7th Grade Chapter19 Studyguide

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GPS: S7L4 – Students will examine the dependence of organisms on one another and their environments.

Chapter 19 Cycles in Our Ecosystems

Anything that has mass and occupies space is matter. This matter must be used over and over again in our closed ecosystem, we call this recycling. We will discuss a few of the very important cycles life depends on.

The Water Cycle

The movement of water among the oceans and our atmosphere, and the movement of fresh water (lakes, rivers, and streams) and our atmosphere make up the water cycle. There are several parts we will consider of the water cycle.

Precipitation

Water moves from the atmosphere to the land or bodies of water as precipitation (rain, snow, sleet, and hail). About 91 % of the water falls into our oceans, the rest falls on lakes, rivers, ponds, streams and the land as fresh water. Remember: fresh water does not necessarily mean it is clean water, it simply means it is low in salt content. Think of ocean water as salt-water.

Evaporation

When water goes from the bodies of water on the Earth back into the atmosphere, evaporation has occurred. This cycle is driven by the energy from the sun. When water vapor cools as it undergoes the process of condensation. Condensation is the process of water going from the gas phase into the liquid phase. In order for water to condensate, the moisture must have some form of particulate to attach to. This particulate can be in the form of dust, smoke, or other forms of pollution as well as solid surfaces. When condensation occurs in the atmosphere and falls back to Earth we again have precipitation. This is why it is called the water cycle.

Ground Water

As the water falls to the Earth, some of it falls onto the land. Some of the water seeps into the ground and enters underground caves, rocks with small pores and is often stored there. This water in under ground is called ground water. Ground water may stay in the Earth for hundreds to thousands of years. It can also slowly flow through the passages underground. Some ground water may drain into rivers, streams, form springs, or enter into the ocean.

Water and Life

All organisms require water to survive. Humans are about 70% water. RECALL: water transports wastes from our tissues and cells. Water also regulates our body temperature when we sweat and the sweat evaporates (this cools our body). Plants also need water in order to survive (they are living organisms). When water is returned from organisms back into the environment or atmosphere, the process is called transpiration. If there was not any water on Earth, there would not be any life.

The Carbon Cycle

Carbon is in all living organisms. The movement of carbon from the environment into living things and back into the environment again is called the carbon cycle.

Photosynthesis (This should be a review)

Photosynthesis is the process by which carbon cycles from the environment into living organisms. During photosynthesis, plants use carbon dioxide from the air to make sugars. Most animals get the carbon they need by eating the plants (when they eat the plants they are taking carbon into their body to make molecules that will contain carbon.

Respiration (This should be a review).

Carbon returns to the environment during respiration. RECALL: Respiration occurs in both plants and animals. When respiration occurs, sugar molecules are broken down to release energy. Carbon dioxide and water are released as by-products. Remember: we exhale carbon dioxide and water.

Decomposition

The breakdown of dead materials into carbon dioxide and water is called decomposition. Recall: Bacteria and some fungi decompose dead materials. When these organisms decompose the dead material, they are returning the carbon to the environment.

Combustion

The carbon in coal, oils and natural gas returns to the atmosphere when we burn the fuels. They release carbon dioxide into the environment when they...
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