How Do Different Parts of Plants Respire?
What is Respiration in Plants
Just like animals, plants respire and require energy as well. They get their portion of energy by the process of respiration wherein the glucose molecules present in the food gets broken down to form carbon dioxide in the presence of water and releases oxygen as a by-product.
Plants make use of this energy to carry out the different life processes and hence, they respire too, just like any other living organism, for their survival. However, if we talk about how do plants respire, their respiration process is much different than that of animals. Unlike animals, every part of the plants can take in oxygen from the surrounding air independently, use it to get energy, and in the end give out carbon dioxide. Let us first define respiration in plants and see how plants respire from different parts.
Respiration Process in Plants
During the process of respiration, in different parts of a plant, a comparatively lower amount of gaseous exchange takes place. Therefore, every part of the plant fulfils and nourishes its own energy requirements.
The leaves, roots and stem of plants tend to exchange gases separately. Leaves consist of tiny pores called stomata which aid in the gaseous exchange. The oxygen which is consumed through stomata gets used up by the cells present in the leaves. This, in turn, helps for disintegrating glucose into carbon dioxide and water.
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Respiration in Leaves
Plant leaves consist of tiny pores which we call stomata. During the process of respiration, the exchange of gases in leaves takes place via stomata. This process is explained below.
Oxygen from the surroundings enters the leaf via stomata and reaches the cells through the process of diffusion. The oxygen that enters the cells of the leaf gets used up in the process of respiration. And the carbon dioxide which gets produced during this process gets diffused out of the leaves through stomata into the air.
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Photosynthesis is the reaction in leaves which makes glucose and the process of respiration breaks it down further. In the photosynthesis reaction, light energy is the energy that goes into the reaction, whereas in respiration, chemical energy is the one that comes out.
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Respiration in Roots
Plant roots are underground but the cells of the roots need oxygen as well for carrying out the process of respiration and releasing energy.
Plant roots take in air from the spaces between the particles of soil. The air present in these soil particles is in contact with the root hair. Oxygen from this air present in the soil particles tends to diffuse into the root hair and reaches the root cells. Here it is used for the respiration process. The carbon dioxide that is produced in the root cells during the process of respiration gets released out via the same root hair through the process of diffusion.
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If a plant in a pot is over-watered for a longer period of time, it would ultimately die because a lot of water expels the air that is present in between the soil particles. Because of this, oxygen does not reach the roots for carrying our aerobic respiration. Hence, the plant roots tend to respire anaerobically and produces alcohol, which might kill the plant. This is the reason the germinating seeds respire through anaerobic respiration since they are coated with a seed coat that prevents oxygen from entering through it.
Respiration in Stems
In the plant stems, the air gets diffused into the stomata and tends to move through various parts of the cells to carry out the process of respiration. At this stage, the carbon dioxide that gets released also gets diffused through the stomata. Lenticels carry out this gaseous exchange in the woody or higher plants.
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Types of Respiration of Plants
If we talk about plant respiration, there are two different respiratory system in plants depending on the presence or absence of oxygen.
Aerobic respiration in plants
Anaerobic respiration in plants
Aerobic Respiration
Aerobic respiration is the respiration that occurs when oxygen is present. In anaerobic respiration in plants, oxygen gets utilized to break the chemical bonds in glucose for liberating energy in higher volumes. Most of the animals respire aerobically and the process of aerobic respiration occurs in the mitochondria of the cell.
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP (energy)
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Anaerobic Respiration
Anaerobic respiration is a respiration which takes place in the absence of oxygen. In the anaerobic respiration, lesser energy gets produced because of incomplete oxidation of food that occurs in the absence of oxygen. During the process of anaerobic respiration, ethyl alcohol and carbon dioxide get produced. This process is also referred to as intramolecular respiration. It occurs in organisms such as yeast, parasitic worms and certain bacteria.
C₆H₁₂O₆ → CO₂ + alcohol + ATP (energy)
FAQs on Types of Respiration in Plants: A Complete Guide
1. What are the two main types of respiration in plants?
Plants exhibit two primary types of respiration based on the availability of oxygen: Aerobic respiration, which occurs in the presence of oxygen and completely breaks down glucose to release a large amount of energy, and Anaerobic respiration (or fermentation), which occurs in the absence of oxygen and results in the incomplete breakdown of glucose, releasing far less energy.
2. What is the overall chemical equation for aerobic respiration in plants?
The balanced chemical equation that summarises aerobic respiration shows the breakdown of glucose using oxygen to produce carbon dioxide, water, and energy in the form of ATP. The equation is: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy (ATP). This process is crucial for providing the energy needed for all metabolic activities in the plant.
3. How do different parts of a plant, like roots and leaves, carry out gaseous exchange for respiration?
Plants lack a specialised respiratory system, so different parts exchange gases independently.
- Leaves and Young Stems: Gas exchange occurs through tiny pores called stomata.
- Mature Stems and Bark: Exchange happens through specialised openings called lenticels.
- Roots: Roots absorb oxygen from the air spaces in the soil through their root hairs via the process of diffusion.
4. What are the main stages of aerobic respiration in a plant cell?
Aerobic respiration in plants is a multi-step process that can be divided into three main stages:
- Glycolysis: The initial breakdown of a glucose molecule into two molecules of pyruvic acid. This occurs in the cytoplasm.
- Krebs Cycle (Citric Acid Cycle): The pyruvic acid is further broken down in the mitochondrial matrix, releasing carbon dioxide and generating energy carriers.
- Electron Transport System (ETS): This final stage occurs on the inner mitochondrial membrane, where oxygen acts as the final electron acceptor, leading to the formation of water and the synthesis of a large number of ATP molecules.
5. What is the key difference between aerobic and anaerobic respiration in plants?
The key difference lies in the presence of oxygen and the final energy yield. Aerobic respiration requires oxygen to completely oxidise glucose into CO₂ and H₂O, producing a high yield of approximately 36-38 ATP molecules. In contrast, anaerobic respiration occurs without oxygen, only partially breaking down glucose into products like ethyl alcohol and CO₂, and yielding only 2 ATP molecules.
6. Do plants respire during the day, or only at night?
Plants respire continuously, 24 hours a day, including during daylight hours. However, the net effect of gas exchange during the day is dominated by photosynthesis, which takes in carbon dioxide and releases oxygen. At night, photosynthesis stops, but respiration continues, which is why there is a net release of carbon dioxide from the plant.
7. How does plant respiration differ from photosynthesis?
Respiration and photosynthesis are opposite yet complementary processes. Key differences include:
- Process Type: Respiration is a catabolic process (breaks down complex molecules), while photosynthesis is an anabolic process (builds complex molecules).
- Energy Flow: Respiration releases energy (exergonic) from glucose, while photosynthesis stores light energy in glucose (endergonic).
- Gas Exchange: Respiration consumes oxygen and releases carbon dioxide, whereas photosynthesis consumes carbon dioxide and releases oxygen.
- Timing: Respiration occurs continuously, while photosynthesis only occurs in the presence of light.
8. Why is the process of respiration considered an amphibolic pathway in plants?
Respiration is considered an amphibolic pathway because it involves both catabolism (breakdown) and anabolism (synthesis). While its primary function is the catabolic breakdown of substrates to release energy, its intermediates can be withdrawn to be used as precursors for the synthesis of other essential biomolecules like amino acids and fatty acids. This dual role makes it a central metabolic pathway connecting various processes.
9. What is the Respiratory Quotient (RQ), and what does its value indicate?
The Respiratory Quotient (RQ) is the ratio of the volume of carbon dioxide evolved to the volume of oxygen consumed during respiration (RQ = Volume of CO₂ / Volume of O₂). Its value is important as it indicates the type of substrate being used. For example, the RQ for carbohydrates is 1, while for fats it is less than 1 (around 0.7). This helps in understanding the metabolic state of the plant.
