Cellular Respiration in Plants

Introduction to Cellular Respiration in Plants:

All living organisms use energy to survive, grow, respond to stimuli, reproduce, and carry out all biological processes. This energy is obtained from food. In their bonds, food molecules store chemical energy.

When these chemical bonds break by a series of chemical reactions, energy is released.

Explanation:

We know that autotrophs, like plants, synthesize their own food (glucose) through the process of photosynthesis and heterotrophs are dependent on autotrophs for food. Plants, as well as animals, need to break down food (glucose) in order to release their chemical energy.

The oxidation of glucose molecules releases energy which is then used to drive all the other processes in your body. This process is called respiration.

Cellular respiration is a series of metabolic reactions that take place inside the cells to convert biochemical energy obtained from the food into a chemical compound called adenosine triphosphate (ATP). In this process, a glucose molecule is gradually broken down in the presence of oxygen into carbon dioxide and water to release ATP.

ATP is a molecule that stores and transfers chemical energy within cells and is also known as the energy currency of the cell.

Photosynthesis and cellular respiration have an important relationship that enables life. The products of one process are the reactants of the other. The reaction for cellular respiration is the direct opposite of photosynthesis.

Photosynthesis makes glucose that is utilized in cellular respiration to produce ATP. This glucose is then turned back into carbon dioxide, which is required during photosynthesis.  During photosynthesis, water is broken down to form oxygen, whereas in cellular respiration, oxygen is combined with hydrogen to form water.

Photosynthesis takes in carbon dioxide and releases oxygen, whereas cellular respiration takes in oxygen and releases carbon dioxide. This released oxygen is used by all living organisms for cellular respiration. Cellular respiration is enhanced in the presence of oxygen. Without oxygen, less ATP would be produced.

In order to carry out cellular respiration, organisms require oxygen and a means of disposing of carbon dioxide. Animals have specialized organs such as lungs that help them breathe oxygen and release carbon-di-oxide.

Plants, however, do not possess any particular organs like animals for the exchange of gases. In the case of plants, every part, such as the roots, stems and leaves carries out respiration.

Do Plants Breathe?

Since plants lack specialized organs like lungs, we can say that plants do not breathe; rather, they respire. Plants respire using their lenticels (stem) and stomata (leaves) which carry out the function of the gaseous exchange.

Plants respire throughout the day, but respiration is more obvious at night as the photosynthesis process finishes. It is very important for the air temperature to be much cooler during the night compared to the daytime as plants can undergo stress. If the temperature at night rises, the respiration rate increases, increasing the overall temperature. This results in plant damage and also in poor plant growth.

Respiration in Roots:

Respiration in plants occurs with the help of roots. Oxygenated air is already present in gaps between soil particles. The root hairs present on the root absorb this oxygen.

The root hair is a lateral tubular outgrowth of the external epidermal cells of a root. The root hair is in direct contact with oxygen present among the soil particles. From root hairs, oxygen is transported to all other parts of the root for respiration. During respiration, oxygen is converted to carbon dioxide, which spreads in the opposite direction, i.e., out of the roots by similar root hairs.

The process of respiration happens all through the day and night. Although, during the day, the amount of CO2 released is insignificant compared to oxygen due to photosynthesis. Whereas at night CO2 is released more. Hence, one should not sleep underneath a tree at night.

Respiration in Stem:

Plants that have herbaceous stems exchange gases through stomata only. While plants that have hard and woody stems exchange gases through lenticels. Lenticels are loosely packed dead cells that are present as tiny pores on the bark of woody plants. They allow oxygen to pass to the intercellular spaces of tissues and carbon dioxide (CO₂) to be liberated into the atmosphere by the phenomena of diffusion.

Respiration in leaves:

The exchange of respiratory gases in leaves occurs through tiny pores called stomata. In plants, the stomata are present in large numbers on the lower side of the leaves.

Each stoma has a tiny pore in the middle, which is enclosed and regulated by two kidney-shaped cells known as guard cells. When the stoma opens, the exchange of gases takes place between the atmosphere and the interior of the leaf by diffusion.

Types of Respiration:

Most of the time, plants need oxygen to carry out respiration, but in some cases, respiration takes place without the presence of oxygen. There are two types of respiration that we categorize based on the absence or presence of oxygen:

1. Aerobic Respiration
2. Anaerobic Respiration

Aerobic Respiration:

The respiration that takes place in the presence of oxygen is named aerobic respiration. In aerobic respiration, oxygen is used for the breaking of chemical bonds in glucose to liberate energy. Animals and plants that use oxygen for respiration are known as aerobes. Most animals have aerobic respiration.

C₆H₁₂O₆ +6O₂ ⟶ 6CO₂ + 6H₂O + Energy

All aerobic organisms cannot survive without oxygen as, without oxygen, they cannot get energy from the food which they consume. Aerobic respiration requires more energy because glucose is broken down completely.

Anaerobic Respiration:

The respiration that happens in the absence of oxygen is called anaerobic respiration. In this process, the incomplete oxidation of food is carried out by carbon dioxide and alcohol. Besides this, other organic compounds like citric acid, oxalic acid, lactic acid, etc., are also produced. This process is also called intramolecular respiration.

Glucose ⟶ Alcohol + CO₂ + (Energy)

Anaerobic respiration is common in organisms like yeast, certain bacteria, and parasitic worms. Animals and plants that can survive and gain energy in the absence of oxygen are called Anaerobes.

Yeast is a single-celled fungus that respires anaerobically and transforms glucose into alcohol. Hence, it is used to prepare alcohol, bread, etc. Anaerobic respiration yields very less energy as glucose is broken down partially. All anaerobes can exist without oxygen.