Science · Earth & Life Science

Cycles of Life — Reading Comprehension Lesson

Reading comprehension passage and printable worksheet about nature’s essential cycles — the water cycle, carbon cycle, nitrogen cycle, and more — for grades 3–6.

Reading Passage

Cycles of Life

Nature works in cycles. A cycle is a series of events that repeats over and over again. Many of the most important processes on Earth — the movement of water, the flow of carbon, and the cycling of nutrients — happen in repeating cycles that support all life. Without these cycles, living things could not survive.

The water cycle describes how water moves continuously through the environment. Water evaporates from oceans, lakes, and rivers when the sun heats it, turning it into water vapor that rises into the atmosphere. As water vapor cools at higher altitudes, it condenses into clouds. Eventually the water falls back to Earth as precipitation — rain, snow, sleet, or hail — and the cycle begins again.

The carbon cycle describes how carbon moves between living things, the air, the oceans, and the soil. Plants absorb carbon dioxide from the air during photosynthesis and use it to build their tissues. When animals eat plants, the carbon moves into their bodies. When living things die and decompose, carbon is released back into the soil and air. Burning fossil fuels also releases carbon dioxide into the atmosphere.

The nitrogen cycle is the process by which nitrogen moves through the environment. Nitrogen is an essential element for all living things — it is a key component of proteins and DNA. Most living things cannot use nitrogen directly from the air. Certain bacteria in the soil convert nitrogen gas into a form that plants can absorb. Animals get nitrogen by eating plants or other animals.

Trees also go through a life cycle. A tree begins as a seed, germinates, grows into a seedling, and eventually becomes a mature tree. Mature trees produce seeds that start the cycle again. When a tree dies and falls, it decomposes and returns nutrients to the soil, helping the next generation of trees grow. These natural cycles connect all living things to each other and to the environment.

Printable Worksheet

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