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NCERT Solutions Class 11 Biology Chapter 11 - Photosynthesis in Higher Plants
NCERT Solutions for Class 11 Biology Chapter 11 (Photosynthesis in Higher Plants) explore the physicochemical process by which plants use light energy to drive the synthesis of organic compounds. As the primary source of all food on earth and the process responsible for releasing oxygen into the atmosphere, photosynthesis is the most vital biological process for sustaining life.
NCERT Solutions for Class 11 Biology Chapter 11 by ALLEN are designed by expert faculty to simplify the complex biochemical pathways of the chloroplast. The solutions focus on the "two-phase" nature of photosynthesis—the Light-dependent reactions (Photochemical phase) and the Light-independent reactions (Biosynthetic phase)—making the energy transformation from photons to glucose easy to follow. For NEET aspirants, this chapter is a core component of Plant Physiology. It requires a deep understanding of electron transport chains, chemiosmotic hypothesis, and the differences between C3 and C4 plants. These solutions provide the technical precision needed to master the Z-scheme and the Calvin Cycle, which are high-weightage topics in medical entrance exams.
1.0Class 11 Biology Chapter 11 Photosynthesis in Higher Plants: Key Concepts
This chapter examines the physico-chemical process by which plants use light energy to drive the synthesis of organic compounds. The key lessons include:
- Pigments involved in Photosynthesis: Understanding the roles of Chlorophyll a, b, Xanthophylls, and Carotenoids. Studying the Absorption and Action spectra.
- Light Reaction (Photochemical Phase): Analyzing light absorption, water splitting, oxygen release, and the formation of ATP and NADPH.
- Electron Transport & Z-Scheme: Detailed study of Photosystem I (PS I) and Photosystem II (PS II) and cyclic/non-cyclic photophosphorylation.
- Chemiosmotic Hypothesis: Understanding how a proton gradient across the thylakoid membrane leads to ATP synthesis.
- The Dark Reaction (Biosynthetic Phase): Studying where ATP and NADPH are used to fix CO_2.
- C_3 Pathway (Calvin Cycle): Mastering the three stages: Carboxylation, Reduction, and Regeneration.
- C_4 Pathway (Hatch-Slack Pathway): Analyzing the "Kranz anatomy" and how C_4 plants minimize photorespiration.
- Photorespiration: Understanding the C_2 cycle and why it is a wasteful process in C_3 plants.
- Factors affecting Photosynthesis: Studying Blackman’s Law of Limiting Factors (Light, CO_2 concentration, Temperature, and Water).
2.0NCERT Solutions Class 11 Biology Chapter 11 - Photosynthesis in Higher Plants: Detailed Solutions
- By looking at a plant externally, can you tell whether a plant is or ? Why and how? Ans. It is not possible to distinguish externally between a and plant, but generally tropical plants are adapted for cycle.
- By looking at which internal structure of a plant you can tell whether a plant is or ? Explain. Ans. plants live in hot moist or arid and nonsaline or saline habitats. Internally the leaves show kranz anatomy. In kranz anatomy, the mesophyll is undifferentiated and its cells occur in concentric layers around vascular bundles. Vascular bundles are surrounded by large sized bundle sheath cells which are arranged in a wreath-like manner (kranz - wreath). The mesophyll and bundle sheath cells are connected by plasmodesmata or cytoplasmic bridges. The chloroplasts of the mesophyll cells are smaller. They have well developed grana and a peripheral reticulum but no starch. Mesophyll cells are specialised to perform light reaction, evolve and produce assimilatory power (ATP and NADPH). They also possess enzyme PEPcase for initial fixation of The chloroplasts of the bundle sheath cells are agranal.
- Even though a very few cells in a plant carry out the biosynthetic - Calvin pathway, yet they are highly productive. Can you discuss why? Ans. Since,through cycle, a plant can photosynthesise even in presence of very low concentration of (upto 10 parts per million), the partial closure of stomata due to xeric conditions would not bring much effect. Therefore, the plants can adapt to grow at low water content, high temperature and bright light intensities. This cycle is specially suited to such plants which grow in dry climates of tropics and subtropics. Besides, the photosynthetic rate remains higher due to absence of photorespiration in these plants. It can be visualised that both cycle and photorespiration are the result of evolution or might have been oneof the reasons of evolution for the adaptation of plants to different environments. plants are about twice to efficient as plants in converting solar energy into production of dry matter.
- RuBisCO is an enzyme that acts both as a carboxylase and oxygenase. Why do you think RuBisCO carries out more carboxylation in plants? Ans. RuBisCO is an enzyme which acts both as carboxylase (carboxylation during photosynthesis) and oxygenase (during photorespiration). But RuBisCO carries out more carboxylation in plants. In plants, initial fixation of carbon dioxide occurs in mesophyll cells. The primary acceptor of is phosphoenol pyruvate or PEP. It combines with carbon dioxide in the presence of PEP carboxylase or PEPcase to form oxaloacetic acid or oxaloacetate. Malic acid or aspartic acid is translocated to bundle sheath cells through plasmodesmata. Inside the bundle sheath cells they are decarboxylated (and deaminated in case of aspartic acid) to form pyruvate and is again fixed inside the bundle sheath Cells through Calvin cycle. RuBP of Calvin cycle is called secondary or final acceptor of in plants. Pyruvate is sent back to mesophyll cells.
- Suppose there were plants that had a high concentration of chlorophyll , but lacked chlorophyll , would it carry out photosynthesis ? Then why do plants have chlorophyll and other accessory pigments ? Ans. Plants that do not possess chlorophyll will not carry out photosynthesis because it is the primary pigment and act as the reaction centre. It performs the primary reactions of photosynthesis or conversion of light into chemical or electrical energy. Other photosynthetic pigments are called accessory pigments. They absorb light energy of different wavelengths and hence broaden the spectrum of light absorbed by photosynthetic pigments. These pigments hand over the absorbed energy to chlorophyll .
- Why is the colour of a leaf kept in the dark frequently becomes yellow, or pale green? Which pigment do you think is more stable? Ans. Carotenoid pigments are found in all photosynthetic cells. They are accessory pigments also found in roots, petals etc. These pigments do not breakdown easily thus temporarily reveal their colour due to unmasking, following breakdown of chlorophylls. Thus the colour of leaf kept in dark is yellow or pale green.
- Look at leaves of the same plant on the shady side and compare it with the leaves on the sunny side. Or, compare the potted plants kept in the sunlight with those in the shade. Which of them has leaves that are darker green? Why? Ans. The leaves of the shaded side are darker green than those kept in sunlight due to two reasons: (i) The chloroplasts occur mostly in the mesophyll cells along their walls for receiving optimum quantity of incident light. (ii) The chloroplasts align themselves in vertical position along the lateral walls of high light intensity and along tangential wails in moderate light.
- The given figure shows the effect of light on the rate of photosynthesis. Based on the graph, answer the following questions.
(a) At which point/s (A, B or C) in the curve light is a limiting factor? (b) What could be the limiting factor/s in region A? (c) What do C and D represent on the curve?
Ans.
(a) At regions A and B light is the limiting factor. (b) In region A, light is the limiting factor. (c) C is the region where the rate of photosynthesis is not increased when light intensity is increased. D is the point where some other factors become limiting.
- Give comparison between the following: (a) and pathways (b) Cyclic and non-cyclic photophosphorylation (c) Anatomy of leaf in and plants.
Ans.
(a)The differences between and
(b) The differences between cyclic and non- cyclic photophosphorylation are as follows :
(c) Differences between the leaf anatomy of and plants are as follows :
3.0Key Features of NCERT Solutions for Class 11 Biology Chapter 11
- Z-Scheme and ETS Clarity:
The solutions provide a detailed breakdown of how electrons move from water to NADP^+, explaining the role of Photosystem II and I in creating reducing power. - C3 vs. C4 Comparative Analysis:
Detailed tables comparing the anatomy (Kranz anatomy), first stable product, and efficiency of C3 and C4 plants, a frequent NEET target. - RuBisCO Dual Nature Logic:
Expertly explained reasoning behind why RuBisCO acts as a carboxylase or oxygenase depending on the O_2/CO_2 ratio. - Chemiosmosis Visualization:
Step-by-step logic of how a proton gradient is established in the lumen of thylakoids and how its breakdown leads to ATP synthesis via F_o-F_1 particles. - Prepared by Expert Faculty:
Prepared by ALLEN subject experts, ensuring that every biochemical equation and pathway description is technically accurate and aligned with the latest syllabus. - Limiting Factors Guidance:
Clear explanation of Blackman’s Law of Limiting Factors, helping students understand why photosynthesis doesn't increase indefinitely with light. - Complete Coverage of NCERT Exercises:
Every question is answered with the depth required to understand the bio-energetic foundation of plant life.