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Revision Notes on Respiration in Plants

Significance of respiration:

Respiration plays a significant role in the life of plants. The important ones are given below:

(i) It releases energy, which is consumed in various metabolic processes necessary for life of plant.

(ii) Energy produced can be regulated according to requirement of all activities.

(iii) It converts in soluble foods into soluble form.

(iv) Intermediate products of cell respiration can be used in different metabolic pathways

Differences between Photosynthesis and Respiration

Photosynthesis

Respiration

Occurs only in chlorophyll containing cells of plants.

Occurs in all plant and animal cells.

Takes place only in the presence of light.

Takes place continually both in light and in the dark.

During photosynthesis, radiant energy is converted into potential energy.

During respiration, potential energy is converted into kinetic energy.

Sugars, water and oxygen  are products.

CO2  and H2O are products.

Synthesizes foods.

Oxidizeds foods.

CO2 and H2O are raw materials.

O2 and food molecules are raw materials.

Photosynthesis is an endothermal process.

Respiration is an exothermal process.

Stores energy.

Releases energy.

It includes the process of hydrolysis, carboxylation etc.

It includes the process of the dehydrolysis, decarboxylation, etc.

Results in an increase in weight.

Results in a decrease in weight.

It is an anabolic process.

It is a catabolic process.

Require cytochrome.

Also require cytochrome.

Differences between cell respiration and combustion

S.No.

Characters

Cell respiration

Combustion

(i)

Nature of process

Biochemical and stepped process.

Physico-chemical and spontaneous process.

(ii)

Site of occurrence

Inside the cells.

Non-cellular.

(iii)

Control

Biological control.

Uncontrolled.

(iv)

Energy release

Energy released in steps.

Large amount of energy is released at a time.

(v)

Temperature

Remain within limits.

Rises very high.

(vi)

Light

No light is produced.

Light may be produced.

(vii)

Enzymes

Controlled by enzymes.

Not controlled by enzymes.

(viii)

Intermediates

A number of intermediates are produced.

No intermediate is produced.

Glycolysis Cycle

                                   

Enzymes of glycolysis and their co-factors

S. No.

Enzyme

Coenzyme (s) and cofactor

Activator (s)

Inhibitor (s)

Kind of reaction catalyzed

(i)

Hexokinase

Mg2+

ATP4-, Pi

Glucose 6-phopshate

Phosphoryl transfer

(ii)

Phosphogluco-isomerase

Mg2-

-

2-dioxyglucose

6-phosphate

Isomerization

(iii)

Phosphofructo-kinase

Mg2+

Fructose 2, 6-diphosphate, AMP, ADP, cAMP, K+

ATP 4-, citrate

Phosphoryl transfer

(iv)

Aldolase

Zn2+

( in microbes)

-

Chelating agents

Aldol cleavage

(v)

Phosphotriose isomerase

Mg2+

-

-

Isomerization

(vi)

Glyceraldehyde

3-phosphate dehydrogenase

NAD

-

Iodoacetate

Phosphorylation coupled to oxidation

(vii)

Phosphoglycerate kinase

Mg2+

-

-

Phosphoryl transfer

(viii)

Phosphoglycerate mutase

Mg2+  2,3-diphos phoglycerate

-

-

Phosphoryl shift

(ix)

Enolase

Mg2+ , Mn2+, Zn2+, Cd2+

-

Fluoride+ phosphate

Dehydration

(x)

Pyruvate kinase

Mg2+, K+

-

Acetyl CoA, analine, Ca2+

Phosphoryl transfer

Total input and output materials in glycolysis

Total Inputs

Total Outputs

1 molecule  of glucose (6 C)

2 molecules of pyruvate (2×3 C)

2 ATP

4 ATP

4 ADP

2 ADP

2 × NAD +

2× NADH + 2H+

2 Pi

H2O

Kreb’s Cycle

Enzymes of Kreb's cycle

Step

Enzyme

(Location in mitochondria)

Coenzyme(s) and cofactor (s)

Inhibitor(s)

Type of reaction catalyzed

(a)

Citrate synthetase

Matrix space

 CoA

Monofluoro-acetyl- CoA

Condensation

(b)

Aconitase

Inner membrane

Fe2+

Fluoroacetate

Isomerization

(c)

Isocitrate dehydrogenase

Matrix space

NAD+, NADP+, Mg2+, Mn2+

ATP

Oxidative decarboxylation

(d)

alpha-ketoglutarate dehydrogenase complex

Matrix space

TPP,LA,FAD,CoA,

NAD+

Arsenite,Succinyl-CoA, NADH

Oxidative decarboxylation

(e)

Succinyl-CoA synthetase

Matrix space

CoA

-

Substrate level

phosphorylation

(f)

Succinate dehydrogenase

Inner membrane

FAD

Melonate, Oxaloacetate

Oxidation

(g)

Fumarase

Matrix space

None

-

Hydration

(h)

Malate dehydrogenase

Matrix space

NAD+

NADH

Oxidation

Products formed during aerobic respiration by Glycolysis and Kreb’s cycle

Total formation of ATP         

ATP formation in Glycolysis

 

Steps

Product of reactions

In terms of ATP

ATP formation by substrate phosphorylation

1, 3-diphosphoglyceric acid (2 moles) ®

 3 phosphoglyceric acid (2 moles)

Phosphoenolpyruvic acid (2 moles) ®

Pyruvic acid (2 moles)

2 ATP

2 ATP

2 ATP

2 ATP

   

Total

4 ATP

ATP formation by oxidative phosphorylation or ETC

1, 3 - disphosphoglyceraldehyde (2 moles)

1, 3 – diphosphoglyceric acid (2 moles)

2 NADH2

6 ATP

 

Total ATP formed

4 + 6 ATP =

10 ATP

ATP consumed in Glycolysis

Glucose (1 mole) ® Glucose 6 phosphate (1 mole)

Fructose 6 phosphate (1 mole) ®

Fructose 1, 6-diphosphate (1 mole)

– 1 ATP

– 1 ATP

– 1 ATP

 

– 1 ATP

   

Total

2 ATP

 

Net gain of ATP = total ATP formed – Total ATP consumed

10 ATP – 2ATP

8 ATP

ATP formation in Kreb’s cycle

ATP formation by substrate phosphorylation

Succinyl CoA (2 mols) ®

Succinic acid (2 mols)

2 GTP

2 ATP

   

Total

2 ATP

ATP formation by oxidative phosphorylation or ETC

Pyruvic acid (2 mols) ®

Acetyl CoA (2 mols)

Isocitric acid (2 mols) ®

 Oxalosuccinic acid (2 mols)

a-Ketoglutaric acid (2 mols) ®

 Succinyl CoA (2 mols)

Succinic acid (2 mols) ®

 Fumaric acid (2 mols)

Malic acid (2 mols) ®

 Oxaloacetic acid (2 mols)

2 NADH2

 

2 NADH2

 

2 NADH2

 

2 FADH2

 

2 NADH2

6 ATP

 

6 ATP

 

6 ATP

 

4 ATP

 

6 ATP

   

Total

28 ATP

 

Net gain in Kreb’s cycle (substrate phosphorylation + oxidative phosphorylation)

2ATP + 28 ATP

30 ATP

Net gain of ATP in glycolysis and Kreb’s cycle

Net gain of ATP in glycolysis + Net gain of ATP in Kreb’s cycle

8 ATP + 30 ATP

38 ATP

Over all ATP production by oxidative phosphorylation or ETC

ATP formed by oxidative phosphorylation in glycolysis + ATP formed by oxidative phosphorylation or ETC.

6 ATP + 28 ATP

34 ATP

Difference between Aerobic, Anaerobic Respiration and Fermentation

Aerobic Respiration

Anaerobic Respiration

Fermentation

Molecular oxygen is the ultimate electron acceptor for biological oxidation. The ETS serves to transfer electrons from oxidisable donor to molecular oxygen. The early enzymatic steps involve dehydrogenation whereas the final steps are mediated by a group of enzyme called cytochromes. Ultimately the electrons are transferred to oxygen which is reduced to water. During aerobic respiration ATP is generated by coupled reaction 

The ultimate electron acceptor is an inorganic compound other than oxygen. The compounds accepting the hydrogen (electrons) are nitrates, sulphates, carbonates or CO2. Anaerobic respiration produces ATP through phosphorylation reaction involving electron transfer systems. (mechanism not known)

The final electron acceptors are organic compounds. Both electron donors (oxidizable substrate) and electron acceptors (oxidizing agent) are organic compounds and usually both substrates arise from same organic molecules during metabolism. Thus part of the nutrient molecule is oxidised and part reduced and the metabolism results in intramolecular electron rearrangement. ATP is generated by substrate level phosphorylation. This reaction differs from oxidative phosphorylation because oxygen itself is not required for ATP generation.    

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