Chapter 14 respiration in plants chapter.

UNIT – IV : PLANT PHYSIOLOGY
CHAPTER 14 : RESPIRATION IN PLANTS.
Exchange gases; Cellular respiration-glycolysis, fermentation (anaerobic), TCA cycle and electron transport system (aerobic); Energy relations-Number of ATP molecules generated; Amphibolic pathways; Respiratory quotient.

1. Biology by Kailash Sir,
Chapter 14
:
Respiration In Plants
.
By Mr.Kailash
Vilegave


1


Chanakya Academy
Shahapur (Maharashtra)
Mob:[phone]



CHAPTER 14: RESPIRATION IN PLANTS.
1. Introduction:
Respiration in Plants
“Plant respiration is the chemical reaction by which plants cells stay alive.”
Do Plants Breathe?
The answer to this question is not direct. Yes, plants need oxygen for respiration but at the same time they also
give out carbon dioxide. Thus, plants have proper system to ensure the availability of oxygen. Unlike animals,
plants do not possess any specialized organs for exchange of gases but they have lenticels and stomata
(present in stems and leaves respectively) that carry out the function of gaseous exchange.
Plants do not have any specialized organ to respire and exchange gases because each part of the plant takes
care of the need of gases themselves.
Glucose + Oxygen → Carbon Dioxide + Water (+ Energy)
Cellular Respiration
 It is the process of oxidation / breakdown of food materials within the cell to release energy.
 Respiratory substrate to be oxidized during respiration is usually glucose, but these can also be proteins, fats or
organic acids.
 In plants respiration gas exchange occurs through stomata and lenticels.
Overall cellular respiration is:

C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy (36 ATPs)



2.Types of respiration:
Respiration is of two types
A. Aerobic respiration.
B. Anaerobic respiration

2. Biology by Kailash Sir,
Chapter 14
:
Respiration In Plants
.
By Mr.Kailash
Vilegave


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Chanakya Academy
Shahapur (Maharashtra)
Mob:[phone]




A. Aerobic respiration.
In this type of respiration, the food substances are completely oxidized into H2O and CO2 with the release of
energy. It requires atmospheric oxygen and all higher organisms respire aerobically. Following figure shows
the steps included in Aerobic Respiration.

A. Anaerobic respiration
In this type of respiration, partial oxidation of food takes place and energy is released in the absence of
oxygen. This type of respiration occurs in prokaryotic organisms like bacteria and yeast. Ethyl alcohol and
carbon dioxide are formed in this process.


Mechanism of respiration:

3. Biology by Kailash Sir,
Chapter 14
:
Respiration In Plants
.
By Mr.Kailash
Vilegave


3


Chanakya Academy
Shahapur (Maharashtra)
Mob:[phone]




Fermentation :
Incomplete oxidation of pyruvic acid, under anaerobic respiration forms lactic acid/ ethyl alcohol. It occurs in
bacteria, yeast and striated muscles.

In yeast fermentation: Pyruvic acid → Ethanol + CO2
o Enzymes involved − Pyruvic acid decarboxylase, Alcohol dehydrogenas.
Only 7% of energy of glucose is released during fermentation.
Yeasts poison themselves to death when alcohol concentration reaches about 13%.
In bacterial fermentation: Pyruvic acid → Lactic acid.
o Enzyme involved − Lactate dehydrogenase.
o While doing severe exercise similar reaction occurs in animal muscles in anaerobic conditions.

 Glycolysis – it is common to both aerobic and anaerobic
respiration
 Citric acid cycle / Krebs cycle - Aerobic respiration in
mitochondria
 Electron transport system – in the inner membrane of
mitochondria
 Both aerobic and anaerobic respiration starts with
Glycolysis.
 In aerobic respiration Glycolysis is followed by Citric acid
cycle and ETS (both occur in mitochondria).
 In anaerobic respiration Glycolysis is followed by
formation of ethyl alcohol / lactic acid in the cytoplasm.

4. Biology by Kailash Sir,
Chapter 14
:
Respiration In Plants
.
By Mr.Kailash
Vilegave


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Chanakya Academy
Shahapur (Maharashtra)
Mob:[phone]



3. Aerobic respiration:
Aerobic respiration follows five step set of reactions.
These are 3.1. Glycolysis
3.2. Link reaction.
3.3. Kreb’s cycle/ citric acid cycle.
3.4. Electron transport system (ETS)
3.5. Oxidative phosphorylation.
3.1. Glycolysis :
It is the process of breaking down of glucose to pyruvic acid.
It was given by Embden, Meyerhof and Parnas
A chain of 10 reactions converts glucose into pyruvate.
Net ATPs produced = 4 (produced) − 2 (consumed) = 2 ATPs
The pyruvate, so produced, may undergo:
 Lactic acid fermentation
 Alcoholic fermentation
 Aerobic respiration (Krebs cycle)
So glycolysis is common pathway for aerobic as well as anaerobic respiration.
3.2. Link reaction/ intermediate phase/ Formation of Acetyl Coenzyme A
 Pyruvate from glycolysis is actively pumped into mitochondria.
 One carbon dioxide molecule and one hydrogen molecule are removed from the pyruvate (called oxidative
decarboxylation) to produce an acetyl group, which joins to an enzyme called CoA to form acetyl CoA.

5. Biology by Kailash Sir,
Chapter 14
:
Respiration In Plants
.
By Mr.Kailash
Vilegave


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Chanakya Academy
Shahapur (Maharashtra)
Mob:[phone]




3.3. Citric acid cycle / Tricarboxylic acid cycle / Kreb’s cycle:
 TCA cycle – it takes place in the mitochondrial matrix – it is the process of complete oxidation of pyruvate by
stepwise removal of all hydrogen atoms, which leaves three molecules of CO2.
 Electron Transport Chain and Oxidative phosphorylation – it takes place in the inner membrane of the
mitochondria – it is the process of synthesis of ATP fron NADH2 and FADH2.
 Overall reaction :

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Chapter 14
:
Respiration In Plants
.
By Mr.Kailash
Vilegave


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2 acetyl CoA + 6NAD
+
+ 2FAD + 2ADP + 2Pi → 4 CO2 + 6 NADH + 6H
+
+ 2 FADH2 + 2ATP


3.4. Electron Transport Chain (ETS)
 NADH2 and FADH2 are oxidized to release the energy stored in them in the form of ATPs.
 Electrons are passed from one carrier to another, and finally to oxygen, resulting in the formation of water.
 Oxidation of 1 NADH produces 3 ATPs.
 Oxidation of 1 FADH2 produces 2 ATPs.

7. Biology by Kailash Sir,
Chapter 14
:
Respiration In Plants
.
By Mr.Kailash
Vilegave


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3.5. Oxidative Phosphorylation
As it turns out, the reason you need oxygen is so your cells can use this molecule during oxidative phosphorylation,
the final stage of cellular respiration. Oxidative phosphorylation is made up of two closely connected components:
the electron transport chain and chemiosmosis.

8. Biology by Kailash Sir,
Chapter 14
:
Respiration In Plants
.
By Mr.Kailash
Vilegave


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Chanakya Academy
Shahapur (Maharashtra)
Mob:[phone]

9. Biology by Kailash Sir,
Chapter 14
:
Respiration In Plants
.
By Mr.Kailash
Vilegave


9


Chanakya Academy
Shahapur (Maharashtra)
Mob:[phone]



4. Respiratory Balance Sheet:
Theoretically, we can calculate the net gain of ATP for every molecule of oxidized glucose and this calculation is
based on following assumptions –
 There is an orderly and sequential functioning of the pathway; with one substrate forming the next with
glycolysis, Krebs cycle and Electron Transport System following one after another.
 The NADH formed during glycolysis is transferred into mitochondria and oxidative phosphorylation takes place.
 None of the intermediates in any process is utilized to synthesize any other compound.
 No alternative substrates except glucose are respired.
All of the pathways work simultaneously but none of the above mentioned assumptions are really valid in living
system. Substrate that enters the pathways are extracted as and when required, ATP is utilized as and when
required, the rate of enzyme is controlled by several means. On the other hand, doing this exercise is important
as it appreciate the efficiency and beauty of the living system in extracting and storing energy. Thus, there can be
net gain of 36 ATP molecules from one molecule of glucose in case of aerobic respiration.
Following figures explains the net gain of ATP:



Theoretically, we can calculate the net gain of ATP for every molecule of oxidized glucose and this calculation is
based on following assumptions –
 There is an orderly and sequential functioning of the pathway; with one substrate forming the next with
glycolysis, Krebs cycle and Electron Transport System following one after another.
 The NADH formed during glycolysis is transferred into mitochondria and oxidative phosphorylation takes place.
 None of the intermediates in any process is utilized to synthesize any other compound.

10. Biology by Kailash Sir,
Chapter 14
:
Respiration In Plants
.
By Mr.Kailash
Vilegave


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Shahapur (Maharashtra)
Mob:[phone]



 No alternative substrates except glucose are respired.
All of the pathways work simultaneously but none of the above mentioned assumptions are really valid in living
system. Substrate that enters the pathways are extracted as and when required, ATP is utilized as and when
required, the rate of enzyme is controlled by several means. On the other hand, doing this exercise is important as it
appreciate the efficiency and beauty of the living system in extracting and storing energy. Thus, there can be net gain
of 36 ATP molecules from one molecule of glucose in case of aerobic respiration.
Following figures explains the net gain of ATP:
 Glycolysis 2ATP + 2NADH2 (6ATP) = 8ATP
 Oxidative decarboxylation 2NADH2 (6ATP) = 6ATP
 Krebs’s Cycle 2GTP (2ATP) + 6NADH2 (18ATP) + 2FADH2 (4ATP) = 24 ATP
 Energy production in prokaryotes during aerobic respiration = 38 ATP
 Energy production in eukaryotes during aerobic respiration = 38 − 2 = 36 ATP
 (2ATP are used up in transporting 2 molecule of pyruvic acid in mitochondria.)

5. Common pathways for Proteins, fats and carbohydrates:
PROTEIN AS AN ENERGY SOURCE
Proteins are used as an energy source only if protein intake is high, or if glucose and fat sources are depleted, in
which case amino acids from protein breakdown are converted into molecules that can enter the TCA Cycle. These
molecules are produced by either of two categories of reactions that alter the structure of amino
acids. Transamination transfers an amino group (NH2) from one amino acid to another,
whereas deamination removes an amino group from an amino acid. As they accumulate, the amino groups removed
by the process of deamination are altered to form a harmful waste product (ammonia), so are converted by the liver
into urea which is excreted by the kidneys.

FAT AS AN ENERGY SOURCE
Fats (lipids) are stored in adipose tissue. These stored fat molecules are synthesized in the body from the breakdown
products of fat digestion (glycerol and fatty acids), in a process known as lipogenesis (p. 501). When needed as an
energy source, the fat reserves are mobilized, moved out of adipose tissue, and broken down into glycerol and fatty
acids in the liver by the process of lipolysis. Glycerol is changed into one of the intermediate products of glycolysis,
so enters the cell respiration pathway. Fatty acids are changed in a series of reactions called beta-oxidation into

11. Biology by Kailash Sir,
Chapter 14
:
Respiration In Plants
.
By Mr.Kailash
Vilegave


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Shahapur (Maharashtra)
Mob:[phone]



acetyl CoA molecules, which enter cell metabolism at the Kreb's Cycle. When fats are being used as the primary
energy source such as in starvation, fasting or untreated diabetes, an excess amount of acetyl CoA is produced, and
is converted into acetone and ketone bodies. This produces the sweet smell of acetone on the breath, noticeable in
a diabetic state.

GLUCOSE AS AN ENERGY SOURCE
The above notes describe the process of carbohydrate (glucose) catabolism for the production of ATP. When glucose
is in adequate supply, such as shortly after consumption of a meal, the hormone insulin from the pancreas
increases glycogen formation (glycogenesis) in the liver. When glucose levels drop between meals, the
hormone glucagon is released from the pancreas and stimulates the conversion of glycogen into glucose (by the
process of glycogenolysis). If all glycogen supplies are depleted, then other substances in the body are converted
into glucose or intermediate products that can enter the above-outlined cellular respiration pathway. The conversion
of fatty acids (from lipids) or amino acids (from proteins) into glucose or intermediate products is
called gluconeogenesis.

6. Respiratory Quotient (RQ):
This is another aspect of respiration. “Respiratory quotient is the ratio of CO2 produced to O2 consumed while food is
being metabolized.”

Where, RQ stands for Respiratory Quotient
RQ depends on the type of respiratory substrate used in respiration. When carbohydrate is used as substrate and is
completely oxidized, RQ becomes 1. It implies equal amount of O2 and CO2 are consumed and evolved. This reaction
is displayed in the figure below –

In case, fats are used during the process of respiration, RQ becomes less than 1. Following equation shows the
calculation for fatty acid and tripalmitin is used as substrate –

When protein is used as respiratory substrates the ratio comes out to be 0.9.
7. Significance of respiration.
Cellular respiration is important because it provides the energy for living organisms to perform all of the other
necessary functions to maintain life. Most single-celled organisms, such as bacteria, do not require much energy
and are able to survive on glycolysis and fermentation.

12. Biology by Kailash Sir,
Chapter 14
:
Respiration In Plants
.
By Mr.Kailash
Vilegave


12


Chanakya Academy
Shahapur (Maharashtra)
Mob:[phone]



8. Factors affecting Respiration in Plants
There are eight environmental factors that has significant impact on respiration in plants –
 Oxygen content of the atmosphere
 Effect of water content
 Effect of temperature
 Effect of availability of light
 Impact of respirable material
 Effect of concentration of carbon dioxide in atmosphere
 Protoplasmic conditions, i.e. younger tissues have greater protoplasm as compared to older tissues.
 Other factors, i.e. fluorides, cyanides, azides, etc.