Respiration in Plants
Chapter-14
Respiration in Plants
Points to Remember
Aerobic respiration : Complete oxidation of organic food in presence of oxygen thereby producing CO2, water and energy.
Anaerobic respiration : Incompleter breakdown of organic food to liberate energy in hte absence of oxygen.
ATP Synthesise : An enzyme complex that catalysis synthesis of ATP during oxidative phsophorylation.
Biological oxidation : Oxidation in a series of reaction inside a cell.
Cytochromes : A group of iron containing compounds of electron transport system present in inner wall of mitochondria.
Dehydrogenase : Enzyme that catalyes removal of H atom form he substrate.
Electron acceptor : Organic compound which receive electrons produced during oxidation-reduction reaction.
Electron transport : Movement of electron form substrate to oxygen through respiratory chain during respiration.
Fermentation : Breakdown of organic substance that takes place in certain microbe like yeast under anaerobic condition with the production of CO2 and ethanol.
Glycolysis : Enzymatic breakdown of glucose inot pyruvic acid that occurs in the cytoplasm.
Oxidation phsophorylation : Process of formation of ATP from ADP and Pi (Inorganic phosphate) using the energy form proton gradient.
Respiration : Biochemical oxidation food to release energy.
Respiratory Quotient : The ration of the volume of CO2 produced to the volume of oxygen consumed
Proton gradient : Difference in proton concentration across the tissue membrane.
Mitochondrial matrix : The ground material of mitochondria in which pyruvic acid undergoes aerobic oxidation through Kreb's cycle.
Electron Transport Chains (ETC) - A series of co-enzyems and electron/ carries where electrons can pass along increasing redox potential losing a bit of energy at every step of transfer.
Abbrevations
| ATP |
→ |
Adenosine-tri-phosphate |
| ATP |
→ |
Adenosine-tri-phosphate |
| ADP |
→ |
Adenosme-di-phosphate |
| NAD |
→ |
Nicotinamide Adenine dinucleotide |
| NADP |
→ |
Nicotinamide Adenine dinucleotide Phosphate |
| NADH |
→ |
Reduced Nicotinamide Adenine dinucleotide |
| PGA |
→ |
Phosphoglyceric acid |
| PGAL |
→ |
Phospho glyceraldehyde |
| FAD |
→ |
Flavin adenine dinucleotide |
| ETS |
→ |
Electron transport system |
| ETC |
→ |
Electron transport chain |
| TCA |
→ |
Tricarboylic acid |
| OAA |
→ |
Oxalo acetic acid |
| FMN |
→ |
Flavin mono nucleotide |
| PPP |
→ |
Pentose phosphate pathway |
Cell Respiration :
The process of oxidation breakdown of food material within the cell to releasee energy. Respiratory substrate to be oxidized during respiration is usually glucose, but these can also be proteins, fats or organic acids. In plants, respiratory gaseous exchange occurs through stomata and lenticels.
Overall cellular respiration is :
C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy (36ATPs)
Aerobic Respiration :
Overall mechanism of aerobic respiration can be studied under the following steps:
(A) Glycolysis (EMP pathway) in cytoplasm
(B) Oxidation Decarboxylation -(Gateway Reaction)- in Mitochondrial matrix.
(C) Kreb's cycle (TCA-cycle)- Matrix of mitochondria.
(D) oxidative phsophorylation
Glycolysis :
The term has originated from the Greek word, glycos = glucose, lysis = splitting, or breakdown means breakdown fo glucose molecules to pyruvic acid. It was given by Embden Meyerhof and Parnas. It is a chain of 10 reaction to convert glucose into pyruvate. It is common for aerobic and anaerobic respiration.
Steps for Glycolysis - (EMP Pathway):
| 1. |
Phsophorylation of Glucose inot Glucose-6-phosphate (ATP used) |
| 2. |
Isomerisation of Glucose-6-Phosphate into fructose-6-phosphate |
| 3. |
Second phsophorylation in which Fructose-6-phosphate changes inot Fructose-1, 6-biphosphate (ATP used) |
| 4. |
Splitting of Fructiose-1, 6-biphosphate into DiHAP and PGAL |
| 5. |
Isomerisation of DiHAP and PGAL |
| 6. |
Oxidation of PGAL inot 1, 3-biphosphosphoglycerate (NADH Produced) |
| 7. |
Synthesis of ATP and converssion of 1, 3-biphosphosphoglycerate into 3-phosphoglycerate |
| 8. |
Isomerisation of 3-biphosphosphoglycerate into 2-phosphoglycerate |
| 9. |
Dehydration of 2-phosphoglycerate into PEP (Removal of water) |
| 10. |
Substrate level ATP synthesis and formation of Pyruvic Acid. |
- It is also called Embden- Meyerhof- Paranas pathway. (EMP pathway)
- It is common in both acrobic and anaerobic respiration.
- It takes place outside the mitochondria, in the cytoplasm.
- One molecules of glucose (Hexose sugar) ultimately produces two molecules of pyruvic acid through glycolysis.
- During this process 4 molecules of ATP are Produced while 2 molecules ATP ar utilised. Thus net gain of ATP is of 2 molecules.
Input and Output of Glycolysis :
Net out put...... 2 Pyruvate + 2ATP + 2NADPH (+H+ OR 2 Pyruvate + 8ATP
The pyruvate so produced, so produced, may under go (i) Lactic acid fermentation, (ii) Alcoholic fermentation (iii) Aerobic Respiration (Krebs Cycle)
B. Oxidative Decarboxylation :
Pyruvic acid is converted into Acetyl CoA in presence of pyruvate dehydrogenase complex.
C. TriCarboylic Acid Cycle (Kereb's cycle) or Citric acid Cycle :
This cycle starts with condensation of acetyl group with oxaloacitic acid and wate to yield citric acid whic under goes.
- It is aerobic and takes a place in mitochondria matrix.
- Each pyruvic acid molecules produces 4 NADH + H+, one FADH2, one ATP.
- One glucose molecules has been broken down to release CO2 and eight molecules of NADH + H+, two molecules of FADH2 and 2 molecules of ATP.
Compensation Point : It is the value of a factor at which the rate of photosynthesis controlled by it is just equal to the rate of respiration and photorspiration so that there is not net exchange of gases between the photosynthetic organ and the enviroment.
At compensation point the photosynthetic tissue manufacture only such amount of food which of sufficient for it to remian alive. No food is supplied to rest of the plant. Therefore, net photosynthesis is zero.
D. Oxidative Phsophorylation :
The synthesis of ATP form ADP and inorganic phosphate using energy form proton gradient is called oxidative phsophorylation. This takes place in elementry paricles present on the inner membrane of cristae of mitochondria. This process in mitochondria is catalyesed by ATP synthestae (complex V). This complex has two major components F0 and and F1, F0 acts a channel for proton and F1 acts as an ATP synthetase.
Electron Transport system and Oxidation Phsophorylation:
Respiratory Balance Sheet :
Glucose + 6O2 + 36ADP + 36Pi → 6CO2 + 6H2O + 36 ATP
Total ATP Production
| Process |
Total ATP Produced |
| 1. Glycolysis |
2ATP + 2NADPH2 (6ATP) = 8ATP |
| 2. Oxidative decarboxylation |
2NADPH2 (6ATP) = 6ATP |
| 3. Kreb's Cycle |
2GTP (2ATP) + 6NADPH2 (18ATP) + 2FADH2 (4ATP) = 24 ATP |
Energy production in prokaryotes during aerobic respiration = 38 ATP
Energy poroduction in eukaryotes during aerobic respiration = 38 - 2 = 36 ATP
In eukaryotes 2 ATP are used in transporting 2 molueules of NADH + H+ formed in glycolsis from cytoplasm to mitochondria for oxidation through ETS shuttle.
(2) Anaerobic Respiration-- In anaerobic respiration, Glycolysis if followed by formation of ethanol or lactic or lactic acid in the cytoplasm.
Fermentation : It is the process of anaerobic respiration which occurs in yeast and some bacteria. Fermentation involves incompleter oxidation of food into enthanol and carbon-dio-oxide. It result in the production of 2 ATP molecules.
(I) Conversion of Acetyl CoA into fatty acid and PGA.
(II) Synthesis of chlorophyll and cytochromes from Succinyl CoA.
(III) Synthesis of Amino acids from OAA and a-ketoglutaric acid
(IV) Synthesis of Alkaloid form OAA.
Enzymes involved-Pyruvic acid decarboxylase, Alcohol dehydrogenase.
Anaerobic respiration in muslces : During vigrous exercise a person feels pain and fatigue in his muslces. This is due to accmulation of lactic acid in muslces. When oxygen is inadequate pyruvic acid is reduced to lactic acid in presence of enzyne-lactic dehydrogenase
During rest lactic acid is reconvertred to pyruvic acid.
Amphibolic Pathway :
During the process of cellular respiration Carbohydrates, fats and proteins are broken down to release energy and hence respiration is a catabolic process/ catabolic pathway. From this pathway many compound are withdrawn for synthesis of substrates. Some anabolic processes are formation of pyruvic acid from amino acids, and formation of Acetyl CoA form Fatty acid. So- Respiratory pathway is involved in both catabolism and anabolism, it is better to consider teh respiratory pathway as an emphilbolic pathway.
RQ (Respiratory Quotient):
(a) RQ = 1 (When carbohydrate is used as substrate)
C6H12O6 → 6CO2 + 6H2O + Energy
(b) RQ is less than 1 (i.e., < 1) (When fats are used as substrate)
2C51H98O6 + 145O2 → 102CO2 + 98 H2O + Energy
Tripalmitin
102 CO2
R.Q. → --------- = 0.7
145 O2
(c) RQ is 0.9 for proteins
(d) RQ is more than 1 (i.e., > 1) for organic acids.
(e) RQ is inifinite is case of anaerobic respiration, beacuse CO2 in evolved but O2 is not consumed.
