Autotrophs, Definition, Types, Examples and MCQs for NEET Exam

 An autotroph is an organism capable of producing its own food using simple substances like carbon dioxide (CO2) and converting abiotic energy into complex organic compounds, such as proteins and carbohydrates. This process is essential for sustaining life, as autotrophs serve as the primary producers in ecosystems, providing energy for all other organisms that cannot produce their own food. Autotrophic organisms are crucial for maintaining ecological balance, and their understanding is important for the NEET Exam.

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Definition of Autotrophs

Types of Autotrophic Bacteria

• Photoautotrophs : These bacteria , also known as photosynthetic bacteria, obtain their energy from sunlight.
• Chemoautotrophs: Also referred to as chemosynthetic bacteria, these organisms harness chemical energy to create their food

Photoautotrophs

• Aerobic Photosynthetic Bacteria: These bacteria require oxygen for photosynthesis. An example is cyanobacteria, also known as blue-green algae, which utilize water molecules in a process called oxygenic photosynthesis. During this process, they release oxygen as a byproduct. While they contain photosynthetic pigments like chlorophyll-a, they lack chloroplasts. The photosynthesis reaction can be summarized as follows:

6CO2​+12H2​O+light→C6​H12​O6​+6O2​+6H2​O

• Examples of aerobic bacteria include Nostoc and Anabaena . These bacteria can form colonies and are capable of nitrogen fixation.
• Anaerobic Photosynthetic Bacteria : Unlike aerobic bacteria, anaerobic photosynthetic bacteria do not require oxygen and instead use hydrogen sulfide or thiosulfate as reducing agents. They contain a different pigment called bacteriochlorophyll instead of chlorophyll. Examples include:
  • Purple Sulfur Bacteria : Found in hot springs and stagnant water, these bacteria thrive in low-oxygen environments and utilize hydrogen sulfide for photosynthesis. They possess bacteriochlorophyll ‘a’ and ‘b’ within their plasma membrane.
  • Purple Non-Sulfur Bacteria : These bacteria utilize hydrogen as a reducing agent instead of hydrogen sulfide. They play a crucial role in producing beneficial substances like vitamins and growth-promoting compounds, enhancing plant yields and resilience against environmental stress.
  • Green Sulfur Bacteria : These bacteria live in deep oceans and low-light conditions. They use hydrogen sulfide, hydrogen, or ferrous ions for photosynthesis, and contain multiple forms of bacteriochlorophyll.

Chemoautotrophs

• Sulfur Bacteria : These bacteria oxidize hydrogen sulfide or thiosulfates to produce sulfur or sulfate. They play an important role in the sulfur cycle. Examples include Beggiatoa , Thiothrix , and Thiobacillus . An example of the reaction is:

2H2​S+O2​→2H2​O+2S+energy

• Nitrogenous Bacteria : These bacteria convert ammonia into nitrite and then nitrate, releasing energy in the process. This converted nitrate is utilized by plants. Examples include Nitrosomonas and Nitrobacter . An example reaction is:

NH3+O2→NO2+H2O+energy

• Hydrogen Bacteria : These bacteria use hydrogen as their energy source. Aerobic hydrogen-oxidizing bacteria use oxygen as an electron acceptor, while anaerobic types may use nitrogen dioxide or sulfate. The reaction is:

2H2+O2→2H2O+energy

• Methanotrophs : These bacteria use methane as their primary carbon source. They can be either aerobic or anaerobic. Aerobic methanotrophs oxidize methane to produce formaldehyde, which is then used in various pathways to create organic molecules.
• Examples include  Methylomonas and Methylococcus capsulatus .
• Iron Bacteria : These bacteria oxidize ferrous ions to ferric ions, allowing them to thrive in iron-rich environments. The energy production reaction is:

4FeCO3+O2+6H2O→4Fe(OH)3+4CO2+energy

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Difference Between Autotrophs and Heterotrophs

MCQs of Autotrophs

Q1. Autotrophs are also known as;

1. consumers
2. heterotrophs
3. producers
4. decomposers

Q2. Which of the following is incorrect about Cyanobacteria?

1. They lack heterocyst.
2. They often form blooms in polluted water bodies.
3. They have chlorophyll ‘a’ similar to green plants.
4. They are photoautotrophs.

Q3. What is the primary mode of energy production for autotrophs?

1. Cellular respiration
2. Fermentation
3. Photosynthesis
4. Oxidative phosphorylation

Answers of MCQs of Autotrophs