Green plants in the sea are useful for the respiration of fish because (UPSC Prelims/1979)

Q. Green plants in the sea are useful for the respiration of fish because
(a) They give out oxygen
(b) They give out carbon dioxide
(c) They give out oxygen and carbon dioxide simultaneously
(d) They take oxygen and give out carbon dioxide

✅ Correct Answer: (a) They give out oxygen

Explanation
Green plants in the sea such as algae and phytoplankton perform photosynthesis in the presence of sunlight.
During photosynthesis they release oxygen into the water, which is used by fish and other aquatic organisms for respiration.

Photosynthesis in Aquatic Plants
Photosynthesis is the process by which green plants use sunlight, carbon dioxide, and water to produce food (glucose) and release oxygen.

Photosynthesis Equation
Carbon dioxide + Water + Sunlight → Glucose + Oxygen

Role of Aquatic Plants
• Produce oxygen required for aquatic life
• Form the base of the aquatic food chain
• Maintain ecological balance in water bodies

Important Marine Producers
• Phytoplankton → Microscopic photosynthetic organisms in oceans
• Seaweeds → Large marine algae
• Algae → Important oxygen producers in water bodies

Importance for Ecosystem
• Supply oxygen for fish respiration
• Support marine food webs
• Absorb carbon dioxide and help regulate climate

Important Related Concepts for Exams
Producers → Organisms that prepare their own food by photosynthesis
Consumers → Organisms that depend on other organisms for food
Food Chain → Transfer of energy from producers to consumers
Aquatic Ecosystem → Ecosystem present in water bodies such as oceans, lakes, and rivers

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