respiration in plants

for agri students

1. RESPIRATION This is a process in which complex organic substances like carbohydrates, proteins,fats are broken down to release CO2 and water. Overall respiration process may be represented as - C 6 H 12 O 6 +6O 2 6CO 2 +6H 2 O+686Kcal It requires substrate, it may be carbohydrate, fats and in certain condition protein.

2. Types of respiration 1] Anaerobic respiration 2] Aerobic respiration Carbohydrates are firstly hydrolysed by the appropriate enzyme system to the hexose sugar. Actively respiring regions are growing regions like floral and vegetative buds , germinating seeds , stem and root apices.

3. • Oxygen is used for the process. • Takes place in the cells of all the higher plants and animals • Glucose is completely oxidized • The end products are carbon dioxide and water • Complete oxidation of one molecule of glucose yields 38 ATP molecules • Process takes place in both cytoplasm and mitochondria of the cell • Oxygen is not utilized for the process. • Takes place in some bacteria, fungi and certain endoparasites . • Glucose is partially oxidized • The end products are carbon dioxide and either ethyl alcohol or lactic acid • Partial oxidation of one molecule of glucose yields only 2 ATP molecules. • Takes place only in cytoplasm of the cell AEROBIC RESPIRATION ANEROBIC RESPIRATION

4. Anaerobic respiration Anaerobic respiration is one in which glucose is partially oxidised without using oxygen to yield lactic acid or ethyl alcohol and energy. C6H12O6 2C2H5OH + 2CO2 + ENERGY (alcoholic fermentation)

5. Fermentation is actually anaerobic respiration by microorganisms. Examples of fermentation are alcohol, lactic acid, acetic acid fermentation. In this process stored food is oxidised to certain compounds instead of CO2 and water. Glucose (C6 H12 O6 ) -------→ 2CH3CHOHCOOH +2ATP (Lactic acid fermentation)

6. Aerobic respiration Stored food gets completely oxidised to CO2 and water with release of some energy. C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O +686kcal Aerobic respiration is one in which molecular oxygen is used for the complete oxidation of glucose to yield CO 2 , H 2 O and 38 ATP molecules .

7. Respiratory quotient Formulae- vol. of CO2 evolved vol. of O2 absorbed R.Q. of some organic compounds – Carbohydrates- 1 Citric acid- 1.33 Fats – 0.7 Oxalic acid- 4 Malic acid- 1.33 Tartaric acid- 1.6

8. Aerobic respiration has 3 steps – Glycolysis Krebs cycle Electron transport system

9. Glycolysis – (Embden,Mayerhof and Paranas pathway , common respiratory pathway, cytoplasmic respiration) In this there is degradation of glucose(6 C) to pyruvic acid(3 C) without utilizing oxygen. It takes place in the cytoplasm of the cell and is common to aerobic and anaerobic respiration.

10. Pyruvic acid Pyruvic acid breakdown Lactate Ethanol Alanin Amino acid synthesis CO2+H2O+ATP Krebs cycle

11. Formation o Acetyl coA The 2 carbon compound Acetyl coA is connecting link between EMP and Krebs cycle

12. Krebs cycle (TCA cycle, organic acid cycle, mitochondrial respiration, oxidation of pyruvate, citric acid cycle) Sir Hans Krebs discovered the intermediate compounds of this cycle. Acetyl coA reacts with OAA (4C) to form citrate (6), first stable product. It operates in matrix of mitochondria. O2 is involved. operates place in aerobic respiration.

13. Electron transport system It is third step of respiration. It takes place in inner mitochondrial membrane (cristae).

14. NADH and FADH2 formed during glycolysis and Kreb’s cycle are oxidized to NAD and FAD. During this oxidation process, electrons pass through series of electron carriers (like co-enzyme Q, cytochromes b, c, a and a 3) and ADP is phosphorylated to ATP by the addition of Pi. Since oxidation of NADH and FADH2 is associated with the synthesis of ATP, it is called Oxidative Phosphorylation ’

15. Significance of respiration It releases energy which is consumed in various metabolic processes essential for plant life. It brings about the formation of other necessary compounds participating as important cell constituents. It converts insoluble food into soluble form It liberates CO2 and plays a part actively in maintaining the balance of carbon cycle.

16. Cyanide resistant respiration In higher plants,the activities of cytochrome oxidase are inhibited in presence of cyanide. Under such circumstances cyanide resistant oxidase or alternate oxidase becomes functional. It is believed that this alternate route deviates from ubiquinone of ETS chain. The e - from ubiquinone passes to flavoprotein to alternate oxidase and finally the e - is accepted by O2. It is also believed that instead of H2O, hydrogen perioxide is formed which is responsible for climactric in the fruits. H2O enhances oxidation and breakdown of membranes in ripening fruits.

17. It is also necessary for perioxide-catalysed reactions necessary for ethylene biosynthesis. Thus cyanide resistant respiration is important in fruit ripening. It is also believed that cyanide resistant respiration helps indirectly to run Kreb’s cycle in continuation to meet the requirement of intermediary organic acids. It keeps kreb’s cycle operative by oxidation of NADH and regeneration of NAD.