Class 11 Biology chapter 12 Photosynthesis Textbook solutions

Maharashtra state board Class 11 Biology chapter 12 Photosynthesis Textbook solutions

Maharashtra state board Biology Textbook Solutions for Class 11 are very important and crusial that helps the students in understanding the hard topics and helps them in the preparation of class 11 board examination as well as verious compititive entrance examinations also. Studying the answers to the questions in the Biology textbook will check your understanding of a particular topic and helps you determine your strengths and weaknesses.

Class 11 Biology textbook Solutions for Class 11, Biology  Chapter 12 Photosynthesis  maharashtra state board are provided here with simple step-by-step  detailed explanations. These solutions for  Photosynthesis are very popular among Class 11 students for biology chapter 12 Photosynthesis  Solutions come handy for quickly completing your homework and preparing for compititive exams like NEET, CET abd verious medical entrance examination also. All questions and answers are taken from the class 11 Biology textbook, Bjology Textbook Solutions of Class  11 Biology Chapter 12 are provided here for you for without any charge its free for you. All Biology textbook Solutions for class 11. Solutions for class 11 Biology subject, These Biology textbook solutions are prepared by   experts in the field and are 100% accurate for you.


1. Choose correct option
A. A cell that lacks chloroplast does not
 a. evolve carbon dioxide
 b. liberate oxygen
 c. require water
 d. utilize carbohydrates.

B. Energy is transferred from the light reaction step to the dark reaction step by 
a. chlorophyll
b. ADP
c. ATP
d. RuBP

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
 c. It is characteristic of C3-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'

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

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

G. C4 pathway is also called as dicarboxylation pathway because
 a. RuBP + CO2 in bundle sheath cells
 b. PEPA + CO2  in mesophyll cells
 c. both 'a' and 'b'
 d. It occurs in presence of intensive light

H. The head and tail of chlorophyll are 
made up of
 a. porphyrin and phytin respectively
 b. pyrrole and tetrapyrrole respectively
 c. prophyrin and phyrol respictively
 d. tetrapyrole and pyrrole respectively

I. 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

J. For fixing one molecule of CO2 in Calvin cycle, are required
 a. 3ATP + 1NADPH2
 b. 3ATP + 2NADPH2
 c. 2ATP + 3NADPH2
 d. 3ATP + 3NADPH2

K. In presence of high concentration of oxygen, RuBP carboxylase converts RuBP carboxylase converts RuBP to
 a. Malic acid and PEP
 b. PGA and PEP
 c. PGA and malic acid
 d. PGA and phosphoglycolate

L. 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


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 are the formation of high-energy chemical intermediates, ATP and NADPH, and it includes light absorption, water splitting and release of oxygen. It takes place in the granal thylakoids of chloroplasts in the presence of sunlight.
Following are the light-dependent steps of photosynthesis:

Production of assimilatory power in photosynthesis: It occurs through two processes:

Non-cyclic photophosphorylation: Non-cyclic photophosphorylation involves both Photosystem I and Photosystem II. These two photosystems work in series, first PS II and the PS I. The two photosystems are connected through an electron transport chain. Both ATP and NADPH+H + are synthesised by this kind of electron flow.

Cyclic photophosphorylation: Cyclic photophosphorylation is a process of photophosphorylation in which an electron released by the excited photocentre is returned to it after passing through a series of electron carriers. It takes place in the stroma lamellae membrane of chloroplasts. The process of cyclic photophosphorylation involves only photosystem I. The excited electron does not pass on to NADP+ and is cycled back to the PS I complex through the electron transport chain. It synthesises ATP only.

Splitting of water and release of oxygen: The electrons that were removed from PS II must be replaced. This is achieved by electrons available due to the splitting of water. The water splitting complex is associated with the PS II, which itself is physically located on the inner side of the membrane. Water is split into H+, [O] and electrons. The protons and oxygen formed by splitting of water are released into the lumen of the thylakoids. The oxygen produced is released as one of the net products of photosynthesis.
2H2O→4H +O2+4e−

Dark reactions are the reactions which are not directly dependent on light. But they are linked to light-dependent steps of photosynthesis because they use assimilatory powers i.e., ATP and NADPH in fixation and reduction of carbon dioxide.


B. Distinguish between: a. respiration 
and photorespiration 
Answer :

  1. respiration is a metabolic pathway which releases energy-rich molecules by the breakdown of sugar molecules such as glucose. Photorespiration is a type of respiration which occurs in plants in presence of light and at high oxygen concentration.
  2. Respiration can also be referred to as Normal respiration or dark respiration. Photorespiration can also be referred to as dark respiration. 
  3. Normal respiration takes place in both in presence of light and dark.Photorespiration only takes place in the presence of light.    


b. absorption spectrum and action spectrum 
Answer : An absorption spectrum defines the spectrum of electromagnetic radiation, or light, plants absorb. This depends on the cellular and molecular build-up of the plant. An action spectrum defines the spectrum of electromagnetic radiation most effective for photosynthesis

c. cyclic photophosphorylation and non-cyclic photophosphorylation
Answer :

  1. In cyclic Only Photosystem I is involved. In Non cyclic Both Photosystem I and II are involved.
  2. In cyclic P700 is the active reaction centre. Non cyclic P680 is the active reaction centre.
  3. In cyclic Electrons travel in a cyclic manner. In non cyclic Electrons travel in a non – cyclic manner.
  4. In cyclic Electrons revert back to Photosystem I In non cyclic Electrons from Photosystem I are accepted by NADP.
  5. In cyclic ATP molecules are produced. In non cyclic Both NADPH and ATP molecules are produced.
  6. In cyclic Water is not required. In non cyclic Photolysis of water is present.
  7. In cyclic NADPH is not synthesized. In non cyclic NADPH is synthesized.
  8. In cyclic Oxygen is not evolved as the by-product In non cyclic Oxygen is evolved as a by-product.


C. What are the steps that are common to C3 and C4 photosynthesis?
Answer : The steps that are common to c3 and c4 photosynthesis:

  1. Photolysis of water in light reaction is common to both c3 and c4 cycle.
  2. In both, dark reaction occurs in stroma region of chloroplast.
  3. Calvin cycle results in the formation of starch in both types of plants.
  4. Both undergo phases of carboxylation and regenration of RUBP during dark reaction.


D. Are the enzymes that catalyse the dark reactions of carbon fixation located inside the thylakoids or outside the thylakoids?
Answer : The dark reactions occur through Calvin cycle. They take place in the stromal matrix of the chloroplast. The enzymes that catalyse the dark reaction of carbon fixation are present outside the thylakoids. These enzymes are present in the stromal matrix of chloroplasts.

E. Calvin cycle consists of three phases, 
what are they? Explain the significance 
of each of them.
Answer : Calvin cycle was discovered by Melvin Calvin while radioactive studies of alga. It occurs in all photosynthetic plants whether they have C3 or C4 pathway.
Calvin cycle can be described under three stages:


Carboxylation: It is the fixation of CO2 into a stable organic intermediate. In this, CO2 is utilised for the carboxylation of RuBP. This reaction is catalysed by the enzyme RuBisCO and it results in the formation of two molecules of 3-PGA (3-Phosphoglyceric acid).

Reduction: These reactions lead to the formation of glucose. The steps involve utilisation of two molecules of ATP for phosphorylation and two of NADPH for reduction, per molecule of CO2 fixed. The fixation of six molecules of CO2 and six turns of the cycle are required for the removal of one molecule of glucose from the pathway.

Regeneration: For the cycle to continue uninterrupted, regeneration of the CO2 acceptor molecule is crucial. This step requires one ATP for phosphorylation to form RuBP. To make one molecule of glucose, six turns of the cycle are required. 18 ATP and 12 NADPH molecules are used to make a molecule of glucose. Hence, for every CO2 molecule entering the Calvin cycle, three molecules of ATP and two molecules of NADPH are required.

F. Why are the plants that consume more than the usual 18 ATP to produce 1 molecule of glucose favoured in tropical regions?
Answer : The C4 plants consume more than the usual 18 ATP, i.e., about 30 ATP, to produce 1 molecule of glucose and are favored in tropical regions. The C4 plants are uniquely adapted to grow better in hot and dry tropical regions because:

The C4 plants have leaves that have a unique structure called the Kranz Anatomy with thick bundle sheath cells and dense mesophyll cells that aid in double carbon fixation.
Unlike in other plants, where the carbon fixation takes place in chloroplasts by the action of Rubisco enzyme, the C4 plants fixate carbon in the cytoplasm activated by the enzyme phosphoenolpyruvate (PEP) carboxylase through the Hatch-Stack Pathway.

G. What is the advantage of having more than one pigment molecule in a 
photocentre?
Answer : Advantages of having more than one pigment molecule in a photocentre are as follows: Having more pigments means more sunlight being captured and trapped, hence facilitating an effective light reaction. The additional pigments would provide protection to the chlorophyll molecule against photo-oxidation.

H. Why does chlorophyll appear green in reflected light and red transmitted 
light? Explain the significance of these 
phenomena in terms of photosynthesis.
Answer : In reflected light, the chlorophyll appears red because of fluorescence. The light absorbed by chlorophyll molecules loses its energy and emitted as red photons. In transmitted light, chlorophyll appears green because it absorbs other lights except green.

I. Explain why photosynthesis is considered the most important process in the biosphere. 
Answer : Photosynthesis is considered the most important process in biosphere due to following reasons: It is the primary source of food on earth. It is also responsible for the release of oxygen into the atmosphere by green plants which is needed by mostly all life forms.

J. Why is photolysis of water accompained 
with non-cyclic photophosphorylation?
Answer : Photolysis of water is mainly carried out to compensate the electrons that are transferred to photosystem I by photosystem II during the non-cyclic photophosphorylation that reduce NADP+ into NADPH.

K. In C-4 plants, why is C-3 pathway 
operated in bundle sheath cells only?
Answer : Since Rubisco can operate under high CO2 concentrations in the bundle sheath cells, it works more efficiently than in C3 plants.  Additionally C4 plants exhibit better water-use efficiency than C3 plants. Because of the CO2 concentration mechanism they can acquire enough CO2 even when keeping their stomata more closed.

L. What would have happed if C-4 plants 
did not have Kranz anatomy?
Answer : Kranz anatomy in c-4 plants
Lack of night-time CO2 fixation indicates it is not acquiring carbon by Crassulacean acid metabolism. ... Now, good %of CO2 already reached these cells, so RUBISCO can do normal Calvin cycle and form Glucose.

M. Why does RnBisCo carry out preferentially carboxylation than 
oxygenation in C4 plants?
Answer : C4 plants utilize this 4-carbon compound to viably "concentrate" CO2 around rubisco, so rubisco is more uncertain re respond with O2. It is called phosphoenolpyruvate (PEP) carboxylase, In C 3 plants photorespiration has the impact of decreasing the pace of photosynthesis, as air oxygen can join with rubisco.

N. What would have happened if plants did not have accessoy pigments?
Answer : The plant would be lacking chlorophyll to some degree but may still survive. Many of these have accessory pigments to supply increased utilization of sunlight. Some are lighter green or yellow looking. Explanation:The plant would be lacking chlorophyll to some degree but may still survive.

O. How can you identify whether the plant is C3 or C4? Explain / Justify.
Answer : If one want to identify these plants morphologically, then the most important point is the climate or area as C4 plants are grown in hot, dry climates whereas C3 plants are found in cool and wet areas.

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 : The amount of carbon dioxide present in a plant is directly proportional to the rate of photosynthesis. C4 plants have a mechanism for increasing the concentration of carbon dioxide. In C4 plants, the Calvin cycle occurs in the bundle-sheath cells. Thus, C4 plants are highly productive

Q. What is functional significance of Kranz anatomy?
Answer : The C4 plants often possess a characteristic leaf anatomy called as Kranz anatomy. The primary function of Kranz anatomy is to provide a site in which CO2 can be concentrated around RuBisCO, thereby avoiding photorespiration.