RBSE Solutions For Class 12 Biology Chapter 10: Photosynthesis | Textbook Important Questions & Answers

RBSE Class 12 Biology Chapter 10-Photosynthesis, provides complete information related to photosynthesis, site of photosynthesis, photosynthetic pigments, chlorophyll structure, light reaction and dark reaction, mechanism of photosynthesis, photophosphorylation, C3 and C4 plants, factors affecting the rate of photosynthesis and photorespiration.

These important questions help students to perform best in their exams. By practising these important questions, students can analyze their preparation.

The Rajasthan Board Class 12 Biology Chapter 10 important questions is the best study material for revisions and last-minute preparations. By practising these important questions, students can gain deep knowledge about the topic and also help them by providing a strategy to prepare for various board examinations and also for medical exams.

RBSE Class 12 Biology Chapter 10 Important Questions

RBSE Biology Chapter 10: MCQ Type Questions

Q.1. Oxygen (O2) evolution is related to_______________.

(a) PS-I.

(b) PS-II.

(c) Phytochrome.

(d) All of the above.

Sol:(b) PS-II.

Q.2. What is the unit of photosynthesis?

(a) Quantasome.

(b) Microsome.

(c) Peroxisome.

(d) Spherosome.

Sol:(a) Quantasome.

Q.3. In PS-I and PS-II the respective reaction centres are _______________.

(a) P700 and P680.

(b) P600 and P700.

(c) P580 and P700.

(d) P700 and P580.

Sol:(a) P700 and P680.

Q.4. The wave length of photosynthetically active radiation is _______________.

(a) 340-450nm.

(b) 400-700nm.

(c) 500-600nm.

(d) 450-950nm.

Sol:(b) 400-700nm.

Q.5.Which of the following is the site of the dark reaction in photosynthesis?

(a) Grana of chloroplast.

(b) Stroma of chloroplast.

(c) Inner membrane of chloroplast.

(d) Outer membrane of chloroplast.

Sol:(b) Stroma of chloroplast.

Q.6. Which of the following sources of oxygen is liberated in photosynthesis?

(a) Water.

(b) Carbon Dioxide

(c) Both water and carbon dioxide

(d) Neither water nor carbondioxide

Sol:(a) Water.

Q.7. Which of the following processes occurs on lin C4 plants?

(a) Glycolysis.

(b) Photorespiration.

(c) Transpiration.

(d) Photosynthesis

Sol:(b) Photorespiration.

Q.8. Which of the following metals are found in the centre of the chlorophyll molecule?

(a) Iron(Fe)

(b) Magnesium (Mg)

(c) Neon(Ne)

(d) Copper(Cu)

Sol:(b) Magnesium (Mg)

Q.9. PS-II is related to_______________.

(a) Photolysis of water.

(b)Reduction of carbon dioxide.

(c) Flowering in plants.

(d) All of the above.

Sol:(a) Photolysis of water.

Q.10. The first stable product of C4 cycle is _______________.

(a) Pyruvic acid.

(b) Malic acid.

(c) Oxaloacetic acid.

(d) Phosphoglyceric acid.

Sol:(c) Oxaloacetic acid.

RBSE Biology Chapter 10: Short Answer Type Questions.

Q.1. What is the first stable product of the photosynthesis reaction?

Sol. The first stable product of the photosynthesis reaction is different for both C3 and C4 plants. In C3 plants, the first stable product of Carbon dioxide (CO2) fixation is PGA – phosphoglyceric acid, whereas in C4 plants, the first stable product is OAA – oxalic acetic acid.

Q.2.What are photosynthetic pigments?

Sol. The pigments that capture the light energy necessary for photosynthesis is called the photosynthetic pigments. These pigments are present in chloroplasts of a plant cell. There are four different pigments involved in photosynthesis –

  1. Carotenoids.
  2. Chlorophyll A.
  3. Chlorophyll B.
  4. Xanthophylls.

Q.3. What is Light Reaction?

Sol. The light reaction takes place in the grana of the chloroplast. In this process of light reaction, the absorbed light energy gets converted to chemical energy –ATP and NADPH. In this very light reaction, the addition of phosphate in the presence of light or the synthesizing of ATP by cells is known as photophosphorylation.

Read more : Cyclic and non cyclic photophosphorylation

Q.4. What is Non-cyclic photophosphorylation?

Sol. The photophosphorylation process which results in the movement of the electrons in a non-cyclic manner for synthesizing ATP molecules using the energy from excited electrons provided by photosystem II is called non-cyclic photophosphorylation.

Q.5. What is the law of limiting factor?

Sol. According to the Blackman law , when some process is affected by more than one factor, then the rate of the process is determined by the factors present in a minimum amount. This is called the Blackman’s law of limiting factor.

Q.6. What are the drawbacks of photorespiration?

Sol. The main drawback or disadvantage of photorespiration is, it can have photoprotective effect and in the process of photorespiration, the food is oxidised in the presence of oxygen and energy, the ATP molecules are not released as the end product of the process.

Q.7. What is the significance of Photosynthesis?

Sol. During photosynthesis, oxygen gas is liberated out into the environment and is utilized by humans, animals and other living species during the process of respiration.

Q.8. What is Photophosphorylation?

Sol. Photophosphorylation is the process of utilizing light energy from photosynthesis to convert ATP- Adenosine-Tri-Phosphate from the ADP- Adenosine -Di-Phosphate. Photophosphorylation is of two types: Cyclic photophosphorylation and Non-cyclic photophosphorylation.

Q.9. Which pigments are involved in the process of photosynthesis?

Sol. The main pigments involved in the process of photosynthesis are Chlorophyll A and Chlorophyll B. Carotenoids and phycobilins act as accessory pigments.

Q.10. What are the different stages of Photosynthesis?

Sol. Photosynthesis occurs in two stages – light-dependent reaction and light-independent reaction. Light-dependent reactions are also called light reactions and occur during the day time. Light-independent reaction is also called the dark reaction or the Calvin cycle.

Q.11.What is Photorespiration?

Sol. Photorespiration is the chemical processes that occur within the cells of higher plants in the presence of sunlight. During the process of photorespiration, oxygen oxidizes the carbon dioxide and releases it to the environment. Compared to the normal respiration, photorespiration does not produce energy. This is also known as the oxidative photosynthetic, or C2 photosynthesis or carbon cycle.

Q.12.What is Dark Reaction?

Sol. The photosynthetic process, which occurs in the absence of sunlight and takes place in the stroma of the chloroplasts is called dark reaction. The following cycles are involved in the process: Calvin Cycle or C3 Cycle and C4 Cycle or Hatch and Slack Pathway.

Q.13. Define Photosynthesis.

Sol. Photosynthesis is a biological process utilized by all green plants to synthesize their own nutrients. The process of photosynthesis requires solar energy, water and carbon dioxide. The by-product of this process is oxygen.

Explore more: Photosynthesis

Q.14. Define Red Drop?

Sol.The lowering in the rate of photosynthesis when a plant is illuminated with light of wavelength more than 680nm, then this lowering is called red drop.

Q.15. Why do photosynthesis occur in chloroplast?

Sol. Photosynthesis occurs in chloroplast because these cell organelles contain special pigments like Carotenoids, Chlorophyll a, Chlorophyll b and Xanthophylls. These pigments absorb light energy and use it in conjunction with water and carbon dioxide gas to produce food for the plant.

Q.16. What is a photosystem?

Sol. Photosystem is defined as the biochemical mechanism in plants by which the photosynthetic pigments absorb light energy for photosynthesis. There are two types of photosystem, Photosystem-I and Photosystem -II. Both have different mechanisms and different chlorophyll–protein complexes and different wavelengths of light.

Q.17. Does the dark reaction occur at night?

Sol. No, the dark reaction does not occur at night. It occurs during the day but the reaction does not use the light directly. The dark reaction occurs in the stroma of the chloroplast where they utilize the products of the light reaction.

Q.18. What is Chlorophyll-A?

Sol. Chlorophyll A is the major pigment used in photosynthesis. It is the universal pigment, which acts as a reaction center in the light reaction. It functions by absorbing light energy from the orange-red and violet-blue areas of the electromagnetic spectrum and is transferred to the reaction center.

Q.19.What is Quantosome?

Sol. Quantosome is defined as the unit of photosynthesis, which is found on the thylakoids membrane of chloroplasts in the form of granular structure. These particles are included in various photosynthetic pigments and redox carriers. They are mainly composed of proteins and lipids. The main function of quantasome is to accept light energy.

Q.20. What is the Calvin Cycle?

Sol. The Calvin cycle is also called the light-independent reaction. The complete process of the Calvin cycle takes place in the stroma of the chloroplasts.

Q.21. What are the end products of light reaction and dark reaction?

Sol. The end products of the light reaction are ATP and NADPH, these molecules are produced during the cyclic and the non-cyclic photophosphorylation reactions.Whereas the end product of dark reaction is Glucose and is produced when both ATP and NADPH combine with CO2 and water.

Q.22. What are the factors influencing Photosynthesis?

Sol. There are several factors that affect the rate of photosynthesis. Temperature, soil pH, water, light intensity, carbon dioxide concentration, temperature and other climatic conditions are the main factors affecting the rate of photosynthesis.

RBSE Biology Class 12: Long Answer Type Questions

Q.1. What is the light and dark reaction of photosynthesis? Draw a neat labelled diagram.

Sol.

Light Reaction

It is a light-dependent process, which includes a series of events such as –

  1. Light absorption
  2. Hydrolysis
  3. Release of oxygen
  4. Formation of ATP and NADPH.

The light reaction of photosynthesis takes place only during the day time.i.e. when it is supplied with light energy. This reaction occurs in the thylakoids of the chloroplast. When the plant cell receives light, the chlorophyll-A pigment gets excited to a higher energy state followed by a series of reactions. In this process, energy is converted into energy molecules ATP and NADPH by using PS-I and PS-II and hydrolysis occurs by releasing oxygen gas.

Dark Reaction

Dark reaction is also called carbon-fixing reaction. It is a light-independent process in which sugar molecules are formed from the carbon dioxide and water molecules.This reaction occurs in the stroma of the chloroplast where they utilize the products of the light reaction. During this reaction, plants capture the carbon dioxide from the atmosphere through stomata and proceed to the Calvin cycle. In the Calvin cycle, the ATP and NADPH formed during light reaction drive the reaction and convert 6 molecules of carbon dioxide into one sugar molecule, i.e. glucose.

Diagram Light and Dark Reaction in Photosynthesis

Diagram Light and Dark Reaction in Photosynthesis

Q.2. Explain the structure of a chloroplast with a neat labelled diagram.

Sol. Chloroplasts are cell organelles present only in a plant cell and other photosynthetic organisms. It consists of green-coloured pigments within the plant cell and are called chlorophyll. Chloroplasts are found in all plants within the cells of the mesophyll in plant leaves.

Structure of a Chloroplast

Structure of a chloroplast

Chloroplasts are oval or biconvex shaped, bounded by a double-membrane envelope. This cell organelle is present within the mesophyll of the plant cell. The size of the chloroplast usually varies between 4-6 µm in diameter and 1-3 µm in thickness. They are with the presence of outer, inner and the thin intermembrane space.

The chloroplast structure consists of the following parts:

Inner membrane –– It is the space between inner and outer membranes. It functions as a more selective membrane and only allows some compounds and metabolites in and out of the organelle.

Intermembrane Space — The inner membrane surrounds the stroma and the grana.

Outer membrane —It is a semi- permeable membrane, which functions by allowing the entry of small molecules and ions, by diffusion. It also functions as the physical barrier between the organelle and the cytoplasmic environment.

Stroma — It is a colourless, alkaline, aqueous, protein-rich fluid present within the inner membrane of the chloroplast present surrounding the grana.

Thylakoid — It is the third membrane, hence also called the Thylakoid membrane . It is an internal membrane system. They are the sight for the process of light reactions of photosynthesis.

Lamella--It is a membrane-bound compartment present with the inside chloroplasts, which consists of a thylakoid membrane surrounding a thylakoid lumen.They are the sight for the process of light reactions of photosynthesis.

Q.3. Write a note on photolysis of water and Photorespiration.

Sol.

Photolysis of water

The process of breakdown of (H2O) water molecules into its component ions by the chlorophyll molecules in the presence of light energy or sunlight is called photolysis of water . This process results in the evolution of oxygen gas (O2)

The process photolysis of water is give by the equation:

2H2O → 4H+ + 4e + O2.

(In the presence of chlorophyll Mn++ and sunlight Cl)

Photorespiration

The process of respiration, taking place in addition to normal respiration in the photosynthetic parts of the plant in the presence of light energy or sunlight is called photorespiration. Photorespiration is influenced by high temperature as well as light intensity and accelerating the formation of glycolate and the flow through the photorespiratory pathway. Both photosynthesis and photorespiration are two biological processes that can function simultaneously beside each other as photosynthesis gives off oxygen as its byproduct and photorespiration gives off carbon dioxide as its byproduct

Q.4. Write the difference between cyclic and non-cyclic photophosphorylation?

Sol. Differences between cyclic and non-cyclic photophosphorylation:

Cyclic Photophosphorylation

Non-Cyclic Photophosphorylation

Water is not required.

Water is required.

NADPH is not synthesized.

NADPH is synthesized.

Photolysis of water does not occur.

Photolysis of water occurs.

Electrons travel in a cyclic manner.

Electrons travel in a non – cyclic manner.

P700 is the active reaction centre.

P680 is the active reaction centre.

Only Photosystem-I is involved.

Both Photosystem -I and II are involved.

Oxygen is not evolved as the by-product

Oxygen is evolved as a by-product.

ATP molecules are produced.

Both NADPH and ATP molecules are produced.

This process is predominant only in bacteria.

This process is predominant in all green plants.

Electrons revert back to Photosystem-I.

Electrons from Photosystem-I are accepted by NADP.

Q.5. What are the internal factors affecting photosynthesis?

Sol. The process of photosynthesis is affected by several internal factors, which are also called plant related factors.

Listed below are the internal factors affecting the rate of photosynthesis.

Chlorophyll.

It is the main pigment of photosynthetic reaction, which converts light energy into chemical energy. Normally the rate of photosynthesis increases with the total amount of chlorophyll in plants.

Amount of stored food.

The end product of photosynthesis is stored as a food in plant cells. Continuous storage of food decreases the rate of photosynthesis. Once after the stored food is transferred or distributed to different parts of the plants, the arte of photosynthesis increases.

Structure of a leaf.

The rate of photosynthesis also depends on the internal structure of a leaf. More stomata and their absorption of carbon dioxide increases the rate of photosynthesis.

Q.6. Write the difference between C3 and C4 plants?

Sol. Difference between C3 and C4 plants.

C3 Plants

C4 Plants

Do not represent Kranz anatomy.

Represent Kranz anatomy.

Also called the Calvin Cycle.

Also called Hatch and Slack Pathway

Photosynthesis occurs in mesophyll cells.

Photosynthesis occurs mesophyll and bundle sheath cells

RuBisCO is a carbon dioxide acceptor.

PEP carboxylase is the carbon dioxide acceptor.

The first stable compound is a three-carbon compound 3-phosphoglyceric acid.

The first stable compound is a 4-carbon compound oxaloacetic acid.

The photorespiratory loss is high.

The photorespiratory loss is low.

The optimum temperature is 20-25°C.

The optimum temperature is 35-44℃.

C3 cycle is found in all plants.

C4 cycle is found only in C4 plant species like Maize, Sorghum and Sugarcane.

Refer more: Difference between Cyclic and Non-Cyclic Photophosphorylation

Q.7. What are the special features of C4 plants?

Sol.

C4 plants are plants which cycle carbon dioxide to 4-carbon sugar compounds in order to enter the C3 or the Calvin cycle. The C4 plants are very productive in both hot and dry climatic conditions and produce a lot of energy. Some examples of C4 plants are pineapple, corn, sugar cane, etc. These plants are called C4 because of the 4 carbon compound oxaloacetate produced during the pathway. Kranz anatomy is a specialized structure in the leaves of C4 plants. The word Kranz is derived from a Greek word meaning “wreath” or “ring”.

The special features of C4 plants are:

  1. There are two types of photosynthetic cells found in C4 plants, which are known as bundle sheath cells and mesophyll cells.
  2. The bundle sheath cells are found around the vascular bundles arranged in one or two layer monlai form.
  3. In C4 plants two types of chloroplasts are found.
  4. The chloroplasts present in the mesophyll cells have a very small chloroplasts cell with well developed grana.
  5. The chloroplasts present in the bundle sheath cells are big and lack grana.
  6. Thylakoids are found in the form of stroma lamellae. Therefore, in C4 plants the light reaction takes place in mesophyll cells and the dark reaction takes place in bundle sheath cells.

Q.8. What are the external factors affecting the photosynthesis?

Sol. The process of photosynthesis is affected by several factors, which are divided into internal factors and external factors.

Listed below are the five external factors affecting the rate of photosynthesis. This is also called the atmospheric factors.

Light.

Light is the most important factor because sunlight is a source of energy for the synthesis of carbohydrates. Light may affect the process of photosynthesis in three forms: Types of sunlight, light intensity and duration of light.

Temperature.

Photosynthesis takes place in a wide range of temperatures. Some gymnosperms perform photosynthesis at -35C and in some xerophytes photosynthesis takes place at 55C. There are plant species found in hot waters, which perform photosynthesis at a high temperature of 75C. In the majority of plants, the rate of photosynthesis gradually increases between 10C to 35C.

Carbon Dioxide.

The amount of carbon dioxide in the atmosphere is around 0.03 percent (300ppm). As the total amount of carbon dioxide increases, the rate of photosynthesis keeps on increasing. Normally the rate of photosynthesis increases by an increase in carbon dioxide concentration up to 1.0 percent.

Water.

Water is an important reactant in the process of photosynthesis. It acts as a hydrogen donor in this process. Only 1.0 percent of total water is absorbed by plants and is used for the process of photosynthesis .

Oxygen.

Increase in the concentration of oxygen affects the rate of photosynthesis . Oxygen acts as a competitive inhibitor for enzymes RuBISCO.

Q.9. Write the difference between Light reaction and Dark reaction.

Sol. Differences between Light reaction and Dark reaction:

Light Reaction

Dark Reaction

It is a photochemical phase.

It is a biochemical phase.

It is the first phase of photosynthesis.

It is the second phase of photosynthesis.

Photolysis occurs in PS-II.

Photolysis does not occur.

Depends on light.

Does not depend on light.

It takes place in the grana of the chloroplast.

It takes place in the stroma of the chloroplast.

It liberates oxygen by splitting water.

It fixes carbon dioxide to produce sugar.

NADP utilizes H+ ions to form NADPH.

The hydrogen of NADPH combines with CO2.

Involves the photosynthetic pigment.

No pigments are involved in this reaction.

It involves the conversion of light energy into cellular energy.

It involves the conversion of cellular energy into chemical energy.

The end products are ATP and NADPH.

Glucose is the end product.

Q.10. Why is the chloroplast green in colour? List out the different functions of Chloroplast.

Sol. Chloroplast contains a green pigment called chlorophyll which gives it a green colour.

The most important function of the chloroplast is to synthesize food by the process of photosynthesis. Other functions of the chloroplast include:

  1. It absorbs light energy and converts it into chemical energy.
  2. Produces NADPH and molecular oxygen(O2) by photolysis of water.
  3. Produces ATP – Adenosine triphosphate by the process of photosynthesis .
  4. The carbon dioxide (CO2) obtained from the air is used to generate carbon and sugar during the Calvin Cycle or dark reaction of photosynthesis.
  5. Chloroplast has a structure called chlorophyll which functions by trapping the solar energy and is used for the synthesis of food in all green plants.

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