Respiration in Plants
* Respiration provides oxygen, which is used for the oxidation of food to provide energy.
* Plants respire through small openings called the stomata on leaves and lenticels on stems and roots.
* Cellular respiration involves breakdown of the C-C bonds of compounds of food. It takes place in the cytoplasm and mitochondria.
* Most of the energy released during oxidation is used for synthesising ATP.
* Aerobic respiration involves the oxidation of food in the presence of oxygen.
* Anaerobic respiration involves the oxidation of food in the absence of oxygen.
Glycolysis
* Cells derive energy by the breakdown of nutrients.
* The energy released is trapped as adenosine tri phosphate or ATP.
* ATP is called the energy currency of the cell.
* Enzymes catalyse biochemical reactions.
* Glycolysis is a ten-step process involving breakdown of glucose to pyruvate. It takes place in the cytoplasm of cells.
* The net gain of glycolysis is 2ATP and 2 NADH2 .
* Pyruvate can be utilised in Krebs’ cycle, lactic acid or alcohol fermentation, based on the availability of oxygen.
Fermentation
* Fermentation is the incomplete oxidation of organic substances into simpler substances under anaerobic condition.
* Yeast carry out alcohol fermentation, and yield ethanol and carbon dioxide using enzymes.
* Bacteria carry out lactic acid fermentation and yield lactic acid.
* Muscle cells undergo anaerobic respiration in the absence of oxygen to produce lactic acid.
* Anaerobic respiration yields less energy as compared to aerobic respiration.
Krebs Cycle
* Aerobic respiration takes place in the presence of oxygen.
* Pyruvate formed in the glycolysis is moved into the mitochondria to enter Krebs’ cycle.
* Krebs’ cycle involves a set of enzymatic chemical reactions that is part of aerobic respiration.
* The net gain of aerobic respiration till Krebs’ cycle is 2 molecules of ATP, 8 molecules of NADH2 and 2 molecules of FADH2.
* Xerophytes are found in xeric habitats where water is scarce and temperatures are high.
Electron Transport System
* Reduced co-enzyme from glycolysis and Krebs’ Cycle are oxidised in the Electron Transport System(ETS).
* Electrons from NADH are transferred to complex I while electrons from FADH2 are transferred to complex II.
* Ubiquinone receives electrons from complex I and II and then transfers them to complex III.
* Cytochrome c acts as a motile carrier and transfers electrons between complex III and complex IV.
* Complex IV transfers the electrons to oxygen, which drives the ETC by removing protons from the system.
* The proton gradient formed by the electron and proton transfer is utilised for the synthesis of ATP.
* ATP synthase of complex V synthesises one molecule of ATP for every 2 protons pumped from inter-membrane space to matrix.
* The net gain of ATP production during aerobic respiration is 38 ATP compared to the fermentation that results in 2ATP molecules.
Amphibolic Pathway
* Respiratory Quotient depends on the respiratory substrates.
* Respiratory Quotient is 1 if the respiratory substrate is carbohydrate.
* Respiratory Quotient is less than 1 if the respiratory substrate is fat or protein.