CELLULAR ENERGY
Types of Energy: Although energy may be classified in a number of different ways and as a
number of different types, two forms of energy are of particular interest to biologists: SOLAR
and CHEMICAL
I.
Solar Energy: Energy emitted from the Sun (essentially a nuclear fusion reactor) in
the form of LIGHT and HEAT. Light can be described by its WAVELENGTH.
Wavelength is the distance between
two identical points on a repeating
wave, in this case peak (crest) to peak,
however any repeating points could be
used (for example, trough [bottom] to
trough)
Wavelength directly relates to the energy
carried by light, with shorter wavelengths carrying more energy than longer wavelengths.
Below is the Electromagnetic Spectrum of light—a useful tool in visualizing the different
forms light can take. REMEMBER SHORTER WAVELENGTH=MORE
ENERGY!!
Reds---------Oranges----Yellows—Greens-----Blues--------Violets
***Note: the units of length are in nanometers which are one billionth of a meter!!
II.
Chemical Energy: Type of potential energy where the energy is stored in the
chemical bonds that form molecules. When certain chemical reactions takes place,
bonds are broken and energy is released. Chemical reactions can be represented using
a chemical equation in the form: ReactantsProducts. The Law of Conservation of
Mass dictates that all matter that enters a chemical reaction must leave (although in
different forms), so this helps in that we can see and track everything going in and
everything going out. SOMETIMES YOU WILL SEE SOMETHING WRITTEN
ABOVE THE ARROW (an enzyme, light, ATP, etc.) THIS MEANS THAT IT
PLAYED A ROLE IN THE REACTION BUT DID NOT DIRECTLY
PARTICIPATE. (EX. An enzyme helps a reaction take place but is not
chemically altered in the process; light is essential for photosynthesis but is not
matter and cannot, therefore, be accounted for in the reaction; the energy to
produce ATP is provided by a chemical reaction, but the reaction itself does not
involve ATP)
What we think of as food is chemical energy! Where does it come from?
Photosynthesis: photo means “light” and synthesis means “putting together”,
so photosynthesis means “putting together with light”. What is being put together?
MoleculesFOOD. Photosynthesis is a process used by plants and other
organisms to convert light energy, normally from the Sun, into chemical energy (in
the form of molecular bonds) that can be later released to fuel the organisms'
activities.
Photosynthesis takes place in a very specialized organelle found
in plant cells called the CHLOROPLAST which contains
specialized pigments that absorb visible light.

Pigment: A chemical/substance that absorbs certain wavelengths of light and reflects
others.
o Absorbance: A wavelength, or series of wavelengths, of light is/are trapped
by a pigment along with energy it/they contain(s) the visible light
wavelengths absorbed never reach your eye and, thus, are not seen.
o Reflection: A wavelength, or series of wavelengths, of light is/are scattered by
a substance the visible light wavelengths reflected are the ones that enter
your eye and are seen.
o Example: A leaf that appears green absorbs all wavelengths except for green,
and reflects it in all directions (some of this light enters your eye and causes
you to perceive the leaf as green); something that appears black absorbs all
wavelengths of visible light and appears to have no color (because no visible
light is reflected into your eye); something that appears white reflects ALL
wavelengths and appears to have every color (light of all visible wavelengths
is reflected into the eye and the brain perceives this as “white”)
**Now you know why light colors keep you cooler in the summer and dark
colors get hot faster…dark colors ABSORB more light and ENERGY (which
dissipates as heat)!!**
Important Pigments used in Photosynthesis:
I.
II.
Chlorophyll- pigment with strong absorbance in the blue and violet wavelengths, and
moderate absorbance in the orange-red wavelengths. There are two types
Chlorophyll-α (A) and Chlorophyll-β (B) CAUSES THE GREEN APPEARANCE
OF PHOTOSYNTHESIZING PLANTSREFLECTS GREEN LIGHT!!
Carotenoids- pigment with moderate absorbance in the blue and green wavelengths.
Causes the orange-yellow-red appearance of photosynthesizing plants. Typically seen
in the Fall when plants stop replenishing their chlorophyll (absorbs orange-red
wavelengths) concentrations in preparation for winter (decreased sunlight).
The Chloroplast—the Site of Photosynthesis:
Thylakoid: Site of the LIGHTDEPENDENT REACTIONS
Granum (plural Grana): Stack
of thylakoids surrounded by
the stroma
Stroma: Watery fluid (like the
cytoplasm, but thicker), site of
the LIGHT-INDEPENDENT
REACTIONS
Photosynthesis takes place through two stages:
I.
II.
The Light-Dependent Reaction (aka Light Reaction)
The Light-Independent Reaction (aka Dark Reaction aka Calvin Cycle)
The Light-Dependent Reaction:
LOCATION: THYLAKOID
 Inputs (what goes in):
o Light energy(from the Sun) In photosynthesis equation as reactant
o Water (H2O) In photosynthesis equation as reactant
o NADP+
o ADP + P
 Outputs (what comes out):
o Oxygen gas (O2) In photosynthesis equation as product
o ATP
o NADPH
The Light-Independent Reaction (Calvin Cycle):
LOCATION: STROMA
 Inputs (what goes in):
o Carbon Dioxide gas
(CO2) In
photosynthesis
equation as reactant
o NADPH
o ATP
 Outputs (what comes out):
o Glucose (C6H12O6) In
photosynthesis
equation as product