Section 1 Energy and Living Things
94 CHAPTER 5Photosynthesis and Cellular Respiration
Energy in Living Systems
You get energy from the food you eat. Where does the energy in food
come from? Directly or indirectly, almost all of the energy in living
systems needed for metabolism comes from the sun. Figure 1 shows
how energy flows through living systems. Energy from the sun
enters living systems when plants, algae, and certain prokaryotes
absorb sunlight. Some of the energy in sunlight is captured and
used to make organic compounds. These organic compounds store
chemical energy and can serve as food for organisms.Building Molecules That Store Energy
Metabolism involves either using energy to build molecules or
breaking down molecules in which energy is stored.
is the process by which light energy is converted to chemical energy.
Organisms that use energy from sunlight or from chemical bonds in
inorganic substances to make organic compounds are called
(AWT oh trohfs). Most autotrophs, especially plants, are
photosynthetic organisms. Some autotrophs, including certain
prokaryotes, use chemical energy from inorganic substances to
make organic compounds. Prokaryotes found near deep-sea vol-
canic vents live in perpetual darkness. Sunlight does not reach the
bottom of the ocean. These prokaryotes get energy, however, from
chemicals flowing out of the vents.autotrophsPhotosynthesisObjectives
Analyzethe flow of energy
through living systems.
Comparethe metabolism
of autotrophs with that of
heterotrophs.
Describethe role of ATP in
metabolism.
Describehow energy is
released from ATP.
Key Terms
photosynthesis
autotroph
heterotroph
cellular respiration- Plants convert light energy
to chemical energy.
2. Rabbits get energy by
eating plants.
3. Foxes get energy by
eating rabbits.
Light energyEnergy flows from sunlight or inorganic substances to autotrophs, such as
grasses, and then to heterotrophs, such as rabbits and foxes.Figure 1 Flow of energy9B9D4B4B