Botany MCQs for NEET — Practice Questions with Answers

Sedimented flocks refer to 'active sludge,' which is formed during the secondary treatment of wastewater. In this process, microorganisms break down organic matter, and the resulting biomass forms flocks that settle at the bottom of the settling tank.

All the given statements are correct for Sewage Treatment Plants (STPs). The value of Biochemical Oxygen Demand (BOD) decreases in the effluent, flocks are sedimented in the settling tank, and biogas is formed at the end of the process. Thus, option 'All the given' is the correct answer.

The correct option is CH₄ (methane). The odd one out is CH₃ because it is not a stable molecule and does not exist under normal conditions. In anaerobic sludge digesters, the gases typically produced include carbon dioxide (CO₂), methane (CH₄), and hydrogen sulfide (H₂S).

Methanogens are a group of archaea that produce methane as a metabolic byproduct in anoxic conditions. They are commonly found in the alimentary canal of herbivores, where they help in the process of digesting cellulose. Other bacteria listed are not typically involved in this specific digestive role.

BOD, or Biochemical Oxygen Demand, is a measure of the amount of oxygen that microorganisms will consume while decomposing organic matter in water. Hence, it indirectly indicates the amount of organic matter present in the water.

Methane gas is produced by bacteria from the compound cellulase. Cellulase breaks down cellulose, a major component of plant cell walls, into simpler sugars which can be further processed by methanogenic bacteria to produce methane. This process is significant in anaerobic digestion and biogas production.

In anaerobic sludge digesters, multiple gases are produced including CO₂, H₂S, and CH₄. This is because the anaerobic digestion process involves the breakdown of organic matter by bacteria in the absence of oxygen, leading to the production of these gases. Therefore, the correct answer is 'All the given' gases.

Algae are generally not used as biocontrol agents. Biocontrol agents typically include viruses, bacteria, and fungi which can target specific pests or pathogens. Algae do not fit well into this category as they do not have the necessary properties to control pests or pathogens in a targeted manner.

Methanogens are a group of archaea that produce methane as a metabolic byproduct in anoxic conditions. They are commonly found in wetlands, ruminant animals, and are crucial for the production of biogas in anaerobic digesters.

Rhizobium is a genus of bacteria that forms a symbiotic relationship with leguminous plants. It colonizes the root nodules of these plants and fixes atmospheric nitrogen ( ext{N}_2) into a form that the plants can use, such as ammonia ( ext{NH}_3), thus aiding in nitrogen fixation.