[Biology Class Notes] on Respiration in Plants Pdf for Exam

All living organisms, containing plants, get the energy necessary for their survival from a series of chemical reactions termed respiration. The process of respiration needs glucose to start the reactions which are changed into energy and later produce carbon dioxide and water as by-products.

 

What is Plant Respiration?

The method by which cells get chemical energy by the consumption of oxygen and the liberating of carbon dioxide is called respiration. In order to carry on respiration, plant cells require oxygen and a means of disposing of carbon dioxide just as animal cells do. In plants, every part such as root, stem executes respiration as plants do not possess any particular organs like animals for the exchange of gases.

The method of respiration is written as:

Oxygen + Glucose → Water + Carbon Dioxide with Energy

We can conclude the same from the equation above as well that respiration uses oxygen and to produce carbon dioxide.

 

Do Plants Breathe?

This is the main question when we think about plant respiration. As plants do not have any specialized organs like lungs so we can say that plants do not breathe rather they respire. Plants respire with the help of lenticels and stomata (exist in stems and leaves individually) which carry out the function of the gaseous exchange.

 

Role of Air Temperature

Plant respiration happens 24 hours a day, but night respiration is more obvious as the photosynthesis process finishes. During the night, it is very vital that the temperature is much cooler as compared to the daytime because plants can undergo stress. Imagine a marathon runner. The runner breathes at higher rates than an individual standing still; so, a runner’s amount of respiration is greater and the temperature of the body rises. The same principle relates to plants, as the temperature at night rises, the respiration rate increases, and similar temperature increases. This action would result in flower damage and also in plant poor growth.

 

Respiration in Roots

In plants, respiration occurs with the help of roots. In soil oxygenated air is already present in spaces between soil particles. This oxygen is then absorbed into the roots with the help of root hair present on the roots. The hairs of the roots are in straight contact with them. In fact, root hair is a lateral tubular outgrowth of the external epidermal cells of a root. The oxygen present among the soil particles diffuses into the root hairs. From root hairs, oxygen is transported to all the parts of roots for respiration. During the respiration process, oxygen is transformed into carbon dioxide gas which is spread in the opposite direction i.e. out of the roots by the same root hairs which complete the respiration process of roots.

If a potted plant is watered over for a long time, then the plant can ultimately die. This is due to too much water exorcizing all the air from in between the soil particles. Because of this, oxygen is not free to the roots for aerobic respiration. In these states, the roots of plants respire anaerobically making alcohol. This can kill the plant. Germinating seeds during the early stage respire anaerobically as they have a seed coat that does not permit the oxygen to enter through it.

 

Respiration in plants occurs throughout the day and night thereby carbon dioxide is formed. Though, during the day, the total of carbon dioxide CO2 released is insignificant compared to the volume of oxygen made as a result of photosynthesis. Therefore, one should not sleep underneath a tree at night.

 

Respiration in Stems

In the plants taking herbaceous stem exchange of gases occurs through stomata and the carbon dioxide CO2 formed during the process that gets diffused into the air with the help of stomata only. While in the plants having hard and woody stems the exchange of gases occurs through lenticels. Lenticels are usually loosely packed dead cells that are present as tiny pores on the bark of woody plants. These allow oxygen to pass to the intercellular spaces of the inside of tissues and carbon dioxide (CO2) to be liberated into the atmosphere by the phenomena of diffusion which completes the process of respiration in stems.

 

Respiration in Leaves

In leaves, the exchange of respiratory gases occurs through very small pores called stomata. The stomata are present in big numbers on the lower side of the leaves of the plant. Every stoma has a tiny pore at its centre which is enclosed and regulated by two kidney-shaped cells known as guard cells. When the stoma opens the exchange of gases occurs between the atmosphere and interior of the leaf by the method of diffusion and that completes the process of respiration in leaves.

Types of Respiration

There are two kinds of respiration that we categorize on the basis of the absence or presence of oxygen:

 

Aerobic Respiration

The respiration that occurs in the presence of oxygen is named aerobic respiration due to ‘air’ which has oxygen. Aerobic respiration contains the utilization of oxygen for the breaking of chemical bonds in glucose to liberate energy in high volumes. It is the central source of energy for plants. Animals and plants that use oxygen for respiration are aerobes. Most animals have aerobic respiration.

 

C6H12O6 +6O2 ⟶ 6CO2 + 6H2O + Energy

All the organisms that gain energy by aerobic respiration cannot exist without oxygen. This is due to no oxygen there; they cannot get energy from the food which they consume. Aerobic respiration takes more energy because a complete breaking of glucose takes place during respiration with the use of oxygen.

 

Anaerobic Respiration

The respiration that occurs in the absence of oxygen is known as anaerobic respiration. In this process, the incomplete oxidation of food substances is being made by carbon dioxide CO2, and alcohol(OH). Besides this other organic matter such as citric acid, oxalic acid, lactic acid, etc are also produced.

 

This process is also called intramolecular respiration. Anaerobic respiration occurs in organisms like yeast, certain bacteria, and parasitic worms. The animals and plants that can exist and gain energy even in the lack of oxygen are called Anaerobic.

 

Glucose ⟶ Alcohol + CO2 + (Energy)

Yeast is known to be a single-celled fungus. In yeast, a single cell signifies the whole organism. A very low volume of energy is liberated in this process. Yeast respires anaerobically and all through this process, yeast transforms glucose into alcohol. So it is used to make alcohol, bread, etc.

 

Anaerobic respiration yields much less energy due to the only partial breakdown of glucose happening in anaerobic respiration in the absence of oxygen. All the organisms which gain energy by anaerobic respiration can exist without oxygen.

 

For instance, yeast is an organism that can exist without the oxygen of air as it obtains energy by the method of anaerobic respiration. Yeast can live in the absence of oxygen.