Biology · Biological Classification · NEET
Heterotrophic means "other-feeding". These bacteria cannot make their own food by photosynthesis or by using inorganic chemicals. So they take ready-made organic carbon from other living or dead organisms. NCERT says heterotrophic bacteria are the most abundant bacteria in nature, and the majority of them are important decomposers (they break down dead matter).
No. This is a very common exam trap. Bacteria show huge metabolic variety. Some are autotrophic: photosynthetic autotrophs (like cyanobacteria) and chemosynthetic autotrophs (that oxidise nitrates, nitrites, ammonia). Heterotrophic bacteria are only ONE group, even though they are the most abundant. So a statement like "Bacteria are exclusively heterotrophic" is WRONG (NEET 2019/2022 tested exactly this).
NCERT lists these helpful roles: (1) making curd from milk, (2) production of antibiotics, and (3) fixing nitrogen in the roots of legumes (like the root nodules of pea and gram plants). Also, as decomposers they recycle nutrients back into nature. Remember: curd, antibiotics, nitrogen-fixing = the three NCERT uses.
Some heterotrophic bacteria are pathogens that damage humans, crops, farm animals and pets. NCERT names four well-known ones: Cholera, Typhoid, Tetanus (in humans) and Citrus canker (a plant disease). Learn these four exactly, because NEET asks the NCERT list, not outside examples.
Because most of them feed on dead organic matter (they are saprophytic). While breaking it down for energy, they release simple nutrients back into the soil and water. This is why NCERT says they are "important decomposers" and play a great role in recycling nutrients like nitrogen, phosphorus, iron and sulphur.
Heterotrophic is the broad label (needs organic food from outside). Within it, a saprophyte feeds on DEAD matter (most decomposers), while a parasite feeds on a LIVING host (many pathogens). So both saprophytes and parasites are heterotrophs, just with different food sources.
Which of the following is a correct statement?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Lactobacillus (lactic acid bacteria) are heterotrophic bacteria that turn milk into curd. NCERT lists "making curd from milk" as a key use of heterotrophic bacteria, though it does not name the genus in this chapter.
Yes. Citrus canker is a plant disease caused by bacteria. NCERT lists it along with cholera, typhoid and tetanus as diseases caused by different bacteria.
Yes, some do. NCERT says heterotrophic bacteria help in fixing nitrogen in legume roots. This is different from cyanobacteria, which fix atmospheric nitrogen in special cells called heterocysts.
Chemosynthetic bacteria are autotrophs: they make food using energy from oxidising inorganic chemicals (nitrates, nitrites, ammonia). Heterotrophic bacteria cannot make their own food and must take organic carbon from other sources.
Both. Most are useful decomposers and help in curd, antibiotics and nitrogen fixing. But some are pathogens causing diseases in humans, crops and animals.
