Respiration In Plants Class 11 Notes Biology Chapter 14 - CBSE

Chapter : 14

What Are Respiration In Plants ?

Exchange Of Gases

In plants, the exchange of gases takes place through stomata. Each of the stomata is surrounded by two guard cells, and these cells contain chloroplasts. A respiratory opening is found under each stoma, and the process of opening and closing of stomata depends on the presence of sugar and starch in the guard cells.

Cellular Respiration

Respiration is an oxidative process in which chemically bound energy from complex organic fuel molecules such as carbohydrates, proteins, and fats is captured in the form of ATP. In plants respiration gas exchange occurs through stomata and lenticels.

$$\text{C}_{6}\text{H}_{12}\text{O}_{6} + 6\text{O}_{2}\xrightarrow{}\\\text{6CO}_2 + 6\text{H}_2 \text{O + Energy (36 ATPs)}$$


It is the partial oxidation (breakdown) of glucose to 2 molecules of pyruvic acid (C3H4O3) in the absence of O2.

  • It occurs in cytoplasm of all living organisms.
  • Its scheme was given by Gustav Embden, Otto Meyerhof and J. Parnas. So it is also known as EMP pathway.
  • In anaerobes, it is the only process in respiration.
  • In plants, glucose is derived from sucrose (end product of photosynthesis) or from storage carbohydrates. Sucrose is converted into glucose and fructose by an enzyme, invertase. These 2 monosaccharides readily enter glycolytic pathway.
  • Glucose and fructose are phosphorylated to form glucose-6-phosphate by the enzyme hexokinase. It is then
    isomerized to produce fructose-6-phosphate. Subsequent steps of metabolism of glucose and fructose are


It is the incomplete oxidation of glucose under anaerobic condition. It occurs in many prokaryotes and unicellular eukaryotes.

Alcoholic fermentation

Here, the pyruvic acid formed from glucose is converted to CO2 and ethanol. The enzymes, pyruvic acid decarboxylase and alcohol dehydrogenase catalyze these reactions. E.g. Yeast.

Lactic acid fermentation

Here, pyruvic acid is converted to lactic acid.

Citric Acid Cycle

The citric acid cycle is a metabolic pathway that connects carbohydrate, fat, and protein metabolism. The reactions of the cycle are carried out by eight enzymes that completely oxidize acetate (a two carbon molecule), in the form of acetyl-CoA, into two molecules each of carbon dioxide and water.

Electron Transport Chain

The electron transport chain is a series of four protein complexes that couple redox reactions, creating an electrochemical gradient that leads to the creation of ATP in a complete system named oxidative phosphorylation. It occurs in mitochondria in both cellular respiration and photosynthesis.

Amphibolic Pathway

“An amphibolic pathway is a biochemical pathway that includes both anabolic and catabolic processes.” In 1961, B. Davis coined the term amphibolic pathway. A biochemical pathway, which involves both catabolism
and anabolism and is known as an amphibolic pathway. The amphibolic pathway can be best explained by Krebs' cycle.

Respiratory Quotient

The ratio of the volume of CO2 evolved to the volume of O2 consumed in respiration is called the respiratory quotient (RQ) or respiratory ratio.

$$\text{RQ} =\frac{\text{Volume of CO}_2\space \text{evolved}}{\text{Volume of O}_2\space \text{consumed}}$$

For carbohydrates- R.Q. = 1.0

For protein- R.Q. = 0.8

For fats- R.Q. = 0.7