Bacteria which derive their energy from sunlight are called?

Appeared in: DSSSB - 29 August 2019 (Shift-1)

Explanation

The term 'photo' refers to light, and 'troph' refers to nourishment or feeding.
Phototrophs are organisms that capture photons (light energy) to produce complex organic compounds and to power their metabolic processes.
The question specifically asks for the term describing organisms that use sunlight as their energy source, which is the definition of a phototroph.
Examples of phototrophic bacteria include Cyanobacteria, which perform photosynthesis similar to plants.

Option A: Autotrophs are organisms that produce their own food from inorganic carbon sources (like CO₂). This term describes the carbon source, not the energy source. While some phototrophs are autotrophs (photoautotrophs), the term 'autotroph' itself doesn't specify that the energy comes from sunlight.
Option B: Chemotrophs derive their energy from chemical reactions (oxidation of chemical compounds), not from sunlight. The prefix 'chemo-' refers to chemical.
Option C: Heterotrophs are organisms that cannot produce their own food and must obtain carbon from organic sources. This term describes the carbon source, not the energy source.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Classification of bacteria based on their energy source as background academic context rather than a clinical decision trigger.
Understanding bacterial nutrition is fundamental in microbiology for culturing microorganisms in the lab, which is essential for diagnosing infections.
For example, chemoheterotrophs are the most common type of pathogenic bacteria, as they thrive by consuming organic matter from their host (e.g., human tissues).
Some phototrophic bacteria, like certain species of cyanobacteria, can produce toxins. In large numbers (blooms) in water bodies, they can be harmful to human and animal health if the water is ingested.

How to Approach the Question

First, identify the key terms in the question stem. The crucial phrase here is 'derive their energy from sunlight'.
Break down the word 'sunlight'. The scientific prefix for light is 'photo'.
Analyze the options provided. Look for the option that incorporates the concept of 'light' as an energy source.
Evaluate each option's prefix: 'Auto-' means self, 'Chemo-' means chemical, 'Hetero-' means other, and 'Photo-' means light.
Match the key term 'sunlight' with the prefix 'Photo-'. 'Phototroph' literally means 'light-feeder'.
Confirm the definitions of the other terms to ensure they are incorrect. Autotrophs and heterotrophs relate to the carbon source, while chemotrophs relate to a chemical energy source.

Concept Tested & Keywords

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E6 Microbiology Applied AnjuDhir 3e Part 1 pp. 76-78, 55-57

Practise the full DSSSB - 29 August 2019 (Shift-1)

Attempt every question from this paper in a timed mock, then review the full solution for each one.