Respiration and Excretion in Plant

Respiration and Excretion in Plants

The topic deals with the process of excretion and respiration in plants. It also involves the various external and internal factors associated with the physiological process.

Respiration and excretion are the two most important physiological and metabolic activities of plants. In respiration, the plants generate Adenosine Triphosphate (ATP) with the help of mitochondria. In the process of excretion, it tries to get rid of the extra nitrogenous waste present in its body in the form of transpiration, guttation or other elements. Both these metabolic activities are very important for the proper working of a plant. 

Respiration in Plants 

The complete combustion of glucose in oxygen releases 32 ATP molecules, whereas the anaerobic respiration process gives only 2 ATP molecules. Glycolysis is the process by which pyruvic acid is prepared from glucose. Glycolysis occurs inside the cell cytoplasm, where glucose is oxidised to glucose-6-phosphate and then fructose-6-phosphate. Then it is broken down into fructose-1,6-phosphate and triose phosphate. Then it breaks into 2-phosphoglycerate followed by 2-phosphoenolpyruvate and finally into a 3C compound called pyruvic acid. 

Then this is followed by the Tricarboxylic acid cycle (TCA cycle), where the acetyl group gets condensed into oxaloacetic acid. This reaction takes place inside the mitochondrial matrix. Finally takes place the electron transport chain (ETC) and oxidative phosphorylation. In ETC, electrons from NADH are produced in the mitochondrial matrix by the NADH dehydrogenase. The ubiquinone and cytochrome complexes play a key role in the respiration process. Next, electrons get passed with the help of carrier proteins and ATP synthetase. This process is also referred to as oxidative phosphorylation. 

Excretion in plants 

Plants usually do not have any such special mechanism for eliminating their wastes. Green plants continue their food manufacturing process in the presence of sunlight, chlorophyll and minerals. One of the most important wastes is the oxygen gas released during the process of photosynthesis. During food manufacturing, the plant uses carbon dioxide gas, and as a byproduct, oxygen gas evolves. This oxygen is passed out into the atmosphere with the help of various small pores called stomata by the physiological process of diffusion. Transpiration is another process by which the different wastewater gets passed out into the atmosphere in the form of water vapour from the aerial parts of the plants. 

By guttation, the waste exudates of the plants get released. It takes place with the help of structures called hydathodes. In many cases, latex, wax and different resins are also considered waste products of the plants, which are of medicinal importance to man. These saps and latex are forced from the interior cytoplasm of the plants and get deposited on the outer bark of the plants. These exudations occur by hydrostatic pressure and absorptive pressure of plants. The turgor pressure, wall pressure and plasmolysis rate also play a key role in plant excretion. 

Factors affecting the rate of respiration and excretion 

The various factors that affect the rate of respiration in plants are as follows:

  • Effect of water concentration
  • Protoplasmic conditions
  • Cytoplasmic conditions
  • Effect of temperature
  • Effect of light
  • Oxygen content in the atmosphere
  • The concentration of carbon dioxide
  • Humidity rate 

High water vapour content in the atmosphere prevents the process of respiration. Temperature and light directly influence the rate of respiration positively. Low oxygen content in the air gives rise to a high respiration rate. High carbon dioxide in the air harms the respiration rate. 

The three modes of excretion in plants are gaseous waste by lenticels in bark and stomata in leaves. Next is the excretion of wastes in the soil. The plants also excrete wastes in the form of resin and gum. In many cases, the plant sheds leaves or fruits which have high concentrations of waste material in them. Finally, the amount of water content of the plant directly affects its excretion rate. The extra water in the plants gets eliminated by the process of transpiration. In guttation, the wastewater only gets eliminated from the hydathodes. 


Respiration gives the plant energy in ATP; hence ATP is often referred to as the cell currency. The respiration process takes place in three steps: glycolysis, TCA cycle and the ETC process. Few of the processes occur in the cytoplasm; the rests take place in the mitochondrial matrix. In plants, no such special mechanism has been developed to eliminate the extra waste inside the body. Carbon dioxide and oxygen get eliminated by diffusion from the stomata. The resins, saps, latex and so on get excreted from the hydathodes and lenticels of the plant bark. Transpiration and guttation also release the extra water content of the plant body