Types of Respiration in Plants and Factors Affecting Them
Introduction:
Respiration is an amphibolic and exergonic cellular process as it takes place in various enzymatic reaction processes, which is also known as internal respiration/tissue respiration/dark respiration/cellular respiration/mitochondrial respiration. As in all living organisms one of the most important processes is respiration where there is a release of metabolic energy in the form of ATP. In case of plants there is a lack of specialised respiratory organs as each plant parts take care of its own gaseous exchange. They are very less dependent on the environment for respiratory gaseous exchange. In the plant body diffusing gases do not travel long distances.
Respiratory Substrate:
Carbohydrate-----fats-------proteins-----others
When respiratory substrates are carbohydrates like glycogen, starch, sucrose, hexose, or fats then respiration is known as floating respiration.
When protein is oxidised in respiration, then respiration is known as protoplasmic respiration in which protoplasmic components or cellular proteins may oxidise at the time of starvation and disease.
Exceptionally oxidation of protein in legume seeds is called floating respiration.
Types of Respiration:
1. Aerobic Respiration:
The complete oxidation of food with use of oxygen and when the entire carbon is released as carbon dioxide is called aerobic respiration.
2. Anaerobic Respiration:
This is a complete oxidation. When food is oxidised into alcohol or organic acids without use of oxygen. During this process most of energy is lost in the form of heat. It occurs in cytoplasm and only 2ATP is produced.
It may take place in bacteria.
When oxygen is not available then in that case the food is incompletely oxidised into some organic compound like ethanol,lactic acid, acetic acid.
In anaerobic respiration the final electron acceptor is a free oxygen molecule.
Steps in Aerobic Respiration:
Glycolysis: Occur in cytosol/cytoplasm.
Formation of acetyl coenzyme A: mitochondrial matrix.
TCA cycle or Kreb Cycle: Matrix of mitochondria.
ETS: Occurs in cristae or inner membrane of mitochondria and oxidative phosphorylation-occurs in oxysome heads.
1. Glycolysis: (Embden,Meyerhof, parnas)pathway
It is the common phase in aerobic and anaerobic respiration.
In glycolysis neither consumption of oxygen nor liberation of carbon dioxide take place.
In glycolysis, 1 glucose produces 2 moles of pyruvic acid.
Glycolysis is also known as oxidative anabolism or catabolism resynthesis because it links with anabolism of fats and amino acids. An intermediate PGAL is used for the synthesis of glycerol that later forms fats or lipids. PGA is used for synthesis of serine, Glycine, Cystine, Alanine forms from pyruvate.
2. Formation of Acetyl Coenzyme A:
When respiration is aerobic, then pyruvic acid is oxidised to form 2C-compound-Acetyl CoA. It occurs in the presence of oxygen and carbon dioxide is released for the first time during it.
Acetyl CoA is the connecting link between glycolysis and kreb cycle. Decarboxylation and dehydrogenation take place during formation of acetyl CoA.
Acetyl CoA is formed in the mitochondrial matrix by enzyme pyruvate dehydrogenase complex.
3. Krebs Cycle or TCA:( tricarboxylic acid)
This cycle was discovered by H.A Krebs.
TCA cycle in mitochondrial matrix or power house of the cell. All the enzymes of TCA cycle, Except marker enzymes succinic dehydrogenase.
Krebs cycle begins by formation of citric acid.
Oxidation occurs at 4 sites in the Kreb cycle. 3NADH2, 1FADH2, 1GTP.
4. ETS and oxidative phosphorylation:
(Terminal oxidation of NADH + H+ and FADH2)
It is associated with release and utilisation of the energy stored in NADH + H+ and FADH2. Oxygen acts as a final H2 acceptor.
UQ and Cyto. C are mobile carriers in mitochondrial ETS.
Fermentation:
1. Alcoholic Fermentation:
This is the oldest and best known type of fermentation performed by yeast and some bacteria.
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2. Lactic Acid Fermentation:
It occurs during curd formation and also in muscles of animals (when oxygen is inadequate).
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Respiratory Quotient:
R.Q= Volume of carbon dioxide liberated/ Volume of oxygen liberated
Volume of R.Q depends upon the type of respiratory substrate used and measured by Ganong’s respirometer.
Carbohydrate: R.Q=1
Fat/oil= R.Q=0.70
Malic acid: R.Q= 1.33
Oxalic acid: R.Q= 4
Citric acid: R.Q=1.3
Protein: R.Q=0.8/0.9<1
Anaerobic bacteria: R.Q= Infinite 2 carbon dioxide/ 0 oxygen = Infinite
Factors Affecting Cell Respiration:
Temperature:
Optimum temperature for respiration is between 20-35 degree celsius. Maximum temperature is about 45 degree celsius.
At low temperature respiration is low due to inactivation of enzymes while at very high temperature as enzymes denatured.
Oxygen:
The inhibition of anaerobic respiration by oxygen concentration is called Pasteur’s effect.
The amount of oxygen at which aerobic and anaerobic respiration take place simultaneously is called transition point.
The minimum amount of oxygen at which aerobic and anaerobic respiration become extinct is called extinction point.
Carbon Dioxide:
Carbon dioxide increases then the rate of respiration decreases in plants.
Preservation of fruits and vegetables at high concentration is called gas storage.
Salts:
If a plant is transferred from water to salt solution, it’s respiration increases this is known as salt respiration.
Light:
Rate of respiration increases with increase in light intensity. Light controls stomatal opening and influence on temperature and also produces respiratory substance.
Age:
Rate of respiration is more in young cells. Rate of respiration at the meristem apex is high.
FAQs on Respiration in Plants: Complete Guide for Biology Students
1. What is respiration in plants as per the Class 11 syllabus?
Respiration in plants is a catabolic process where complex organic compounds, like glucose, are broken down to release energy in the form of ATP (Adenosine Triphosphate). This process occurs in every living cell of the plant and is essential for providing the energy needed for various metabolic activities, growth, and maintenance.
2. What are the main types of respiration found in plants?
Plants exhibit two primary types of respiration based on the availability of oxygen:
- Aerobic Respiration: This is the complete oxidation of glucose in the presence of oxygen, releasing a large amount of energy (36-38 ATP). The end products are carbon dioxide and water.
- Anaerobic Respiration (Fermentation): This is the incomplete breakdown of glucose in the absence of oxygen. It releases significantly less energy (only 2 ATP), and the end products are typically ethanol and carbon dioxide.
3. What are the four main stages of aerobic respiration in plants?
Aerobic respiration is a multi-step process that can be divided into four main stages:
- Glycolysis: The breakdown of one molecule of glucose into two molecules of pyruvic acid. This occurs in the cytoplasm.
- Pyruvate Oxidation (Link Reaction): The conversion of pyruvic acid into acetyl-CoA, which takes place in the mitochondrial matrix.
- Krebs Cycle (TCA Cycle): A series of chemical reactions in the mitochondrial matrix where acetyl-CoA is completely oxidised.
- Electron Transport System (ETS): The transfer of electrons through a series of carriers on the inner mitochondrial membrane, leading to the synthesis of a large number of ATP molecules.
4. Where do the different stages of cellular respiration occur inside a plant cell?
The different stages of cellular respiration are precisely compartmentalised within the plant cell to ensure efficiency:
- Glycolysis takes place in the cytoplasm.
- The Krebs Cycle or TCA cycle occurs in the mitochondrial matrix.
- The Electron Transport System (ETS) is located on the inner membrane of the mitochondria.
5. What factors can affect the rate of respiration in plants?
Several environmental and internal factors influence the rate of respiration in plants. The key factors include:
- Temperature: The rate increases with temperature up to an optimum (around 25-35°C) and then declines as high temperatures denature enzymes.
- Oxygen Concentration: The availability of oxygen is crucial for aerobic respiration. A lack of oxygen forces the plant into less efficient anaerobic respiration.
- Carbon Dioxide Concentration: An increased concentration of CO₂ generally leads to a decrease in the rate of respiration.
- Water: Proper hydration is necessary for enzymatic activity. Water stress can lower the respiration rate.
6. Do plants respire only at night? Explain.
No, this is a common misconception. Plants respire continuously, 24 hours a day, just like animals, to produce the energy they need to live. During the day, the rate of photosynthesis is usually much higher than the rate of respiration, so there is a net release of oxygen. At night, in the absence of light, photosynthesis stops, but respiration continues, resulting in a net release of carbon dioxide.
7. Why is the respiratory pathway in plants considered an amphibolic pathway?
The respiratory pathway is considered amphibolic because it involves both catabolism (breakdown) and anabolism (synthesis). While its primary function is catabolic (breaking down carbohydrates, fats, and proteins to release energy), its intermediates can be withdrawn from the pathway to be used as precursors for the synthesis of other essential molecules like amino acids and fatty acids. This dual role makes it a central metabolic pathway for both breaking down and building up compounds.
8. How does anaerobic respiration in plants differ from aerobic respiration in terms of ATP yield?
There is a vast difference in energy efficiency. Aerobic respiration is highly efficient, producing a net total of 36 to 38 ATP molecules from the complete oxidation of one glucose molecule. In sharp contrast, anaerobic respiration is much less efficient, yielding only a net gain of 2 ATP molecules per glucose molecule because the substrate is only partially broken down.
9. What is the significance of the Respiratory Quotient (RQ) in plants?
The Respiratory Quotient (RQ) is the ratio of the volume of carbon dioxide evolved to the volume of oxygen consumed during respiration (RQ = CO₂ evolved / O₂ consumed). Its significance lies in its ability to indicate the type of respiratory substrate being used by the plant. For example:
- An RQ of 1 indicates that carbohydrates are being respired.
- An RQ of less than 1 suggests that fats or proteins are the respiratory substrate.
- An RQ of more than 1 is found when organic acids are being respired.
