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Chapter: Biology: Physiological Activities in Plants Nutrition

Respiration: Respiratory substrate, Types of respiration

Every living being (Plants and Animals) have organic activities. Any work/function outside or inside the body there need energy.


Every living being (Plants and Animals) have organic activities. Any work/function outside or inside the body there need energy. The main source of this energy is the Sun. Green plants trapped light energy in carbohydrates (and others) food. This food successively being oxidised release energy. Using these energy living world performed all functions and reactions. O2 is needed to oxidize these organic compounds. As a result of oxidation CO2 is formed inside the living body. Therefore it is revealed that organic compounds oxidize by the reaction with O2, which is absorbed from the atmosphere. As a result of oxidation energy and CO2 are releases. Living bodies utilize the energy but release CO2 to the atmosphere. The process ran in both plant and animal cells. The process, by which energy and CO2 are produce by oxidation of food materials combining with O2, is called Respiration.


In respiration carbohydrate, protein, fat, organic acid etc. are oxidize and produce energy. The substances which take part in respiration are known as


Respiratory substrate.

Respiration occurs in cytoplasm and mitochondria of a living cell. There is no definite time for respiration. This process runs 24 hours throughout the day and night. Though respiration occur in all the cells yet the rate of respiration is more in developing region like flower and leaf buds, germinating seeds, apical region of root and stem. The process of respiration is explained by the following reaction.


Types of respiration


Respiration is of two types . (1) Aerobic Respiration and (2) Anaerobic Respiration. The respiration where O2 is essential called aerobic respiration The respiration that does not require O2 is called anaerobic respiration. Aerobic respiration occurs in all higher plants. Only few lower plants (some Bacterial and Fungi) have anaerobic respiration. The processes are discussed below:-


1. Aerobic Respiration: Aerobic Respiration is the normal respiration in plantand animals. In this process Carbohydrates break down and produce CO2 water and energy. Usually aerobic respiration is completed in four steps. the steps are as follows: -


Step - 1: Glycolysis: In this step one molecule of glucose, a 6-Carboncompound, after 9 successive reactions produces two molecules of Pyruvic, Acid, a 3- Carbon compound. In this step 4 molecules of ATP (2 molecules utilised) and 2 molecules of NADPH2 are produced.

Step - 2: Formation of Acetyle CO-A: Each molecule of Pyruvic Acidproduce during glycolysis after four successive reactions produces, one molecule of Acetyle Co-A, a 2-Carbon compound, one molecule of CO2 and one molecule of NADH2. [From 2 molecules of pyruvic acid there produces 2 molecules of Acetyle CO-A, 2 molecules of CO2 and 2 molecules of NADH2Step - 3: Krebs Cycle: Every molecule of Acetyle Co-A enter Krebs Cycle andafter 10 successive reactions produces 2 molecules of CO2, 3 molecules of FADH2, and I molecule of GTP (=ATP). From two molecules of Acetyle CO-A there produces 4 molecules of CO2, 6 molecules of NADH2, 2 molecules of FADH2, and 2 molecules of GTP (=ATP).


Step - 4: Electron Transport System: NADH2and FADH2produced in thefirst step, being oxidized produce ATP and water.

In aerobic respiration the complete oxidation of one molecule glucose totally produces 6 molecules of water and 38 ATP (686 K. Cal. Energy). First two steps occur in cytoplasm and next two steps occur in mitochondria. Every reaction of respiration is completed with the help of special types of Enzymes.


2. Anaerobic Respiration: Anaerobic Respiration does not require any O2. Itoccurs in two steps, they are: -


Step - 1: Glycolysis: In this step from one molecule of glucose there produces2 molecules of Pyruvic Acid, 4 molecules of ATP (2 molecules utilised) and 2 molecules of NADH2.


Step - 2: In this step from each molecule of Pyruvic Acid there produces onemolecule of Ethanol (Alcohol) and one molecule of CO2. Or from each molecule of Pyruvic Acid there produces only one molecule of Lactic Acid.


Importance of Aerobic Respiration:


1.    Energy produced in this process is utilised by living beings to perform all sorts of reaction and other functions.


2.        CO2, released in this process is utilised directly or indirectly in photosynthesis and produces carbohydrate food.


3.        This process helps plants in absorption of water, which indirectly keeps running growth and other organic processes.


4.        Organic acid that produces in respiration is necessary for other organic activities, Respiratory energy also heps cell divinion.


Importance of Anaerobic respiration :


1.     Some Bacteria cannot live in presence of oxygen. Among them the only process of producing energy is anaerobic respiration.


2.     In this process Ethyl alcohol is produced, industries, which is used in different industries.


3.  The process is utilised in Lactic Acid fermentation.


Factors Affecting Respiration:


Affecting Factors may either be external or internal: -


(a) External Factors:


1. Temperature: Below 20¡C and above 45¡C the rate of respirationreduces. The optimum temperature for respiration is 20¡C - 45¡C.

2. Oxygen: If the amount of oxygen is reduced the rate of respiration willreduce.

3. Water: Optimum supply of water maintains the rate of respiration normal.Rate of respiration reduces for scarcity of water.

4. Light: The stomata opens in light, so rate of respiration comparatively highin day time.

5. Carbon dioxide: With the increase of CO2in air, rate of respirationdecreases slightly.


(b) Internal Factors:


1.        Food materials: During respiration food materials break to release water andCO2. So the quality and quantity of food materials in the cell regulates the rate of respiration.


2.      Age of cell: Rate of respiration is maximum in young cells especially inmeristamatic cells (as there is much protoplasm).


3.        Enzymes: Different reactions of respiration need different kinds of enzymes.The process completely depends on their presence.


4.        Inorganic salts: Rate of respiration increases if there is more inorganic salts in the cell.

1. Experiment to prove that Heat is evolved during Respiration

Requirements:  One Thermo flask, some germinating Gram seeds and  athermometer.              

Procedure: Some germinating gram seeds are taken in the Thermo flask and closed its mouth tightly with a cork. A thermometer is introduced through the cork so that its bulb rests among the gram seeds. Note themercury reading of the thermometer.

Observation:  After some  time  an  increase  in  theobserved.

Conclusion: Rise of mercury indicates the rise of temperature. And thistemperature is produced by the respiration of the germinating seeds.


2. Experiment of Anaerobic Respiration


Requirements: One small beaker, one test tube, a stand with clamp, mercury,some gram seeds, a piece of caustic potash and a pair of forceps.


Procedure: Partly filled up the beaker with mercury. Fill up a test tubecompletely with mercury and invert it with the help of the thumb and put it over the beaker containing mercury. Now keep the test tube upright by clamping with a stand in such a condition as if the mouth of the test tube remain in the mercury but not touched the bottom of the beaker. Now introduce some germinating gram seeds into the test tube with the help of a pair of forceps. As the seeds are lighter than mercury, they will float over Mercury. Leave the experimental set for observation.

Observation: After several hours it will be seen that the mercury at the top ofthe test tube has displaced downwards by a gas released by germinating gram seeds. Now introduce the caustic potash stick into the test tube with the help of a pair of forceps. It will be observed that the test tube is completely filled up with the displaced mercury as the gas is absorbed by caustic potash stick.


Conclusion: The gas is absorbed by caustic potash so it was CO2andrespiration of gram seeds released the gas. Air cannot be present in the mercury and the gram seeds were present in mercury. So the respiration of gram seeds was anaerobic. Therefore in anaerobic respiration O2 is not required.

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