NCERT Class 11 Biology Chapter 13 Notes Photosynthesis In Higher Plants - Download PDF Notes

NCERT Class 11 Biology Chapter 11 Notes Photosynthesis is the process that supports life on Earth by harnessing the power of sunlight and converting it into chemical energy. It happens in green plants, algae, and certain bacteria, enabling them to produce food with sunlight, carbon dioxide, and water. Photosynthesis not only enables the plant to have a source of energy, but it also enables all living things to exist since it produces oxygen and is the source of the food chain.

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This Story also Contains

1. Photosynthesis
2. Phases of Photosynthesis
3. Important Topics of Class 11 Biology Chapter 11: Photosynthesis in Higher Plants
4. Most Important Questions of Class 11 Biology Chapter 11
5. Approach to solve questions of Class 11 Biology Chapter 11 Photosynthesis in Higher Plants
6. Chapter-Wise NCERT Class 11 Notes Biology

It is important to know about photosynthesis in order to understand plant physiology, agriculture, and the balance of nature. The NCERT Notes for Class 11 Biology Chapter 11 discusses the complex mechanisms of photosynthesis in higher plants, such as light and dark reactions, photophosphorylation, C₃, C₄, and CAM pathways, and the factors affecting photosynthetic efficiency. A better understanding of these principles assists in scientific progress, such as increasing crop production and resolving climate change issues.

Also, students can refer,

• NCERT Solutions for Class 11 Biology Chapter 11 Photosynthesis in Higher plants
• NCERT Exemplar Class 11 Biology Chapter 11 Photosynthesis in Higher plants

Photosynthesis

Photosynthesis is a biochemical process by which green plants, algae, and some bacteria transform light energy into chemical energy in the form of glucose. Photosynthesis also produces oxygen as a byproduct, which is vital for the existence of all aerobic organisms.

Importance of Photosynthesis

Primary Source of Energy: Photosynthesis is the beginning of all food chains since plants and algae form organic matter that feeds herbivores and, consequently, carnivores.

Oxygen Production: Photosynthesis maintains the oxygen content in the atmosphere, making aerobic respiration possible.

Carbon Dioxide Regulation: It maintains the equilibrium of CO₂ content in the atmosphere, minimizing the greenhouse effect.

Fossil Fuel Basis: Fossil fuels such as coal and petroleum have been formed through the contribution of ancient plants and algae, by photosynthesis.

Crop Productivity Necessity: Crop productivity is dependent on increased photosynthetic efficiency, which provides improved crop yield, essential to ensure food security globally.

Site of Photosynthesis

Photosynthesis takes place in the chloroplasts, which are specialized organelles found in plant cells. Leaf mesophyll cells have the maximum number of chloroplasts and are therefore the main site for photosynthesis.

Structure of Chloroplast

• Outer Membrane – Permeable to small molecules.
• Inner Membrane – Selectively permeable, regulating material exchange.
• Thylakoids – Flattened sacs that house chlorophyll; location of the light reactions.
• Grana – Thylakoid stacks where photophosphorylation takes place.
• Stroma – A fluid-filled area in which the Calvin cycle (dark reaction) occurs.

Photosynthetic Pigments

Plants employ various pigments to trap light energy:

Chlorophyll a – The primary pigment responsible for trapping light.

Chlorophyll b – Assists in transferring energy to chlorophyll a.

Carotenoids (Xanthophylls & Carotenes) – Accessory pigments that capture light of varying wavelengths and guard against damage to chlorophyll.

Also Read:

Phases of Photosynthesis

Photosynthesis occurs in two main stages:

1. Light Reactions (Photochemical Phase)

• Location: Chloroplast thylakoid membranes.
• Process: Light is trapped, and its energy is utilized for generating ATP (energy currency) and NADPH (reducing power).
• Water molecules are cleaved (Photolysis), with oxygen gas as a by-product.

2. Dark Reactions (Biosynthetic Phase or Calvin Cycle)

• Location: Chloroplast stroma.
• Process: ATP and NADPH from light reactions are utilized to fix CO₂ into glucose through the Calvin cycle.
• Does not need light directly, but relies on byproducts of the light reaction.

Light Reaction (Hill Reaction)

The light-dependent reactions involve two photosystems:

Photosystem I (PSI)

• Absorbs 700 nm wavelength light.
• Synthesizes NADPH for dark reaction.

Photosystem II (PSII)

• Absorbs 680 nm wavelength light.
• Photolysis of water molecules, oxygen release.

Types of Photophosphorylation

• Cyclic Photophosphorylation – PSI is used alone, and only ATP is synthesized.
• Non-Cyclic Photophosphorylation – Both PSI and PSII are used and ATP, NADPH, and O₂ are synthesized.

Dark Reaction (Calvin Cycle or C₃ Cycle)

The Calvin cycle takes place in the stroma and involves three steps:

• Carbon Fixation – CO₂ is fixed by RuBP (Ribulose-1,5-bisphosphate) and is reduced to 3-PGA.
• Reduction – ATP and NADPH are utilized to produce G3P (glyceraldehyde-3-phosphate), a glucose precursor.
• Regeneration – RuBP is regenerated to allow the cycle to repeat.

C₄ Pathway (Hatch and Slack Pathway)

• Present in tropical crops (e.g., sugarcane, maize).
• Substitutes PEP carboxylase for RuBisCO in first CO₂ fixation, minimizing photorespiration.
• Easier under hot and dry conditions.

CAM Pathway (Crassulacean Acid Metabolism)

• Camivorous plant adaptation in deserts (e.g., pineapple, cactus).
• Stomata are opened during the night for CO₂ fixation without transpiration.
• CO₂ is saved in the form of organic acids and utilized when in sunlight.

Photorespiration

• Occurs when RuBisCO binds with O₂ instead of CO₂.

• Leads to the loss of fixed carbon and energy.

• More common in C₃ plants under high temperatures and low CO₂ conditions.

Factors Affecting Photosynthesis

• Light Intensity – Increases the rate up to a saturation point.

• Carbon Dioxide Concentration – Higher CO₂ enhances photosynthesis.

• Temperature – Optimal range depends on the plant type.

• Water Availability – Essential for photolysis and stomatal function.

Differences Between C₃, C₄, and CAM Plants

Subject-Wise NCERT Solutions

• NCERT Solutions for Class 11 Mathematics
• NCERT Solutions for Class 11 Chemistry
• NCERT Solutions for Class 11 Physics

• NCERT Solutions for Class 11 Biology

Important Topics of Class 11 Biology Chapter 11: Photosynthesis in Higher Plants

The essential points from this chapter are listed below for quick and easy revision:

• Overview of Photosynthesis

• Light-Dependent Reactions

• Light-Independent Reactions (Calvin Cycle)

• Factors Affecting Photosynthesis

• Photophosphorylation

Most Important Questions of Class 11 Biology Chapter 11

Provided below are some key questions from Photosynthesis in Higher Plants to help you prepare better and focus on important concepts.

Question 1: The reaction centre in PS II has an absorption maxima at

A. 680 nm

B. 700 nm

C. 660 nm

D. 780 nm

Answer:

The reaction center in Photosystem II (PS II) has an absorption maximum at approximately 680 nm. This means that the reaction center is most efficient in capturing light energy at this specific wavelength.

Hence, Option 1 is the correct answer, 680 nm

Question 2: How are chloroplasts affected when cells are irradiated with high-intensity blue light?

Answer:

When photosynthesizing cells are irradiated with high-intensity blue light, the chloroplasts within the cells tend to move toward the side walls. This phenomenon is known as chloroplast avoidance or chloroplast positioning response.

Question 3: Which environmental factor can limit the rate of photosynthesis?

Answer:

The rate of photosynthesis increases with increasing light intensity. More light can be captured by the chloroplasts to produce energy to power the photosynthetic reaction if the light's intensity is increased.

Question 4: What happens when a chlorophyll molecule absorbs a photon with the same energy?

Answer:

When a photon with an energy level matching the energy gap between the ground state and excited state of the chlorophyll molecule is absorbed, the chlorophyll molecule gains energy and transitions to an excited state. This energy can be used to initiate various biochemical reactions involved in photosynthesis, such as the transfer of electrons and the synthesis of energy-rich molecules like ATP and NADPH.

Question 5: Why is the CO₂ compensation point higher in C3 plants compared to C4 plants?

Answer:

The CO₂ compensation point for C₃ plants is higher (greater) than that of C₄ plants because C₃ plants undergo photorespiration. Photorespiration is a process that occurs in C₃ plants when the enzyme Rubisco, which is involved in carbon fixation, binds to oxygen instead of carbon dioxide. This results in the release of carbon dioxide and the consumption of energy and fixed carbon.

Subject Wise NCERT Exemplar Solutions

• NCERT Exemplar Class 11 Solutions
• NCERT Exemplar Class 11 Maths
• NCERT Exemplar Class 11 Physics
• NCERT Exemplar Class 11 Chemistry
• NCERT Exemplar Class 11 Biology

Approach to solve questions of Class 11 Biology Chapter 11 Photosynthesis in Higher Plants

To deal with questions from this chapter effectively, students need to get a clear understanding of the key processes involved in photosynthesis. They should concentrate on topics like the structure of chloroplasts, types of pigments, and the major events in light and dark reactions. Going through the NCERT textbook, pathways such as the Calvin cycle, C₄ pathway, and CAM pathway should be easily understood, and by making flow charts it's easy to do revision as well. Concepts like photolysis of water, photorespiration, and environmental factors affecting photosynthesis must be studied in detail. Diagrams should be practiced regularly, and solving different questions can allow students to grasp the concepts.

Chapter-Wise NCERT Class 11 Notes Biology

Given below are the chapter-wise NCERT Class 11 Biology notes for quick and easy revision.