Which of the following best explains how light and depth influence the distribution of organisms in marine ecosystems?

• A. Only temperature, not light or depth, determines where marine organisms are found.
• B. Light decreases with depth, so photosynthetic organisms are mostly found in shallow waters, while deeper zones are inhabited by organisms adapted to low light or darkness.
• C. Light increases with depth, allowing photosynthetic organisms to thrive in the deepest parts of the ocean.
• D. Depth has no effect on light availability, so organisms are evenly distributed throughout all marine zones.

Answer: (B)

Verified step by step guidance

1. Understand the relationship between light and depth in marine ecosystems: Light availability decreases as depth increases because water absorbs and scatters light. This is a key factor influencing the distribution of organisms.
2. Recognize the role of photosynthetic organisms: Photosynthetic organisms, such as algae and phytoplankton, require sunlight to produce energy through photosynthesis. These organisms are typically found in the photic zone, the upper layer of the ocean where sunlight penetrates.
3. Consider the adaptations of organisms in deeper zones: In deeper zones, where light is minimal or absent, organisms have adapted to survive in low-light or dark conditions. These adaptations may include bioluminescence, reliance on detritus (organic matter falling from above), or chemosynthesis (using chemical energy instead of light).
4. Eliminate incorrect statements: The statement 'Light increases with depth' is incorrect because light decreases with depth. Similarly, 'Depth has no effect on light availability' is incorrect because depth directly affects light penetration. Temperature alone does not determine organism distribution, so that statement is also incorrect.
5. Identify the correct explanation: The correct explanation is that light decreases with depth, so photosynthetic organisms are mostly found in shallow waters, while deeper zones are inhabited by organisms adapted to low light or darkness.