What is Respiration in Plants Class 11: Definition & Explanation

Definition and Importance of Respiration in Plants

Respiration in plants is the biochemical process in which glucose molecules are broken down to release energy. This energy is stored in the form of adenosine triphosphate (ATP), which fuels various cellular activities essential for plant growth, repair, and maintenance.

The general definition can be stated as:

> Respiration in plants is the process of oxidizing food substances (mainly glucose) to release energy.

Unlike photosynthesis, which stores energy, respiration releases energy. It occurs continuously in all living cells of the plant, day and night, making it vital for survival.

Why is respiration important?

• Provides energy for active transport, cell division, and synthesis of new molecules.
• Helps in seed germination and root growth.
• Supports maintenance of cell structure and function.

Understanding this process is crucial for Class 11 students as per the NCERT syllabus, as it forms the basis for many physiological functions in plants.

Types of Respiration in Plants: Aerobic and Anaerobic

Plants perform two main types of respiration:

1. Aerobic Respiration

• Requires oxygen.
• Glucose is completely broken down into carbon dioxide and water.
• Releases a large amount of energy.

The chemical equation for aerobic respiration is:

$$\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{Energy (ATP)}$$

2. Anaerobic Respiration

• Occurs in absence of oxygen.
• Glucose is partially broken down.
• Produces less energy and forms by-products like ethanol or lactic acid.

For example, in some plants under waterlogged conditions, anaerobic respiration produces ethanol:

$$\text{C}_6\text{H}_{12}\text{O}_6 \rightarrow 2\text{C}_2\text{H}_5\text{OH} + 2\text{CO}_2 + \text{Energy}$$

Class 11 NCERT students should focus on these differences for exams.

Stages of Aerobic Respiration in Plants

Aerobic respiration involves multiple stages that gradually release energy from glucose:

1. Glycolysis

• Occurs in the cytoplasm.
• Glucose (6-carbon) breaks into two molecules of pyruvate (3-carbon).
• Produces 2 ATP molecules and 2 NADH.

2. Krebs Cycle (Citric Acid Cycle)

• Takes place in mitochondria.
• Pyruvate is further broken down.
• Produces CO2, NADH, FADH2, and 2 ATP molecules.

3. Electron Transport Chain (ETC)

• Located in mitochondrial inner membrane.
• NADH and FADH2 transfer electrons.
• Oxygen acts as the final electron acceptor, forming water.
• Produces about 32 ATP molecules.

Total ATP Yield: Approximately 36 ATP molecules per glucose.

This stepwise breakdown ensures maximum energy extraction. Class 11 students must understand these stages for conceptual clarity.

Comparison Between Photosynthesis and Respiration in Plants

Photosynthesis and respiration are two fundamental processes in plants but serve opposite functions.

Understanding this contrast helps Class 11 students grasp plant metabolism holistically.

Factors Affecting Respiration in Plants

Several factors influence the rate of respiration in plants:

• Temperature: Respiration rate increases with temperature up to an optimum point, then declines.
• Oxygen Availability: Adequate oxygen is essential for aerobic respiration.
• Glucose Availability: More glucose means more substrate for respiration.
• Water Availability: Water stress can reduce respiration.
• Plant Age and Type: Young and actively growing tissues respire more.

Example:

If temperature rises from 20 °C to 30 °C, respiration rate may double due to enzyme activity increase. Beyond 40 °C, enzymes denature, reducing respiration.

Class 11 students should remember these factors for practical understanding and exams.

Worked Example: Calculating Energy Yield from Glucose Respiration

Let's calculate the total ATP produced from one molecule of glucose during aerobic respiration.

• Glycolysis produces 2 ATP.
• Krebs cycle produces 2 ATP.
• Electron Transport Chain produces about 32 ATP.

Total ATP = 2 + 2 + 32 = 36 ATP molecules

This energy is used for various cellular processes like nutrient transport and synthesis of biomolecules.

Formula Summary:

$$\text{Glucose} + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + 36\text{ATP}$$

This example helps Class 11 students quantify energy release in respiration.