MCQ Detailed View

The ocean is vast and deep, yet sunlight does not reach its entire depth. When sunlight enters water, it is scattered and absorbed by water molecules, dissolved substances, and tiny particles. The distance sunlight can travel underwater depends on water clarity, with clear open ocean water allowing the deepest penetration.

On average, sunlight can reach a depth of around 200 meters in the ocean. This upper layer of the ocean, where sunlight is still strong enough to support photosynthesis, is called the photic zone or euphotic zone. It is within this zone that microscopic plants known as phytoplankton, algae, and other marine plants produce oxygen and form the base of the marine food chain.

Most of the sunlight is absorbed in the first few meters of the ocean surface. Around 50% of sunlight is absorbed within the first 10 meters, and below 100 meters, the light intensity is very low. At 200 meters, sunlight becomes too weak to support photosynthesis. Beyond this, the aphotic zone begins, where no sunlight penetrates, and the environment remains in permanent darkness.

The options given are evaluated as follows:

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  80 meters: Too shallow, as sunlight can penetrate deeper than this.

  
  


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  120 meters: Also less than the typical maximum sunlight penetration.

  
  


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  200 meters: The scientifically accepted average maximum depth for sunlight in clear ocean waters.

  
  


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  None: Incorrect, since sunlight does reach measurable depths.

  
  

This Everyday Science concept explains why most marine plants and animals live near the surface of the ocean, where sunlight is available. The depth of sunlight penetration is crucial for oceanic ecosystems, photosynthesis, underwater visibility, and the global oxygen cycle.

Thus, the correct answer is 200 meters (Option B).