Anaerobic respiration, Respiratory quotient, Compensation point, Kuhne’s fermentation tube experiment

Anaerobic respiration, Respiratory quotient, Compensation point, Kuhne’s fermentation tube experiment

Anaerobic respiration

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Anaerobiosis means life in the absence of oxygen.

Certain organisms can survive in the absence of oxygen.

The respiration which takes place in the absence of free oxygen molecules is called anaerobic respiration.

It occurs in yeast and some bacteria.

Hence, they are known as anaerobes.

Glycolysis alone occurs in these organisms.

The splitting of glucose into two molecules of pyruvic acid is given in the following equation.

In anaerobic respiration, the respiratory substrate is not completely
oxidized to release energy.

Glucose is split into two molecules of pyruvic acid.

The pyruvic acid is further converted into either ethanol or organic acids like lactic acid.

Fermentation is a good example for anaerobic respiration.

Respiratory quotient

Respiratory quotient may be defined as “the ratio between the volume of carbondioxide given out and oxygen consumed during respiration”.

This value depends upon the nature of the respiratory substrate and its rate of oxidation.

Respiratory quotient for anaerobic respiration

In anaerobic respiration, carbondioxide is evolved but oxygen is not
consumed.

Therefore, the respiratory quotient in such case is infinity.
For example,

Compensation point

At a given low concentration of carbondioxide and nonlimiting light
intensity, the photosynthetic rate of a given plant will be equal to the total amount of respiration, which includes both dark respiration and
photorespiration.

The concentration of CO2 at which photosynthesis just compensates the respiration is referred to as carbondioxide compensation point.

At carbondioxide compensation point, the amount of CO2 uptake for photosynthesis is equal to that of CO2 generated.

Through respiration including photorespiration, so the net photosynthesis is zero under these conditions.

Fermentation

Fermentation literally means a chemical change accompanied by
effervescence.

The anaerobic breakdown of glucose to  carbondioxide and ethanol is a form of respiration referred to fermentation.

It is normally carried by yeast cells and accounts for the production of alcohol in alcoholic beverages.

In fermentation process, if glucose is converted into ethanol then it is called ethanolic fermentation.

When glucose is converted into organic acids such as lactic acid,
then this type of fermentation is known as lactic acid fermentation.

It is carried out by the bacterium Bacillus acidilacti.

Kuhne’s fermentation tube experiment

Kuhne’s fermentation tube consists of an upright glass tube and a
side tube with a bulb.

10 per cent glucose solution mixed with baker’s yeast is taken in the Kuhne’s tube and the tube is completely filled.

After some time, the glucose solution is fermented and gives out an alcoholic smell.

The level in the upright tube will fall due to the accumulation of CO2 gas.

It is because yeast contains the enzyme zymase which converts glucose solution into alcohol and CO2.

When a crystal of KOH is introduced into the tube, the KOH will absorb CO2 and the level of the solution will rise in the upright tube.

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For more details about Anaerobic respiration, Respiratory quotient, Compensation point, Kuhne’s fermentation tube experiment click here

Other links 

Plant tissue culture – origin and techniques

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Plant physiology – photosynthesis and its significance

---

Site of photosynthesis and Mechanism of photosynthesis

---

Electron transport system and photophosphorylation types

---

Dark reaction

---

C3 and C4 pathways

---

Photorespiration or C2 cycle

---

Factors affecting photosynthesis

---

Test tube and funnel experiment, Ganong’s light screen experiment

---

Mode of nutrition – Autotrophic, Heterotrophic

---

Chemosynthesis

---

Mechanism of Respiration – Glycolysis

---

Mechanism of Respiration – Oxidative decarboxylation , Krebs cycle

---

Mechanism of Respiration – Electron Transport Chain, Energy Yield

---

Ganong’s respiroscope, Pentose phosphate pathway

---

Plant growth and Measurement of plant growth

---

Phytohormones Auxins

---

Phytohormones Gibberellins

---

Phytohormones Cytokinin, Ethylene, Abscisic Acid, Growth Inhibitors – Physiological Effects

---

Photoperiodism and vernalization, Phytochromes and flowering

 

Ganongs respiroscope, Pentose phosphate pathway

Ganongs respiroscope, Pentose phosphate pathway

Demonstration of respiration by Ganongs respiroscope

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The aim of this experiment is to demonstrate liberation of carbon
dioxide during respiration.

The respiroscope is a glass apparatus consisting of a bulb like part with a bent neck and vertical tube.

Germinating seeds are taken in the bulb and the mouth of the tube is kept immersed in the beaker containing KOH solution as shown in the figure.

The respiroscope is fixed in the vertical position with the help of a stand.

Thus, the enclosed air in the bulb is completely cut off from the atmosphere.

The apparatus is kept undisturbed for few hours.

It is observed that the level of KOH solution in the limb is raised.

The KOH solution absorbs carbondioxide released by the seeds and a vacuum is created. It results in the raise of KOH level.

Pentose phosphate pathway

Generally, majority of living organisms obtain energy for various biochemical activities from glucose.

In aerobic organisms, it is degraded in three major phases namely, glycolysis, Krebs cycle and electron transport system.

In anaerobes, glucose is partially degraded by glycolysis and fermentation.

In 1938, Dickens discovered an alternate pathway for the utilization of glucose by the living cells.

This pathway is called pentose phosphate pathway or hexose monophosphate pathway or direct oxidation pathway.

This pathway consists of major phases – oxidative and nonoxidative phases.

Pentose phosphate pathway takes place in the cytoplasm only.

Oxidative phase

In this phase, glucose is oxidized and decarboxylated with the
formation of pentose through phosphogluconic acid as shown in the flow
chart.

The essential feature of this phase is the production of NADPH2.

1. Glucose is phosphorylated to glucose-6-phosphate by hexokinase.

2. The glucose-6-phosphate is oxidized to 6-phospho-gluconolactonate
in the presence of NADP+ by enzyme glucose-6-phosphate dehydrogenase.

NADP+ is reduced to NADPH2.

3. The 6-phosphogluconolactone is hydrolysed by gluconolactonase
to form 6-phosphogluconic acid.

4. The 6-phosphogluconic acid undergoes oxidative decarboxylation
again in the presence of NADP+ to form Ru5P. This reaction is catalyzed by 6-phosphogluconic dehydrogenase. NADP+ is reduced to NADPH2.
In this reaction CO2 is released.

Nonoxidative phase

In this phase, various intermediates such as 3C, 4C, 5C and 7-carbon
phosphorylated sugars are produced.

They are phosphoglyceraldehyde (3C), erythrose phosphate (4C), xylulose phosphate (5C) and sedoheptulose phosphate (7C).

To summarize, six molecules of glucophosphate enter this pathway.

After oxidation, six molecules of CO2 are released as shown in the step 4
and twelve molecules of NADPH2 are produced as shown in the steps 2
and 4.

In other words, after oxidation one molecule of glucose produces
six molecules of CO2 and twelve molecules of NADPH2.

Out of six glucose molecules one is completely oxidized and other five molecules are involved in the formation of 3C, 4C, 5C, and 7- carbon sugar intermediates.

From these intermediates, five molecules of glucose-6-phosphate are regenerated.

Significance of pentose phosphate pathway

It provides alternative route for carbohydrate breakdown.

The generates NADPH2 molecules which are used as reductants in
biosynthetic processes.

Production of NADPH2 is not linked to ATP generation in pentose phosphate pathway.

It provides ribose sugar for the synthesis of nucleic acids.

They provides erythrose phosphate required for the synthesis of aromatic compounds.

It plays an important role in fixation of CO2 in photosynthesis through Ru5P.

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For more information about Ganongs respiroscope, Pentose phosphate pathway click here

Other links 

Plant tissue culture – origin and techniques

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Plant physiology – photosynthesis and its significance

---

Site of photosynthesis and Mechanism of photosynthesis

---

Electron transport system and photophosphorylation types

---

Dark reaction

---

C3 and C4 pathways

---

Photorespiration or C2 cycle

---

Factors affecting photosynthesis

---

Test tube and funnel experiment, Ganong’s light screen experiment

---

Mode of nutrition – Autotrophic, Heterotrophic

---

Chemosynthesis

---

Mechanism of Respiration – Glycolysis

---

Mechanism of Respiration – Oxidative decarboxylation , Krebs cycle

---

Mechanism of Respiration – Electron Transport Chain, Energy Yield

---

Anaerobic respiration, Respiratory quotient, Compensation point, Kuhne’s fermentation tube experiment

---

Plant growth and Measurement of plant growth

---

Phytohormones Auxins

---

Phytohormones Gibberellins

---

Phytohormones Cytokinin, Ethylene, Abscisic Acid, Growth Inhibitors – Physiological Effects

---

Photoperiodism and vernalization, Phytochromes and flowering

 

Mechanism of Respiration – Electron transport chain

Mechanism of Respiration – Electron Transport Chain

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Electron transport system (ETS) is a chain of electron carriers
consisting of NAD+, FAD+, CoQ and cytochromes (cyt. b, cyt. c, cyt. a
and cyt. a3).

The glucose molecule is completely oxidized by the end of
the citric acid cycle.

But, energy is not released, unless NADH2 and FADH2 are oxidized through electron transport system.

Transfer of electrons and protons from NADH2 and FADH2 to oxygen through a series of components like flavoprotein, cytochrome is called electron transport chain.

This process leads to coupling of electrons to form high-energy
phosphate bonds in the form of ATP from ADP is called oxidative
phosphorylation.

The electron transport components are arranged in the
inner membrane of mitochondria.

According to modern concept, the electron carriers in the electron
transport system are arranged in four complexes – complex I, complex II,
complex III and complex IV.

When NAD+ is a primary acceptor of electrons, the electrons are transported from complex I to II, II to III and then to complex IV. When electrons are transported from one complex to next complex, an ATP is produced.

Thus, one molecule of NADH2 generates three ATPs. When FAD+ is a primary acceptor of electrons, the electrons are transported from complex II to III and then to complex IV.

Thus, one molecule of FADH2 generates two ATPs.

The molecular oxygen forms the terminal constituent of the electron
transport system.

It is the ultimate recipient of electrons and picks up the protons from the substrate to form water.

Energy yield

Complete oxidation of one glucose molecule yields a net gain of 38ATP.

Out of 38ATP molecules, 4ATP are obtained by direct substrate level
phosphorylation, 30ATP through oxidation of NADH2 and 4ATP through
oxidation of FADH2.

Since, a large number of ATP molecules are produced in the mitochondria, they are called the ‘power houses of the cell’.

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For more information about Electron Transport Chain click here

Other links 

Plant tissue culture – origin and techniques

---

Plant physiology – photosynthesis and its significance

---

Site of photosynthesis and Mechanism of photosynthesis

---

Electron transport system and photophosphorylation types

---

Dark reaction

---

C3 and C4 pathways

---

Photorespiration or C2 cycle

---

Factors affecting photosynthesis

---

Test tube and funnel experiment, Ganong’s light screen experiment

---

Mode of nutrition – Autotrophic, Heterotrophic

---

Chemosynthesis

---

Mechanism of Respiration – Glycolysis

---

Mechanism of Respiration – Oxidative decarboxylation , Krebs cycle

---

Ganong’s respiroscope, Pentose phosphate pathway

---

Anaerobic respiration, Respiratory quotient, Compensation point, Kuhne’s fermentation tube experiment

---

Plant growth and Measurement of plant growth

---

Phytohormones Auxins

---

Phytohormones Gibberellins

---

Phytohormones Cytokinin, Ethylene, Abscisic Acid, Growth Inhibitors – Physiological Effects

---

Photoperiodism and vernalization, Phytochromes and flowering

 

Mechanism of Respiration – Oxidative decarboxylation , Krebs cycle 

Mechanism of Respiration – Oxidative decarboxylation , Krebs cycle

Oxidative decarboxylation of pyruvic acid

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The two molecules of pyruvic acid formed from a glucose molecule
move into mitochondria and are oxidized, decarboxylated to two molecules
of acetyl coenzyme A (acetyl Co~A).

These 2 carbon compounds are formed by

2 Pyruvic acid + 2NAD⁺ →  2 Acetyl Co~A + 2NADH₂+ 2CO₂

decarboxylation and dehydrogenation.

This reaction is catalyzed by pyruvic dehydrogenase and two molecules of NAD+ are reduced to NADH2.

Duringthis reaction two molecules of CO2 are released.

Oxidative decarboxylation of pyruvic acid occurs only under aerobic condition.

Under anaerobic conditions, the pyruvic acid is reduced either to lactic acid or ethyl alcohol depending on the nature of the organism.

Krebs cycle

In 1937, Sir Hans Adolf Krebs described the catalytic role of pyruvic
acid for the production of energy in the cell.

The series of cyclic reactions involved in converting pyruvic acid to carbondioxide and water in mitochondria is called Krebs cycle.

It is also known as citric acid cycle or tricarboxylic acid cycle – TCA cycle.

1. In the first reaction of citric acid cycle, one molecule of acetyl
Co~A combines with oxaloacetic acid to form citric acid. This reaction
is catalyzed by citric acid synthetase. Citric acid contains three carboxylic
acid groups.

2. Citric acid is dehydrated to form cis-aconitic acid in the presence
of aconitase

3. The same enzyme aconitase catalyzes the formation of isocitric
acid from cis-aconitic acid by the addition of a molecule of water. Citric
acid, cis-aconitic acid and isocitric acid contain three carboxylic acid
groups.

4. The isocitric acid is oxidatively decarboxylated to a – ketoglutaric
acid. This reaction is catalyzed by isocitric dehydrogenase. During this
reaction, one NADH2 is formed.

5. The a – ketoglutaric acid is oxidatively decarboxylated to form
succinyl Co~A. This reaction is catalyzed by a – ketoglutaric
dehydrogenase. The energy released during this reaction is conserved in
NADH2.

6. The succinyl Co~A is hydrolysed to succinic acid in the presence
of succinyl Co-A synthetase. In this reaction, ADP is phosphorylated to
ATP. This is called substrate level phosphorylation.

7. The succinic acid is oxidized to form fumaric acid by succinic
dehydrogenase. Here, FAD+ is reduced to FADH2.

8. The fumaric acid is converted to malic acid by the addition of a
molecule of water. This reaction is catalyzed by fumarase.

9. The malic acid is oxidized to oxaloacetic acid by the enzyme malic
dehydrogenase. Here, NAD+ is reduced to NADH2.

Significance of Krebs cycle

2 molecules of acetyl CoA enter into Krebs cycle which on subsequent
oxidation generate 6NADH2, 2FADH2.

When 6NADH2, 2FADH2 enter into the electron transport system generate 22ATP molecules.

In one step, there is substrate level phosphorylation whch directly yield 2ATP molecules.

So, during Krebs cycle, every 2 molecules of acetyl CoA enter into Krebs cycle 24 ATP molecules are generated.

So, primarily it is a energy producing system.

Since, Krebs cycle involves with both anabolic and catabolic processes, it is also described as amphibolic process.

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For more information about Krebs cycle click here

Other links 

Plant tissue culture – origin and techniques

---

Plant physiology – photosynthesis and its significance

---

Site of photosynthesis and Mechanism of photosynthesis

---

Electron transport system and photophosphorylation types

---

Dark reaction

---

C3 and C4 pathways

---

Photorespiration or C2 cycle

---

Factors affecting photosynthesis

---

Test tube and funnel experiment, Ganong’s light screen experiment

---

Mode of nutrition – Autotrophic, Heterotrophic

---

Chemosynthesis

---

Mechanism of Respiration – Glycolysis

---

Mechanism of Respiration – Electron Transport Chain, Energy Yield

---

Ganong’s respiroscope, Pentose phosphate pathway

---

Anaerobic respiration, Respiratory quotient, Compensation point, Kuhne’s fermentation tube experiment

---

Plant growth and Measurement of plant growth

---

Phytohormones Auxins

---

Phytohormones Gibberellins

---

Phytohormones Cytokinin, Ethylene, Abscisic Acid, Growth Inhibitors – Physiological Effects

---

Photoperiodism and vernalization, Phytochromes and flowering

 

Mechanism of Respiration – Glycolysis

Mechanism of Respiration – Glycolysis

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Respiration

In the previous chapter, you have learnt that light energy is converted into chemical energy and stored in complex organic molecules called carbohydrates – glucose and starch.

The breaking of C – C bonds of such compounds through oxidation releases a considerable amount of energy.

This energy is utilized for various metabolic activities at cellular level.

This phenomenon of release of energy by oxidation of various organic molecules is known as respiration.

The compounds that are oxidised during this process are known as respiratory substrates.

Carbohydrate is the common respiratory substrate.

During respiration, the whole energy contained in the respiratory substrate is not released all at once.

In respiration, oxygen is utilized and carbondioxide, water and energy are released.

Respiration is an exothermic reaction and the oxidation of glucose is given in the following equation.

C₆H₁₂O₆ + 6O₂ ⟶ 6CO₂ + 6H₂O + ENERGY (2900 kJ)

The energy released during this process is transformed into usable form of energy as adenosine triphosphate (ATP).

ATP molecules act as carriers of free energy between energy yielding and energy requiring reactions of the cell.

Thus, ATP is described as energy currency of the cell.

It is a nucloetide consisting of adenine, ribose sugar and three phosphate groups.

It is an energy rich compound and contains two high energy terminal bonds.

A large amount of free energy is liberated, when these bonds are broken by hydrolysis.

Mechanism of respiration on glycolysis

Oxidation of glucose involves following four distinct stages –
glycolysis, oxidative decarboxylation of pyruvic acid, Krebs cycle and
Electron transport chain.

In the first three stages, the hydrogen acceptor Nicotinamide adenine dinucleotide – oxidized form (NAD+) and Flavin adenine dinucleotide – oxidized form (FAD+) are reduced to NADH2 and FADH2 respectively.

Both the coenzymes, (NAD+) and (FAD+) act as hydrogen carriers from respiratory substrate to electron transport chain, where H+ and electrons are transferred to oxygen to form water.

This electron transport results in the release of energy, which is used to phosphorylate ADP to ATP.

Hence, the electron transport chain reactions are referred to as oxidative phosphorylation.

Glycolysis

The process by which the glucose (6C compound) is split into two
molecules of pyruvic acid (3C compound) is called glycolysis.

Three German Microbiologists – Embden, Meyerhof and Parnas, first
demonstrated this process in yeast cell.

Hence, it is otherwise known as EMP pathway.

It occurs in cytoplasm.

It is common in all organisms.

It is divided into two phases – hexose phase and triose phase. Glyceraldehyde 3-phosphate and DHAP are the products of hexose phase and two molecules of pyruvic acid are the products of triose phase.

The overall reaction of glycolysis is given in the following equation.

C6H12O6 + 2ADP + 2Pi + 2NAD ⟶  2C3H4O3 + 2ATP + 2NADH2

Reactions involved in glycolysis are as follows

1. The glucose is phosphorylated with ATP to form glucose-6- phosphate. The reaction is catalyzed by the enzyme hexokinase.

2. Glucose-6-phosphate is isomerized to form fructose-6-phosphate by phosphoglucoisomerase.

3. Fructose-6-phosphate is then phosphorylated using ATP to form fructose 1,6-bisphosphate. This reaction is catalyzed by phosphofructokinase. The ATP is dephosphorylated to ADP.

4. Fructose 1,6-bisphosphate is cleaved by the enzyme aldolase to two molecules of 3C compounds – dihydroxy acetone phosphate (DHAP) and glyceraldehyde 3-phosphate. These two trioses are isomers.

5. DHAP and glyceraldehyde-3-phosphate are interconvertible by the action of triose phosphate isomerase. These five series of reaction constitute hexose phase and produce two molecules of 3-carbon compound called 3-  phosphoglyceraldehyde. In hexose phase two ATP molecules are
consumed.

6. A molecule of glyceraldehyde-3-phosphate is phosphorylated and oxidized to 1,3-bisphosphoglyceric acid in the presence of glyceraldehyde- 3-phosphate dehydrogenase. During this reaction, one NADH2 is formed.

7. 1,3-bisphosphoglyceric acid is dephosphorylated to a molecule of
3-phosphoglyceric acid by phosphoglyceric kinase. During this reaction one ATP is formed. This type of ATP synthesis is called direct phosphorylation or substrate level phosphorylation.

8. A molecule of 3-phosphoglyceric acid is then converted into a molecule of 2-phosphoglyceric acid by phosphoglyceric mutase. In this reaction, phosphate molecule is shifted form third carbon to second carbon.

9. A molecule of 2-phosphoglyceric acid is dehydrated to a molecule
of 2-phosphoenol pyruvic acid by enolase. Removal of water molecule
from the substrate is called enolation.

10. A molecule of 2-phosphoenol pyruvic acid is dephosphorylated
to pyruvic acid and ADP is phosphorylated to ATP. This reaction is
catalyzed by pyruvic kinase.

Thus, in the triose phase, two molecules of a molecule of 3-phospho glyceraldehyde produce 2 molecules of pyruvic acid.

In glycolysis, 4ATP and 2NADH2 molecules are formed and 2ATP
molecules are consumed in hexose phase.

Hence, the net gain is 2ATP and 2NADH2.

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For more details about Glycolysis click here

Other links 

Plant tissue culture – origin and techniques

---

Plant physiology – photosynthesis and its significance

---

Site of photosynthesis and Mechanism of photosynthesis

---

Electron transport system and photophosphorylation types

---

Dark reaction

---

C3 and C4 pathways

---

Photorespiration or C2 cycle

---

Factors affecting photosynthesis

---

Test tube and funnel experiment, Ganong’s light screen experiment

---

Mode of nutrition – Autotrophic, Heterotrophic

---

Chemosynthesis

---

Mechanism of Respiration – Oxidative decarboxylation , Krebs cycle

---

Mechanism of Respiration – Electron Transport Chain, Energy Yield

---

Ganong’s respiroscope, Pentose phosphate pathway

---

Anaerobic respiration, Respiratory quotient, Compensation point, Kuhne’s fermentation tube experiment

---

Plant growth and Measurement of plant growth

---

Phytohormones Auxins

---

Phytohormones Gibberellins

---

Phytohormones Cytokinin, Ethylene, Abscisic Acid, Growth Inhibitors – Physiological Effects

---

Photoperiodism and vernalization, Phytochromes and flowering

 

Chemosynthesis

Chemosynthesis

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Chemosynthesis is a process by which certain organisms synthesize carbohydrates by using energy obtained by the oxidation of inorganic substances.

Most of the bacteria obtain their food materials from external sources and they cannot synthesize their food by themselves.

These are called heterotrophic organisms.

Whereas, some bacteria are capable of synthesizing their food either by photosynthesis or chemosynthesis.

Organisms which use sunlight energy for synthesis of food materials are called photosynthetic organisms or photoautotrophs.

Those organisms which use chemical energy for the synthesis of carbon compounds are called chemosynthetic organisms.

There are two groups of chemosynthetic organisms namely, chemosynthetic autotrophs and chemosynthetic heterotrophs.

Chemosynthetic autotrophs

Examples for chemosynthetic autotrophs are Nitrosomonas, Beggiatoa.

Nitrosomonas oxidizes ammonia into nitrite.

The energy liberated during this process is used for the synthesis of carbohydrates.

2NH₃ +3O₂  → 2NO₂^– +2H₂O + 2H⁺ + Energy

Beggiatoa oxidises H2S to sulphur and water.

During this, energy is released and used for its growth.

Sulphur is stored as granules inside cell.

H₂S + [O] → H₂O + S + Energy

Chemosynthetic heterotrophs

Examples for chemosynthetic heterotrophs are fungi, most bacteria, animals and man.

These organisms cannot prepare their food materials, hence they are heterotrophs.

They obtain the energy for growth by chemi- cal reactions ie. by oxidizing the organic compounds.

For example, en- ergy is released when glucose is oxidised in the process of respiration.

Thus, these organisms are chemosynthetic heterotrophs.

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Other links 

Plant tissue culture – origin and techniques

---

Plant physiology – photosynthesis and its significance

---

Site of photosynthesis and Mechanism of photosynthesis

---

Electron transport system and photophosphorylation types

---

Dark reaction

---

C3 and C4 pathways

---

Photorespiration or C2 cycle

---

Factors affecting photosynthesis

---

Test tube and funnel experiment, Ganong’s light screen experiment

---

Mode of nutrition – Autotrophic, Heterotrophic

---

 

Mechanism of Respiration – Glycolysis

---

Mechanism of Respiration – Oxidative decarboxylation , Krebs cycle

---

Mechanism of Respiration – Electron Transport Chain, Energy Yield

---

Ganong’s respiroscope, Pentose phosphate pathway

---

Anaerobic respiration, Respiratory quotient, Compensation point, Kuhne’s fermentation tube experiment

---

Plant growth and Measurement of plant growth

---

Phytohormones Auxins

---

Phytohormones Gibberellins

---

Phytohormones Cytokinin, Ethylene, Abscisic Acid, Growth Inhibitors – Physiological Effects

---

Photoperiodism and vernalization, Phytochromes and flowering

 

Mode of nutrition in plants – Autotrophic, Heterotrophic 

Mode of nutrition – Autotrophic, Heterotrophic

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Mode of nutrition – Autotrophic nutrition

Most of the green plants are self- dependent, because they synthesize their own food materials by photosynthesis.

Such a mode of nutrition is described as autotrophic.  Autotrophic  plants are of different   types   according   to   their ecological environments.

Different environments cause differences in their morphology.

Thus, we find special adaptations in aquatic plants, terrestrial plants, xerophytes, mangrove plants etc.

Among the autotrophic plants, epiphytes are peculiar.

These plants usually grow on the branches of the trees.

Epiphytic plants are not parasitic on these trees, but they only make use of the place to grow.

They have two types of roots – clinging roots and aerial roots.

Clinging roots fix the epiphytes to the bark of the tree and also absorb the little nutrients found in the debris accumulating on the bark.

The aerial roots hang about in the air.

These roots are usually green and covered by a spongy tissue called velamen which absorbs the moisture in the air as well as rain water.

eg. Vanda.

Mode of nutrition – Heterotrophic  nutrition

Due to lack of chlorophyll or nitrogen defeciency, some plants have to depend on other plants, insects or dead organic matter for their food.

Such type of nutrition is known as heterotrophic.

Heterotrophic plants are grouped into saprophytic, parasitic and insectivorous plants.

Saprophytic plants

These plants obtain nutrition from non-living organic matter.

They are called saprophytic plants.

Many fungi and bacteria are saprophytes.

Certain angiosperms like Monotropa lack chlorophyll and have mycorrhizal roots.

This plant absorbs nourishments from the humus through their mycorrhizal roots.

Parasitic  plants

Some plants get their nourishments from other living plants or animals.

They are called parasitic plants.

The plants or animals from which the parasites get their nourishments are called hosts.

Parasites have some special roots, which penetrate the host plants and absorb food from the phloem and water and minerals from xylem.

These roots are called haustoria.

Parasitic angiosperms are of two types.

They are total parasites and partial parasites.

Some plants completely lack chlorophyll and do not grow in the soil.

Therefore, it is totally dependent on the host stem for organic food materials, water and minerals.

They are called total parasites.

eg. Cuscuta.

Cuscuta has thin, pale yellow and leafless stem.

It twines around the stem of the host and sends haustoria into it to absorb nourishments.

Some plants absorb only water and mineral salts from the stem of host plant.

They can manufacture their own food due to the presence of green leaves.

The haustoria of these plants have connection only with the xylem of the host to absorb water and mineral salts.

These plants are called partial parasites.

eg. Viscum.

Insectivorous plants

Though insectivorous plants are capable of manufacturing carbohydrates by photosynthesis, they are not able to synthesize enough proteins due to the deficiency of nitrogen.

They overcome this deficiency by catching small insects and digesting them.

Their leaves are modified in various ways for this purpose.

Such plants are called insectivorous plants. eg Drosera.

Drosera

Drosera is a small plant growing in marshy places.

This plant is also known as sundew plant.

The leaves of this plant have numerous hair-like structures called tentacles.

Each tentacle has got a gland at the tip.

The gland secretes a sticky fluid.

This fluid shines in sunlight and appears as dew;

hence the plant is called sundew plant.

When an insect is attracted by the shining sticky fluid and tries to sit on the leaf, it is entangled in the sticky fluid.

At once, the sensitive tentacles surround the insect and curve inward on it.

Then the glands secrete digestive juices which contain proteolytic enzymes.

The enzymes digest the proteins of the insect body.

The digested food is finally absorbed by the leaves and the tentacles again come in their original straight position.

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For more details about Mode of nutrition in plants click here

Other links 

Plant tissue culture – origin and techniques

---

Plant physiology – photosynthesis and its significance

---

Site of photosynthesis and Mechanism of photosynthesis

---

Electron transport system and photophosphorylation types

---

Dark reaction

---

C3 and C4 pathways

---

Photorespiration or C2 cycle

---

Factors affecting photosynthesis

---

Test tube and funnel experiment, Ganong’s light screen experiment

---

Chemosynthesis

---

Mechanism of Respiration – Glycolysis

---

Mechanism of Respiration – Oxidative decarboxylation , Krebs cycle

---

Mechanism of Respiration – Electron Transport Chain, Energy Yield

---

Ganong’s respiroscope, Pentose phosphate pathway

---

Anaerobic respiration, Respiratory quotient, Compensation point, Kuhne’s fermentation tube experiment

---

Plant growth and Measurement of plant growth

---

Phytohormones Auxins

---

Phytohormones Gibberellins

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Phytohormones Cytokinin, Ethylene, Abscisic Acid, Growth Inhibitors – Physiological Effects

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Photoperiodism and vernalization, Phytochromes and flowering

 

EXPERIMENTS ON PHOTOSYNTHESIS

Test tube and funnel experiment

Test tube and funnel experiment procedure is explain below.

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The test tube funnel experiment demonstrates that oxygen is evolved during photosynthesis.

A few branches of Hydrilla are kept in a beaker containing pond water in which a small amount of sodium bicarbonate is dissolved.

The branches are covered with a glass funnel and a test tube full of water is kept inverted over the stem of the funnel as shown in the figure.

Now the apparatus is kept in sunlight for 4 to 6 hours.

The gas bubbles may be observed from the ends of hydrilla branches kept within the glass funnel.

These gas bubbles are collected in the test tube by the downward displacement of water.

The gas is tested for oxygen.

When a burnt splinter is taken near the mouth of the tube, it glows brightly and proves that the gas is oxygen.

The test tube and funnel experiment demonstrates that oxygen evolves during photosynthesis.

Ganong’s light screen experiment

Ganong’s light screen experiment

Ganong’s light screen experiment demonstrates that light is essential for photosynthesis.

When a pot plant is kept for 48 hours in dark room, the leaves become free from starch.

Thus dark treated plant is called destarched plant.

Ganong’s light screen is a clip like instrument with a tin foil disc having a star shaped opening through which light can enter.

This closes the lower hollow cylindrical box like structure.

The advantage of light screen is to allow free ventilation and at the same time it cuts off light.

The light screen is fixed to a leaf of the destarched potted plant as shown in the figure.

The entire experimental setup is placed in sunlight for 4 to 6 hours.

The leaf subjected for experiment is tested for starch.

Only the star shaped part of the leaf exposed to the sunlight turns blue.

The Ganong’s light screen experiment demonstrates that light is essential for photosynthesis.

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For more detail about Test tube and funnel experiment click here

Other links 

Plant tissue culture – origin and techniques

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Plant physiology – photosynthesis and its significance

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Site of photosynthesis and Mechanism of photosynthesis

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Electron transport system and photophosphorylation types

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Dark reaction

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C3 and C4 pathways

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Photorespiration or C2 cycle

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Factors affecting photosynthesis

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Mode of nutrition – Autotrophic, Heterotrophic

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Chemosynthesis

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Mechanism of Respiration – Glycolysis

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Mechanism of Respiration – Oxidative decarboxylation , Krebs cycle

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Mechanism of Respiration – Electron Transport Chain, Energy Yield

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Ganong’s respiroscope, Pentose phosphate pathway

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Anaerobic respiration, Respiratory quotient, Compensation point, Kuhne’s fermentation tube experiment

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Plant growth and Measurement of plant growth

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Phytohormones Auxins

---

Phytohormones Gibberellins

---

Phytohormones Cytokinin, Ethylene, Abscisic Acid, Growth Inhibitors – Physiological Effects

---

Photoperiodism and vernalization, Phytochromes and flowering

 

Factors affecting photosynthesis

Factors affecting photosynthesis

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Photosynthesis is influenced by both environmental and genetic factors.

The environmental factors include light, availability of CO2, temperature, soil, water and nutrient supply  apart from age of leaf, leaf angle and leaf  orientation.

Photosynthesis is not affected by all environmental factors at a given time.

According to Blackmann who postulated Law of Limiting factor in 1905, photosynthesis is limited by slowest step of the most limiting factor in the pathway.

This means that at a given time, only the factor that is most limiting among all will determine the rate of photosynthesis.

For example, if CO2  is available in plenty but light is limiting due to cloudy weather, the rate of photosynthesis under such situation is controlled by the light.

Further,  if both CO2  and light are limiting, then the factor which is the most limiting of the two will control the rate of photosynthesis.

Both quality and intensity of light influence photosynthesis.

Light between the wavelength of 400nm to 700nm is most effective for photosynthesis and this light is called photosynthetically active radiation.

As the intensity of light increases the rate of photosynthesis increases.

However,  if the light intensifies, the rate of photosynthesis decreases.

This is because of higher intensity of light destruction of chlorophyll occurs.

Factors affecting photosynthesis – photochemical and dark reaction

Photochemical reactions and dark reactions of photosynthesis respond differently to temperature.

Photochemical reactions in the thylakoid remain unharmed by temperature, whereas the enzymatic dark reactions get influenced adversely.

At higher temperature, the enzymes become inactive.

Low temperature also inactivates the enzymes.

The current level of CO2  is about 0.036 per cent or 360 ppm (parts per million), which is very low as compared to the concentration of other gases in the atmosphere such as O2  and N2.

The rate of photosynthesis in all plants increases with increase in the concentration of  CO2  upto 500 ppm, when other factors are not limiting.

Availability of water in soil has a prominent effect on photosynthesis.

If the soil water becomes limiting factor, the rate of photosynthesis declines.

Among various nutrients, nitrogen has a direct relationship with photosynthesis.

Since, nitrogen is a basic constituent of chlorophyll and all enzymes involved in dark reactions, any reduction in nitrogen supply to plants has an adverse effect on photosynthesis.

In general all essential elements affect the rate of photosynthesis.

Among leaf factors, such as leaf age, leaf angle and leaf orientation, leaf age has the most prominent effect on photosynthesis.

If leaf undergoes, senescence, loss of chlorophyll occurs.

The photosynthetic enzymes also get inactivated resulting in reduced rate of photosynthesis.

Back to botany topic list

For more details about Factors affecting photosynthesis click here

Other links 

Plant tissue culture – origin and techniques

---

Plant physiology – photosynthesis and its significance

---

Site of photosynthesis and Mechanism of photosynthesis

---

Electron transport system and photophosphorylation types

---

Dark reaction

---

C3 and C4 pathways

---

Photorespiration or C2 cycle

---

Test tube and funnel experiment, Ganong’s light screen experiment

---

Mode of nutrition – Autotrophic, Heterotrophic

---

Chemosynthesis

---

Mechanism of Respiration – Glycolysis

---

Mechanism of Respiration – Oxidative decarboxylation , Krebs cycle

---

Mechanism of Respiration – Electron Transport Chain, Energy Yield

---

Ganong’s respiroscope, Pentose phosphate pathway

---

Anaerobic respiration, Respiratory quotient, Compensation point, Kuhne’s fermentation tube experiment

---

Plant growth and Measurement of plant growth

---

Phytohormones Auxins

---

Phytohormones Gibberellins

---

Phytohormones Cytokinin, Ethylene, Abscisic Acid, Growth Inhibitors – Physiological Effects

---

Photoperiodism and vernalization, Phytochromes and flowering

 

Photorespiration or C2 cycle

Photorespiration or C2 cycle

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In animals and bacteria, only one kind of respiration known as dark respiration occurs.

This is not affected by the presence or absence of light.

But in certain green plants, there are two distinct types of respiration – photorespiration and dark respiration.

Respiration that occurs in photosynthetic tissues in the presence of light and results in increased rate of carbondioxide evolution is called photorespiration or light respiration.

Photorespiration involves three organelles – chloroplasts, peroxisomes and mitochondria.

Oxidation of RuBP in the presence of high oxygen is the first reaction of photorespiration.

This reaction is catalysed by Rubisco* enzyme called carboxylase.

It leads to the formation of 2C compound – phosphoglycolic acid and 3C compound PGA.

When PGA is used up in the Calvin cycle, the phosphoglycolic acid is dephosphorylated to form glycolic acid in the chloroplasts.

From the chloroplast, the glycolic acid diffuses into the peroxisome where it is oxidised to glyoxalic acid and hydrogen peroxide.

In peroxisome from glyoxalic acid, glycine is formed.
Note : * Rubisco = Ribulose bisphosphate carboxylase

Glycine molecules enter into mitochondria where two molecules of glycine combine to give a molecule of serine, NH3 and CO2.

During this process, NAD+ is reduced to NADH2.

The aminoacid serine is taken to peroxisome where, it is converted into hydroxy pyruvic acid.

Hydroxy pyruvic acid is reduced by NADH2 to form glyceric acid.

The glyceric acid leaves peroxisome and enters chloroplast, where it is phosphorylated to PGA, which enters into Calvin cycle.

During the photorespiratory pathway, one CO2 molecule released in mitochondria is to be re-fixed.

Photorespiration is also known as photosynthetic carbon oxidation cycle or C2 cycle.

Under the conditions of high light and limited CO2 supply, photo respiration protects the plants from photooxidative damage.

This means that, if enough CO2 is not available to utilize light energy, excess energy causes damage to plant.

However, photo respiration utilizes part of the light energy and saves the plant from photooxidative damage.

Increased O2 level increases photo – respiration whereas increased CO2 level decreases photorespiration and increases photosynthesis.

Difference between photorespiration and dark respiration

Back to botany topic list

For more details about c2 cycle click here

Other links 

Plant tissue culture – origin and techniques

---

Plant physiology – photosynthesis and its significance

---

Site of photosynthesis and Mechanism of photosynthesis

---

Electron transport system and photophosphorylation types

---

Dark reaction

---

C3 and C4 pathways

---

Factors affecting photosynthesis

---

Test tube and funnel experiment, Ganong’s light screen experiment

---

Mode of nutrition – Autotrophic, Heterotrophic

---

Chemosynthesis

---

Mechanism of Respiration – Glycolysis

---

Mechanism of Respiration – Oxidative decarboxylation , Krebs cycle

---

Mechanism of Respiration – Electron Transport Chain, Energy Yield

---

Ganong’s respiroscope, Pentose phosphate pathway

---

Anaerobic respiration, Respiratory quotient, Compensation point, Kuhne’s fermentation tube experiment

---

Plant growth and Measurement of plant growth

---

Phytohormones Auxins

---

Phytohormones Gibberellins

---

Phytohormones Cytokinin, Ethylene, Abscisic Acid, Growth Inhibitors – Physiological Effects

---

Photoperiodism and vernalization, Phytochromes and flowering