Chapter 17

Chapter 17

Chapter Overview

Biology is a vast subject that deals with the study of living organisms and their interactions with the environment. The chapter we are about to explore is a crucial part of understanding the fundamental principles of biology. This chapter will delve into the world of Cellular Respiration, a process that is essential for the survival of living organisms. Cellular respiration is the process by which cells generate energy from the food they consume. It involves the breakdown of glucose and other organic molecules to produce ATP, which is the primary energy currency of the cell. This process is crucial for the proper functioning of cells and is essential for the survival of living organisms.

Learning Objectives

• Understand the concept of cellular respiration
• Learn about the different stages of cellular respiration
• Understand the importance of cellular respiration in living organisms
• Learn about the energy yield from cellular respiration

Important Concepts

Aerobic Respiration

Aerobic respiration is the process by which cells generate energy from the breakdown of glucose in the presence of oxygen. It involves the breakdown of glucose to produce ATP, carbon dioxide, and water. The overall equation for aerobic respiration is:

C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP

The process of aerobic respiration can be divided into three stages:

1. Glycolysis: This is the first stage of aerobic respiration, where glucose is broken down into pyruvate. Glycolysis occurs in the cytosol of the cell and is the only stage of cellular respiration that does not require oxygen. The equation for glycolysis is:

C6H12O6 + 2ADP + 2Pi → 2C3H6O3 + 2ATP + 2NADH + 2H+

Glycolysis is an important stage of cellular respiration as it produces ATP, NADH, and pyruvate, which are all important molecules for the subsequent stages of cellular respiration.

2. Citric Acid Cycle: This stage involves the breakdown of pyruvate to produce ATP, NADH, and FADH2. The citric acid cycle occurs in the mitochondria and is also known as the Krebs cycle. The equation for the citric acid cycle is:

C3H6O3 + 3O2 → 2CO2 + 2H2O + 2ATP + 2NADH + 2FADH2

The citric acid cycle is an important stage of cellular respiration as it produces ATP, NADH, and FADH2, which are all important molecules for the electron transport chain.

3. Electron Transport Chain: This is the final stage of aerobic respiration, where the electrons from NADH and FADH2 are passed through a series of electron carriers to produce a proton gradient, which is used to produce ATP. The electron transport chain occurs in the mitochondria and is also known as oxidative phosphorylation. The equation for the electron transport chain is:

2NADH + 2FADH2 → 2ATP

The electron transport chain is an important stage of cellular respiration as it produces the majority of the ATP that is produced during cellular respiration.

Anaerobic Respiration

Anaerobic respiration is the process by which cells generate energy from the breakdown of glucose in the absence of oxygen. It involves the breakdown of glucose to produce ATP, lactic acid, and ethanol. The overall equation for anaerobic respiration is:

C6H12O6 → 2C2H5OH + 2CO2 + ATP

Anaerobic respiration occurs in muscle cells during intense exercise and in yeast during fermentation.

Fermentation

Fermentation is a type of anaerobic respiration that involves the breakdown of glucose to produce ATP and lactic acid or ethanol. It is an important process that occurs in muscle cells during intense exercise and in yeast during the production of beer and bread.

Key Definitions

• Cellular Respiration: The process by which cells generate energy from the breakdown of glucose.
• Aerobic Respiration: The process by which cells generate energy from the breakdown of glucose in the presence of oxygen.
• Anaerobic Respiration: The process by which cells generate energy from the breakdown of glucose in the absence of oxygen.
• Glycolysis: The first stage of aerobic respiration, where glucose is broken down into pyruvate.
• Citric Acid Cycle: The second stage of aerobic respiration, where pyruvate is broken down to produce ATP, NADH, and FADH2.
• Electron Transport Chain: The final stage of aerobic respiration, where electrons from NADH and FADH2 are passed through a series of electron carriers to produce a proton gradient.

Important Terms

Term	Meaning
ATP	Adenosine triphosphate, the primary energy currency of the cell.
Glucose	A simple sugar that serves as the primary source of energy for cells.
Oxygen	A molecule that is essential for aerobic respiration.
Pyruvate	A molecule that is produced during glycolysis and serves as the starting material for the citric acid cycle.
NADH	A molecule that is produced during glycolysis and the citric acid cycle and serves as an electron carrier.
FADH2	A molecule that is produced during the citric acid cycle and serves as an electron carrier.

Important Formulas

• Glycolysis: C6H12O6 + 2ADP + 2Pi → 2C3H6O3 + 2ATP + 2NADH + 2H+
• Citric Acid Cycle: C3H6O3 + 3O2 → 2CO2 + 2H2O + 2ATP + 2NADH + 2FADH2
• Electron Transport Chain: 2NADH + 2FADH2 → 2ATP

Diagrams (Description Only)

The diagram of the citric acid cycle shows the different stages of the cycle, including the breakdown of pyruvate to produce acetyl-CoA, the formation of citrate, and the regeneration of oxaloacetate.

Deep-Dive Case Studies and Real-Life Applications

• Exercise: Cellular respiration is essential for muscle cells during intense exercise. When muscles are exercised, they require a lot of energy to contract and relax. This energy is produced through the breakdown of glucose and other organic molecules during cellular respiration.
• Food Production: Cellular respiration is used in the production of ethanol and lactic acid. Yeast is used to ferment glucose to produce ethanol, which is then used to produce beer and bread.
• Medical Applications: Understanding cellular respiration is essential for the treatment of diseases such as diabetes and heart disease. In diabetes, the body is unable to produce enough insulin, which leads to high blood sugar levels. In heart disease, the heart is unable to pump enough blood to the body, leading to high blood pressure.

Step-by-Step Problem Solving Strategies & Detailed Proofs

• Problem: What is the energy yield from the breakdown of glucose during cellular respiration?
• Solution: The energy yield from the breakdown of glucose during cellular respiration is 36-38 ATP molecules.
• Proof: The energy yield from the breakdown of glucose during cellular respiration can be calculated by summing the ATP molecules produced during each stage of cellular respiration. During glycolysis, 2 ATP molecules are produced. During the citric acid cycle, 2 ATP molecules are produced. During the electron transport chain, 32-34 ATP molecules are produced. Therefore, the total energy yield from the breakdown of glucose during cellular respiration is 36-38 ATP molecules.

Higher-Order Thinking Skills (HOTS) Questions

• Question: Compare and contrast aerobic and anaerobic respiration.
• Answer: Aerobic respiration occurs in the presence of oxygen, while anaerobic respiration occurs in the absence of oxygen. Aerobic respiration produces more ATP molecules than anaerobic respiration. Anaerobic respiration is used by muscle cells during intense exercise, while aerobic respiration is used by muscle cells during low-intensity exercise.
• Question: What is the importance of glycolysis in cellular respiration?
• Answer: Glycolysis is the first stage of cellular respiration and produces 2 ATP molecules. It also produces pyruvate, which is used as the starting material for the citric acid cycle.

Previous Year Questions (PYQs) with solutions

• Question: What is the energy yield from the breakdown of glucose during cellular respiration? (CBSE 2019)
• Answer: The energy yield from the breakdown of glucose during cellular respiration is 36-38 ATP molecules.
• Solution: The energy yield from the breakdown of glucose during cellular respiration can be calculated by summing the ATP molecules produced during each stage of cellular respiration. During glycolysis, 2 ATP molecules are produced. During the citric acid cycle, 2 ATP molecules are produced. During the electron transport chain, 32-34 ATP molecules are produced. Therefore, the total energy yield from the breakdown of glucose during cellular respiration is 36-38 ATP molecules.

NCERT Textbook Questions & Detailed Answers

Question 1

What is the importance of glycolysis in cellular respiration?

Answer

Glycolysis is the first stage of cellular respiration and produces 2 ATP molecules. It also produces pyruvate, which is used as the starting material for the citric acid cycle.

Question 2

Compare and contrast aerobic and anaerobic respiration.

Answer

Aerobic respiration occurs in the presence of oxygen, while anaerobic respiration occurs in the absence of oxygen. Aerobic respiration produces more ATP molecules than anaerobic respiration. Anaerobic respiration is used by muscle cells during intense exercise, while aerobic respiration is used by muscle cells during low-intensity exercise.

Question 3

What is the energy yield from the breakdown of glucose during cellular respiration?

Answer

The energy yield from the breakdown of glucose during cellular respiration is 36-38 ATP molecules.

Question 4

What is the role of the electron transport chain in cellular respiration?

Answer

The electron transport chain is the final stage of cellular respiration and produces the majority of the ATP molecules produced during cellular respiration. It occurs in the mitochondria and involves the passing of electrons through a series of electron carriers to produce a proton gradient, which is used to produce ATP.

Question 5

What is the importance of the citric acid cycle in cellular respiration?

Answer

The citric acid cycle is the second stage of cellular respiration and produces 2 ATP molecules. It also produces NADH and FADH2, which are used as electron carriers in the electron transport chain.