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What Characteristic Is Used to Divide Aquatic Biomes into Three Zones? — Reading Comprehension

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MS-LS1-3

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This NGSS-aligned reading passage explains how aquatic biomes such as oceans and lakes are divided into three zones based on the amount of sunlight. Designed for middle school readers, the passage explores the photic (sunlight) zone, the twilight zone, and the aphotic (midnight) zone, describing the life forms and energy sources found in each. It introduces key science terms like photosynthesis, bioluminescence, and chemosynthesis while highlighting how organisms adapt to varying levels of light. This science comprehension activity helps students understand how energy flows in aquatic ecosystems and why certain plants and animals are found at specific depths. Aligned to NGSS MS-LS2-1, this passage builds knowledge in life science, ecosystems, and biological adaptation.

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Aquatic biomes, such as oceans, lakes, and ponds, are divided into three main zones based on the amount of sunlight that reaches the water. Sunlight is a key factor because it affects how much photosynthesis can happen, which in turn affects what kinds of plants and animals can survive in each zone.

The sunlight zone, also called the photic zone, is the top layer of water where sunlight can easily reach. This zone supports a large variety of life because it has enough light for producers like algae and phytoplankton to grow. These tiny plants form the base of the food chain. Fish, sea turtles, and coral reefs are commonly found in this zone.

Below that is the twilight zone, or disphotic zone, where only a small amount of sunlight filters through. There is not enough light for most plants to perform photosynthesis. Animals that live here, such as squid and lanternfish, often have special adaptations like bioluminescence—the ability to produce light.

The deepest layer is called the midnight zone, or aphotic zone. In this zone, no sunlight reaches at all. It is cold, dark, and under great pressure. Only specially adapted organisms, like deep-sea fish and giant tube worms, can survive here. These creatures often rely on chemosynthesis, a process where energy is made from chemicals instead of sunlight.

Understanding these zones helps scientists study marine ecosystems and how energy moves through them. It also explains why different types of life are found at different depths in the water.

Fun Fact: The Mariana Trench, Earth's deepest ocean point, is part of the midnight zone—it's so deep that Mount Everest could fit inside it and still be underwater!

What main factor is used to divide aquatic biomes into zones?

Water temperatureType of fishAmount of sunlightDepth of sediment

What is another name for the sunlight zone?

Twilight zoneAphotic zoneMidnight zonePhotic zone

Which aquatic zone receives no sunlight?

Photic zoneTwilight zoneAphotic zoneSurface zone

What kind of organisms live in the photic zone?

Only bacteriaDeep-sea wormsCoral reefs and algaeNone, it’s too dark

Why can plants not grow well in the twilight zone?

The water is frozenThere's not enough lightThere are too many fishThe water is polluted

What special ability helps animals survive in the twilight zone?

FlyingBioluminescencePhotosynthesisHibernation