Water Cycle
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About 75% of Earth’s surface is covered with water.
The water cycle is a continuous process that renews the fresh water on Earth.
The sun is the energy source for the water cycle.
The steps of the water cycle include: evaporation, condensation, precipitation,
transpiration, and accumulation.
Evaporation is the process of a liquid turning into a gas. In this case, water is
heated by the sun and turned into water vapor (gas).
Condensation is the process of a gas turning into a liquid. As the water vapor
rises into the atmosphere, the temperature cools causing the gas to turn back into a
liquid. These tiny drops of water, combined with dust particles, form clouds.
Precipitation is any form of water that falls to the Earth. This could include rain,
snow, sleet or hail.
Transpiration occurs when the stomata of plant leaves open and release water.
This water can then be evaporated and cycled through the water cycle.
Accumulation occurs when precipitated water collects in rivers, ponds, lakes,
oceans, and other water sources.
Questions:
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What is the water cycle?
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What are the steps of the water cycle?
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What causes water to evaporate?
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Why does water vapor turn back into a liquid during condensation?
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What is precipitation? What are some examples of precipitation?
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What is transpiration, and how does it fit into the water cycle?
Carbon Dioxide – Oxygen Cycle
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Air contains both carbon dioxide and oxygen gases.
Plants use carbon dioxide gas and animals use oxygen gas.
The movement of carbon dioxide and oxygen between organisms and the air is
called the carbon dioxide – oxygen cycle.
Carbon dioxide in the air is taken into plant leaves during photosynthesis. The
plants use carbon dioxide to make food and then release oxygen into the air as a
waste product.
Animals breathe in oxygen during cellular respiration (breathing). Animals use
this oxygen and then release carbon dioxide back into the air as a waste product.
Decomposers also give off carbon dioxide as a waste product.
The burning of fossil fuels puts carbon dioxide into the air.
Questions:
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What is the carbon dioxide- oxygen cycle?
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What organisms take in carbon dioxide from the air?
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What organisms take in oxygen from the air?
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If all the trees on Earth were cut down, which gas would increase in the air?
Photosynthesis
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Photosynthesis is the process by which plants make their own food.
Plants use energy from the sun to change water and carbon dioxide into food.
This food is called glucose (a sugar).
During photosynthesis, a waste product is made (oxygen). A waste product is
anything an organism cannot use. In this case, plants cannot use oxygen and
therefore get rid of it as waste.
The plant leaves release oxygen into the atmosphere through the stomata (tiny
openings on the underside of leaves that open and close).
Questions:
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What is photosynthesis?
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What do plants need to go through photosynthesis?
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Would a plant be able to undergo photosynthesis if it was kept in the dark? Why?
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What waste product is given off during photosynthesis?
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What part of the plant takes in water for photosynthesis?
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What part of the plant takes in carbon dioxide for photosynthesis?
Nitrogen Cycle
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The nitrogen cycle is the process that turns nitrogen gas in the air into usable
substances that plants and animals can use.
Nitrogen gas makes up 78% of the air.
All organisms need nitrogen to build and grow, but organisms cannot breathe in
nitrogen.
Plants get nitrogen from the soil. Animals get nitrogen by eating plants or by
eating animals that have eaten plants.
Nitrogen gas is changed by special nitrogen fixing bacteria in the soil into
compounds that plants can take up through their roots.
Nitrogen is put back into the soil by animal waste (solid or liquid) and by
decaying (rotting) organisms. Decomposers break down these dead organisms or
waste products and return the nitrogen to the soil.
Once back in the soil, the nitrogen can be taken up by a plant or returned back to
the atmosphere as a gas.
Questions:
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How much of the air is made up of nitrogen gas?
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Can animals breathe nitrogen?
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How do plants get nitrogen?
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How can animals get nitrogen?
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If organisms can’t use nitrogen in the gas form, what changes it into usable
compounds?
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How is nitrogen returned to the soil?