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SR. INTER UNIT III A- PLANT PHYSIOLOGY – ABSORPTION OF
WATER TO PHOTOSYNTHESIS
Absorption of Water, Ascent of Sap and Transpiration
The path of water in plants which includes entry of water into the plant, its movement within the plant and its exit from the
plant together referred as Plant water relations. This movement is due to difference in water potentials between the systems
as well as cells of the plant.
Out of 4 forms of soil water, Capillary water is absorbed by the plant.
Water potential term was given by Slatyer and Taylor and measured in Bars or Mega Pascals. It is indicated with the symbol
ψ. Its components are Osmotic potential, Pressure potential and Matric potential.
The change in the ψ of a system due to addition of solute is called as Osmotic or Solute potential(π or ψs). It always has
negative value.
The change in ψdue to positive hydrostatic pressure is called as Pressure potential or ρorψP. It has positive value. It is zero in
flaccid and plasmolysed cells. It is negative in open systems under tension.
The change in ψdue to adsorption of water to hydrophilic substances is called as Matric potential(ψmor Τ). It has negative
value.
The water potential of a system or solution is algebraic sum of pressure potential, osmotic potential and matric potential. ψ = π
+ Ρ + Τ. In a normal living cell the influence of matric potential on the water potential is negligible. Hence the ψof a cell is
π+ Ρ.
Increase in the volume of solids due to adsorption of water to its hydrophilic colloids is called as imbibition. The pressure
created in the imbibent is called as Imbibitional pressure.
Diffusion of a solvent from a region of low concentrated solution to a region of high concentrated solution through
semipermeable membrane is called as Osmosis. It is demonstrated by Thistle Funnel and Potato Osmoscope experiments.
Shrinkage of protoplast of a plant cell when kept in hypertonic solution due to exosmosis is called as Plasmolysis. In this state
the Ρ of cell is zero. Hence the ψ= π. First signs of plasmolysis during which protoplast is withdrawn from the cell at the
corners is called as Incipient Plasmolysis.Regaining normal condition by a plasmolysed cell when kept in low conc. solution is
called as Deplasmolysis. This principle prevents the spoilage of salted pickles and sugared jams and jellies.
Plants mostly absorb the soil water by passive osmotic mechanism driven by the difference in water potentials of soil solution
and root hair.
Absorbed water mostly moves from root hair to endodermis through cell walls. It is called as Apoplasticpathway. From
endodermis it move into xylem via pericycle through protoplasm and cell membrane. It is called as Symplastic pathway.
Unidirectional upward movement of water from Root to topmost part of the plant through xylem against gravitational force is
called as Ascent of Sap.
Gymnosperms like Sequoia sempervirens (113.1m) and Pseudosugamenziensii (119.8m), and Angiosperms like Eucalyptus
regnans (132.6m) and Eucalyptus amygdalina (143m) are the tallest plants in PlantKingdom.
Out of all theories, Dixon’s Cohesion and Tension theory best explains Ascent of sap. It is based on 3 principles i.e.
Transpiration Pull, Cohesive force of Water (-30MPa) and Adhesive force of water. The main force is Transpiration pull or
tension developed in the xylem due to transpiration.
Tension or ∆ψ of more than 1.3MPa (up to 4MPa) exists in plants which is sufficient to pull the water column of xylem to
topmost region of any tallest plant in the plant kingdom.
The 2 drawbacks of the theory are 1. Fail to explain ascent of sap when there is embolism due to cavitation and 2. Stating
tracheids as more efficient than vessels.
Transpiration
It is loss of water in the form of vapour through aerial plant parts. Bell-jar and Cobalt chloride experiments demonstrate
transpiration.
Stomatal transpiration (80-95%), Cuticular transpiration (5-10%) and Lenticular transpiration (1-2%) are the 3 types of
transpiration.
Stomata are the pores in the epidermis of aerial plant parts. Each stoma has 2 Kidney (Dicots) or Dumb-bell (Monocots) shaped
guard cells with unevenly thickened walls and chloroplasts, 2 or more subsidiary cells and a pore which together called as
Stomatal complex.
Opening and closing of stomata is controlled by size, shape, turgor changes of guard cells. Photoactive stomata are opened
during day time and scotoactive during night time (Bryophyllum).
Levitt and Bowlings K+ pump hypothesis best explains stomatal movement. In light, Malic acid formation from starch,
expulsion of H+ of Malic acid into subsidiary cells by using ATP, influx of K+ and Cl- in to guard cells decreases ψ of guard
cells and stomata are opened – Active process.
In the absence of light K+, Cl-, malate- move passively into subsidiary cells and H+ into guard cells. Malic acid is oxidized in
respiration. It results in increased ψ, water moves into subsidiary cells and stomata are closed – Passive process.
In the presence of light, increase in temperature, availability of more water, gentle wind velocity and less atmospheric humidity,
transpiration rates increase.
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With increase in leaf area, stomatal frequency, root-shoot ratio, transpiration rates increase.
Transpiration has several advantages and few disadvantages to plant. Hence it is described as necessary evil by Curtis and as
unavoidal evil by Barnes.
PMA, ABA, Asprin decrease transpiration by acting as metabolic inhibitors. Waxes, Silicon oils and Plastic emulsions are film
forming antitranspirants. High CO2 concentration also acts as anti-transpirant.
Questions from previous EAMCET exams.
1. Which of the following forms of soil water can be readily absorbed by plants. EAMCET - 2005
*1) Capillary Water
2) Hygroscopic Water
3) Runaway Water
4) Gravitational Water
2. The values of osmotic potential (π) and pressure potentials (Ρ) of cells A, B, C and D are given. Identify the correct sequence
of water movement. EAMCET – 2005
π
-1.0
-0.6
-1.2
-0.8
Cell A
Cell B
Cell C
Cell D
3.
4.
5.
6.
7.
Ρ
0.5
0.3
0.6
0.4
1) D>C>A>B
*2) B>D>A>C
3) B>C>D>A
4) C>B>A>D
Study the following and identify the correct match. EAMCET – 2006
A. Water potential in 10% salt solution
I. Positive
A
B
C
D
B. Pressure potential in a normal cell
II. Negative
*1) II
III
V
IV
C. Pressure potential in plasmolysed cell
III. Positive
2) IV
III
II
I
D. Matric potential on the surface of wood
IV. Negative
3) I
II
IV
III
V. Zero
4) V
IV
II
I
When pea seeds and wheat grains are soaked in water, pea seeds showed more swelling than the wheat. The reason is
EAMCET - 2007
*1) Imbibition capacity of proteins is more than starch
2) Presence of less hydrophilic colloids in wheat grains.
3) Cell membrane of pea seeds is more permeable.
4) Cell walls of wheat grains are less permeable.
Study the following table showing the components of Water potentials in closely arranged mesophyll cells namely A, B and
C. EAMCET - 2008
Cell
Osmotic potential
A
B
C
-0.21
-0.22
-0.23
Pressure
potential
0.05
0.02
0.05
Identify two of the following which show correct direction of water between two cells
I. A to B
II. B to C
III. C to A
IV. C to B
1) I, II
2) II, III
*3) I, IV
4) II, IV
Identify the correct statements from the following
EAMCET - 2005
I. Accumulation of K+ in the guard cells does not require energy.
II. A high pH favoursstomatal opening
III. Movement of chloride ions into the guard cells is in response to the electrical differential created by K+ ions
IV. With the entry of several K+ ions and chloride ions, the water potential of guard cells increases.
1) I and III
2) I and II
*3) II and III
4) III and IV
In photoactive plants, during day time the following ionic flux of guard cell is directly involved in the expenditure of energy.
EAMCET - 2008
1) Outward movement of malate
2) Inward movement of Potassium ions
*3) Outward movement of Protons
4) Inward movement of chloride ions
Some Important Questions
1.
Identify the relatively less hydrated cell, among the following
Cell A :Ψ = –30, P = 20, π = –50
Cell B :Ψ = –40, P = 20, π = –50
Cell C :Ψ = –20, P = 10, π = –30
Cell D :Ψ = –50, P = 10, π = –65
1) Cell D
2) Cell C
*3) Cell B
2.
If a tissue of plant has the cells with the given
4) Cell A
A
π = –8
P=6
C
B
π = –6
P=4
π = –10
P=9
osmotic values, the direction of movement of water among the cells is
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*1)
A
3.
4.
5.
2)
B
C
3)
B
A
C
4)
B
A
C
B
C
A
Match the following and identify the correct match
Cell of Root
Osmotic values
A
B
C
D
A. Trichoblast
I) π = –20, P = 12
1)
II
III I
IV
B. Cortical cell
II) π = –25, P = 23
2)
III II
I
IV
C. Endodermal cell III) π = –30, P = 25
*3) II
IV III I
D. Pericycle cell
IV) π = –22, P = 18
4)
II
III IV I
Arrange the following plants with gradual increase in their height
i) Pseudotsugamenziensii
ii) Eucalyptus amygdalina
iii) Sequoia sempervirence
iv) Eucalyptus regnans
1) ii, iv, iii, i
*2) iii, i, iv, ii
3) iii, i, ii, iv
4) i, iii, ii, iv
In the experiment to demonstrate ascent of sap by cohesion and tension theory, A can be compared with
A
1) Root
2) Leaf
3) Stem
*4) Mesophyll
B
6. Assertion : Vessels are more efficient than tracheids in ascending the sap.
Reason : Vessels have perforation plates.
D
C
*1) Both A and R are true and R is the correct explanation of A
2) Both A and R are true but R is not the correct explanation of A
3) A is true but R is false
4) A is false but R is true
7.
The chemical that is used to demonstrate that plants transpire is
1) Calcium chloride
*2) Cobalt chloride
3) Mercuric chloride
4) Potassium chloride
8. Arrange the following events in correct sequence during the opening of stomata as explained by Bowling
ii) Exit of H+ from guard cells
i) Entry of Cl– into guard cells
iii) Formation of malic acid
iv) Entry of K+ into guard cells
1) iii, iv, ii, i
*2) iii, ii, iv, i
3) ii, iii, iv, i
4) ii, iii, i, iv
9. If in a unit area of leaf there are 500 epidermal cells, 1500 mesophyll cells and 20 stomata, the stomatal index of the leaf is
*1) 0.04
2) 0.004
3) 0.03
4) 0.05
10. The actual form of soil water, that is transpired is
1) Hygroscopic water
*2) Capillary water
3) Gravitational water
4) Run-away water
Nutrition in Plants
The importance or Soil in Plant Growth was experimentally shown in spearmint plant by Woodward. De Saussure showed
increase in dry weight of plant grown in mineral solution than grown in distilled water.
Arnon and Stout’s 3critaria are 1. An essential element must be involved in growth and reproduction of plant. 2. Its functions
should not be carried out by some other element. 3. The element must be involved in metabolism. By following these criteria,
17 elements were found as essential. They are C, H, O, N, P, K, Ca, Mg, S, Fe, Mn, B, Cu, Zn, Mo, Cl and Ni. The first 9 are
Macro elements and the rest Microelements.
C, H and O are frame work elements and non-mineral elements. They are absorbed as CO2 and H2O. without these there is no
formation of organic substances.
Nitrogen is absorbed mainly as NO2, and it is integral part of Porphyrin structure of Chlorophyll and Cytochromes and one of
the major components of cell membranes, proteins, and nucleic acids.Phosphorus is a structural component of cell membranes,
some proteins, nucleic acids and ATP.Potassium is required for ionic balance in the cell and helps in stomatal
movement.Calcium is part of Middle lamellum and helps in cell division. Mg is activator of several respiratory and
Photosynthetic enzymes and part of Middle lamellum and Chlorophyll. Sulphur is a component of amino acids methionine,
Cystein and Cystine and Vitamins such as Biotin, Thiamine and Co.A. It stabilizes the structure of proteins.
Fe is a part of cytochromes and needed for chlorophyll formation. Mn helps in photolysis of water and activator of IAA
oxidase. Zn is activator of Carbonic anhydrase and needed for IAA synthesis. Cu is a part of Plastocyanin and cytochrome
oxidase. Boran is required for pollen germination and helps in transport of photosynthates. Mo is a part of Nitrogenase and
activator of Nitrate reductase. Chlorine is needed for photolysis of water and helps in maintaining the cationic and anionic
balance in the cells.
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Absorption of ions according to concentration gradient without utilizing metabolic energy is called as Passive or Nonmetabolic abosorption.
Entry of ions into the cytoplasm against concentration gradient by using ATP or energy is called as Active absorption. It was
shown by using respiratory inhibitors such as Azide and Cyanide.
In Active absorption ions are carried by carrier proteins of membrane known as Porter. They are uniporters which carry a single
ion at a time (H+ ATPase, Na+ ATPase). Cotransporter carry two ions either in same direction (Symporters) or in opposite
directions (Antiporters).
Movement of ions against concentration gradient by direct usage of ATP is called as Primary Active Transport. In H+ ATPase
pump it generates Proton Motive Force which is responsible for the movement of other ion against concentration gradient and it
is known as Secondary Active Transport. The carriers such as Symporter is subjected to 3 conformational changes during
secondary active transport.
Rhizobium is used as biofertiliser in Legume crops, Azospirillum in cereal other than Paddy, Cyanobacteria like Nostoc and
Anabaena and PteridophyteAzolla in Paddy fields. Mycorrhizal fungi like Glomus are used as fertilizers in crops like Potato,
Red gram, Soybeans, Wheat, Maize etc. which not only improve mineral uptake but also make the crops tolerant to water stress
and pests. Mycorhiza increase Phosphorus uptake.
Questions from previous exams
1.
[A]:Salt resistant plants survive in saline habitats by maintaining low internal Na+ levels.
[R]: Salt resistant plants get rid off excess Na+ by ATP energized antiporter
EAMCET 2009
*1) Both A and R are true and R is the correct explanation of A
2) Both A and R are true but R is not the correct explanation of A
3) A is true but R is false
4) A is false but R is true
2.
The right sequence of carriers which involve in the transport of excess Na+ ions out of the cell in salt resistant
palnts is
EAMCET - 2010
1) Uniporter, Symporter
2) Sumporter, Antiporter
3) Antiporter, Uniporter *4) Uniporter, Antiporter
Some Important Questions
1.
Match the following
List – I
A) Plants are made of soil material
Essentiality of soil for plant
B)
growth
List – II
I) Julius Sachs
1)
A
V
B
IV
C
II
D
I
II) Daniel Arnon
2)
V
III
IV
II
3)
IV
III
I
II
*4)
V
III
IV
I
Increase in dry weight of the
III) Woodward
plant grown in soil solution
Discovery of some essential
D)
IV) Saussure
elements
C)
2.
3.
4.
V) Aristotle
The essential elements that can bind to clay particles in ionic form are
1) N, K, Fe, Mg, Ca, B, Mo
*2) N, K, Ca, Mg, Fe, Mn, Zn, Cu
3) Cl, S, Mo, B, P
4) All macro elements
[A]: Sulphur stabilizes the protein structure.
[R]: In a protein disulphide bonds are formed between Methionine and Alanine
1) Both A and R are true and R is the correct explanation of A
2) Both A and R are true but R is not the correct explanation of A
*3) A is true but R is false 4) A is false but R is true
Study the following table and choose the correct combination
Essential Element
Part of component I
Part of component II
I) N
Chlorophyll
Xanthophyll
II) P
ATP
Proteins
III) S
Cystein
Vitamin B1
IV) Mg
5.
Chlorophyll
3) All except IV
4) All
I. Mo
II. Fe
III.Cu
IV.Mn
2) II and III
3) only I
*4) I and II
1) I and III
6.
Middle lamellum
1) All except II
*2) All except I
The micro elements of Nitrogenase are
+
During the mediation of H ATPase pump for active transport of ions
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+
*1) H are carried by Uniporters, Symporters and Antiporters
-
2) NO3 is carried by Symporter and Antiporter
+
3) Movement of H through uniporters is down the concentration gradient
4) Movement of H+ through Cotransporters is against the concentration gradient.
7.
8.
These are used as biofertilizer to increase wheat production
I. Anabaena
II. Azolla
1) I and II
*2) III and IV
+
III. Glomus
IV.Azospirillum
3) II and III
4) I and IV
+
In an epidermal cell of root, there were 800 H , 100 Na , 30 NO3 and 50 sucrose molecules in the solution present between
cell wall and cell membrane. After sometime, due to operation of H+ ATPase pump, the apoplast had showed the presence of
+
+
+
850 H , 125 Na , 3 NO3 and 5 sucrose molecules. The net utilization of ATP and the total number of H recycled back to
symplast are respectively are
1) 147, 50
9.
2) 47, 97
*3) 147, 97
4) 150, 100
Zn is essential for the formation of
*1) Rooting hormone
2) Flowering hormone
3) Anti-aging hormone
4) Anti-transpiration hormone
Enzymes
Dixon and Web defined enzyme as protein with catalytic properties due to its power of specific activation. The term enzyme
was given by Kuhne.
Pasteur called enzymes as Ferments, Buchner as Zymase and Sumner crystallized the enzyme Urease and discovered the
protein nature which was later confirmed by Northrop. Haldane wrote a book on enzymes.
The properties of enzymes are Catalytic, specificity, activity in minute quantity, reversibility, thermolability, thermolability,
sensitivity to pH, Proteinaceous nature (Holoenzyme, cofactor, Apoenzyme) and lowering the activation energy.
Enzymes are named on the basis of substrate name, type of reaction and both (Succinate dehydrogenase).
IUB system of enzyme classificatioin has 6 classes with sub classes, sub-sub classes and numbering in the sub-sub class. The
classes are 1. Oxidoreductases (dehydrogenases, reductases, oxidases), Transferases (Transaminases, Kinases), Hydrolases
(Phosphatases, Peptidases), Lyases, Isomerases and Ligases.
Lock and Key model of Fisher, Paul Fields and Woods and Induced fit theory of Koshland best explains the mechanism of
enzyme action.
Enzyme activity is either reduced or totally hampered by agents or substances named as Competitive inhibitors (Malonic acid
of Succinate dehydrogenase), Non-competitive inhibitors (Cyanide, Salts of heavy metals) and Allosteric inhibitors (end
products of biochemical pathways or reactions.
Some Important Questions
1.
2.
Study the following and identify the correct match
Enzyme
Cofactor
A. Catalase
I) Mg2+
B. Cytochrome oxidase II) Mo
C. Hexokinase
III) Mn2+
D. IAA oxidase
IV) Cu2+
V) Fe2+
Study the following and identify the correct groups
Enzyme
i) Transferase
ii) Hydrolase
iii)
Oxidoreductase
iv) Lyase
3.
*1)
2)
3)
4)
Substrate
Aspartic acid
Fructose-6-PO4
Glycolic acid
Product
Oxaloacetic acid
Fructose 1,6 bisphosphate
Glyoxylic acid
Arginosuccinic
acid
Arginine, succinic acid
1) i and iv
2) ii and iii
*3) i and iii
[A] : Cyanides can inhibit enzymatic activity.
[R] : Cyanides compete with the substrate for active site of the enzyme.
1) Both A and R are true and R is the correct explanation of A
2) Both A and R are true but R is not the correct explanation of A
*3) A is true but R is false 4) A is false but R is true
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A
V
IV
IV
V
B
IV
III
IV
IV
4) ii and iv
C
I
I
I
II
D
III
II
III
III
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Photosynthesis
Chloroplast of green cells is involved in this process. Thylakoids carry out light reaction and stroma dark
reaction of photosynthesis. Thylakoid membranes have photosynthetic pigments, e- carriers. Pigments
are organized as Photosystems which have a reaction centre with specialized chlorophyll a molecule as
P700 (PSI) or P680 (PSII) and surrounding it the LHC with different photosynthetic pigments. LHC
absorbs photons and transfers them to RC by inductive resonance where it is converted as excitation
energy used for the transfer of electrons among various electron carriers.
Chlorophylls (Chl.a-C55H72O5N4Mg, Chl.b-C55H70O6N4Mg), Carotenes (C40H56), Xanthophylls
(C40H56O2) and Phycobilins are the photosynthetic pigments.
Only visible light is absorbed in photosynthesis. Red light is absorbed more and least absorbed one is
Green light. A pigment molecule (P700 or P680) is in excited state for 10-9 S.
Robert Hill showed the liberation of O2 from isolated illuminated chloroplasts in the presence of
Potassium Ferric oxalate (Hill reagent). Liberation of O2 from water was shown by Ruben et.al by using
O18 isotope.
Decrease in photosynthetic rate when a green organism is exposed to longer wavelength of red light
(>680nm) is called as Red drop. Increase in Photosynthetic rate when the organism is subjected to both
longer and shorter (<680) wavelengths of red light is called as Emersons enhancement effect. From this
Emerson concluded that two Photosystems (PSI and PSII) are operated in Photosynthetic light reaction.
PSI is present in non-appressed regions of grana thylakoids and stroma thylakoids, has P700 as reaction
centre, LHC has 100 chlorophylls with chla andchl b in 4:1 ratio, has more carotenes and absorgs longer
wavelength of red light.
PSII is mainly present in appressed regions of grana thylakoids and a little in non-appressed regions, has
P680 as its reaction centre, LHC has 250 chlorophyll molecules with Chla andChl b in 1:1 ratio, rich in
xanthophylls and absorbs shorter wavelength of red light.
During Non-cyclic electron transport, by absorbing 2 photons by PSII and 2 by PSI, the 2 electrons or a
water molecule are carried to NADP+ via Oxygen evolving complex, P680, Pheo, Plastoquinone,
Cytochromeb/f complex, PC, P700, Fe-S protein, Fd to form NADPH + H+. During this 2 H+ of water
and 4 H+ of stroma (through PQ cycle)are accumulated in lumen of thylakoid. This e- transport is
inhibited by DCMU.
In Cyclic e- transport discovered by Frankel in Rhodospirillumrubrum, only PSI is involved. The eliberated from P700 reach the same P700 after passing through Fd, Cytochrome b6, PQ, Cytochrome f,
and PC during which 2H+ of stroma are carried into lumen by PQ cycle operation.
Photophosphorylation was discovered by Arnon. It is best explained by P. Mitchel’s Chemiosmotic
hypothesis. This theory states that formation of ATP in CF1 of CF is due to establishment of proton
gradient across thylakoid membrane between stroma and Lumen during electron transport. For each 3 H+
carried through CF0 of CF there is formation 1 ATP in CF1.NADPH + H+ and ATP formed in light
reaction are used for the assimilation of CO2 into carbohydrates (Sucrose or Starch) in dark reaction.
Hence the chemical energy is called as Assimilatory Power.
CO2 is fixed during dark reaction through C3, C4 and CAM pathways by using ATP and NADPH formed in light reaction. It
takes place in the stroma of chloroplast.
C3 cycle was discovered by Calvin and his associates in Chlorella by using C14 isotope and Autoradiography and
Chromatography techniques. In this, the CO2 acceptor is RuBP and first formed stable product is PGA. It has Carboxylation
(1 reaction), Reduction (2 reactions) and Regeneration (10 reactions) stages. Both ATP and NADPH are used in Reduction
stage and only ATP is used in Regeneration stage.
The intermediates of this cycle in a swquence are 1. PGA (Rubisco), 2. BPGA (Kinase), 3. GAP (Dehydrogenase), 4. DHAP
(Isomerase), 5. FBP (Aldolase), 6. FMP (Phosphatase), 7. EMP and XMP (Transketolase), 8. SBP (Transaldolase), 9. SMP
(Phosphatase), 10. RMP and XMP (Transketolase), 11. RuMP (Epimerase) and 12. RuBP (Kinase) and has 13 reactions.
Sucrose is formed in Cytosol and Starch in Chloroplast stroma. For the fixation each CO2, 2 NADPH and 3 ATP are used.
Though Malate formation in C4 cycle was first noticed by Kortschak, Hartt and Burr, the reactions of this cycle were
described in detail by Hatch and Slack in Sugarcane. It is also known as βcarboxylaton pathway and Hatch Slack cycle. C4
plants show Kranz (Garland) Anatomy with chloroplasts in both mesophyll and bundle sheath cells of its leaves.
Primary carboxylation takes place in Mesophyll cell cytosol and Malic acid and PEP are formed in the chloroplast stroma.
Calvin cycle and Pyruvate formation take place in Bundle sheath cell chloroplast. For formation of 1 Hexose, 12 NADPH and
30 ATP are used. C4 plants are more efficient than C3 plants.
Light induced CO2 liberation in green cells of C3 plants is called as Photorespiration. It is also known as C2 cycle and
Glycolate pathway. Chloroplast, Peroxisomes (usage of O2) and Mitochondria (liberation of CO2 ) are involved in this
metabolism. NADH and ATP are used. 10% of the fixed carbon is lost as CO2. 75% of carbon of Glycolate is recovered as
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PGA. The various intermediates formed are PGA, Phospho Glycolic acid, Glycolic acid (Chloroplast), Glyoxylate, Glycine,
Hydroxy Pyruvic acid, Glyceric acid (Peroxisome) and Serine (Mitochondria).
Photosynthesis is influenced by External factors (Light, Temperature, CO2, O2, H2O) and Internal factors (Chlorophyll, Leaf
structure, End products).
Upto certain light intensity, the photosynthetic rate increases. Oxidation of chlorophylls at high light intensity is called as
Solarisation. Heliophytes grow in direct sunlight and Sciophytes in shades. Light intensity at which Photosynthesis is equal to
Respiration is called as Light Compensation Point. Photosynthetic rate is more in Intermittent light than continuous light of
same duration. Only visible light is used in Photosynthesis.
Temperature influence is different in the photosynthesis of C3 and C4 plants. In general the photosynthetic rate in creasesupto
400C. Conifers can perform photosynthesis at -60C and Algae of hot springs at 700C.
Photosynthetic rate increases upto 0.1% CO2 concentration. C4 plants have less Carbondioxide Compensation Point than C3
plants.
Decrease in photosynthetic rate with incrase in O2 concentration is called as Warburg effect. It is due to photorespiration. It
shown by C3 plants but not or negligible in C4 plants.
Decrease in H2O decreases photosynthetic rate because of less enzymatic activity, cell expansion and stomatal closure.
Dark grown plants are etiolated and show less photosynthetic rates because of decrease in chlorophyll content which has
direct influence on photosynthesis.
Accumulation of end products or carbohydrates in green cells decreases photosynthetic rate due to Feedback inhibition.
Leaves with thick cuticle, thick epidermis, less mesophyll show less photosynthesis.
Law of limiting factors was proposed by Blackman. It is base on Liebeg’s law of minimum. In photosynthesis the most
common limiting factors are CO2 (0.03% in atmosphere) and Light (during cloudy days).
Questions from previous EAMCET
1.
2.
3.
Study the following table and choose the correct match EAMCET – 2006
List I
List II
A. Oxygen evolving complex
I. Potassium ferric oxalate
B. Proton gradient
II. High oxygen concentration
C. Hill reagent
III. ATP synthesis
D. Photorespiration
IV. Pheophytin
V. Photolysis of water
A
B
C
D
*1) V
III
I
II
2)
I
II
IV
V
3)
V
I
IV
II
4)
I
IV
III
V
The net requirement of assimilatory power for the formation of 6 hexose molecules in maize plant is EAMCET - 2008
1) 72 ATP, 48 NADPH 2) 90 ATP, 60 NADPH 3) 108 ATP, 72 NADPH *4) 180 ATP, 72 NADPH
Identify the correct combination of the following.
EAMCET – 2007
Substrate
Enzyme
Product
I) Phosphoenol Pyruvate PEP – Carboxylase
C4 acid
II) Malate
Malic enzyme
C4 acid
III) RuBP
Ribulose-5-phosphate
C3 acid
Kinase
IV) Pyruvate
Pyruvatedikinase
C3 acid
The correct combination is
1) III and IV
2) I and II
3) II and III
*4) I and IV
Some important Questions
1. Match the following
A. Carries electron to P700
I) Fd
A
B
C
*1) III V
IV
B. Give e– to cytochrome b6/f complexII) NADP
C. Accepts electron from P680
III) PC
2)
IV V
II
D. Gets electron from Fd
IV) Pheo
3)
III IV I
V) PQ
4)
III V
IV
2. The phenomenon of inductive resonance is involved in the transfer of energy from
1) PS II to PS I
2) P680 to Pheo
3) PC to P700
*4) β-carotene to P700
3. Transketolasecatalyses the following reactions
I) Fructose 6P + G-3P → Xylulose-5P + erythrose-4P
II) Sedoheptulose 7P + G3P → Ribose 5P + Ribulose-5P
III) Sedoheptulose 7P + G3P → Ribose 5P + Xylulose-5P
1) I and II
*2) I and III
3) II only
4.
4) I, II and III
Non-chloroplast reaction of photosynthesis is
1) Reduction of NADP+
*2) Carboxylation of PEP
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D
II
I
II
I
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5.
6.
7.
8.
3) Carboxylation of RUBP
4) Decarboxylation of Malic acid
This enzyme of C4 cycle helps in NADPH2 generation
1) Pyruvic enzyme
2) Aspertate enzyme
*3) Malic enzyme
4) Oxaloacetate enzyme
Arrange the formation of following intermediates of C3 cycle in a sequence
i) Phosphoglyceric acid
ii) Phosphoglyceraldehyde
iv) Fructose biphosphate
iii) Xylulose-5-PO4
1) iii, ii, i, iv
2) i, ii, iii, iv
*3) i, ii, iv, iii
4) i, iv, ii, iii
The intermediates of photorespiration formed by transamination reaction are
I. Glycine
II. Serine
III.Hydroxypyruvic acid IV. Glycolic acid
1) I and II
2) II and IV
*3) I and III
4) III and IV
Assertion: CO2 can behave has limiting factor of photosynthesis
Reason: The concentration of CO2 in the atmosphere is 0.03%
*1) Both A and R are true and R is the correct explanation of A
2) Both A and R are true but R is not the correct explanation of A
3) A is true but R is false
4) A is false but R is true
9. If 8 molecules of RuBP take part in photorespiration, How many Carbons of it are removed as CO2 in
mitochondria ?
1) 8
*2) 4
3) 6
4) 12
10. Match the following
List – I
List – II
A B C D
A) Feed back inhibition
I) Rate of photosynthesis is
1) II IV I III
equivalent
to
rate
of
respiration
B) Warburg effect
II) Inhibition of photosynthesis
*2) II V I III
by
accumulation
of
photosynthates
C) CO2
compensation III) Agranal chloroplast
3) V IV II I
point
D) Kranz anatomy
IV) High CO2 conc. inhibits
4) II I V III
photosynthesis
V) High
O2
inhibits
photosynthesis
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