Download Chapter 2 Cell Processes and Energy

Chapter 2
Cell Processes and Energy
Section 1
Photosynthesis
What Is Photosynthesis?
• Every living thing needs energy to carry out its
functions.
• Our food contains the energy we need, but
plants and bacteria-like organisms get energy
in a different way.
• Photosynthesis is the process by which a cell
captures the energy in sunlight and uses it to
make food.
A Two-Stage Process
• During photosynthesis, plants and some other
organisms use energy from the sun to convert
carbon dioxide and water into oxygen and
sugars, including glucose.
• The entire process can be put into two stages:
– Capturing the sun’s energy
– Producing sugars
Capturing the Sun’s Energy
• The chloroplasts of a cell
give the plant its green
color due to the presence
of pigments, which are
colored chemical
compounds that absorb
light (like a solar panel).
• The main pigment found in
the chloroplasts of plants is
chlorophyll.
Producing Sugars
• The cell needs H2O and
CO2 to produce sugars.
• The plant can obtain H2O
from its roots and CO2
from the air around it
through little openings
on the underside of
leaves called stomata
(the singular would be
stoma).
Producing Sugars
• Once inside the
chloroplasts, H2O and CO2
undergo a number of
chemical reactions
powered by the sunlight
captured by the pigments.
• These reactions create O2
and sugars, including
glucose (C6H12O6)
The Photosynthesis Equation
• The cells break down the sugars to use for
energy or to store them for later use.
• Most of the oxygen is released through the
stomata and into the air.
Photosynthesis and Life
• About 21% of our atmosphere contains
oxygen, thanks to photosynthesis, which we
need to survive.
• Nearly all living things obtain energy either
directly (autotrophs) or indirectly
(heterotrophs) from the energy of sunlight
captured during photosynthesis.
Photosynthesis and the Circle of Life