Methanogens are a group of archaebacteria that live without oxygen (anaerobic) and produce methane gas, which is the main part of biogas. They are found in the rumen and dung of cattle like cows and buffaloes, and in marshy areas. Memory hook: "Methano-gens generate methane" — no air, cow dung, gas out.
Methanogens are anaerobic archaebacteria that act on cattle dung (and other organic waste) in the absence of oxygen to release methane, the burnable gas of biogas. They also live in the rumen of cattle and in marshy areas.
Your doubts, answered
Are methanogens bacteria or archaebacteria?
Methanogens are archaebacteria (also called archaea), not eubacteria or true bacteria. NCERT groups them with halophiles and thermoacidophiles because all three have a different cell wall structure that lets them live in harsh habitats. In NEET 2016 the answer 'Methanogens belong to Archaebacteria' was tested directly, so remember: methanogens = archaebacteria.
Do methanogens need oxygen to make methane?
No. Methanogens are strictly anaerobic, meaning they work only where there is no oxygen. This is why they thrive in the oxygen-free environment inside cattle dung and inside a closed biogas tank. NEET has trapped students with the false statement 'they grow aerobically' — that option is wrong because methanogens are anaerobic.
Where exactly are methanogens found?
Three NCERT places: (1) marshy areas, (2) the gut/rumen of ruminant animals such as cows and buffaloes, and (3) the excreta (dung) of these animals. In the rumen they help break down the cellulose in food and produce methane, which is why cattle dung is used to make biogas.
Is methane the same as biogas?
Not fully. Methane (CH4) is the main and the burning part of biogas, but biogas is a mixture that also contains carbon dioxide and small amounts of hydrogen sulphide and other gases. Methanogens produce the methane; this methane makes biogas useful as a fuel for cooking and lighting.
What raw material do methanogens act on?
Methanogens act on the organic matter in cattle dung (gobar) and the slurry made from it. During anaerobic digestion, the leftover material from other microbes (like the sludge in sewage treatment) is broken down further by methanogens to release methane. So dung and digested sludge are their food source.
⚠️ The NEET trap ✗ Methanogens are aerobic bacteria that break down cellulose-rich food. ✓ Methanogens are strictly anaerobic archaebacteria; they work only without oxygen and produce methane. 🧠 If an option says methanogens 'grow aerobically', it is always WRONG — methane is made only in the absence of oxygen.
Real NEET questions
NEET 2016 (Phase 2)
Methanogens belong to
A · Eubacteria
B · Archaebacteria ✓
C · Dinoflagellates
D · Slime moulds
Solution: Methanogens are archaebacteria that live in marshy areas and in the gut of ruminants like cows and buffaloes, where they produce methane (biogas) from dung. They are grouped with other extremophilic archaebacteria such as halophiles and thermoacidophiles because of their different cell wall structure.
NEET 2016 (Phase 1)
The primitive prokaryotes responsible for the production of biogas from the dung of ruminant animals, include the:
A · Halophiles
B · Thermoacidophiles
C · Methanogens ✓
D · Eubacteria
Solution: Methanogens are present in the gut of ruminant animals like cows and buffaloes and produce methane (biogas) from their dung. Halophiles live in salty areas and thermoacidophiles in hot springs, so they are not linked to dung biogas; eubacteria are 'true bacteria', not the specific group named here.
NEET 2016 (Phase 1) / NEET 2019 (Odisha)
Which of the following statements about methanogens is not correct?
A · They can be used to produce biogas.
B · They are found in the rumen of cattle and their excreta
C · They grow aerobically and breakdown cellulose-rich food. ✓
D · They produce methane gas.
Solution: Methanogens are strictly anaerobic archaebacteria, so they cannot grow aerobically — statement C is the incorrect one. They do occur in the rumen and excreta of cattle, produce methane gas, and are used to make biogas, so the other three statements are correct.
Solved Microbes in Human Welfare NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Methanobacterium is a common example of a methanogen mentioned in NEET-level study. It is the archaebacterium that produces methane from cattle dung and sewage sludge.
Why are methanogens important in biogas production?
They carry out the final anaerobic step that converts organic waste (dung, sludge) into methane, the burnable gas in biogas. Without methanogens there would be no methane and hence no biogas fuel.
How do methanogens help in sewage treatment?
In an anaerobic sludge digester, methanogens break down the activated sludge (dead microbial biomass) and produce a mixture of methane, carbon dioxide and hydrogen sulphide — this biogas can be used as fuel, and the process reduces waste.
Why do cattle produce methane?
Methanogens live in the rumen of cattle and act on the cellulose-rich food they eat, producing methane as a by-product. This is the same reason their dung is a good raw material for biogas plants.
