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PREP FOR THE AP EXAM
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AP EXAM TIP
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CO 2 You should know that matter and energy both flow through
communities, but they take different paths. Matter travels
Energy in a cycle, with the same atoms moving back and forth
among organisms and the physical environment. By
contrast, energy is not recycled. Instead, an input of energy
from the environment is constantly required to sustain cells
and organisms. Be prepared to give examples of the ways
that matter and energy flow through communities and
therefore sustain life.

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shown in Figure 1.1 Plants, algae, and certain bacteria cap-
ture energy from the sun and use it to synthesize energy-
rich organic molecules. Where sunlight is absent, especially
Matter in the vast depths of the ocean, energy instead comes from
chemical compounds.
FIGURE 1.1 Flow of matter and energy
Organisms transform energy. That is, they acquire
Matter, such as a carbon atom, cycles among organisms and the energy from the environment and convert it into a chemical
physical environment. Energy, like solar and chemical energy, is form that their cells can use. For instance, some of the solar
harnessed by organisms to do work and needs to be constantly
added to the system to sustain life. energy striking a forest is captured by plants, which trans-
form it into chemical energy in the form of sugars. Some
of this energy is used by the organism to do work— such
as building cellular components, moving, and reproducing.
The carbon cycle also teaches that matter moves through
organisms and the physical environment in a cycle, as shown The rest of this energy is dissipated as heat and is no longer
available for the organism to use. We will look more closely

in FIGURE 1.1 . In other words, the same atoms are reused at the flow of energy and the cycling of matter in Units 3

over and over. Organisms must exchange matter with other and 8. “Analyzing Statistics and Data: Standard Deviation
organisms and the environment to grow, reproduce, and and Error Bars” gives you an opportunity to practice using
maintain organization. For instance, when a leaf or a plant data analysis skills on a question involving plants and energy
in the forest dies, it is usually consumed by the animals or capture.
microbes in the forest. These organisms use the dead leaf to
build their biomass. In turn, these organisms recycle mat-
ter through the wastes they release or when they die. The PREP FOR THE AP EXAM
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released matter is used by other organisms, including plants, AP EXAM TIP
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animals, and microbes, to build their biomass.
Make sure you understand that no overlap between error
bars indicates a statistically significant difference.
Flow of Energy
As organisms move carbon, they also transfer energy. Carbon
and energy are closely intertwined for the simple reason that
the energy sources for many organisms are the carbon- rich
organic molecules in the organisms they eat or the mole- ✓ Concept Check
cules they build themselves. Unlike carbon, energy does not 1. Describe how matter and energy flow through
move in a cycle. Instead, energy must continually be har- living systems.
vested from the environment to sustain the community. In 2. Describe how the flow of matter depends on the
essentially all habitats where sunlight is available, the sun flow of energy in communities.
provides the entry point for energy into living systems, as

MODULE 1 ELEMENTS OF LIFE 27

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