Methanogens are a type of archaebacteria. They live without oxygen (anaerobic) inside the gut of ruminant animals like cows and buffaloes, and in marshy areas. There they break down cellulose in dung and make methane gas, which we call biogas or "gobar gas". Memory hook: "Methano-gens GENERATE methane" — cow dung goes in, cooking gas comes out.
Methanogens in a biogas plant break down cellulose in cow dung without oxygen to release methane, the main gas in biogas (gobar gas).
Your doubts, answered
Are methanogens eubacteria or archaebacteria?
Methanogens are ARCHAEBACTERIA, not eubacteria. This is a very common trap. Archaebacteria live in harsh places and have a different cell wall structure. NEET has asked "Methanogens belong to?" and the answer is Archaebacteria. If an option says eubacteria, it is wrong.
Do methanogens need oxygen to live?
No. Methanogens are strictly ANAEROBIC. They can only grow where there is NO oxygen, like the gut of cattle or inside a sealed biogas tank. If a statement says "methanogens grow aerobically", it is FALSE. NEET tested exactly this in 2016 and 2019.
How do methanogens make biogas from cow dung?
Cow dung has a lot of cellulose (plant fibre) that the cow could not fully digest. Methanogens live in the cow's gut and in the dung. Without oxygen, they break down this cellulose and release methane gas (CH4). This methane, mixed with some CO2 and H2, is the biogas we burn for cooking.
Why does biogas come from cow dung and not from anything else?
Because cow dung is full of methanogens (they came from the cow's rumen) and is rich in cellulose for them to eat. Ruminant animals like cows and buffaloes keep methanogens in their gut, so their dung already carries the bacteria needed to start making methane.
What is the difference between methanogens, halophiles and thermoacidophiles?
All three are archaebacteria but live in different harsh homes. Halophiles live in extreme salty areas. Thermoacidophiles live in hot springs (hot + acidic). Methanogens live in marshy areas and in the gut of ruminants and make methane. NEET loves to match these three to their habitats.
Is Methanobacterium the same as methanogen?
Methanobacterium is one common example of a methanogen. "Methanogen" is the group name for all methane-making bacteria; Methanobacterium is a specific member. It is used in biogas plants and is found in sewage sludge too.
⚠️ The NEET trap ✗ Methanogens grow aerobically (with oxygen) and break down cellulose-rich food. ✓ Methanogens grow ANAEROBICALLY (without oxygen) on cellulose-rich food and produce methane. 🧠 NEET asks the NOT-correct statement. The trap word is "aerobically". Methanogens are always anaerobic — no oxygen. Everything else about them (make methane, found in rumen/excreta, used for biogas) is true.
Real NEET questions
NEET 2016
Methanogens belong to
A · Eubacteria
B · Archaebacteria ✓
C · Dinoflagellates
D · Slime moulds
Solution: Methanogens are archaebacteria. They 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 extremophile archaebacteria such as halophiles and thermoacidophiles, which have a different cell wall structure. Eubacteria are the ordinary 'true bacteria', so that option is wrong.
NEET 2016
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 live in the gut of ruminant animals (cows, 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 is too general and not the specific group asked for.
NEET 2016 / 2019
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 — they grow WITHOUT oxygen on cellulose-rich material. So the statement that they "grow aerobically" is the incorrect one. The other three statements are all true: they make methane, live in the rumen/excreta of cattle, and are used to make biogas.
Solved Biological Classification NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
They mainly produce methane (CH4). Biogas is methane mixed with some carbon dioxide and hydrogen. Methane is the part that burns and gives energy for cooking and lighting.
What is another name for biogas?
Biogas from cow dung is popularly called gobar gas, because 'gobar' means cow dung in Hindi. It is used as a clean fuel in rural areas.
Are methanogens prokaryotes or eukaryotes?
Methanogens are prokaryotes. Being archaebacteria, they belong to Kingdom Monera and have no true nucleus or membrane-bound organelles.
Where else are methanogens found besides cow gut?
They are also found in marshy areas (marsh gas is methane) and in the anaerobic sludge during sewage treatment. Anywhere there is no oxygen and rotting plant material, methanogens can grow.
Why are methanogens important for NEET?
They are a favourite NEET topic because they connect three ideas at once: archaebacteria (classification), anaerobic life, and biogas production. NEET has repeatedly tested that methanogens are archaebacteria and that they are anaerobic.
