Chapter 2 Directed Reading Worksheet: Cycles in Nature

Chapter 2 of the directed reading worksheet likely focuses on fundamental cycles essential for life on Earth. These cycles, typically including the water, carbon, nitrogen, and phosphorus cycles, illustrate the continuous movement and transformation of matter, ensuring the sustainability of ecosystems. Understanding these cycles is crucial for comprehending ecological balance and the impacts of human activities.

The Water Cycle

The water cycle, also known as the hydrologic cycle, is the continuous movement of water on, above, and below the surface of the Earth. Key processes include:

• Evaporation: The transformation of liquid water into water vapor, primarily from bodies of water like oceans, lakes, and rivers.
• Transpiration: The release of water vapor from plants through their leaves.
• Condensation: The process by which water vapor changes into liquid water, forming clouds.
• Precipitation: Any form of water that falls from the atmosphere to the Earth’s surface, such as rain, snow, sleet, or hail.
• Infiltration: The process by which water seeps into the ground and becomes groundwater.
• Runoff: Water that flows over the land surface, eventually reaching bodies of water.

The worksheet probably explores the roles each of these components plays and may ask how pollution can impact the cycle and ultimately the availability of clean drinking water.

The Carbon Cycle

The carbon cycle describes the movement of carbon atoms through the Earth’s atmosphere, oceans, land, and living organisms.

• Photosynthesis: Plants and algae absorb carbon dioxide from the atmosphere and convert it into organic compounds.
• Respiration: Organisms release carbon dioxide back into the atmosphere as they break down organic compounds for energy.
• Decomposition: Decomposers break down dead organisms and waste products, releasing carbon into the soil and atmosphere.
• Combustion: Burning fossil fuels and wood releases carbon dioxide into the atmosphere.
• Ocean Absorption: The ocean absorbs carbon dioxide from the atmosphere.

The directed reading likely highlights the increasing concentration of carbon dioxide in the atmosphere due to human activities, specifically the burning of fossil fuels, and its contribution to climate change. Questions may focus on the carbon sinks (oceans, forests) and their importance.

The Nitrogen Cycle

The nitrogen cycle is the process by which nitrogen is converted between its various chemical forms. Nitrogen is a crucial component of proteins and nucleic acids.

• Nitrogen Fixation: Bacteria convert atmospheric nitrogen into ammonia (NH3).
• Nitrification: Bacteria convert ammonia into nitrites (NO2-) and nitrates (NO3-), which plants can absorb.
• Assimilation: Plants absorb nitrates and use them to build proteins and nucleic acids.
• Ammonification: Decomposers break down dead organisms and waste products, releasing ammonia.
• Denitrification: Bacteria convert nitrates back into atmospheric nitrogen.

The worksheet will possibly cover the importance of nitrogen-fixing bacteria and how human activities, such as the use of fertilizers, can disrupt the natural balance of the cycle, leading to eutrophication in aquatic ecosystems.

The Phosphorus Cycle

The phosphorus cycle describes the movement of phosphorus through the Earth’s lithosphere, hydrosphere, and biosphere. Unlike other cycles, the phosphorus cycle does not have a significant atmospheric component.

• Weathering: Rocks release phosphate ions (PO43-) into the soil.
• Absorption: Plants absorb phosphate ions from the soil.
• Consumption: Animals obtain phosphorus by eating plants or other animals.
• Decomposition: Decomposers release phosphorus back into the soil.
• Sedimentation: Phosphorus can accumulate in sediments and eventually form rocks.

The directed reading likely emphasizes that phosphorus is a limiting nutrient in many ecosystems and that mining phosphorus for fertilizer can impact the cycle. Eutrophication resulting from excess phosphorus runoff is also likely covered.

The directed reading worksheet likely concludes by emphasizing the interconnectedness of these cycles and the importance of maintaining their balance for the health of the planet. Understanding these cycles is vital for addressing environmental challenges and promoting sustainable practices.