Respiration in Plants, Biology tutorial


Respiration is basically a procedure of oxidation and decomposition of the organic compounds, specifically simple carbohydrate like glucose, in the living cells by the release of energy. The most significant characteristic of respiration is that the potential energy stored in the organic compounds in the living cells is discharged in a systematic approach in the form of active or kinetic energy under the persuade of a series of enzymes and is made accessible, to the protoplasm for its manifold essential activities like preparation of food, growth, movement, reproduction and so on.

The store food materials which undergo oxidation are generally simple carbohydrate mainly glucose and at times other substances like complex carbohydrates, fats and protein, these are obviously first hydrolyzed and then oxidized. The main facts related with respiration are:

  • Consumption of atmospheric oxygen.
  • Oxidation and decomposition of a part of the stored food.
  • Liberation of carbon-dioxide and a little amount of water
  • Release of energy by the break-down of organic food.

The chemical reaction might be described thus:

C6H1206 + 602 → 602 + 6H20 + Energy

Glucose + oxygen → carbon dioxide + water + energy

Respiratory System in Plants:

Respiration is the procedure via which energy stored in the organic molecules is liberated to do metabolic work. A stepwise procedure conducted in all living cells, it is controlled through enzymes and releases carbon-dioxide and water.


Stomata are extremely thin openings found in the epidermis of leaves and stems of the seedlings. Each stoma is enclosed by two bean-shaped cells termed guard cells. Stomata are more plentiful in the lower epidermis of leaves and some in the upper epidermis. The closing and opening of the stomata are controlled through the guard cells.

Lenticels (Breathing Pores):

Lenticels are tiny openings or breathing pores found in the bark of older stems. Lenticels comprises of a loose mass of small thin-walled cells that permit simple diffusion of gases in and out of the plant.

Root Hairs:

These give a big surface area for the absorption of water, mineral salts and oxygen. Oxygen in the soil air, dissolve in the soil moisture and diffuses to the root hairs. From there, it diffuses into the other root cells. The carbon-dioxide generated by the cells diffuses out of the root into the soil through the root hairs.

Types of respiration:

There are basically two kinds of respirations as follows:

1) Aerobic Respiration:

The respiration that employs oxygen is termed as aerobic respiration. It is termed aerobic respiration as it employs air which includes oxygen (aerobic stands for air). In aerobic respiration, the glucose food is fully broken down into carbon-dioxide and water by means of oxidation. Aerobic respiration generates a considerable quantity of energy for utilize by the organism which gets stored in the ATP molecules.

2) Anaerobic Respiration:

The respiration which occurs devoid of oxygen is termed as anaerobic respiration. It is termed anaerobic respiration as it occurs with no air that contains oxygen (anaerobic stands for without air). In anaerobic respiration, the micro-organisms such as yeast break down glucose (food) into ethanol and carbon-dioxide and discharge energy.

Steps in the Aerobic respiration:

1) Glycolysis

2) Kreb's cycle or Citric acid cycle

3) Electron transport system (ETS).


Glycolysis occurs in the cytoplasm of the cell and is general to both aerobic and anaerobic respirations. In this step, glucose (6C) is broken down in a systematic manner into two molecules of 3C Pyruvic acid, without using oxygen. The general reaction of glycolysis is:

Glucose + 2ATP + 4ADP + 2NAD → 2 Pyruvic acid + 2ADP + 4ATP + 2NADH

Kreb's Cycle:

The Kreb's cycle as well termed as Citric Acid Cycle includes a sequence of cyclic reactions that start with the pyruvic acid made up from glycolysis that joint with acetyl co-enzyme A to form the citric acid. The reaction carries on in a cyclic form and it repeats itself constantly. Kreb's cycle occurs in the presence of oxygen and in the mitochondria of all the cells. At different phases of the Kreb's cycle, hydrogen and carbon-dioxide are generated. The hydrogen discharged combines with oxygen to generate water.

Throughout the complete procedure, huge energy in the form of adenosine triphosphates (ATPs) is released to the cell for use. Dissimilar to glycolysis, which yields total ATPs of two, Kreb's cycle all along generates total ATPs of 36. Thus, the whole breaking down of a glucose molecule from glycolysis to Kreb's cycle gives a net formation of 38 ATPs.

Electron Transport System (ETS):

The next step is to release and make use of the energy stored in NADH+H+ and FADH2. This is achieved if they are oxidized via the electron transport system and the electrons are passed on to O2 resultant in the making of H2O.

The metabolic pathway, via which the electron passes from one carrier to the other, is termed as the electron transport system (ETS). This pathway is present in the internal mitochondrial membrane.

Factors or Conditions influencing Respiration:

A) Oxygen: The presence of oxygen is necessary for respiration (only in Kreb cycle). The rate of respiration beneath varying concentration of oxygen differs. When the concentration of oxygen falls beneath 5%, then the rate of respiration quickly drops. Beneath this situation more carbon-dioxide is evolved than oxygen absorbed. By the gradual rise in oxygen concentration, there is a corresponding steady rise in the rate of respiration.

B) Light:  The result of light is only indirect; in bright sunlight, the respiratory activity is quite more than in the subdued light. This might be due to the fact that in bright light stomata stay wide open and oxygen is simply and rapidly absorbed.

C) Temperature:  The lowest rate of respiration is achieved at 0oC or even at 10oC. By the rise in temperature, the rate of respiration rises.

D) Supply of Water:  Protoplasm saturated by means of water respires more dynamically than that in a desiccated condition, as in dry seed. Therefore, with the supply of water the rate of respiration rises.

E) Concentration of Carbon-dioxide:  If as an outcome of respiration carbon-dioxide be permitted to accumulate within the plant as a outcome of stomata closure or the plant, surroundings respiration rate reduces and slowly ceases. When the carbon-dioxide is eliminated though respiration rate rise. Carbon-dioxide has a miserable effect on respiration.

F) Vitality of Cells:  Respiration in young active cells is highly rapid as compared to in old cells vegetative buds, floral buds and germinating seeds respire more dynamically than older parts of the plant.

G) Nutritive Materials:  Food materials, more specifically soluble carbohydrates, influence respiration to a considerable extent. By means of the supply of oxygen such materials become rapidly broken down.

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