Chapter 2 Notes

“Cycles in Nature”

The Water Cycle

The water cycle is the movement of water between the oceans, atmosphere, land, and living things.

Stages of the Water Cycle Evaporation – The change of a substance from a

liquid to a gas, where the water is cycled back into the atmosphere.

Condensation- The change of state from a gas to a liquid due to the cooling of water vapor.

Precipitation- Any form of water that falls to the Earth’s surface from the clouds. It is water that moves from the atmosphere to the land and oceans- includes rain, snow, sleet and hail

Ground Water (collection)- The precipitation that seeps into the ground, where it is stored in spaces between or within porous rocks and underground caverns.

The Carbon CycleThe carbon cycle is the exchange of

CARBON between the environment and living things (it moves from the environment into living things and back into the environment).

Stages of the Carbon CyclePhotosynthesis – The basis of the carbon cycle, in

which plants use carbon dioxide from the air to make sugars.

Respiration – The process by which sugar molecules are broken down to release energy. Carbon dioxide and water are released as byproducts.

Decomposition – The breakdown of substances into simpler molecular substances. It The breakdown of dead materials into carbon dioxide and water

Combustion – The process of burning a substance, such as wood or fossil fuels. Releases CO2

The Nitrogen CycleThe nitrogen cycle is the movement of

NITROGEN from the environment to living things and back again because organisms need nitrogen to build proteins and DNA for new cells.

Nitrogen is found in the form of gas in the:

Since most organisms cannot use the nitrogen gas, it is changed into usable forms by ◦This is called

Organisms get the nitrogen they require by eating

When an organism dies the nitrogen is returned to land by

plants or eating organisms that eat plants.

Earth’s atmosphere.

Bacteria, lightning.nitrogen fixation.

decomposers breaking down remains.

SuccessionSuccession is the replacement of one type of community by another at a single place over a period of time.

There are types of succession.◦ and

2Primary SuccessionSecondary Succession

Primary SuccessionPrimary succession is when a small

community of living things starts to live in an area that had no soil, plants or animals. ◦Starts with bare rock ◦Then organisms live and die on rock

◦Then rock slowly turns into soil

An example of primary succession is when◦

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A glacier exposes bare rock where nothing lives.Acids from lichens break rocks into small particles, and mix with remains of dead lichens to form soil.After many years, there is enough soils for mosses to grow & replace lichens. Insects & other organisms begin to live there. When they die, their remain adds to soils.

Over time, soil deepens, grass, flowers, & trees form.

Over time or thousands of years, soil can deepen to support a forest.

Secondary SuccessionSecondary succession is the

regrowth of the original plant community in an existing area that was destroyed by a natural disaster, but soil was left intact

An example of secondary succession is when:

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After a year that a farmer stops growing crops, weeds and crab grass start to grow.

In 5 to 15 years, small conifers start growing among weeds and trees continue to grow. After about 100 years, a forest may form.

By the second year, new weeds such as horseweed appears. Insects or the wind carries seeds.

As older conifers die, they may be replaced by hardwoods, such as oak or maple trees if the climate can support them.