Biological Oxygen Demand (BOD) is a standard criterion for
- A.Measuring oxygen levels in blood
- B.Computing oxygen levels in forest ecosystems
- C.Pollution assay in aquatic ecosystems
- D.Assessing oxygen levels in high altitude regions
Correct answer
Explanation
The correct answer is C, Pollution assay in aquatic ecosystems. BOD tells how much organic pollution a body of water carries.
Biological, or biochemical, Oxygen Demand is the amount of dissolved oxygen that aerobic micro-organisms use up while breaking down the organic matter in a water sample, usually measured over five days at 20 degrees Celsius and expressed in milligrams per litre. Sewage and industrial waste add organic matter, so the more polluted the water, the higher its BOD. A high BOD leaves less oxygen for fish and other aquatic life. Clean river water has a low BOD, and Indian standards for bathing water ask for a BOD of 3 mg per litre or less.
A is wrong because oxygen in blood is measured as oxygen saturation with a pulse oximeter or a blood gas test. B is wrong because forest oxygen is not assessed by BOD. D is wrong because thin air at high altitude is described by partial pressure of oxygen.
Exam tip: high BOD = more organic pollution, less dissolved oxygen for aquatic life.
Practice Questions
View allWhich of the following is/are renewable source(s) of energy? 1. Fossil fuel 2. Biofuel 3. Uranium 4. Hydropower Select the correct answer using the code given below.
- A.2 only
- B.3 and 4
- C.1 and 3
- D.2 and 4
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Biofuel and hydropower are renewable because nature replaces them within a human lifetime, while fossil fuels and uranium are not.
Read the full explanation →Which one of the following is NOT decomposed by bacterial action ?
- A.Vegetable remains
- B.Plastic materials
- C.Animal carcasses
- D.Wastes of flowers
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Ordinary plastics are non-biodegradable, so bacteria and fungi cannot break them down in any useful length of time. Most plastics, such as polyethylene, polypropylene and PVC, are long synthetic polymers made from petroleum.
Read the full explanation →According to the Environmental Protection Agency (EPA), which one of the following is the largest source of sulphur dioxide emissions?
- A.Locomotives using fossil fuels
- B.Ships using fossil fuels
- C.Extraction of metals from ores
- D.Power plants using fossil fuels
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The EPA names the burning of fossil fuels by power plants and other industrial facilities as the largest source of sulphur dioxide.
Read the full explanation →Free swimming macroscopic animals in an aquatic environment are referred to as
- A.Plankton
- B.Periphyton
- C.Benthos
- D.Nekton
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Nekton are animals large enough to be seen with the naked eye that swim actively and can move against water currents.
Read the full explanation →Artificial way of causing rainfall to reduce air pollution makes use of
- A.silver iodide and potassium iodide
- B.silver nitrate and potassium iodide
- C.silver iodide and potassium nitrate
- D.silver nitrate and potassium chloride
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These salts are the usual seeding agents in cloud seeding, the artificial way to make rain. Cloud seeding sprays tiny particles into clouds that already hold moisture, from aircraft, rockets or ground generators.
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