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Respiration In Plants NCERT Textbook With Solutions PDF Free Download
Chapter 14: Respiration in Plants
All of us breathe to live, but why is breathing so essential to life? What happens when we breathe? Also, do all living organisms, including plants and microbes, breath?
If so, how? All living organisms need energy for carrying out daily life activities, be it absorption, transport, movement, reproduction or even breathing.
Where does all this energy come from? We know we eat food for energy – but how is this energy taken from food? How is this energy utilized?
Do all foods give the same amount of energy? Do plants ‘eat’? Where do plants get their energy from? And micro-organisms – for their energy requirements, do they eat ‘food’? You may wonder at the several questions raised above – they may seem to be very disconnected.
But in reality, the process of breathing is very much connected to the process of release of energy from food. Let us try and understand how this happens.
All the energy required for ‘life’ processes is obtained by oxidation of some macromolecules that we call ‘food’.
Only green plants and cyanobacteria can prepare their own food; by the process of photosynthesis they trap light energy and convert it into chemical energy that is stored in
the bonds of carbohydrates like glucose, sucrose, and starch.
We must remember that in green plants too, not all cells, tissues, and organs photosynthesize; only cells containing chloroplasts, which are most often located in the superficial layers, carry out photosynthesis.
Hence, even in green plants all other organs, tissues and cells that are non-green, need food for oxidation. Hence, food has to be translocated to all nongreen parts.
Animals are heterotrophic, i.e., they obtain food from plants directly (herbivores) or indirectly (carnivores).
Saprophytes like fungi are dependent on dead and decaying matter. What is important to recognize is that ultimately all the food that is respired for life processes comes from
This chapter deals with cellular respiration or the mechanism of breakdown of food materials within the cell to release energy, and the trapping of this energy for synthesis of ATP
Photosynthesis, of course, takes place within the chloroplasts (in the eukaryotes), whereas the breakdown of complex molecules to yield energy takes place in the cytoplasm and in the mitochondria (also only in eukaryotes).
The breaking of the C-C bonds of complex compounds through oxidation within the cells, leading to the release of a considerable amount of energy is called respiration.
The compounds that are oxidized during this process are known as respiratory substrates.
Usually, carbohydrates are oxidized to release energy, but proteins, fats and even organic acids can be used as respiratory substances in some plants, under certain conditions.
During oxidation within a cell, all the energy contained in respiratory substrates is not released free into the cell, or in a single step.
It is released in a series of slow step-wise reactions controlled by enzymes, and it is trapped as chemical energy in the form of ATP.
Hence, it is important to understand that the energy released by oxidation in respiration is not (or rather cannot be) used directly but is used to
synthesise ATP, which is broken down whenever (and wherever) energy needs to be utilised.
Hence, ATP acts as the energy currency of the cell. This energy trapped in ATP is utilized in various energy-requiring processes of the organisms, and the carbon skeleton produced during
respiration is used as a precursor for the biosynthesis of other molecules in the cell.
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NCERT Solutions Class 11 Biology Chapter 14 Respiration in Plants
1. What are respiratory substrates? Name the most common respiratory substrate.
Organic substrates that are oxidized during respiration to liberate energy inside the living cells are respiratory substrates. Carbohydrates, proteins, fats, and organic acids are the most common respiratory substrate.
2. What are the main steps in aerobic respiration? Where does it take place?
Main steps in aerobic respiration are as follows
- Glycolysis: Occurs in the cytoplasm(cytosol) where glucose is broken down to pyruvic acid.
- Oxidative decarboxylation of pyruvic acid to acetyl coenzyme-A: Takes place inside the mitochondrial matrix.
- TCA or Krebs cycle takes place in the Mitochondrial matrix where pyruvic acid is oxidized to transform the energy contained in these molecules into ATP.
- Electron transport chain occurs in mitochondrial membrane involves ATP synthase complex.
3. What are the assumptions made during the calculation of the net gain of ATP?
Assumptions made during the calculation of net gain of ATP are as follows
- NADH generated inside the mitochondria synthesizes 3 ATP molecules during its oxidation.
- NADH formed during glycolysis sends its reducing power into mitochondria via the shuttle system.
- During oxidation of FADH2, 2 molecules of ATP is produced inside mitochondria
- Formation of 3 ATP in the malate-aspartate shuttle (heart, liver and kidney) and 2 ATP in the glycerol phosphate shuttle (muscles and nerve cells).
4. Discuss “The respiratory pathway is an amphibolic pathway.”
Organic substances such as fats, carbohydrates, proteins etc liberate energy when they are disintegrated in the respiratory pathway.
This phenomenon is said to be catabolic in nature. The respiratory process that serves as a catabolic pathway for the respiratory substrates also serves as an anabolic pathway to produce different metabolic products and secondary metabolites.
Thus, the respiratory pathway serves as a catabolic and anabolic pathway. Therefore, the respiratory pathway is an amphibolic pathway.
5. What is oxidative phosphorylation?
Oxidative phosphorylation is the conversion of ADP into ATP by an electron transport system. Phosphorylation takes place in the inner mitochondrial membrane via the ATP synthetase complex when the hydrogen protons pass through it.
The energy essential for phosphorylation is derived from the oxidation-reduction phenomena in respiration. Thus the process is known as oxidative phosphorylation.
NCERT Class 11 Biology Textbook Chapter 14 Respiration in Plants With Answer PDF Free Download