NCERT Class 11 Biology Chapter 14 Notes Respiration In Plants - Download PDF Notes

NCERT Class 11 Biology Chapter 12 Respiration in Plants: Download PDF

This chapter explains how plants release energy from the food they make through different types of respiration. It includes processes like glycolysis, fermentation, and the role of mitochondria. Studying these topics becomes easier when everything is available in one place. Students can now download the PDF of NCERT Class 11 Biology Chapter 12 Notes and revise anytime. For quick and smart preparation, the NCERT Class 11 Biology Notes are best.

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• NCERT Solutions for Class 11 Biology Chapter 12 Respiration in Plants

Class 11 Biology Chapter 12 Respiration in Plants Notes

Respiration in Plants explains how plants break down food to release energy for their activities and covers topics like glycolysis, the Krebs cycle, and electron transport in a simple way. Students will learn how plants take in oxygen and produce energy at the cellular level. The Respiration in Plants Class 11 Notes also include diagrams and key terms, which are prepared according to the latest NCERT curriculum, making it easier to understand.

Respiration in Plants

Respiration in Plants is a metabolic process where organic compounds, mainly glucose (C₆H₁₂O₆), are decomposed to release energy in the form of Adenosine Triphosphate (ATP). This energy is used in different physiological processes like cell division, growth, repair, transportation of nutrients, and biosynthesis of vital compounds. The overall chemical equation for respiration is:

$C_{6}H_{12}O_{6} + 6O_{2} \rightarrow 6CO_{2} + 6H_{2}O + \text{Energy (ATP)}$

In contrast to animals, plants lack specialised respiratory organs. They depend on simple diffusion for gas exchange via stomata (in leaves), lenticels (in stems), and root hairs (in roots). Respiration in all living cells takes place constantly to supply their energy needs. The process depends on oxygen availability, temperature, and the respiratory substrate type.

Respiration in plants may be aerobic (oxygen-involving) or anaerobic (oxygen-absent). Aerobic respiration yields a large quantity of ATP, but anaerobic respiration yields less energy and usually results in ethanol or lactic acid production. Respiration is important as it directly affects the survival, productivity, and general metabolic equilibrium of plants.

Types of Respiration in Plants

Plants respire in different ways depending on the availability of oxygen. The two major types of respiration are aerobic respiration and anaerobic respiration, with fermentation being a specific type of anaerobic respiration.

Aerobic respiration

Aerobic respiration is the process by which glucose is fully oxidised in the presence of oxygen (O₂) and yields carbon dioxide (CO₂), water (H₂O), and a lot of ATP (energy).

Location

• The process occurs mainly in the plant cells' mitochondria.

• Glycolysis, the initial step, happens in the cytoplasm, whereas the subsequent stages (the Krebs cycle and the Electron Transport Chain) happen in the mitochondria.

Process

• In Glycolysis (in the cytoplasm), glucose is converted into two molecules of pyruvate, generating a little ATP and NADH.

• In the Krebs Cycle (in Mitochondria), Pyruvate is further converted into CO₂, yielding NADH and FADH₂ molecules.

• In the Electron Transport Chain (in Mitochondria), the electrons from NADH and FADH₂ are passed through protein complexes, generating ATP. Oxygen serves as the terminal electron acceptor, forming water (H₂O).

End Products

• Carbon dioxide (CO₂) is emitted into the air.

• Water (H₂O) is used or emitted as a gas.

• ATP (Adenosine Triphosphate) is used as the cell's energy currency.

Energy Yield

Aerobic respiration is very efficient, yielding 36-38 molecules of ATP per molecule of glucose, which is vital for different cellular processes in plants, including nutrient transportation, plant growth, and development.

Anaerobic Respiration

Anaerobic respiration is carried out without oxygen. Glucose is partially broken down instead of completely oxidised, forming less energy and byproducts such as ethanol or lactic acid.

$C_{6}H_{12}O_{6} \rightarrow 2C_{2}H_{5}OH + 2CO_{2} + \text{Energy (ATP)}$

Location

Anaerobic respiration is located in the cytoplasm because mitochondria need oxygen to work.

Process

• In Glycolysis, Glucose is broken down to form pyruvate in the cytoplasm.

• In the Fermentation Pathway, pyruvate is reduced to form ethanol and CO₂ (in plants) or lactic acid (in certain microorganisms such as bacteria) rather than going into the Krebs cycle.

End Products

• Ethanol (C₂H₅OH) or Lactic Acid (C₃H₆O₃)

• Carbon dioxide (CO₂) is released during the process of fermentation.

• Only 2 ATP molecules for every glucose molecule.

Energy Yield

Anaerobic respiration is wasteful in comparison to aerobic respiration, as it yields much less ATP (only 2 molecules per molecule of glucose).

Where Does It Take Place in Plants?

• Where plant roots are in a low oxygen supply in waterlogged conditions.

• In some plant tissues, like seeds during germination, there's a shortage of oxygen.

• In some microorganisms that are part of the plant fermentation processes.

Example

• Root cells under flooded conditions resort to anaerobic respiration owing to oxygen shortage.

• Yeast cells employ anaerobic respiration to produce alcohol.

Fermentation

Fermentation is a special type of anaerobic respiration where glucose is broken down into simpler compounds like ethanol or lactic acid, producing a small amount of ATP.

Types of Fermentation

The types of fermentation include:

Alcoholic Fermentation (in Yeast & Some Plants)

• Pyruvate is converted into ethanol (alcohol) and CO₂.

• Used in the brewing and baking industries.

• $C_{6}H_{12}O_{6} \rightarrow 2C_{2}H_{5}OH + 2CO_{2} + \text{Energy (ATP)}$

Lactic Acid Fermentation (in Some Microorganisms)

• Pyruvate is converted into lactic acid instead of ethanol.

• Occurs in certain bacteria and muscle cells (during heavy exercise in animals).

• $C_{6}H_{12}O_{6} \rightarrow 2C_{3}H_{6}O_{3} + \text{Energy (ATP)}$

End Products

• Alcoholic Fermentation → Ethanol (C₂H₅OH), CO₂, ATP

• Lactic Acid Fermentation → Lactic acid (C₃H₆O₃), ATP

Energy Yield

• Produces only 2 ATP molecules per glucose molecule, similar to anaerobic respiration.

Importance of Fermentation

• Used in the production of bread, beer, and wine.

• Helps in preserving foods like yoghurt and cheese.

• Important in some plants and microorganisms for survival in low-oxygen environments.

Comparison of Aerobic, Anaerobic Respiration, and Fermentation

The difference between Aerobic, Anaerobic Respiration, and Fermentation is given below:

Respiratory Substrates

• The main substrate for respiration is glucose (C₆H₁₂O₆).

• Other molecules, like fats and proteins, can also be used as respiratory substrates.

• Respiratory Quotient (RQ) is the ratio of CO₂ released to O₂ consumed:

• For carbohydrates (Glucose): RQ = 1

• RQ= CO₂ released/O₂ consumed

• For fats and proteins: RQ < 1

Steps of Respiration in Plants

Plant respiration is a process of successive biochemical reactions that gradually degrade glucose to produce ATP, which is used in cellular functions. It has three primary phases: Glycolysis, the Krebs Cycle (TCA Cycle), and the Electron Transport Chain (ETC) & Oxidative Phosphorylation.

Glycolysis (Cytoplasmic Pathway)

Glycolysis is the initial process of respiration and is carried out in the cytoplasm of the cell. Glycolysis does not involve oxygen and occurs in aerobic as well as anaerobic respiration.

Process

Glucose Activation: A glucose molecule of 6-carbon (C₆H₁₂O₆) is phosphorylated with the help of ATP and converted into fructose-1,6-bisphosphate.

Cleavage of Glucose: The molecule of 6-carbon is divided into two molecules of 3-carbon of glyceraldehyde-3-phosphate..

Energy Harvesting Phase: The G₃P molecules go through a series of phosphorylation and oxidation reactions to yield:

• 2 molecules of Pyruvate (C₃H₄O₃)

• 2 molecules of ATP (Net gain)

• 2 molecules of NADH (utilised further in the ETC)

End Products of Glycolysis

• Pyruvate (moved to the next phase: the Krebs cycle if oxygen is available, or fermentation if oxygen is not available).

• ATP (utilised directly for cellular functions).

• NADH (utilised in the electron transport chain for the production of ATP).

Krebs Cycle (Citric Acid Cycle / TCA Cycle)

The Krebs cycle, otherwise known as the Tricarboxylic Acid (TCA) Cycle or the Citric Acid Cycle, is the second process of aerobic respiration. It takes place within the mitochondrial matrix and is where pyruvate is fully oxidised.

Process

Conversion of Pyruvate to Acetyl-CoA

Pyruvate from glycolysis is converted to Acetyl-CoA by the removal of one CO₂ molecule and the generation of one NADH.

Entry into the Krebs Cycle

Acetyl-CoA (a 2-carbon molecule) and oxaloacetate (a 4-carbon molecule) join together to create citrate (a 6-carbon molecule).

Series of Oxidation Reactions

Citrate is transformed through a series of reactions, losing two CO₂ molecules and generating NADH, FADH₂, and ATP.

Regeneration of Oxaloacetate

• Oxaloacetate is regenerated at the end of the cycle so that the cycle can repeat.

• End Products per Glucose Molecule (Two Pyruvates)

• 6 NADH (utilised in the electron transport chain).

• 2 FADH₂ (utilised in the electron transport chain).

• 2 ATP (available for use in cellular processes).

• 4 CO₂ (excreted as a waste product).

Electron Transport Chain (ETC) & Oxidative Phosphorylation

The Electron Transport Chain (ETC) is the last stage of aerobic respiration, which takes place in the inner mitochondrial membrane. This process produces the maximum number of ATP via a process called oxidative phosphorylation.

Electron Transfer

NADH and FADH₂ (formed in previous stages) transfer electrons (e⁻) to the electron transport chain, a chain of protein complexes in the inner mitochondrial membrane.

Proton Gradient Formation

As electrons travel through the complexes, protons (H⁺ ions) are pumped through the inner mitochondrial membrane into the intermembrane space, establishing a proton gradient.

ATP Synthesis (Oxidative Phosphorylation)

The protons flow back to the mitochondrial matrix via an enzyme known as ATP synthase, which powers the reaction

$ADP + P_{i} \rightarrow ATP$

Oxygen as the Final Electron Acceptor

Oxygen (O₂) accepts electrons at the end of the chain and combines with protons to make water (H₂O). This is the reason why oxygen is vital for aerobic respiration.

End Products

• 34 ATP molecules (principal ATP production location).

• Water (H₂O) (created when oxygen accepts electrons).

Factors Affecting Respiration in Plants

• Higher temperatures increase enzyme activity up to an optimum level.

• More oxygen increases aerobic respiration; limited oxygen promotes anaerobic respiration.

• Dry conditions reduce respiration as enzymes need water to function.

• Carbohydrates are preferred; fats and proteins require more oxygen for breakdown.

Also Read

• NCERT Notes for Class 11 Physics

• NCERT Notes for Class 11 Chemistry

• NCERT Notes for Class 11 Mathematics

Chapter 12 Biology: Previous Year Question and Answers

Some of the questions that have come in past years from the chapter are given below. In exams, to solve these questions effectively, students are advised to read the NCERT Class 11 Biology Chapter 12 Notes Respiration in Plants.

Question 1. Choose the correct statement:

Option 1. Pyruvate is formed in the mitochondrial matrix.

Option 2. During the conversion of succinyl-CoA to succinic acid, a molecule of ATP is synthesised.

Option 3. Oxygen is vital in respiration for the removal of hydrogen.

Option 4. There is a complete breakdown of glucose in fermentation.

Answer :

Oxygen drives the whole process of aerobic respiration and is responsible for driving out hydrogen, which is an important process.

Hence, the correct answer is option (3). Oxygen is vital in respiration for the removal of hydrogen.

Question 2. The Electron Transport System (ETS) is located in the mitochondria

Option 1. outer membrane

Option 2. intermembrane space

Option 3. inner membrane

Option 4. matrix

Answer :

ETS is the electron transport system, which is a carrier molecule that can act as an electron acceptor as well as a donor, and it is present in the inner membrane of mitochondria. The electron transport chain is present in multiple copies in the inner mitochondrial membrane of eukaryotes and the plasma membrane of prokaryotes. It results in oxidative phosphorylation. The ETC is a series of proteins that receive the high-energy electrons from NADH and FADH₂ and move them to the final acceptor, molecular oxygen.

Hence, the correct answer is option (3) Inner membrane.

Question 3. Pyruvic acid, the key product of glycolysis, can have many metabolic fates. Under aerobic conditions, it forms

Option 1. lactic acid

Option 2. CO₂ + H₂O

Option 3. acetyl-CoA + CO₂

Option 4. ethanol + CO₂

Answer :

Explanation: Acetyl CoA, CO₂, and NADH are the products obtained when Pyruvic acid undergoes a dehydrogenation reaction. An organic molecule with a backbone of three carbons, pyruvate is essential to an organism's processes of synthesis and degradation. It is used in bodybuilding supplements, the food business, and cancer screening, and when it is present in abnormal amounts, it is linked to some illnesses.

Hence, the correct answer is option 3) Acetyl-CoA + CO₂

Also Read:

• NCERT Solutions
• NCERT Solutions for Class 11
• NCERT Solutions for Class 11 Biology

How to Use Respiration in Plants Class 11 Notes Effectively?

Respiration is the process through which plants release the energy stored in glucose to carry out life activities. Understanding this chapter requires regular practice and a step-by-step approach.

• Understand the concepts in stages like glycolysis, the Krebs cycle, and the electron transport chain, for easy learning.
• Use Class 11 Biology Chapter 12 Respiration in Plants Notes to revise the differences between aerobic and anaerobic respiration.
• Draw and label diagrams of mitochondria and pathways to make the process clearer.
• Practice previous year questions and MCQs based on respiration to test the understanding.
• Revise Class 11 Biology Chapter 12 Respiration in Plants Notes before exams for quick revision of important reactions and enzymes.

Chapter-Wise NCERT Class 11 Notes Biology

Here are the links to the notes for each chapter to help with your Biology revision.