Respiration in Plants Chapter Notes | Biology Class 11 - NEET PDF Download

Respiration

• Respiration is a amphibolic & exergonic cellular process.
  
  Respiration in Plants

  • Respiration is an enzymatic process, which is also known as internal respiration / tissue respiration/dark respiration / cellular respiration / mitochondrial Respiration.

  • An important feature of respiration is liberation of metabolic energy as ATP.

Respiratory Substrate

• When respiratory substrates are carbohydrates like glycogen, starch, sucrose, hexose or fats, then respiration is known as floating respiration.
• When protein is oxidized in respiration, then respiration is Known as protoplasmic respiration protoplasmic components or cellular proteins may oxidised at the time of starvation & disease.
• Exceptionally oxidation of proteins in legume seeds is called floating respiration.

Types of Respiration

(A) Aerobic Respiration: The complete oxidation of food with the use of oxygen and when entire carbon released, as CO₂ is called as aerobic respiration.

Aerobic Respiration

(B) Anaerobic Respiration: This is an incomplete oxidation.

• When food is oxidized into alcohol or organic acids without use of oxygen. During it most of the energy is lost in form of heat. It occurs in cytoplasm and only 2ATP are produced.

• Anaerobic respiration was first reported by Kostytchev.
• Anaerobic respiration may takes place in bacteria, some lower parasitic animals (Ascaris, Taenia) plants, RBCs. & muscles of human body. When oxygen is not available, then food is incompletely oxidised in to some organic compounds like ethanol, acetic acid, lactic acid. 
• In muscle cells & some bacteria, the energy is produced by breaking of glucose into lactic acid inside the cells.
• The amount of energy released in anaerobic respiration is much less than aerobic respiration. 
• Fermentation is performed by only some fungi & some bacteria (only by microbes) and is an extracellular process. No ATP is produced. If occur inside the cell then 2ATP forms.

• In energy generating processes either inorganic or organic compounds function as electron acceptors. The terms aerobic respiration, anaerobic respiration and fermentation are often used on energy generating processes.
•  In aerobic respiration the final electron acceptor is free O₂.
•  In anaerobic respiration the final electron acceptors is organic compound or inorganic compounds (nitrates) other than free O₂
•  In fermentation, the final electron acceptor is organic intermediates of the process, no external substance.
• Both anaerobic respiration and fermentation are incomplete oxidations.

Inhibitory effect on respiration high conc. of oxygen is called Pasteur Effect.

Steps of Respiration

(1) Glycolysis – Occurs in cytosol/cytoplasm
(2) Formation of Acetyl COA – (Link Reaction) Peri mitochondrial space (outer chamber
(3) TCA cycle or Kreb's cycle  – Matrix of mitochondria & cytosol in bacteria
(4) ETS – Occurs in cristae or inner membrane of mitochondria and Oxidative phosphorylation – Occurs in Oxysome head (F₁ particle)

1. Glycolysis – EMP – (Embden, Meyerhof, Parnas) Pathway

5 steps of glycolysis

1. The glycolysis is common phase for aerobic & anaerobic respirations both.
2. Glycolysis involves a series of ten biochemical reactions in cytoplasm.
3. In glycolysis, neither consumption of oxygen nor liberation of CO₂ take place.
4. In glycolysis, 1 glucose, produces 2 mol. of pyruvic acids (3C)
5. 2 NADH 2 & 2 ATP are generated in glycolysis, which are equal to 8 ATP.
6. Substrate level phosphorylation forms 4 ATP :- [When the substrate releases energy for phosphorylation of ADP OR formation of ATP, without ETS then called as substrate level phosphorylation]
7. Glycolysis is also known as oxidative anabolism or catabolic resynthesis, because it links with anabolism of fats and amino acids. An intermediate  GAL is used for the synthesis of glycerol later forms fats or lipid . PGA is used for synthesis of Serine, Glycine, Cystine. Alanine forms from pyruvate.
8. 1, 3, 10 are irrev. reactis in EMP pathway.

• Phosphofructokinase is an allosteric enzyme. The phosphorylation of fructose 6 phosphate is the most important regulation point of glycolysis.

• Phosphofructokinase has multiple allosteric modulator. It's activity is inhibited by ATP (–ve modulator) and stimulated by ADP & AMP (+ve modulator). Most of the biochemical reactions catalysed by allosteric enzymes are irreversible type and these are control point of glycolysis.

2. Formation of Acetyl Co-A (Link/Gateway Reaction)

• When respiration is aerobic, then pyruvic acid is oxidised to form 2C compound – Acetyl Co-A. It occurs in presence of O₂ and CO₂ is released first time during it.

• Acetyl Co-A is a connecting link between glycolysis & Krebs-cycle. Decarboxylation and dehydrogenation (Oxidative decarboxylation) take place during formation of acetyl Co-A.

• Acetyl Co-A is formed in perimitochondrial space by enzyme pyruvate dehydrogenase complex. (Mg⁺⁺, LA (Lipoic Acid), TPP(Thiamine pyrophosphate), NAD, CoA)

• Acetyl Co-A is also common intermediate between fat & carbohydrate metabolism.