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Respiration In Plants Class 11 Notes

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In plants, respiration is the mechanism through which energy for plant development is produced by combining oxygen and the sugars created during photosynthesis. Respiration contrasts photosynthesis in several ways. For survival in the natural world, plants make their own food. They create oxygen (O2) and sugars (carbohydrates) from carbon dioxide (CO2) in the atmosphere, which can then be used as an energy source. Respiration happens in the leaves, stems, and roots of the plant, whereas photosynthesis only occurs in the leaves and stems.

Table of Content

  • Respiration in Plants
  • Difference between Photosynthesis and Respiration
  • Do Plants Breathe?
  • Types of Respiration in Plants
  • Glycolysis
  • Fermentation
  • Oxidative Decarboxylation
  • Krebs Cycle
  • Electron Transport System
  • Respiratory Balance Sheet
  • Amphibolic Pathway
  • Respiratory Quotient
  • FAQs on Respiration in Plants

Respiration in Plants

To carry out the oxidation of glucose into the byproducts of carbon dioxide, water, and energy, plants respire continuously throughout the day and night. Using sunlight and chlorophyll, a plant converts carbon dioxide and water into glucose and oxygen during photosynthesis.

Energy: The glucose molecules act as the fuel for the cells; their chemical energy can be obtained through procedures like cellular respiration and fermentation, which result in the production of adenosine triphosphate (ATP), a small energy-carrying molecule, to meet the immediate energy requirements of the cell.

Carbon: The incorporation of inorganic carbon from carbon dioxide into organic molecules is known as carbon fixation; the carbon in organic molecules is also referred to as fixed carbon. During photosynthesis, carbon is fixed and incorporated into sugars. This carbon can then be used to create additional organic molecules that are required by cells.

Difference between Photosynthesis and Respiration

Difference between Respiration and Photosynthesis are as follows:



All green plants that contain chlorophyll undergo this process All living things, including plants, animals, birds, and others, go through this process.
Food synthesis occurs Food is oxidized
Energy stored Energy released
Undergoes in the anabolic process Undergoes in the catabolic process
Need carbon dioxide, water, and light energy Need glucose and oxygen
Produces food and captures the energy Takes in oxygen and liberates carbon dioxide
It takes place in chloroplasts It takes place in the cytoplasm and mitochondria

Chemical reaction: 

6CO2 + 6H2O → C6H12O6 + 6O2

Chemical reaction: 

C6H12O6 + 6O2 → 6CO2 + 6H2O

Do Plants Breathe?

Plants also breathe like other organisms but in different ways. Plants have different organs to breathe such as leaves, stems, and roots each exchanging gases separately. Stomata, which are microscopic pores for gas exchange, are present in leaves. Cells in the leaves use up the oxygen taken in by stomata to break down glucose into water and carbon dioxide. 

Process of Respiratrion in Plants

Significantly less gas exchange occurs during respiration in various plant sections. As a result, each component nourishes and meets its own energy needs. As a result, plants’ leaves, stems, and roots each exchange gases separately. Stomata, which are microscopic pores for gas exchange, are present in leaves. Cells in the leaves use up the oxygen taken in by stomata to break down glucose into water and carbon dioxide.

Respiration in Roots

The roots of plants, which are located underground, take in air from the spaces and air gaps between the soil particles. As a result, oxygen taken up by the roots is used to release energy that will later be used to move salts and minerals from the soil.

Respiration in Stem

To breathe, the air in a stem diffuses into the stomata and travels through various regions of the cell. The released carbon dioxide is distributed through the stomata at this time. In higher or woodier plants, lenticels are known to perform the gaseous exchange.

Respiration in Leaves



Stomata, or small pores, are part of leaves. The gaseous exchange takes place by stomata-mediated diffusion. Every stoma is regulated by guard cells. When the stoma between the inferior leaves and the atmosphere is closed and opened, gases are exchanged.

Stomata: It’s a plant’s specialized part present in the epidermis layer of the leaves and stems. Bean-shaped guard cells form stomatal pores and promote stomatal opening and closing during the gaseous exchange. Carbon dioxide and oxygen are the gases exchanged during the daytime.

Types of Respiration in Plants

In plants respiration takes place in two ways, aerobic and anaerobic respiration. Let us study them in detail:

Aerobic Respiration

All eukaryotic organisms’ mitochondria do aerobic respiration. In the presence of oxygen, food molecules totally oxidize into carbon dioxide, water, and energy. All higher species exhibit this kind of respiration, which requires ambient oxygen. It includes the following 4-stages; 

Glycolysis ⇢ Oxidative decarboxylation ⇢ Kreb’s cycle ⇢ Electron Transport System

Phases of Respiration


Anaerobic Respiration

The cytoplasm of prokaryotic organisms like yeast and bacteria is where this kind of respiration takes place. In this instance, less energy is released as a result of the food’s incomplete oxidation in the absence of oxygen. In anaerobic respiration, ethanol, and carbon dioxide are generated. It includes Glycolysis  ⇢ Fermentation. 

Also Read: Respiration


Glycolysis Pathway


The first stage of cellular respiration, which takes place in all organisms, is called glycolysis. The process by which glucose is broken down to provide energy is known as glycolysis. It generates two pyruvate molecules, ATP, NADH, and water. There is no need for oxygen throughout the process, which occurs in the cytoplasm of a cell. Both aerobic and anaerobic creatures experience it. The Krebs cycle comes after glycolysis during aerobic respiration. Small amounts of ATP are produced by the cells in the absence of oxygen as fermentation follows glycolysis.


In anaerobes, incomplete oxidation of glucose takes place in which the pyruvic acid is either converted into lactic acid or ethanol. However, fermentation does not yield any energy. So, the only energy generated is during the process of glycolysis. 

In human muscle cells during rigorous exercises due to lack of oxygen lactic acid is produced and in Yeast cells, ethanol and carbon-dioxide is generated. 



Oxidative Decarboxylation

In the case of aerobes, pyruvic acid produced during glycolysis enters the mitochondria where it is converted into Acetyl CoA in the presence of pyruvate dehydrogenase. This Acetyl CoA then further enters the Krebs cycle. 

Oxidative decarboxylation

Krebs Cycle

It is also called the tricarboxylic acid cycle or citric acid cycle. It begins with the Acetyl CoA condensate with oxaloacetic acid and water to form citric acid and ends with malic acid getting oxidized to regenerate the oxaloacetic acid to undergo the next cycle. 

Calvin Cycle

Krebs cycle results in the generation of; 2 CO2 molecules, 3 NADH2 molecules, 1 FADH2 molecule, and 1 GTP molecule. 

Electron Transport System

In the Electron Transport System step, the energy-containing electron passes through a chain of carrier complexes. It takes place in the inner mitochondrial membrane to activate the proton pump and then finally the oxidative phosphorylation of ADP takes place to form the ATP in the presence of oxygen which accepts the electron to generate water.

Electron Transport System

Respiratory Balance Sheet

The net gain in ATP per glucose molecule is calculated theoretically using the respiration balance sheet. One mole of glucose is converted into 38 ATP during the entire process.

  • In glycolysis; 1 ATP + 2 NADH2 (=6 ATP) = 8 ATPs
  • In Oxidative decarboxylation; 2 NADH2 = 6 ATPs
  • In Krebs Cycle; 2 GTP (2 ATP) + 6 NADH2 (=18 ATP) + 2 FADH2 (= 4ATP) = 24 ATPs
  • Total ATPs generated during aerobic respiration = 38 ATPs – 2 ATPs utilized during glycolysis = 36 ATPs
  • Total ATPs generated during anaerobic respiration = 2 ATPs 

Amphibolic Pathway

Respiration is considered an amphibolic pathway in which both anabolism and catabolism are involved. As glucose is the favorable substrate of respiration carbohydrates, fats, and proteins are first converted into glucose or related product and then enters the pathway. 

Amphibolic Pathway

Respiratory Quotient

The respiratory quotient refers to the actual volume of carbon dioxide removed to the actual volume of oxygen used during the process of cellular respiration. The respiratory ratio is another name for it. RQ designates it.

RQ=volume of carbon dioxide eliminate/ The volume of oxygen consumed

The type of respiratory substrate employed during the act of respiration affects the respiratory quotient. In addition, the respiratory quotient, which is derived from carbon dioxide generation, is a dimensionless number utilized in the estimation of the basal metabolic rate, or BMR. 

The respiratory quotient reaches zero when the substrate of carbohydrates is completely oxidized. Here, the amount of carbon dioxide released and the amount of oxygen absorbed is equal.

C6H12O6 + 6O2 ———-> 6CO2 + 6H2O+ energy

RQ=6CO2/ 6O2

Carbohydrates have an RQ of about 1

Additionally, fats contribute to cellular respiration. In contrast to carbohydrate molecules, fat molecules undergo partial oxidation. The respiratory quotient is, therefore, lower than. 

2(C51H98O6) + 145O2 —————> 102CO2 + 98H2O + energy


Fats have an RQ of about .70

Proteins have an RQ of about 0.9

FAQs on Respiration in Plants

1. What is Respiration in Plants? 


All cells are supplied with oxygen as it diffuses into the stomata from the air and this process is called repiration in plants. Additionally, carbon dioxide diffuses from the stomata. The bark of woody stems has lenticels for gaseous exchange. All inner cells receive oxygen that diffuses into the woody stem and reaches them for respiration.

2. How Respiration takes place in Leaves? 


Stomata are part of leaves. The gaseous exchange takes place by stomata-mediated diffusion. Every stomata is regulated by guard cells. When the stoma between the inferior of leaves and the atmosphere is closed and opened, gases are exchanged. 

3. What are the Steps of Respiration in Plants? 


Glycolysis, the first process, takes place in the cytoplasm of the cell without the usage of oxygen. The Krebs Cycle, which takes place in the mitochondria and consumes oxygen to produce the waste product, carbon dioxide, is the second phase. Oxidative phosphorylation serves as the culmination of cellular respiration.

4. Why do Plants Respire at Night? 


During the course of their nighttime respiration, plants exhale carbon dioxide, take in oxygen, and oxidize food that has been stored. For this reason, it is advised against spending the night under a tree.

5. Why is Respiration Important in Plants?


All plant tissues must breathe in order to grow and remain healthy. Additionally, respiration is crucial for the global carbon cycle as well as the carbon balance of individual cells, entire plants, and ecosystems.

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Last Updated : 28 Aug, 2023
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