Respiration in plants is a process which makes the use of oxygen for the oxidation of glucose and other respiratory substrates like fats or proteins. Respiratory substrates are the high energy biomolecules which produce energy, carbon dioxide and water as a result of breakage in C-C bond. Plants undergo cellular respiration, which is generally of two types:
Dark respiration: This kind of respiration may occur in the presence or absence of light.
Photorespiration: It strictly occurs under the action of light.
Plants undergo cellular respiration that involves three stages:
Glycolysis is the first stage of cellular respiration which takes place inside the cytoplasm. It produces energy in the anaerobic condition.
Kreb’s cycle is the second stage of aerobic respiration, which occurs inside the mitochondrial matrix.
Oxidative phosphorylation is the last stage of cellular respiration that occurs in the inner mitochondrial membrane via an electron transport system. It also occurs in aerobic conditions.
Content: Respiration in Plants
- Definition of Respiration in Plants
- Plant Respiration Cycle
- Cellular Respiration in Plants
- Types of Plant Respiration
- Mechanism of Respiration
Definition of Respiration in Plants
Respiration in plants can define as a cellular mechanism which involves complete combustion of glucose and oxygen to yield by-products like water and carbon-dioxide and energy in the form of heat.
In cellular respiration, some of the energy dissipates as heat while some energy is harnessed by a plant for the growth processes. Respiration in plants occurs through stomata and lenticels.
Stomata: It is the specific part of the plant that is present in the epidermis layer of the leaves and stems. The stomatal pore is formed by the bean-shaped guard cells which promote opening and closing of stomatal pore during the gaseous exchange. Carbon dioxide and oxygen exchange occur during day time.
Lenticels: It is a part which appears as a pore in the woody trucks or bark of a tree. Lenticels allow gaseous exchange between the cells and the environment. It is present in the periderm of the stem and allows gaseous exchange during the night time.
Plant Respiration Cycle
Plants respire 24 hours day and night, to carry out the oxidation of glucose into by-products like carbon dioxide and water with the release of high energy. A plant produces glucose and oxygen during the photosynthesis, by the conversion of carbon dioxide, water in the presence of chlorophyll and sunlight. The plant respiration continues in a way, given in the diagram.
Important Note: Respiration in plants is a process that spontaneously occurs the whole day, but photosynthesis only occurs during the day time, under the sunlight. The respiration rate of plants is higher during the night as the photosynthesis ceases.
Cellular Respiration in Plants
Cellular respiration in plants involves three major pathways to oxidize glucose into energy (in the form of ATP). In plants, ATP formed by the cellular respiration acts as an “Energy currency” helps is the formation and functioning of different cells. It involves glycolysis, Krebs cycle and electron transport system for the complete oxidation of glucose into 38 ATP molecules. The whole process of cellular respiration is depicted in a diagram:
In cellular respiration, glucose first oxidizes into pyruvate by a series of enzymes. Then, pyruvate undergoes oxidation and converts into Acetyl coenzyme-A by the enzyme pyruvate dehydrogenase. The Acetyl coenzyme-A enters the Krebs cycle and oxidizes to produce carbon dioxide, protons and electrons. To know more about glycolysis and Krebs cycle, one can look out the article difference between glycolysis and Krebs cycle.
Then the protons and electrons released during the Krebs cycle participate in the electron transport system, where the oxygen accepts an electron and combine with a proton to release water molecule. There are 38 ATP molecules produces per glucose molecule, after the completion of cellular respiration.
Types of Plant Respiration
This type of respiration occurs in the presence of atmospheric oxygen. A plant uses oxygen for the oxidation of high energy organic compound glucose to release low energy molecules like water, carbon dioxide. Aerobic respiration in plants releases a high amount of energy which is not directly used up by the plants but use for the synthesis of ATP.
The ATP is further breakdown into ADP and inorganic phosphate and releases energy that is used up by the plant to perform cellular functions. Aerobic respiration occurs in the mitochondria with a net production of 38 ATP molecules by the complete oxidation of one glucose molecule.
This type of respiration also refers as “Intramolecular respiration”. In majority, occurs in succulent plants like cacti, meristematic tissue, germinating seeds etc. and in the absence of oxygen. Anaerobic respiration results in incomplete oxidation of the respiratory substrates into carbon dioxide and ethyl alcohol with very little energy.
Thus, anaerobic respiration in plants is related to alcoholic fermentation. The energy released during anaerobic respiration is then used to maintain the protoplasmic activity. Anaerobic respiration occurs in the cytoplasm with a net production of 2 ATP molecules, results from incomplete oxidation of one glucose molecule.
Mechanism of Respiration
Like other living organisms, plants also need oxygen to respire and produce energy. A plant then supplies energy to the different parts of a plant. In plants, respiration occurs in the roots, stems and leaves. Root hairs, stomata, lenticels are the respiratory parts of the plant through which they exploit oxygen and releases carbon dioxide.
Respiration in roots
Root respires by getting the oxygenated air from the soil particles via root hairs. Root hairs are the tubular structures that are in direct contact with the soil particles. Diffusion of oxygen occurs from the soil particles to the root hairs and finally to the other parts. During respiration, roots consume oxygen and release carbon dioxide to the atmosphere. A plant again uses the released carbon-dioxide to prepare food and release oxygen.
The soil must not be soggy, or soil with excessive water can block the availability of free oxygen in the soil. During seed germination, there is no oxygen requirement in the initial stage, as the testa or seed covering does not allow oxygen to enter.
Respiration is Stems
Stems of herbaceous plants respire through a stomatal pore found in the epidermis of the stem. Stems of woody plants respire via lenticels found in the periderm of the stem and usually arranged as loosely packed dead cells. Thus, both stomata and lenticels allow:
The entry of oxygen inside the intercellular spaces of the plant and release of carbon dioxide into the atmosphere.
Respiration in Leaves
Small pores present in the lower epidermis layer of the leaf refers as “Stomata” which allow gaseous exchange between leaves and environment. Guard cells control the stomatal activity, which enables opening and closing of stomatal pore for the gaseous exchange.