Biogas is a renewable source of energy that is produced by the anaerobic decomposition of organic matter, such as agricultural waste, sewage, and food waste. The process involves the breakdown of complex organic compounds into simpler compounds by microorganisms in the absence of oxygen. This results in the production of biogas, which mainly consists of methane, carbon dioxide, and small amounts of other gases.

Anaerobic Breakdown of Biomass
The anaerobic breakdown of biomass involves the decomposition of organic matter by microorganisms in the absence of oxygen. This process is carried out in a sealed container, called a biogas digester or anaerobic digester. The organic matter is fed into the digester, and the microorganisms break it down into simpler compounds through a series of biochemical reactions. The main products of anaerobic digestion are biogas and a nutrient-rich slurry called digestate.

With the Help of Methanogenic Bacteria
Methanogenic bacteria are a type of microorganism that play a crucial role in the production of biogas. These bacteria are responsible for converting the simple compounds produced during anaerobic digestion into methane, which is the main component of biogas. Methanogenic bacteria are strict anaerobes, meaning they can only survive in the absence of oxygen. They are able to produce methane by using carbon dioxide and hydrogen, which are also produced during anaerobic digestion.

Both (b) and (c)
The production of biogas involves both the anaerobic breakdown of biomass and the activity of methanogenic bacteria. Without anaerobic digestion, there would be no organic matter for the methanogenic bacteria to feed on, and without methanogenic bacteria, the simple compounds produced during anaerobic digestion would not be converted into methane. Therefore, the correct answer is option D, which states that biogas is produced by both the anaerobic breakdown of biomass and with the help of methanogenic bacteria.