Chapter 15 Section 1 What is the environment? Objectives: Describe the cycles in nature. Define pollution.

A Support System for Life Living things get everything they need from their environment. The environment is everything that surrounds a living thing. The atmosphere, the hydrosphere, and the lithosphere are parts of the environment. For example, the atmosphere supplies living things with important gases. The hydrosphere provides water. The lithosphere provides important materials such as minerals and soil.

A Support System for Life Some of these resources pass through cycles. For example, the water cycle allows Earth’s water to be used again and again. Carbon dioxide, oxygen, and nitrogen also cycle through the environment.

DESCRIBE: What is the environment?

Pollution Anything that harms the environment is called pollution. Pollution occurs when harmful substances, or pollutants, are released into the environment. Pollutants harm Earth’s air, water, and land. They upset nature’s cycles.

Pollution An example of how humans upset nature’s cycles is thermal pollution. Thermal pollution raises water temperatures in aquatic systems. The problems result mostly from industry using water to cool equipment or materials during various processes. The electric power industry, steel mills, oil refineries, and paper mills all use huge amounts of water for cooling.

Pollution After the equipment has cooled, the “waste” water is often returned to where it came from. However, its temperature is higher than it was before. This temperature change can upset nature’s cycles and the balance of the environment.

Pollution Farming also causes pollution. Pesticides are meant to protect food supplies from pests such as insects, rodents, weeds, molds, and bacteria. However, pesticides can kill birds and fish as well as pests. They can also poison the foods people eat.

2. EXPLAIN: How does pollution upset nature’s cycles and the balance of the environment?

The Nitrogen Cycle One important cycle in the environment is the nitrogen cycle. In the nitrogen cycle, bacteria take nitrogen gas from the air and make it into compounds. Both plants and animals use these compounds. Bacteria that make these compounds are called nitrogen- fixing bacteria.

The Nitrogen Cycle Nitrogen-fixing bacteria live in the soil, and in the roots of plants such as legumes. Farmers who grow crops often plant legumes in their fields to add nitrogen compounds to the soil. When plants and animals die, the nitrogen compounds are broken down by different bacteria. Nitrogen is then released into the air or soil.

3. DESCRIBE: What happens in the nitrogen cycle?

The Carbon Cycle Living things are made up of organic compounds. These contain carbon. Carbon is found in the atmosphere in the form of the gas carbon dioxide. The process by which carbon is recycled is called the carbon cycle. It is the repeated movement of carbon between Earth’s atmosphere and living things. Green plants are producers. They use carbon dioxide to make food in photosynthesis.

The Carbon Cycle Some carbon dioxide is returned to the atmosphere when the food is used for energy during cellular respiration. The rest is stored as sugar. Animals are consumers. They eat producers or other consumers and use the food for energy. Some stored carbon dioxide is released when they breathe out.

The Carbon Cycle All organisms eventually die. Their bodies are broken down by decomposers. Decomposers also release carbon dioxide into the atmosphere. Fossil fuels are formed from the remains of ancient organisms. When fossil fuels are burned to release energy, most carbon dioxide is released into the atmosphere. This affects the carbon cycle.

4. IDENTIFY: What gas do animals release when they breathe out?

Classwork CHECKING CONCEPTS What resources cycle through the environment? What part of the environment supplies water? What gas do animals that have lungs take in from the air when they breathe in? What happens to the nitrogen compounds used by plants and animals when they die? When does pollution occur?

Classwork THINKING CRITICALLY 6. ANALYZING: How do animals get nitrogen compounds? 7. OBSERVE: What living things make nitrogen compounds?