CBSE Class 11 Biology Chapter 13: Photosynthesis in Higher Plants NCERT Solutions

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NCERT Solutions PDF Class 11 PDF

This resource provides detailed NCERT Solutions for Class 11 Biology, Chapter 13, focusing on Photosynthesis in Higher Plants. It covers essential topics such as the role of chlorophyll, the function of different pigments, the Photosynthetically Active Radiation (PAR) range, the effectiveness of different light wavelengths in photosynthesis, and the energy sources for chemosynthetic bacteria and ATP synthesis in Photosystem II. The solutions also explain the products formed during the light-dependent reactions of photosynthesis. These explanations are designed to clarify complex processes, helping students grasp the fundamental mechanisms of how plants convert light energy into chemical energy. This chapter is crucial for understanding plant physiology and its role in ecosystems. The solutions are structured to aid students in their exam preparation, offering clear explanations and reinforcing key concepts for better retention and application.

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BoardCBSE
ClassClass 11
SubjectBiology Exemplar
Session2026
LanguageEnglish
TypeNCERT Solutions
ChapterChapter 13

Chapter summary

Chapter 13 of the CBSE Class 11 Biology syllabus, 'Photosynthesis in Higher Plants,' is explained through these NCERT Solutions. The solutions cover the essential components and processes of photosynthesis, including chlorophyll's role, accessory pigments, the PAR spectrum, light effectiveness, energy sources for chemosynthesis and photophosphorylation, and the outcomes of light reactions. This chapter is vital for understanding plant life and energy flow in ecosystems. The provided solutions aim to simplify these concepts for effective learning and revision.

Learning outcomes

  • Identify the metal ion present in chlorophyll.
  • Distinguish between primary photosynthetic pigments and accessory pigments.
  • Define and identify the range of Photosynthetically Active Radiation (PAR).
  • Explain the effectiveness of different wavelengths of light in photosynthesis.
  • Describe the energy source for chemosynthetic bacteria.
  • Explain the origin of energy for ATP synthesis in Photosystem II.
  • List the products formed during the light-dependent reactions of photosynthesis.

Topics covered

Paper topics

  • Chlorophyll structure and function
  • Accessory pigments in photosynthesis
  • Photosynthetically Active Radiation (PAR)
  • Effectiveness of different light wavelengths
  • Chemosynthesis
  • Energy sources for ATP synthesis
  • Photosystem II (PS II)
  • Light-dependent reactions
  • Products of light reactions
  • Role of metal ions in photosynthesis

Important topics

  • Role of Chlorophyll and Accessory Pigments
  • Photosynthetically Active Radiation (PAR)
  • Light Effectiveness and Spectrum
  • Light-Dependent Reactions and Products
  • ATP Synthesis Mechanism

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Questions and Solutions

Multiple Choice Questions (MCQs) - Question 1

Q. 1 Which metal ion is a constituent of chlorophyll?
  1. Iron (b) Copper (c) Magnesium (d) Zinc
Solution: The correct answer is (c) Magnesium. Magnesium is a vital component located at the center of the porphyrin ring structure of chlorophyll molecules. This central position is crucial for chlorophyll's ability to absorb light energy. Other metal ions like iron are important for cytochromes and ferredoxin, copper is involved in redox enzymes, and zinc is associated with auxin synthesis, but magnesium is specifically integral to chlorophyll.

Multiple Choice Questions (MCQs) - Question 2

Q. 2 Which pigment acts directly to convert light energy to chemical energy?
  1. Chlorophyll-a (b) Chlorophyll-b
  2. Xanthophyll (d) Carotenoid
Solution: The pigment that directly converts light energy into chemical energy is (a) Chlorophyll-a. While chlorophyll-b, xanthophyll, and carotenoids are also photosynthetic pigments, they function as accessory pigments. They absorb light energy across a broader spectrum and transfer this energy to chlorophyll-a, which then initiates the energy conversion process.

Multiple Choice Questions (MCQs) - Question 3

Q. 3 Which range of wavelength (in nm) is called Photosynthetically Active Radiation (PAR)?
  1. 100-390 (b) 390-430 (c) 400-700 (d) 760-100,00
Solution: The correct answer is (c) 400-700 nm. This range represents the visible spectrum of light, which is utilized by plants for photosynthesis. Other wavelength ranges are associated with different types of radiation: 100-300 nm is the ultraviolet (UV) range, 390-430 nm is near the infrared (NIR) range, and 760-100,000 nm is the mid-infrared (MIR) range, none of which are primarily used for photosynthesis.

Multiple Choice Questions (MCQs) - Question 4

Q. 4 Which light range is most effective in photosynthesis?
  1. Blue (b) Green (c) Red (d) Violet
Solution: The most effective light range for photosynthesis is (c) Red light. Although photosynthesis occurs in blue and violet light, the rate is slower compared to red light. Green light is the least effective because plants reflect most of the green wavelengths, which is why they appear green.

Multiple Choice Questions (MCQs) - Question 5

Q. 5 Chemosynthetic bacteria obtain energy from
  1. sun (b) infrared rays
  2. organic substances (d) inorganic chemicals
Solution: Chemosynthetic bacteria obtain their energy from (d) inorganic chemicals. These bacteria are capable of synthesizing their own food by oxidizing inorganic compounds like hydrogen sulfide (H₂S) or nitrites (NO₂⁻) to gain energy. They do not use sunlight (like photosynthetic organisms) or organic substances as their primary energy source.

Multiple Choice Questions (MCQs) - Question 6

Q. 6 Energy required for ATP synthesis in PS II comes from
  1. proton gradient (b) electron gradient
  2. reduction of glucose (d) oxidation of glucose
Solution: The energy required for ATP synthesis in Photosystem II (PS II) comes from the (a) proton gradient. During the light-dependent reactions, the splitting of water molecules and electron transport lead to the accumulation of protons (H⁺) within the thylakoid lumen, creating a proton gradient. The flow of these protons back into the stroma through ATP synthase drives ATP production.

Multiple Choice Questions (MCQs) - Question 7

Q. 7 During light reaction in photosynthesis the following are formed
  1. ATP and sugar (b) hydrogen, O<sub>2</sub> and sugar
  2. ATP, hydrogen donor and O<sub>2</sub> (d) ATP, hydrogen and O<sub>2</sub> donor
Solution: During the light-dependent reactions of photosynthesis, the products formed are (c) ATP, hydrogen donor (in the form of NADPH), and O₂. Solar energy is captured to produce ATP and NADPH, which are then used in the light-independent reactions (Calvin cycle) to synthesize sugar. Oxygen is released as a byproduct from the photolysis of water (H_2O \rightarrow 2H^+ + \frac{1}{2}O_2). Sugar is produced in the subsequent dark reactions, not the light reactions.

Common mistakes

  • Confusing the central metal ion of chlorophyll with other essential plant micronutrients.
  • Misidentifying the primary pigment responsible for converting light energy.
  • Incorrectly recalling the specific wavelength range for PAR.
  • Not understanding why green light is least effective for photosynthesis.
  • Confusing the energy source for chemosynthetic bacteria with photosynthetic organisms.

Revision tips

  • Focus on memorizing the specific metal ion in chlorophyll and its function.
  • Clearly differentiate between chlorophyll-a and accessory pigments.
  • Understand the significance of the 400-700 nm range for PAR.
  • Review the reasons behind the varying effectiveness of different light colors.
  • Pay attention to the distinct energy sources used by chemosynthetic versus photosynthetic organisms.

Practice MCQs

Q1. Which metal ion is a crucial component of the chlorophyll molecule?

Q2. Which pigment directly converts light energy into chemical energy during photosynthesis?

Q3. What is the wavelength range, in nanometers (nm), defined as Photosynthetically Active Radiation (PAR)?

Q4. Which color of light is most effective for driving the process of photosynthesis?

Q5. Chemosynthetic bacteria derive their energy from:

Q6. The energy required for ATP synthesis in Photosystem II (PS II) originates from:

Q7. What are the primary products generated during the light-dependent reactions of photosynthesis?

Frequently asked questions

What is the main function of chlorophyll in photosynthesis?

Chlorophyll is the primary pigment that absorbs light energy from the sun, initiating the process of converting light energy into chemical energy.

What is PAR and why is it important?

PAR stands for Photosynthetically Active Radiation, which is the range of light wavelengths (400-700 nm) that plants use for photosynthesis. It's crucial because it defines the usable light spectrum for plant energy production.

Why is red light considered the most effective for photosynthesis?

Red light is most effectively absorbed by chlorophyll and drives photosynthesis at a higher rate compared to other wavelengths in the visible spectrum. Green light is least effective as it is mostly reflected.

What is the difference between photosynthetic and chemosynthetic bacteria?

Photosynthetic bacteria use light energy to produce food, similar to plants. Chemosynthetic bacteria, however, obtain energy from the oxidation of inorganic chemicals to synthesize their food.

What are the key outputs of the light-dependent reactions in photosynthesis?

The light-dependent reactions produce ATP (energy), NADPH (a reducing agent or hydrogen donor), and oxygen (O₂) as a byproduct.

Which metal ion is essential for the structure of chlorophyll?

Magnesium (Mg) is the central metal ion in the porphyrin ring of chlorophyll, making it indispensable for the pigment's function.

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