Cycles in Nature
Study Guide
Matter moves between the environment and living things in all cycles of matter
(water, carbon and nitrogen).
Water Cycle:
 Evaporation is a change of water from __liquid_____ to ___gas_________.
 Condensation is the change of water from ____gas____ to __liquid________.
 Precipitation is when __water____falls back to __Earth______ in the form of
rain, __snow___, sleet or hail.
 Most _precipitation______ that falls to Earth’s surface falls directly into
__oceans_____
 ___ Transpiration __________ is when plants release water.
 __Groundwater_______(water under the Earth’s surface) is an important
part of the water cycle.
Earth
snow
Groundwater
Transpiration
liquid
vapor
liquid
vapor
oceans
water
precipitation
Carbon Cycle:
 All _organic____ (living) molecules contain __carbon_________.
 Carbon is important to _living___ things because it transports the material
_cells___ use for energy.
 Carbon from the __environment____becomes a part of living organisms
through the process of __photosynthesis______.
 Photosynthesis is when plants use _carbon__ _dioxide____ from the air to
make _glucose (sugar)________.
 Most animals get the carbon they need by eating _plants_____.
carbon
living
carbon dioxide
organic
cells
photosynthesis
environment
plants
glucose
 Combustion is the _burning____ of a substance.
 Respiration is when sugar __molecules_____ are broken down by
__plants___ to release energy. Carbon dioxide and __water___ are
released as byproducts of this process.
 Combustion, respiration and ___decomposition____ all release carbon
dioxide into the environment.
_Photosynthesis____ does not.
 Decomposition is the _breaking___ __down___ of substances into simpler
molecules.
 Bacteria’s breaking down organic matter and returning carbon dioxide
and water to the environment is an example of ___ decomposition.
molecules
decomposition
breaking down
Photosynthesis
burning
plants
decomposition
water
Nitrogen Cycle:
 78_% of the Earth’s ___atmosphere___ is nitrogen gas, but most organisms
cannot __use__ it in this form.
 Nitrogen is important to living things because it builds new __cells___.
 Nitrogen gas must be chemically ____transformed____ (changed) before it
can be used by plants.
 __Bacteria____ that live in the soil have the important function of nitrogen
__fixation______.

__Lightning___can cause nitrogen fixation.
atmosphere
Lightening
Bacteria
transformed
cells
use
fixation
Ecological Succession:
 Succession is the replacement of one type of ___community _____ by
another over time_________.
 Rock slowly transforming into soil is an example of __primary____
succession.
 _Lichen_____ is an example of a pioneer species.
 Secondary succession is when an existing community is _destroyed______
by a natural _disaster_____ or other type of disturbance.
 A forest __growing_______ back after a forest fire is an example of
_secondary________ succession.
community
Lichen
destroyed
primary
disaster
secondary
growing
time
 The first plants that would grow on __abandoned__________ farmland
would be __weeds____.
 Secondary succession _differs____ from primary succession in that it occurs
in an area that has __soil___________.
 Climax species grow slowly and are well-adapted________ to an
environment.

A __mature____
community always has well-adapted organisms.
 Biodiversity is when a variety____ of species are present in an area.
abandoned
soil
adapted
variety
differs
weeds
Be able to answer the following questions.
mature
 Does the process of succession end? Explain.
 Suppose a scientist proposes a plan to destroy all bacteria on Earth in
order to get rid of diseases caused by bacteria.
Explain why it would be a good idea to approve this plan or not.
 Carbon may be in the environment for millions of years before it is
released into the air where living things can use it. Give an example of
how this may happen.
Be able to label a diagram of the water cycle:
precipitation
evaporation
condensation
transpiration
run-off
groundwater
Be able to label a diagram of the carbon cycle:
respiration
photosynthesis
decomposition
Be able to trace the steps of primary succession or secondary succession in a
picture.