Sampling Microbes for Lab Observation — NEET Biology
📚 Practice ConceptBacteria cannot be seen with the naked eyes, but these can be seen with the help of a microscope. If you have to carry a sample from your home to your biology laboratory to demonstrate the presence of microbes with the help of a microscope, which sample would you carry and why?
Which of the following statements are correct regarding Biochemical Oxygen Demand (BOD) in the context of sewage treatment and water pollution? S1: BOD is a direct measure of the concentration of dissolved oxygen available for aquatic life in a given water sample. S2: The greater the BOD of waste water, the higher is its polluting potential due to excessive consumption of oxygen by microbes. S3: During secondary sewage treatment, aerobic microbes reduce the BOD by consuming the organic matter present in the primary effluent. S4: The BOD test essentially quantifies the amount of organic matter that can be oxidized by microorganisms in one liter of water. S5: Untreated sewage typically has a lower BOD value compared to secondary effluent because it contains less organic matter.
View solution & NCERT explanation
Correct answer: B — S2, S3, and S4 are correct
BOD is a critical parameter in assessing water quality and the effectiveness of sewage treatment. S1: This statement is incorrect. BOD is not a measure of the dissolved oxygen *available*, but rather the amount of oxygen that would be *consumed* by microbes to oxidize organic matter. S2: This statement is correct. NCERT explicitly states, 'The greater the BOD of waste water, more is its polluting potential' because high organic matter content leads to high oxygen consumption by microbes, depleting oxygen for aquatic life. S3: This statement is correct. In secondary treatment, aerobic microbes actively consume organic matter in the primary effluent, which directly leads to a significant reduction in BOD. S4: This statement is correct. BOD indirectly measures the organic matter present in water because it reflects the oxygen needed to oxidize this organic matter by bacteria. S5: This statement is incorrect. Untreated sewage contains a large amount of organic matter, hence it has a *much higher* BOD value compared to secondary effluent, which has undergone organic matter reduction. Therefore, statements S2, S3, and S4 are correct. The tested concept is the definition, measurement, and significance of BOD in environmental pollution and sewage treatment.
What does NCERT say about Bacteria cannot be seen?
Has this concept appeared in NEET?
Which chapter is this from?
Through deep analysis of NEET and NTA, 176 of the 180 ReNEET 2026 (June 21) questions were already in the MedicNEET question bank before the exam.
176/180MedicNEET's Biology question bank is built from the same NCERT lines NTA picks repeatedly. Not random MCQs — questions crafted exactly like NTA crafts them.