Q1. Which of the following is the primary cause of cultural (manmade) eutrophication?
- Volcanic eruptions
- Fertilizer runoff from agricultural fields
- Earthquake activity
- Ocean currents
Correct Option: 2. Fertilizer runoff from agricultural fields
Explanation: Cultural eutrophication is caused by excess nutrients, especially nitrogen and phosphorus, entering water bodies due to human activities, primarily from fertilizer runoff, untreated sewage, and waste. These nutrients promote algal growth, leading to oxygen depletion.
Q2. What is the main consequence of bacterial decomposition during eutrophication?
- Increase in sunlight penetration
- Increase in fish population
- Depletion of dissolved oxygen
- Reduction in algal bloom
Correct Option: 3. Depletion of dissolved oxygen
Explanation: When algae die, bacteria decompose them, a process that consumes large amounts of oxygen. This leads to anoxic (oxygen-depleted) conditions, which can kill fish and other aquatic organisms.
Q3. Which term best describes the condition where oxygen is completely absent in a water body?
- Aerobic
- Anoxia
- Hypoxia
- Osmosis
Correct Option: 2. Anoxia
Explanation: Anoxia is the absence of oxygen, while hypoxia is low oxygen levels. Anoxic conditions often result from eutrophication and cause the death of most aquatic life.
Q4. What is a Harmful Algal Bloom (HAB)?
- A growth of algae producing toxins harmful to aquatic life and humans
- A freshwater fish breeding season
- A natural aquatic plant bloom
- A sudden growth of marine mammals
Correct Option: 1. A growth of algae producing toxins harmful to aquatic life and humans
Explanation: HABs are caused by algae that produce toxins which can harm marine life, birds, and humans. They are often fueled by nutrient enrichment and warm water.
Q5. Why is the term “Red Tide” considered a misnomer?
- It always occurs at night
- It only happens in freshwater
- Not all algal blooms are red, nor caused by tides, and not always toxic
- It has no impact on ecosystems
Correct Option: 3. Not all algal blooms are red, nor caused by tides, and not always toxic
Explanation: The term “Red Tide” is misleading. Algal blooms can be green, brown, or red, are not related to tides, and may not always be harmful. The scientific term is Harmful Algal Blooms (HABs).