(B) Energy is transferred from the light reaction step to the dark reaction step by
(a) chlorophyll
(b) ADP
(c) ATP
(d) RuBP
Answer :
(c) ATP
(C) Which one is wrong in photorespiration
(a) It occurs in chloroplasts
(b) It occurs in day time only
(c) It is characteristic of C4-plants
(d) It is characteristic of C3-plants
Answer :
(c) It is characteristic of C4-plants
(D) Non-cyclic photophorylation differs from cyclic photophosphorylation in that former
(a) involves only PS I
(b) Include evolution of O2
(c) involves formation of assimilatory power
(d) both 'b' and 'c'
Answer :
(d) both 'b' and 'c'
(E) For fixation of 6 molecules of CO2 and formation of one molecule of glucose in
Calvin cycle, requires
(a) 3 ATP and 2 NADPH2
(b) 18 ATP and 12 NADPH2
(c) 30 ATP and 18 NADPH2
(d) 6 ATP and 6 NADPH2
Answer :
(b) 18 ATP and 12 NADPH2
(F) In maize and wheat the first stable products formed in bundle sheath cells respectively are
(a) OAA and PEPA
(b) OAA and OAA
(c) OAA and 3PGA
(d) 3PGA and OAA
Answer :
(c) OAA and 3PGA
(G) The head and tail of chlorophyll molecule are made up of
(a) porphyrin and phytin respectively
(b) pyrrole and tetrapyrrole respectively
(c) prophyrin and phyrol respictively
(d) tetrapyrole and pyrrole respectively
Answer :
(c) prophyrin and phyrol respictively
(H) The net result of photo-oxidation of water is release of .................
(a) electron and proton
(b) proton and oxygen
(c) proton, electron and oxygen
(d) electron and oxygen
Answer :
(c) proton, electron and oxygen
(I) For fixing one molecule of CO2 in Calvin cycle .............. are required
(a) 3ATP + 1NADPH2
(b) 3ATP + 2NADPH2
(c) 2ATP + 3NADPH2
(d) 3ATP + 3NADPH2
Answer :
(b) 3ATP + 2NADPH2
(J) In presence of high concentration of oxygen, RuBP carboxylase converts RuBP to ................
(a) Malic acid and PEP
(b) PGA and PEP
(c) PGA and malic acid
(d) PGA and phosphoglycolate
Answer :
(d) PGA and phosphoglycolate
(K) The sequential order in electron transport from PSII to PSI of photosynthesis is
(a) FeS, PQ, PC and Cytochrome
(b) FeS, PQ, Cytochrome and PC
(c) PQ, Cytochrome, PC and FeS
(d) PC, Cytochrome, FeS, PQ
Answer :
(c) PQ, Cytochrome, PC and FeS
Question 2.
Answer the following questions
(A) Describe the light-dependent steps of photosynthesis. How are they linked to the dark reactions?
Answer :
The light dependent steps of photosynthesis include cyclic and non-cyclic photophosphorylation
Cyclic photophosphorylation :
When photosystem-I is illuminated, electrons migrate continually out of and back into the reaction centre.
The photophosphorylation of ADP to create ATP is accompanied by the cyclic electron flow. This process is known as cyclic photophosphorylation.
Because this process solely involves pigment system I, photolysis of water and the subsequent evolution of oxygen does not occur.
Non-cyclic photophosphorylation :
It involves both photosystems- PS-I and PS-II.
In this case, electron transport chain starts with the release of electrons from PS-II.
In this chain high energy electrons released from PS-II do not return to PS-ll but, after passing through an electron transport chain, reach PS-I, which in tum donates it to reduce NADP+ to NADPH.
The reduced NADP+ (NADPH) is utilized for the reduction of CO2 in the dark reaction.
Electron-deficient PS-II brings about oxidation of water-molecule. Due to this, protons, electrons and oxygen atom are released.
Electrons are taken up by PS-II itself to return to reduced state, protons are accepted by NADP+ whereas oxygen is released.
As in this process, high energy electrons released from PS-II do not return to PS-II and it is accompanied with ATP formation, this is called Non-cyclic photophosphorylation
Link between light-dependent and dark reactions: -
The two phases of photosynthesis, i.e. light and dark reactions are dependent on each other, because neither of them can continue the process of photosynthesis alone.
Light reaction of photosynthesis generates ATP and NADPH which are necessary for the fixation of carbon dioxide into glucose that occurs during the dark phase.
ATP and NADPH2 molecules function as vehicles for transfer of energy of sunlight into dark reaction leaving to carbon fixation. In this reaction CO2 is reduced to carbohydrate.
During dark reaction, ATP and NADPH2 are transformed into ADP, iP and NADP which are transferred to the grana in which light reaction takes place.
(B) Distinguish between:
(a) respiration and photorespiration
Answer :
Respiration
Photorespiration
Occurs in all aerobic and anaerobic organisms.
Occurs in all green plants.
A light independent process, occurs in both presence and absence of light.
A light dependent process, occurs in presence of light.
Produce energy rich molecules like ATP, GTP, FADH2, NADH2.
Do not produce energy rich molecules such as ATP.
Respiration is an energy producing process.
Photorespiration is an energy wastage process.
(b) absorption spectrum and action spectrum
Answer :
Absorption spectrum
Action spectrum
The curve which shows the amount of light absorbed at each wavelength is termed as Absorption spectrum.
The curve that shows the rate of photosynthesis at different wavelengths is called Action spectrum.
It explains the relationship between quality of light and absorbing capacity of the pigments.
It explains the relationship between photosynthetic activity in relation to different wavelengths of light.
In absorption spectrum, absorption of different wavelengths of light pigments can be measured by spectrophotometer.
In action spectrum, the rate of photosynthesis is measured as amount of CO2 fixation, oxygen production. NADP+ reduction.
(c) cyclic photophosphorylation and non-cyclic photophosphorylation
Answer :
Cyclic photophosphorylation
Non-cyclic photophosphorylation
Electrons emitted by chlorophyll return back to the same chlorophyll.
The electrons emitted by chlorophyll do not return back to the same chlorophyll.
First electron acceptor is FRS.
First electron acceptor is CO-Q.
It forms only ATP.
NADPH2 and ATP are formed.
Does not involve photolysis of H2O.
Involves photolysis of H2O.
No evolution of O2.
There is evolution of O2.
Only Photosystem-I (P700) is involved in this
Both Photosystem PS-I (P700) as well as PS-II (P680) are involved.
(C) What are the steps that are common to C3 and C4 photosynthesis?
Answer :
Steps that are common to C3 and C4 photosynthesis are Carboxylation, Reduction, Glucose synthesis, Regeneration.
(D) Are the enzymes that catalyse the dark reactions of carbon fixation located inside the thylakoids or outside the thylakoids?
Answer :
Carbon fixation occurs in the stroma by series of enzyme catalyzed steps. The enzymes that catalyze the dark reactions of carbon fixation are located outside the thylakoids.
(E) Calvin cycle consists of three phases, what are they? Explain the significance of each of them.
Answer :
The cycle is divided into the following phases:
(i) Carboxylation phase:
Carbon dioxide reduction starts with a five-carbon sugar ribulose-1, 5-bisphosphate (RuBP). It is a 5-carbon sugar with two phosphate groups attached to it.
RuBP reacts with CO2 to produce an unstable 6 carbon intermediate in the presence of Rubisco.
It immediately splits into 3 carbon compounds called 3-phosphoglyceric acid.
Rubisco is a large protein molecule and comprises 16% of the chloroplast proteins.
(ii) Glycolytic reversal:
3-phosphoglyceric acid form 1,3-diphosphoglyceric acid by utilizing ATP molecule.
These are then reduced to glyceraldchydc-3-phosphate (3-PGA) by NADPH supplied by the light reactions of photosynthesis.
In order to keep Calvin cycle continuously running there must be sufficient number of RuBP and regular supply of ATP and NADPH.
Out of 12 molecules of 3-phosphoglyceraldehyde, two molecules are used for synthesis of one glucose molecule.
(iii) Regeneration of RuBP:
10 molecules of 3-phosphoglyceraldehyde are used for the regeneration of 6 molecules of RuBP at the cost of 6 ATP.
Therefore, six turns of Calvin cycle are needed to get one molecule of glucose.
Thus, RUBP (the initial acceptor), which is necessary for the reduction of CO3, is regenerated to keep the process going.
Significance of each pahse :
Carboxylation: RuBisCO is the most abundant enzymes in the world. It is responsible for fixing carbon in the form of CO2 into sugar.
Reduction: NADPH2 donates electrons to 1,3-Bisphoshoglycerate to form 3-phosphoglyceraldehyde molecules.
Regeneration: Some 3-phosphoglyceraldehyde molecules are involved in production of glucose while others are recycled to regenerate the 5-carbon compound RuBP which used to accept new carbon molecules.
(F) Why are the plants that consume more than the usual 18 ATP to produce 1 molecule of glucose favoured in tropical regions?
Answer :
C4 plants are favoured in tropical regions as they require 30 ATP to produce 1 molecule of glucose,
C4 pathway minimizes the losses due to photorespiration.
C4 plants contain a special leaf anatomy called Kranz anatomy. This helps the plant in efficient assimilation of atmospheric carbon dioxide.
It helps C4 plants to survive in conditions of high daytime temperatures, intense sunlight and low moisture
(G) What is the advantage of having more than one pigment molecule in a photocentre?
Answer :
Advantages of having more pigment molecules in a photocenter are as follows:
More sunlight is absorbed and, thus, more light is produced when the photocenter contains several pigment molecules.
The chlorophyll molecule will be protected from photo-oxidation.
More pigments will capture more energy to start the initial reactions, which is not possible by single pigment.
(H) Why does chlorophyll appear green in reflected light and red transmitted light? Explain the significance of these phenomena in terms of photosynthesis.
Answer :
Chlorophyll is a light absorbing pigment. It absorbs light in red and blue regions of the visible light spectrum. Absorption spectrum of chlorophyll for red light is maximum so chlorophyll appears red in transmitted light. Green light is not absorbed but reflected so chlorophyll appear green in reflected light.
Chlorophyll predominantly absorbs red and violet-blue light and it allows plants to use this light as a form of energy for photosynthesis process.
It is most effective wavelength of light in photosynthesis as it has exactly right amount of energy to excite electrons of chlorophyll and boost them out of their orbits to higher energy level.
(I) Explain why photosynthesis is considered the most important process in the biosphere.
Answer :
Because of the following factors, photosynthesis is regarded as the most essential process in the biosphere.
All plants (primary producers) manufacture food through the biochemical process of photosynthesis.
It is in charge of the release of oxygen into the atmosphere.
Heterotrophs rely on autotrophs for energy and other supplies, either directly or indirectly.
As a result, photosynthesis is regarded as the most important process in the biosphere.
(J) Why is photolysis of water accompanied with non-cyclic photophosphorylation?
Answer :
Photolysis of water provides new electrons to Photosystem-II.
The water molecule is lysed into three components: (i) Protons (H+) which are used as part of reactions that makes NADPH (ii) Second component formed is electrons which replaces the electrons lost by PS-II (iii) The third component is oxygen (O2) which is released into the atmosphere.
Photosystem-I sends electrons to reduce NADP+
Then, Photosystem-II sends replacement electrons to Photosystem-I.
Finally photolysis of water replaces the electrons lost by Photosystem-II
Water is the ultimate source of electrons for photosynthesis.
Therefore. photolysis of water is accompanied with non-cyclic photophosphorylation.
(K) In C-4 plants, why is C-3 pathway operated in bundle sheath cells only?
Answer :
In C-4 plants, Calvin cycle occurs in chloroplast of bundle sheath cells because it protects the Calvin cycle from effects of photorespiration.
(L) What would have happed if C-4 plants did not have Kranz anatomy?
Answer :
Photorespiration would occur if C-4 plants did not have Kranz anatomy
(M) Why does RnBisCo carry out preferentially carboxylation than oxygenation in C4 plants?
Answer :
In C4 plants, CO2 taken from the atmosphere is accepted by a 3-carbon compound, phosphoenolpyruvic acid in the chloroplasts of mesophyll cells.
This leads to the formation of 4-carbon compound oxaloacetic acid with the help of enzyme phosphoenolpyruvate carboxylase.
It is converted to another 4-carbon compound called malate.
Malate is transported to chloroplasts of bundle sheath cells where malate is converted to pyruvate and releases CO2 in the cytoplasm thus increasing the concentration of CO2 in the bundle sheath cells.
Chloroplasts of bundle sheath cells contains enzymes of Calvin cycle.
Thus, due to high concentration of CO2, RuBisCO participates in carboxylation and not in oxygenation
(N) What would have happened if plants did not have accessory pigments?
Answer :
In photosynthetic organisms, accessory pigments are light-absorbing molecules that transport absorbed light to chlorophyll-a, boosting the rate of photosynthetic activity.
Without accessory pigments, less light will be absorbed and chlorophyll molecules won't be protected from photo-oxidation.
(O) How can you identify whether the plant is C3 or C4? Explain / Justify.
Answer :
By observing the cross section of a leaf we can identify whether the plant is a C3 plant or a C4 plant.
C4 plants possess a special anatomy of leaves called Kranz anatomy. In Kranz anatomy two types of chloroplasts are present, agranal in bundle sheath cells and granal in mesophyll cells.
In C3 plants Kranz anatomy is absent.
(P) In C4 plants, bundle sheath cells carrying out Calvin cycle are very few in number. Through also, C4 plants are highly productive. Explain.
Answer :
C4 plants can produce more sugar in condition of bright light and high temperature
They have a special type of leaf anatomy called Kranz anatomy.
Photorespiration is absent in C4 plants.
They are able to tolerate high temperature.
They show response to high light intensities.
(Q) What is functional significance of Kranz anatomy?
Answer :
Functional significance :
Leaves of C4 plants show some structural peculiarities called Kranz anatomy. This helps the plant in efficient assimilation of atmospheric carbon dioxide.
The mesophyll of the leaf is undifferentiated, i.e. all the cells are of one type -and are compactly arranged.
Vascular bundles are surrounded radially arranged large bundle sheath cells.
Chloroplasts are dimorphic, i.e. of two types: (i) Chloroplasts of mesophyll cells are smaller, more in number and are abundant with grana, contain a very little stroma and are arranged centrifugally. (ii) Chloroplasts of bundle sheath cells are larger, less in number and are without grana, only with stroma and arranged centripetally.
Kranz anatomy prevents photorespiration in C4 plants.
Question 3.
Correct the pathway and name it
Answer :
The pathway shown is C4 Pathway
Question 4.
Is there something wrong in following schematic presentation? If yes, correct it so that photosynthesis will be operated
Answer :
It involves both photosystems- PS-I and PS-II.
In this case, electron transport chain starts with the release of electrons from PS-II.
In this chain high energy electrons released from PS-II do not return to PS-ll but, after passing through an electron transport chain, reach PS-I, which in tum donates it to reduce NADP+ to NADPH.
The reduced NADP+ (NADPH) is utilized for the reduction of CO2 in the dark reaction.
Electron-deficient PS-II brings about oxidation of water-molecule. Due to this, protons, electrons and oxygen atom are released.
Electrons are taken up by PS-II itself to return to reduced state, protons are accepted by NADP+ whereas oxygen is released.
As in this process, high energy electrons released from PS-II do not return to PS-II and it is accompanied with ATP formation, this is called Non-cyclic photophosphorylation.
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