Lesson 5



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Organisms need many resources to survive. These resources include water, sunlight, soil, and air. Ecosystems change when resources change.

There are several things that may cause changes to the ecosystem. One event is drought which is a long period without rain or precipitation. Plants may die during a drought. Diseases such as the Dutch Elm Disease destroyed about 43 million trees. The Dutch Elm Disease also harms insects and animals that make their homes in these trees. The trees also give off oxygen, and their destruction would decrease the oxygen in the air. Soil erosion and fire can change an ecosystem. Overpopulation can also alter the ecosystem. Overpopulation occurs when there are too many of at least one kind of living thing. This means resources will be depleted for plants and animals.

Pollution occurs when harmful substances are added to Earth’s air, water, or land. Water pollution is caused by wastes from homes and factories. Water pollution can kill plants and animals. Air pollution comes from forest fires, volcanoes, cars and factories. Burning gasoline, coal, and fuel can cause acid rain. This can ruin lakes, forests, soils, and crops. It can harm plants and animals. Land pollution such as acid rain, smog, trash, and chemical wastes can harm land. To reduce pollution, you should use resources wisely. You can conserve energy, clean up litter, recycle, and not dump wastes into the water.

Ecosystems can change naturally. Land left alone may support perennial plants and grasses. Over time, the land will begin to support shrubs and softwood trees. Eventually, the land may support a hardwood forest.

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