: NADPH produced from light rxn used to reduce CO2 to carbohydrate
ATP provide necessary E
Q: Describe the fates of triose phosphate
A: Regenerate 5C cpd as CO2 acceptor
Form carbohydrate
sucrose
TP
hexose phosphate
hexose
starch
Form lipid
3C acid
pyruvic acid
acetyl CoA
fatty acid
lipid
TP
glycerol
Form amino acid
3C acid
pyruvic acid
protein
amino acid
acetyl CoA
Krebs Cycle
Krebs Cycle acids
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-> 2.1.4 Factors affecting the rate of photosynthesis
Q: Describe and explain the effects of various factors on the rate of photosynthesis
A: Light intensity ↑ => rate↑
[CO2] ↑ => rate↑ (under normal condition, [CO2] always the limiting factor)
Temp. dark rxn enzyme-controlled
Water shortage of water => stomata closed => lack of CO2 (not bcz water limiting, indirect)
O2 compete with CO2 for active site of enzyme which combine CO2 & 5C cpd in dark rxn
Q: Explain the concept of limiting factors
A: rate of a process is limited by one factor which is in shortest supply and by that factor alone
2.2 Chemosynthesis
Q: Realise the occurrence of chemosynthesis
Q: Point out the difference between chemosynthesis and photosynthesis
A: photosynthesis use light as energy source (green plant)
Chemosynthesis use E obtained by oxidation of inorganic cpds as energy source (nitrification)
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2.3 Respiration
Q: Define respiration
A: convert chemical E in food to chemical E in ATP so as to obtain E for all other metabolic processes
-> 2.3.1 The sites of respiration
Q: State the sites of diff. stages of respiration
A: glycolysis occurs in matrix of cell cytoplasm (anaerobic)
Krebs Cycle occurs in matrix of mitochondria (aerobic)
e- transport chain occurs in cristae of mitochondria (aerobic)
Q: Relate the structure of mitochondrion to its function
A: 1) double membrane => ensure glycolysis to take place in cytoplasm
2) matrix => provide a liquid medium for Krebs Cycle to take place
3) mitochondrion fold up to form cristae
=> ↑surface area for embedding more ATP synthetase & e- carriers
=> facilitate respiration
-> 2.3.2 Glycolysis
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Q: Describe the main steps of glycolysis
A: phosphate group added to glucose using energy from ATP
=> phosphorylated glucose splitted into 2 triose phosphate (TP)
=>
=>
TP converted to pyruvic acid by NAD, NADH formed
E release to synthesize ATP (substrate-level phosphorylation)
Flow chart:
-> 2.3.3 Aerobic pathway
Q: Describe the main steps of Krebs Cycle
A: in the presence of O2, pyruvic acid enter mitochondria and converted to acetyl-CoA, CO2 given off
=> acetyl-CoA combine with 4C cpd to form 6C cpd
=> 4C cpd regenerated from 6C cpd after a series of rxns, known as Krebs Cycle
=> CO2, NADH and ATP produced in the Cycle
*Q: Describe the main steps of e- transport chain
A: H atoms produced in glycolysis & Krebs Cycle, carried by NADH, pass through a series of e- carriers
+ O2 act as final e- acceptor
=>
H2O formed + energy released to form ATP (oxidative phosphorylation)
in the presence of ATP synthetase
Flow chart:
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Q: Review the interrelationships between glycolysis, Krebs Cycle and e- transport chain
A: Glycolysis
1) NADH => provide e- for e- transport chain
2) pyruvic acid => provide first substrate in Krebs Cycle
Krebs Cycle
1) NADH
e- transport chain
1) as e- acceptor
2) prevent inhibition to glycolysis & Krebs Cycle
-> 2.3.4 Anaerobic pathway
Q: Outline the biochemical pathways of alcoholic fermentation and lactic acid fermentation
A: alcoholic fermentation
Glucose phosphorylated and then splitted into 2 TP
=> TP converted to pyruvic acid by NAD, NADH formed
=> E release to synthesize ATP
=> pyruvic acid converted to ethanal by losing a CO2 molecule
=> ethanol reduced to ethanol by NADH
lactic acid fermentation
Glucose phosphorylated and then splitted into 2 TP
=> TP converted to pyruvic acid by NAD, NADH formed
=> E release to synthesize ATP
=> pyruvic acid directly converted to lactic acid by NADH
-> 2.3.5 Energy yield
-> 2.3.6 Role of ATP
Q: Explain the role of ATP in energy transfer
A: ADP converted to ATP by phosphorylation
=> ATP easily transported, as energy carrier, store E temporarily
=> in the presence of ATPase, terminal high E phosphate bond hydrolyzed to release E