Q: PEP is primary CO2 acceptor in

C4 plants have evolved PEP as primary acceptor of CO2 to avoid the sensitivity of RuBP carboxylase-oxygenase to high concentration of oxygen, so that they can avoid photorespiratory loss of CO2 occuring in them.Other options (b), (c) and (d) are incorrect. PEP is not primary acceptor in them.

Question 1

Which metal ion is a constituent of chlorophyll?

Accepted Answer

(c) Magnesium (Mg) is present in the centre of porphyrin ring of the chlorophyll molecule. Other ions, i.e., iron, copper and zinc participate in other metabolic processes which areFe is an important part of cytochrome and ferridoxin. Cu plays an important role in enzyme catalysing redox reactions. Zn is associated with auxin (a phytohormone) synthesis

Question 2

Which pigment acts directly to convert light energy to chemical energy?

Accepted Answer

(a) Chlorophyll-a acts directly to convert light energy to chemical energy. The other pigments chlorophyll-b, xanthophyll and carotenoids are accessory pigments associated with the main pigment, i.e., chlorophyll-a to harvest the light energy.

Question 3

Which range of wavelength (in nm) is called Photosynthetically Active Radiation (PAR)?

Accepted Answer

(c) Photosynthetically Active Radiation (PAR) ranges from 400−700 nm. This is the visible range of light energy.The range of other wavelength are associatic with100−300 nm390−430 nm760−100,00 nm​: Ultraviolet (UV) range : Infrared (NIR) range : Mid Infrared (MIR) range ​

Question 4

Which light range is most effective in photosynthesis?

Accepted Answer

Red light is most effective in photosynthesis.In other lights namely blue and violet the photosynthesis takes place but the rate is slow, whereas in green light the photosynthesis is least because plants do not absorb this range of light reflect back thus, they appear green.

Question 5

Chemosynthetic bacteria obtain energy from

Accepted Answer

In Inorganic Chemicals Chemosynthetic bacteria were the first organism on earth synthesise their own food by obtaining energy from chemicals like H2​ S,NO2​, etc. Photosynthetic bacteria have taken their origin from chemosynthetic bacteria.Sun, infrared rays and organic substances are not used as the sources of energy for chemosynthetic bacteria.

Question 6

Energy required for ATP synthesis in PS II comes from

Accepted Answer

(a) The synthesis of ATP is directly linked to the development of proton gradient across the thylakoid membranes of a chloroplast. It results when the water molecule splits inside the inner membrane and form H+and OH−ions.The energy for ATP synthesis comes from proton gradient which develops along the inner membrane, e.g., in case of mitochondria in electron transport chain and in chloroplast in the PS II.The other options (b), (c) and (d) are not involved in the synthesis of ATP molecule.

Question 7

During light reaction in photosynthesis the following are formed

Accepted Answer

Light dependent reaction uses solar power to generate ATP and NADPH2​  which provide chemical and reducing power respectively to sugar synthesising reaction of the Calvin cycle, while the O2​  in released as a by product of light dependent reaction. Other options are incorrect because (a) ATP is produced in light reaction but sugar is produced in dark reaction. (b) H2​  is produced by splitting of water (H2​O→2H++21​O2​)H+ are released. The 2H+  is accepted by NADP to form NADPH and oxygen (O2​ ) is of course produced but sugar is not. (c) O2​  donor and ATP is produced in light reaction but not the hydrogen.

Question 8

Dark reaction in photosynthesis is called so because

Accepted Answer

(b) Dark reaction is called so because it does not depend on light. It is also called as light independent reaction.

Question 9

PEP is primary CO2​ acceptor in

Accepted Answer

C4​ plants have evolved PEP as primary acceptor of CO2​ to avoid the sensitivity of RuBP carboxylase-oxygenase to high concentration of oxygen, so that they can avoid photorespiratory loss of CO2​ occuring in them.Other options (b), (c) and (d) are incorrect. PEP is not primary acceptor in them.

Question 10

Splitting of water is associated with

Accepted Answer

(d) The thylakoid is a photosynthetic unit in the chloroplast. It is a membrane bound structure. The membrane has photosystems I and II embedded in it, in the form of chemicals and molecules. Splitting of water is associated with PS-II, which occurs in presence of Mn2+ and Cl−ions on the inner surface of thylakoid membrane.2H2​OMn+⟶Cl−​​4H++O2​+4e− Photosystem I and II are associated with light reactions.

Question 11

The correct sequence of flow of electrons in the light reaction is

Accepted Answer

Option (a) is the correct sequence of movement of electrons. The options (b), (c) and (d) do not give this correct sequence of events.

Question 12

The enzyme that is not found in a C3​ plant is

Accepted Answer

(b) PEP carboxylase enzyme is found in C4​ plants to carry out initial fixation of CO2​. The functions of other enzymes in options (a),(c) and (d) are as follows(a) RuBP carboxylase operates in C3​ plants.(c) NADP reductase is involved in electron transport chain.(d) ATP synthase is used in ATP synthesis.

Question 13

The reaction that is responsible for the primary fixation of CO2​ is catalysed by

Accepted Answer

In C3​ cycle RuBP carboxylase is used to fix atmospheric CO2​ whereas, in C4​ plants PEP carboxylase is involved in primary CO2​ fixation. So, both are used in CO2​ fixation but in different cycles.Other options are incorrect because in (a) and (b) option is giving incomplete information and option (d) PGA synthase is not at all involved in CO2​ fixation.

Question 14

When CO2​ is added to PEP, the first stable product synthesised is

Accepted Answer

(d) Oxaloacetate is a four carbon compound formed in C4​ cycle and is a first stable product, that is why such plants are called C4​ plants.Rest of the options are incorrect as because(a) Pyruvate is formed in glycolysis.(b) Glyceraldehyde-3-phosphate is also an intermediate compound of glycolysis.(c) Phosphoglycerate is also an intermediate compound of glycolysis.

Question 15

Examine the figure (a) Is this structure present in animal cell or plant cell? (b) Can these be passed on to the progeny? How? (c) Name the metabolic processes taking place in the places marked (A) and (B).

Accepted Answer

(a) The above figure show the chloroplast which is green in colour and performs photosynthesis in plants thus, The structure is present in plant cell. (b) Yes, chloroplast has the power of self replication because of presence of extranuclear DNA. (c) The metabolic that occurs in the marked places are as follows. A–It is the stroma of chloroplast where dark reaction of photosynthesis takes place. B–It is the structure of extra nuclear DNA and is responsible for replication of chloroplast, when it is required in the photosynthesising cells.

Question 16

2H2​O→4H++O2​+4e− Based on the above equation, answer the following questions (a) Where does this reaction take place in plants? (b) What is the significance of this reaction?

Accepted Answer

(a) The reaction takes place in reaction centre PS II, located on the inner surface of thylakoid membrane. It is known as water splitting centre where electrons are extracted from water. The Mn+and Cl−ions catalyse this reaction.(b) Splitting of water is an important event in photosynthesis as(i) It releases molecular oxygen as byproduct of photosynthesis and is the significant source of oxygen in air, or is essential for all living beings on earth.(ii) Hydrogen ions produced, are utilised in reducing NADP to NADPH, a strong reducing agent.(iii) The electrons released are transferred from PS II to PS I through a series of electron carriers thus, creating a gradient for the synthesis of ATP.

Question 17

3CO2​+9ATP+6NADPH+ water ⟶ Glyceraldehyde 3-phosphate  +9ADP+6NADP++8Pi Analyse the above reaction and answer the following questions(a) How many molecules of ATP and NADPH are required to fix one molecule of CO2​ ?(b) Where in the chloroplast does this process occur?

Accepted Answer

(a) 2 molecules of ATP for phosphorylation and two molecules of NADPH for reduction are required per CO2​ molecule fixed.(b) The Calvin cycle occurs in the stroma of the chloroplast.

Question 18

Cyanobacteria and some other photosynthetic bacteria don’t have chloroplasts. How do they conduct photosynthesis?

Accepted Answer

The cyanobacteria and photosynthetic bacteria are prokaryotes. They do not have well defined membrane bound cell organelles, but these organisms have photosynthetic pigments in a membranous form, which are primitive in nature but can trap and use solar energy. So, they can carry out photosynthesis.

Question 19

(a) NADP reductase enzyme is located on ......... . (b) Breakdown of proton gradient leads to release of ......... .

Accepted Answer

(a) NADP reductase enzyme is located on the outer side of thylakoid membrane. It is bounded to the thylakoid membrane in light and becomes free in stroma during dark. (b) ATP Molecules The movement of H + ions across the membrane is coupled with the formation of ATP synthesis in presence of enzyme ATP synthase.

Question 20

Can girdling experiments be done in monocots? If yes, How? If no, why not?

Accepted Answer

The girdling experiment cannot be done in monocots. The monocot stem has vascular bundles scattered all over the width of stem so, we cannot reach that specific band of the phloem tissues as we get in dicots.

Chapter 13 : Photosynthesis in Higher Plants