Please refer to Photosynthesis in Higher Plants Class 11 Biology Exam Questions provided below. These questions and answers for Class 11 Biology have been designed based on the past trend of questions and important topics in your class 11 Biology books. You should go through all Class 11 Biology Important Questions provided by our teachers which will help you to get more marks in upcoming exams.
Class 11 Biology Exam Questions Photosynthesis in Higher Plants
Class 11 Biology students should read and understand the important questions and answers provided below for Photosynthesis in Higher Plants which will help them to understand all important and difficult topics.
Very Short Answer Type Questions:
Question. Cyanobacteria and some other photosynthetic bacteria don’t have chloroplasts. How do they conduct photosynthesis?
Ans. 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. (a) NADP reductase enzyme is located on ……… .
(b) Breakdown of proton gradient leads to release of ……… .
Ans. (a) NADP reductase enzyme is located on the outer side of thylakoid membrane. It is bounded to the thylakoid membrance 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. ATPase enzyme consists of two parts. What are those parts? How are they arranged in the thylakoid membrane? Conformational change occur in which part of the enzyme?
Ans. ATP synthase enzyme has two parts
(a) F1-head piece is a peripheral membrane protein complex and contain the site for synthesis of ATP from ADP +pi (inorganic phosphate).
(b) F0-integral membrane protein complex that forms the channel through which proton cross the inner membrane.
The arrangment of F1 and F0 in thylakoid membrane is as follaws
F0-portion is present within the thylakoid membrane.
F1-portion of ATP synthase enzyme is present in the stroma if chloroplast.
The conformational change occurs in F1 portion of ATP synthase thus, facilitaling the ATP synthesis.
Question. Can girdling experiments be done in monocots? If yes, How? If no, why not?
Ans. 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.
Question. Examine the figure
(a) Is this struture 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).
Ans. (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.Where is NADP reductase enzyme located in the chloroplast? What is the role of this enzyme in proton gradient development?
Ans. NADP reductase enzyme is located on the outer side of lamella or thylakoid of the chloroplast. This enzyme causes breakdown of proton gradient to release energy, i.e., NADPH.
Question. Which products formed during the light reaction of photosynthesis are used to drive the dark reaction?
Ans. ATP and NADPH formed during light reaction of photosynthesis are used in dark reaction for fixing CO2 and to form glucose molecule.
Question. 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?
Ans. (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. Does moonlight support photosynthesis? Find out.
Ans. Plants cannot carry out photosynthesis in moonlight because it does not carry enough energy to excite chlorophyll molecule, i.e., reaction centres PS I and PS II, so light dependent reactions does not get initiate. Thus, no photosynthesis occurs in presence of moonlight.
Question. What is the basis for designating C3 and C4 pathways of photosynthesis?
Ans. The basis for designating C3 and C4 pathways of photosynthesis is as follows
Question. 2H20 → 4H+ + 02 + 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?
Ans. (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. Some of these terms/chemicals are associated with the C4 cycle. Explain.
(a) Hatch Slack pathway (b) Calvin cycle
(c) PEP carboxylase (d) Bundle sheath cells
Ans. The terms associated with C4 cycle are
Hatch Slack Pathway The process of synthesis of glucose in C4 plants is different from C3 plants which was discovered by two scientists MD Hatch and CR Slack (1977). Hence, named Hatch Slack pathway.
PEP Carboxylase It is an enzyme present in mesophyll cells of C4 plants. It fixes CO2 to form 4-carbon compound, i.e., oxaloacetate (OAA).
Bundle Sheath Cells These are specialised sclerenchymatous cells present arround the vascular bundle, in the veins of monocot leaves. These have agranal chloroplast. C3 cycle occurs in these cells to manufacture glucose in C4 plants.
Calvin Cycle This cycle operates in bundle sheath cells and fixes CO2 to form glucose molecules.
Short Answer Type Questions:
Question. Do reactions of photosynthesis called, as ‘Dark Reaction’ need light? Explain
Ans. Dark reactions are actually light independent reactions. CO2 is reduced through various biochemical reactions to produce C6 H12 O6 (glucose) which does not need light. But they depend on the products formed during light reactions, i.e., NADPH2 and ATP.
Question. Suppose Euphorbia and maize are grown in the tropical area.
(a) Which one of them do you think will be able to survive under such conditions?
(b) Which one of them is more efficient in terms of photosynthetic activity?
(c) What difference do you think are there in their leaf anatomy?
Ans. (a) Euphorbia is a CAM plant. It fixes CO2 during night and uses it in day time. It will be able to survive in hot tropical climate.
(b) Maize being a C4 plant is more efficient in terms of photosynthetic activity as it is able to use CO2 at lower level as well as high O2 and temperature.
(c) Maize plants show kranz anatomy in their leaves. They have granal chloroplast in mesophyll cells and agranal in bundle sheath cells. Euphorbia does not have C4 cycle so kranz anatomy is not found in them.
Question. Succulents are known to keep their stomata closed during the day to check transpiration. How do they meet their photosynthetic CO2 requirements?
Ans. Succulent plants grow in dry and xeric conditions so, they have to shut down the stomata during day time, to prevent water loss through transpiration. So and the gaseous exchange does not take place.
Thus plants have developed the mechanism to fix CO2 during night in the form of malic acid, which is a 4 carbon compound and store CO2, release it during day, inside the photosynthetic cells.
Question. Tomatoes, carrots and chillies are red in colour due to the presence of one pigment. Name the pigment. Is it a photosynthetic pigment?
Ans. The different colours other than green are present in the plant because of presence of chromoplasts. It is a kind of plastid and develops different coloured pigments which are not photosynthetic. Pigment lycopene present in tomato, carrot and chillies, imparts red colour to them.
Question. How are photosynthesis and respiration related to each other?
Ans. Photosynthesis and respiration are related, as in both mechanisms, the plants gain energy.
In photosynthesis, plants gain energy from solar radiations whereas, in respiration, they break down glucose molecule to get energy in the form of ATP molecules.
They are releted also because they are dependent on each other. The product of photosynthesis i.e., glucose (food) is utilised in respiration to yield energy (ATP). Which doing so, it releases many other simple molecules (CO2 + H2O) whcih are utilised in photosynthesis to produce more sugers.
Question. A cyclic process is occurring in C3 plant, which is light dependent and needs O2. This process doesn’t produce energy rather it consumes energy.
(a) Can you name the given process?
(b) Is it essential for survival?
(c) What are the end products of this process?
(d) Where does it occur?
Ans. (a) Photorespiration is the process, which do not produce energy rather consum it.
(b) It is not needed for the survival of C3 plant.
(c) The end product of this process is H2 O2.
(d) This process involves three cell organelles of the plant cell.
(i) Chloroplast (ii) Peroxisome
Question. Explain how during light reaction of photosynthesis, ATP synthesis is a chemiosmotic phenomenon.
Ans. In light reaction plants trap solar radiation by photosynthetic pigments which convert light energy into chemical energy. Main event of light reaction is photophosphorylation,
i e . ., formation of ATP from ADP + Pi by using energy of excited electron movement through electron transport chain, present in thylakoid membrane.
Chemiosmosis is the movement of ions across a selectively permeable membrane, down the electrochemical/ proton gradient.
Chemiosmosis hypothesis of ATP formation was first proposed by Mitchell (1961) according to which the enzyme ATP synthase generales ATP via a membrane, proton pump and proton gradient. ATP synthase allows ions O2 protons to pass through membrane and proton pump.
This creales a high cocentration of protons (H+) in the lumen and hence diffuses across the membrane to activale ATPase, releasing ATP molecules. One molecule of ATP is released for every two (H+) ions passing Through ATPase.
Question. Photosynthetic organisms occur at different depths in the ocean. Do they receive qualitatively and quantitatively the same light? How do they adapt to carry out photosynthesis under these conditions.
Ans. Plant present at various depth in ocean are mostly algae. These show great variations in its photosynthetic pigments. These can absorb different wave lengths of light and performs photosynthesis.
Green algae–chlorophyll-a, (absorbs red) and b(absorbs blue violet).
Brown algae–chlorophyll-a, c and fucoxanthin (absorbrs yollow).
Rhodophyceae–chlorophyll-a, d and phycoerythrin.
Question. Find out how Melvin Calvin worked out the complete biosynthetic pathway for synthesis of sugar.
Ans. Melvin Calvin used Chlorella as an experimental material and discovered the first stable compound of photosynthesis, i.e., 3 phosphoglyceric acid so as to trace the path of carbon by using a radioactive isotope of carbon (C14) and autoradiography technique.
He then, compared the radioactive compounds on the chromatogram as a result of which he found and concluded that the PGA (phosphoglyceric acid), as the first stable product of photosynthesis and gradually the other sugars including hexoses, tetroses and pentoses etc.
Thus, he derived the pathway of CO2 fixation from these radioactive products (sugars) formed.
Question. Six turns of Calvin cycle are required to generate one mole of glucose. Explain.
Ans. Ribulose 5 phosphate is a five carbon compound which accepts atmospheric CO2 in presence of RuBisCo and form 2 molecules of 3PGA, a3c carbon compound. It uses 3 ATP and 2 NADPH to fix one molecule of CO2 per cycle of Calvin.
So, to fix 6 CO2 molecules to form 6 carbon compound glucose 6 cycles are required as mentioned below.
Question. Chlorophyll-‘a’ is the primary pigment for the light reaction. What are accessory pigments? What is their role in photosynthesis?
Ans. Accessory pigments are also photosynthetic pigments. These are chlorophyll-b, xanthophyll and carotenoids. These are not directly involved in emission of excited electrons, but they help in harvesting solar radiation and pass it on to chlorophyll-a.
This pigment itself absorbs maximum radiation at blue and red region. So, Chlorophylla is the chief pigment of photosynthesis and others (i.e., chlorophyll-b, xanthophyll and carotinoion) are accessory pegment.
Question. Complete the flow chart for cyclic photophosphorylation of the photosystem-I.
Ans. The following flow chart show cyclic photophosphorylation and the missing part of this flow chart are
Question. Why do we believe chloroplast and mitochondria to be semi-autonomous organelle?
Ans. Both the cell organelles, chloroplast and mitochondria have extra chromosomal DNA and 70S type of ribosomes. The presence of DNA enables then to duplicate, when cell need more mitochondria and the chloroplasts. So they are called as semi-autonomous cell organelles.
Question. If a green plant is kept in dark with proper ventilation, can this plant carry out photosynthesis? Can anything be given as supplement to maintain its growth or survival?
Ans. The plant in given conditions can not carry out photosynthesis. Light is must for any green plant to make its own food.
The plant should be watered properly for its survival.
Question. A process is occurring throughout the day, in ‘X’ organism. Cells are participating in this process. During this process ATP, CO2 and water are evolved. It is not a light dependent process.
(a) Name the process.
(b) Is it a catabolic or an anabolic process?
(c) What could be the raw material of this process?
Ans. (a) The name of the process is cellular respiration.
(b) It is a catabolic process which involves break down of glucose molecule.
(c) Raw material for this process is glucose molecule and oxygen, which are products of photosynthesis, occurring in plants.
Question. In tropical rain forests, the canopy is thick and shorter plants growing below it, receive filtered light. How are they able to carry out photosynthesis?
Ans. The plants carry out photosynthesis in presence of light. The quality and intensity of light affect only the rate of photosynthesis. So, plants growing in different canopy will carry out photosynthesis, but rate could be different depending upon the intensity and quantity of light recevied.
Question. In what kind of plants do you come across ‘Kranz anatomy’? To which conditions are those plants better adapted? How are these plants better adapted than the plants, which lack this anatomy?
Ans. Kranz anatomy refers to the dimorphism in the chloroplast structure. It is found in C4 plants. The cells of leaves have two types of chloroplast in them.
Granal Chloroplast It is found in the mesophyll cells of leaves. Chloroplast have well developed grana in them. These chloroplast effectively fix CO2 even if it is present in lower concentrations. PEP carboxylase is present which fix CO2 and to form oxaloacetic acid (4 carbon compound).
Agranal Chloroplast Present in bundle sheath cells of the leaves. C3 cycle occurs in these cells with the presence of RuBisCo enzyme.
The C4 plants are well adapted to high O2 concentrations and high temperature.
C4 plants can absorb CO2 even when CO2 concentration in much low thus C4 plants can perform high rate of photosynthesis even the stomata are closed or there is the shortage of water thus, they can conserve water.
Since, PEP-carboxylase is insensitive to O2 thus excess O2 has us inhibitory effect in C4 pathway and there is no photosynthesis in C4 plant.
Thus, C4 plants are better adapted to tropical and desert (hot acid habitats) areas than the plants, that lack this anatomy.
Question. What conditions enable RuBisCO to function as an oxygenase? Explain the ensuing process.
Ans. RuBisCo is an enzyme which has dual nature. It acts as carboxylase, when CO2 concentration is good enough in atmosphere. But if O2 concentration increases, its nature changes and it binds with O2 and acts as oxygenase enzyme, which forces CO2 to enter C2 cycle thus leading to photorespiration and loss of CO2.
Question. Observe the diagram and answer the following.
(a) Which group of plants exibit these two types of cells?
(b) What is the first product of C4 cycle?
(c) Which enzyme is there in bundle sheath cells and mesophyll cells?
Ans. (a) Monocot plants belonging to Graminae/Poaceae family, e.g., sugarcane, maize etc., possess these two types of cells. i.e., bundle sheath and mesophyll cell (in kranz anatomy).
(b) A 4-carbon compound oxaloacetic acid is the first product of C4 cycle.
(c) Mesophyll cells have PEP carboxylase to fix atmospheric CO2 to form a 4-carbon compound oxalo acetic acid, whereas bundle sheath cells have RuBP carboxylase which fix CO2 by this enzyme to form 3-carbon compound 3 PGA (3 phosphoglyceric acid).
Long Answer Type Questions:
Question. Which property of the pigment is responsible for its ability to initiate the process of photosynthesis? Why is the rate of photosynthesis higher in the red and blue regions of the spectrum of light?
Ans. The chlorophyll pigments are present in the thylakoid membranes. They have the property of excitability and emits e− in the excited stage, though this e− is replaced and transferred by the e− generated from splitting of water molecules.
Red and Blue Light have maximum energy which a chlorophyll pigment absorbs and get excited and initiate the process of photosynthesis. Also, its wavelength are (400-700 nm) i.e., between the Photosynthetic Active Radiation (PAR).
Thus, the rate of photosynthesis is higher in blue and red light.
Question. In the figure given below, the black line (upper) indicates action spectrum for photosynthesis and the lighter line (lower) indicates the absorption spectrum of chlorophyll-a, answer the following
(a) What does the action spectrum indicate? How can we plot an action spectrum? Explain with an example.
(b) How can we derive an absorption spectrum for any substance?
(c) If chlorophyll-a is responsible for light reaction of photosynthesis, why do the action spectrum and absorption spectrum not overlap?
Ans. (a) The effectiveness of different wavelengths of light on photosynthesis is measured and the rate of photosynthesis is plotted. This is called the action spectrum of photosynthesis.
(b) Absorption of different wavelengths of light by a particular pigment is plotted and the graph is called the absorption spectra of that pigment.
(c) Chlorophyll-a is responsible for light reaction of photosynthesis, but the action spectrum and absorption spectrum do not overlap because, though chlorophyll-a is the main pigment responsible for absorption of light, other thylakoid pigments like chlorophyll-b, xanthophylls, carotenoid, which are accessory pigments, also absorb and transfer the energy to chlorophyll-a.
Indeed they not only enable a wider range of wavelength of incoming light to be utilised for photosynthesis but also protect chlorophyll-a from photooxidation.
Question. What special anatomical features are displayed by leaves of C4 plants?
How do they provide advantage over the structure of C3 plants?
Ans. Kranz Anatomy, is the feature exhibited by C4 plant. These possess two types of chloroplast in their leaves. Agranal chloroplast found in bundle sheath cells whereas granal
chloroplast is found in the mesophyll cells.
Bundle sheath cell perform C3 cycle (dark reaction) where as mesophyll cell performC4 cycle.
C4 plants are more efficient even in high O2 concentration and temperature as compared to C3 plants. Many important crop plants (monocots) show C4 cycle like maize, sorghum, sugarcane and millet.
Question. What are the important events and end products of the light reaction?
Ans. The important events of light reaction are (i) Excitation of chlorophyll molecule to emit a pair of electrons and use of their energy in the formation of ATP from ADP + Pi. This process is called photophosphorylation.
(ii) Splitting of water molecule
End products of light reaction are NADPH and ATP.
Reducing power is produced in the light reaction i.e., ATP and NADPH2 molecules which are
used up in dark reaction, O2 is evolved as a by product by the splitting of water.
Question. Is it correct to say that photosynthesis occurs only in leaves of a plant?
Besides leaves, what are the other parts that may be capable of carrying out photosynthesis? Justify.
Ans. Photosynthesis is a process which mainly occurs in leaves of all green plants. The plants have designed their leaf in such a way that it is able to trap solar radiation and effectively convert solar/light energy to chemical energy.
But biology is science of exceptions. Some plants carry out photosynthesis in modified plant parts other then leaves.
Few examples are as follows
1. Root as Photosynthetic Organ
When roots develop chlorophyll and start photosynthesis, they are called assimilitory roots.
Trapa and Tinospora are the examples of assimilatory roots.
2. Stem as Photosynthetic Organ
In Opuntia, the stem gets modified to take up the function of leaves. It becomes flattened, thick and succulent and perform photosynthesis. Such structures are called phylloclade.
3. Petiole as Photosynthetic Organ In Australian Acasia the petiole takes the shape and function of photosynthesis because leaf lamina soon falls off.
Question. Why is RuBisCo enzyme the most abundant enzyme in the world?
Ans. RuBisCo, now termed as RuBP carboxylase-oxygenase, is widely occurring enzyme because RuBisCo is used in the Calvin cycle to catalyse the first major step of carbon fixation.
RuBisCO is thought to be the most abundant protein in the world since, it is present in every plant that undergoes photosynthesis and molecular synthesis through the Calvin cycle.
It makes about 20-25% of the soluble protein in leaves and is made on the earth at the rate of about 1000 kg/s. It is estimated that every person on earth is supported by about 44 kg of RuBisCo.
Question. Under what conditions are C4 plants superior to C3?
Ans. C4 plants are advantageous in following ways
(i) These plants can carry out photosynthesis even at low concentration of CO2 in the atmosphere and in the shortage of water.
(ii) These plants can tolerate high O2 concentration and temperature as enzyme PEP carboxylase in C4 cycle in insensitive to O2 and do not show- photorespiration in comparison to the C3 plants, which start process of photorespiration and lose CO2 fixation in the form of glucose molecule.
Thus, C4 plants are superior to C3 plants.
Question. Name the two important enzymes of C3 and C4 pathway, respectively.
What important role do they play in fixing CO2?
Ans. The important enzyme of C3 cycle is RuBP carboxylase oxygenase which catalyses reaction of carboxylation of ribulose bis-phosphate, which is 5-carbon compound. to form PGA, the first stable product in C3 cycle.
In C4 cycle, the important enzyme is phosphoenol pyruvate carboxylase (PEP carboxylase) which help in fixing CO2 to form oxaloecetate (4-carbon compound), the first stable product of dark reaction is C4 cycle.
Question. The entire process of photosynthesis consists of a number of reactions.
Where in the cell do each of these take place?
(a) Synthesis of ATP and NADPH ……… .
(b) Photolysis of water ……… .
(c) Fixation of CO2 ……… .
(d) Synthesis of sugar molecule ……… .
(e) Synthesis of starch ……… .
Ans. (a) Synthesis of ATP and NADPH takes place in outer side of thylakoid membrane.
(b) Photolysis of water occurs in inner side of thylakoid membrane.
(c) Fixation of CO2 occurs in stroma of chloroplast.
(d) Synthesis of sugar molecule occurs in chloroplast.
(e) Synthesis of starch occurs in cytoplasm.
Question. In the diagram shown below label A, B, C. What type of phosphorylation is possible in this?
Ans. A–Electron acceptor
C–Chlorophyll (photosystem I) P700
The cyclic photophosphorylation is shown in the above figure.
Question. Why does not photorespiration take place in C4 plants?
Ans. Photorespiration is associated with C3 cycle, where plant lose CO2 fixation because of the increase in concentrate ion of O2 and change the nature of activity of RuBP carboxylase-oxygenase.
C4 plants have evolved a mechanism to avoid loss of CO2. There is not a direct contact of RuBP carboxylase-oxygenase as C3 cycle operates in bundle sheath cells (where both temperature and oxygen level low).
CO2 fixation is done by another enzyme PEP carboxylase in mesophyll cells and oxaloacetate is formed which is converted to malic acid and transported to bundle sheath cells.
There, it gives off CO2 which is used in Calvin cycle, operating in bundle sheath cells of C4 plants.
Question. Why is the RuBisCo enzyme more appropriately called RUBP carboxylase-oxygenase and what important role does it play in photosynthesis?
Ans. RuBP carboxylase and oxygenase has dual nature. It has affinity for both CO2 and O2 but has more affinity for CO2 than O2. Thus, the concentrations of two determines which of the two will bind to the enzyme.
Consider the following two situations
(i) In a normal condition when CO2 and O2 concentrations are normal, it acts as carboxylase and fix CO2 by combining with ribulose bisphosphate and C3 cycle operates normally, producing glucose molecule as an first product of photosynthesis.
(ii) If O2 concentration goes up and CO2 goes down, it starts acting as an oxygenase enzyme and C2 cycle (photorespiration) starts where RuBP binds with O2 to frorm phosphoglycolate.
(iii) C4 plants have mechanisms to increase the concentration of CO2 at enzyme site, and increasing the intracellular concentration of CO2. Thus, here RuB is Co acts as carboxylase, minimising the affect of oxygenase.
Question. What can we conclude from the statement that the action and absorption spectrum of photosynthesis overlap? At which wavelength do they show peaks?
Ans. Absorption Spectrum This depicts the absorption of light of different wavelength by chlorophyll-a, b, xanthophyll and carotenoids.
Action Spectrum This shows the rate of photosynthesis in the plant in the light of different wavelengths.
Super Imposed Absorption and Action Spectrum When we superimposed both action
and absorption spectrum, it shows that in the region of red and blue light, the chlorophyll-a
and b harness the maximum light energy and are the main photosynthetic pigments.
So, the rate of photosynthesis is high in these two regions. It shows maximum activity peak
at wavelength (red light) i.e., 660-670 nm, 430-470 nm (blue) and 390-430 nm (violet).