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Phosphorus Cycle — Reading Comprehension

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MS-LS2-3

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This comprehensive science reading passage introduces middle school students to the phosphorus cycle, a critical process in ecosystems that traces the movement of phosphorus through rocks, soil, water, plants, and animals. Aligned with NGSS MS-LS2-3, the passage explains why phosphorus is vital for living things, details each step of the cycle, and examines how human activities like fertilizer use and mining can disrupt natural systems. Students will explore the unique aspects of the phosphorus cycle, including its lack of an atmospheric component and its role as a limiting nutrient. The passage is supported by a glossary, differentiated reading level version, Spanish translations, a multiple-choice quiz, writing prompts, and graphic organizers, making it accessible and engaging for grades 6-8. Audio integration further enhances accessibility and comprehension for diverse learners.

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Phosphorus is an essential element that supports life on Earth, yet its movement through the environment follows a unique pattern. Unlike carbon or nitrogen, the phosphorus cycle does not include a gas phase in the atmosphere. Scientists have discovered that phosphorus mostly travels through rocks, soil, water, plants, and animals. This element is crucial for building DNA, cell membranes, and energy molecules like ATP. Without phosphorus, living things could not grow or reproduce efficiently.

Weathering and Soil Absorption
Phosphorus begins its journey locked inside rocks as phosphate minerals. Over time, weathering, or the slow breakdown of rocks by wind, rain, and temperature changes, releases phosphate into the soil. Plants absorb these phosphates through their roots, using them to develop tissues and store energy. In many ecosystems, phosphorus is a limiting nutrient, meaning its scarcity can restrict plant growth. For example, in some lakes and forests, less than 0.1% of the soil contains available phosphorus, so even a small increase can lead to rapid plant growth.

Movement Through Food Webs and Water
Animals obtain phosphorus by eating plants or other animals. When these organisms produce waste or die, decomposers like bacteria and fungi break down their remains, returning phosphorus to the soil. Some phosphorus dissolves in water and is carried by runoff into rivers, lakes, and oceans. In water bodies, phosphorus supports the growth of aquatic plants and algae. However, too much phosphorus—often from fertilizer runoff—can cause harmful algal blooms that deplete oxygen and damage aquatic life.

Sedimentation and Human Impact
Phosphorus that reaches oceans or lakes may eventually settle to the bottom as sediment. Over millions of years, these sediments can become new rock, restarting the cycle. Human activities, such as mining phosphate rock for fertilizers and detergents, have greatly accelerated phosphorus movement. Excess fertilizer use leads to more runoff, increasing pollution in water bodies. Scientists have measured that up to 50% of phosphorus applied as fertilizer can be lost from fields and end up in waterways.

Understanding the phosphorus cycle helps us see the connections within ecosystems and the impacts of our choices. Protecting this cycle is vital for maintaining healthy environments and ensuring sustainable food production for the future.

Interesting Fact:
Phosphorus is so important that, unlike many other nutrients, its shortage can limit the productivity of entire ecosystems—even if all other resources are abundant.

Which element is the focus of the passage and is essential for DNA and cell energy?

PhosphorusNitrogenCarbonOxygen

What process releases phosphate from rocks into the soil?

DecompositionWeatheringPhotosynthesisRespiration

Why is phosphorus often called a limiting nutrient?

It is always found in the air.Its shortage can restrict plant growth.It is the most common nutrient in soil.Animals do not need it.

Which vocabulary word from the passage means bacteria and fungi that return nutrients to the soil?

WeatheringRunoffDecomposersSediment

What effect does excess fertilizer runoff have on aquatic ecosystems?

It causes algal blooms that harm aquatic life.It increases oxygen for fish.It decreases plant growth.It removes sediment from water.

Which term refers to the process in which phosphorus settles at the bottom of lakes or oceans?

PhotosynthesisSedimentationRespirationRunoff

Why is the phosphorus cycle different from the carbon and nitrogen cycles?

It does not have an atmospheric gas phase.It involves animals only.It does not affect plants.It happens very quickly.

True or False: Human activities like mining and fertilizer use can speed up the movement of phosphorus in the environment.

TrueFalse

True or False: The phosphorus cycle includes a stage where phosphorus is found in the atmosphere as a gas.

TrueFalse

If phosphorus is added to a lake ecosystem, what is a likely result?

Faster plant and algae growth.Less oxygen in the water.Possible algal blooms.All of the above.

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Phosphorus Cycle — Reading Comprehension

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