What Is the Main Source of Carbon in an Ecosystem? — Reading Comprehension

Grades

Standards

MS-LS2-3

About This Reader

This NGSS-aligned science reading passage helps middle school students explore the main source of carbon in ecosystems: atmospheric carbon dioxide. It explains how CO₂ enters the ecosystem through photosynthesis, becomes part of food chains, and moves through decomposers, plants, and animals. The passage highlights the carbon cycle, the importance of carbon in living things, and how burning fossil fuels adds more carbon to the atmosphere. Vocabulary such as photosynthesis, decomposers, fossil fuels, and carbon cycle are introduced in context to support understanding of ecosystem energy flow and environmental science. This passage supports NGSS Life Science standards and reading comprehension.

CONTENT PREVIEW

Carbon is a key element in all living things. It is part of the molecules that make up our bodies, the food we eat, and the air we breathe. In an ecosystem, the main source of carbon is carbon dioxide (CO₂) in the atmosphere. This gas plays a major role in the carbon cycle, which moves carbon through the air, water, soil, and living organisms.

Plants use carbon dioxide during photosynthesis, a process where they take in CO₂ from the air and use sunlight to make food. This is how carbon enters the food chain. When animals eat plants (or other animals), the carbon in the plant becomes part of their bodies. In this way, carbon moves through the ecosystem as energy and matter are passed from one organism to another.

When living things die or release waste, decomposers like bacteria and fungi break them down. This releases carbon back into the air or soil. In some cases, carbon gets stored underground for millions of years as fossil fuels like coal and oil. When humans burn these fuels, carbon returns to the atmosphere as carbon dioxide, increasing greenhouse gases and affecting climate.

Carbon is constantly cycling, but the original and ongoing source in most ecosystems is atmospheric CO₂. Without it, plants couldn’t grow, animals couldn’t survive, and life as we know it wouldn’t exist.

Fun Fact: A single large tree can absorb over 40 pounds of carbon dioxide from the atmosphere in just one year!

What is the main source of carbon in most ecosystems?

Fossil fuelsSunlightCarbon dioxide in the airSoil nutrients

How does carbon enter the food chain?

Animals release itPlants absorb it through their rootsDecomposers break it downPlants take in carbon dioxide during photosynthesis

What role do decomposers play in the carbon cycle?

They produce oxygenThey trap carbon in soilThey release stored carbon back into the environmentThey block carbon from entering the air

What process do plants use to take in carbon dioxide?

RespirationPhotosynthesisFermentationDecomposition

What happens when fossil fuels are burned?

They form new plantsThey produce more oxygenThey return carbon to the atmosphereThey stop the carbon cycle

Why is carbon important in living things?

It helps control temperatureIt gives color to organismsIt is a basic building block of lifeIt makes up soil minerals

What is the main idea of the passage?

Trees store all carbonFossil fuels are dangerousCarbon dioxide is the key source of carbon in ecosystemsDecomposers remove carbon from the air

If plants disappeared from an ecosystem, what would happen to carbon flow?

It would speed upIt would stop entering the food chainIt would increase oxygen levelsIt would create more fossil fuels

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