Chapter 4, Ecosystems and Biomes
Lesson 1, Cycles in Ecosystems
Objectives:
□ List the steps in the water, carbon, and nitrogen cycles and explain their
importance.
□ Explain how recycling and composting benefit the ecosystem.
Essential Question:
How are nutrients cycled through ecosystems?
Vocabulary:
Water cycle
Evaporation
Condensation
Precipitation
Watershed
Runoff
Groundwater
Carbon cycle
Nitrogen cycle
Compost
1. What is the Water Cycle?
a. All water on Earth is recycled, or reused
b. Water cycle: the continuous movement of water between earth’s
surface and the air, changing from liquid into gas into liquid.
i. Is driven by the Sun’s energy – heat speeds evaporation.
ii. Evaporation: is the changing of a liquid into a gas.
iii. Condensation: is the changing of a gas into a liquid.
1. Water droplets rise into the air and gather with tiny dust
particles to form clouds.
iv. Precipitation: is any form of water that falls from the
atmosphere and reaches the ground. Rain, snow, sleet, hail
1. When clouds become too heavy the condensed water falls.
v. Watershed: an area from which water is drained.
vi. Runoff: precipitation that flows across land that is not absorbed flows into
rivers, lakes, or streams.
vii. Groundwater: is underground water. Stored in holes, or pores, in soil and rocks.
Side note:
 Plants participate in the water cycle, during photosynthesis they give off
water, called transpiration
 Animals take in water and let it out into the atmosphere as respiration.
Summary:
Heat causes water to evaporate from oceans, rivers, lakes, streams, and ponds.
Evaporating water rises and cools. Cooling causes condensation, which causes water
to form droplets. The droplets gather and form clouds. When the droplets become too
heavy they drop out of clouds, or precipitate. The water collects and the cycle starts
over again.
Questions:
Which would you expect to have a higher rate of evaporation – hot water or cold
water? Why do you think so?
Hot water has a higher rate of evaporation because heat speeds the process.
2. What is the carbon cycle?
a. Carbon in everywhere – 18% of our body, CO2 is a gas in the
atmosphere.
b. Carbon Cycle: is the continuous exchange of carbon among living
things.
i. Plants take in carbon from the air to make oxygen
ii. Plants combine carbon with water to make sugars and protein
iii. We obtain carbon by eating plants and animals
c. Carbon in plants, especially trees, is stored until the plant:
i. Is eaten or decomposes.
d. Decomposers, such as bacteria, break down dead or decaying plants
and animals.
i. This breakdown releases carbon into the air.
e. Decaying plants and animals over a very long period of time get
pushed down into the earth, and over millions of years becomes
natural gas, oil, and coal.
i. When we burn these fossil fuels we release carbon into the air.
This is not always a good thing.
Summary:
Carbon is converted to food by plants. Next, for things can happen:
1. The carbon-rich food can be burned (respired) by the plant and returned to
the atmosphere.
2. The food can be eaten by animals, burned, and returned to the atmosphere.
3. The plant and animal decaying material gets turned into oil and other fossil
fuels.
4. The decaying plants and animals get broken down by bacteria and fungi and
carbon returns to the atmosphere as a result of decomposition.
Question:
Would removing animals from the carbon cycle stop the cycle?
No. The carbon cycle could keep going. Animals add to the carbon cycle, but they are
not need.
3. What is the Nitrogen Cycle
Nitrogen Cycle: the continual trapping of nitrogen gas into compounds in the
soil and its return to the air.
a. Nitrogen gas in the atmosphere is “fixed” by bacteria that are attached
to the roots of legumes and turned into ammonia.
b. Soil bacteria change the ammonia into nitrates.
c. Other bacteria turn the nitrites into nitrates.
i. These unusable nitrogen compounds get incorporated into the
tissues of plants.
ii. Animals then eat the plants and use the nitrogen they contain.
iii. Extra nitrogen is excreted. This excreted nitrogen, along with
nitrogen from decayed plants and animals, gets decomposed and
returns to the soil as ammonia.
iv. Some bacteria changes nitrates back into nitrogen gas.
* I am not going to ask specific questions about the nitrogen cycle, but know the
definition.
4. How is matter recycled?
a. Renewable Resources: trees (can be replanted), water, wind, sunlight.
All these can be replaced.
b. Nonrenewable resources: oil, metals, and fossil fuels cannot be
replaced in the environment once they are used.
c. We can conserve some natural resources by recycling them. We can
make new objects or material out of the old materials.
d. Compost is a mixture of dead organic material that can be used as
fertilizer.
i. Composting is a way to recycle nitrogen.
ii. It also reduces the amount of trash we make.
e. How does compost enrich the soil?
i. Decomposers breakdown decaying plant and animal materials.
ii. Ammonia is a product of decomposition.
iii. Soil bacteria change ammonia into nitrites and nitrates.
iv. Compost replenishes the nitrogen used by plants as they grow.
Summary:
Decomposers break down plant and animal material into ammonia. Ammonia then
enters the nitrogen cycle.
Question:
Compost is useful, but it often has a bad smell. What might give compost its smell?
The breakdown of chemicals by bacteria.