12th botany neet school




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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


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