Chapter 8:
Cellular
Energy
Section 1: How
Organisms
Obtain Energy
Transformation of Energy
All cellular activities require
( The ability to do work).
Energy!!
•The study of flow and the transformation
of energy is called Thermodynamics.
There are two laws of
thermodynamics.
Laws of Thermodynamics
1.The law of conservation of energy.
• Energy can be converted to one form
to another, but cannot be created nor
destroyed.
Ex. Stored energy in food is converted
to chemical energy when you eat and
into mechanical energy when you run
or kick a ball.
• 2. Energy cannot be converted without the loss of
usable energy. Energy that is “lost” is converted
without the loss of usable energy.
•
Entropy- Is the measure of disorder, or
unusable energy, in a system.
• Ex. Food chain ( energy decreases with the next
trophic level)
Organisms that make their own
food are called Autotrophs.
• Some autotrophs
(Chemoautotrophs) use
inorganic substances such as
hydrogen sulfide as a source of
energy while others, such as
plants, convert light energy
from the sun into chemical
energy.
• Autotrophs that convert energy
from the sun are called
Photoautotrophs.
Heterotrophs are
organisms that need
to ingest food to
obtain energy.
Metabolism
All of the chemical reactions in a cell
are referred to as the Cell’s
Metabolism.
• A series of chemical reactions in which
the products is the substrate (starting
products) for the next reaction is
called a metabolic pathway.
There are two broad categories of
metabolic pathways.
1. Catabolic Pathways
• Release energy by breaking down larger molecules
to smaller molecules.
2. Anabolic Pathways
• Use the energy released from catabolic pathways to
build larger molecules from smaller molecules.
The relationship between these two pathways results
in the continual flow of energy within an organism.
Photosynthesis
• The anabolic pathway in which
light energy from the sun is
converted to chemical energy
for use by the cell.
• In this reaction autotrophs use
light energy, carbon dioxide,
and water to form glucose and
oxygen.
• The energy stored in the
glucose produced can be
transferred to other organisms
when those molecules are
consumed as food.
Cellular Respiration
• The catabolic pathway in
which organic molecules
are broken down to
release energy for use
by a cell.
• In cellular respiration
oxygen is used to break
down organic molecules,
producing carbon dioxide
and water.
ATP: The Unit Of Cellular Energy
• Adenosine triphosphate (ATP) is the most
important biological molecule that provides
chemical energy.
ATP Structure:
• Nucleotide made of an adenine base,
a ribose sugar, and three phosphate groups.
ATP Function
• ATP releases
Energy when the
bond between the
second and third
phosphate group
is broken.
(forming ADP)
Section 2:
Photosynthesis
Phase # 1
Photosynthesis
Process by which most autotrophs,
including plants, make organic
compounds such as sugars.
Recall that during this process Light
energy is converted into chemical
energy(Glucose and Oxygen).
6𝐶𝑂2 + 6𝐻2 𝑂 → 𝐶6 𝐻12 𝑂6 + 6𝑂2
Photosynthesis Occurs in Two Phases
In Phase 1
(lightdependent reactions)
light is absorbed and
converted into chemical
energy in the form of
NADPH and ATP.
In Phase 2 ( lightindependent reactions)
the ATP and NADPH
that were formed in
phase one are used to
make glucose.
• Once glucose is
produced, it can be
joined to other simple
sugars to form larger
molecules.
• Their larger molecules
are complex
carbohydrates(such as
starch) and other
organic molecules
(proteins, lipids and
acids).
Phase one: Light Reactions
• The first step in photosynthesis is the
absorption of light.
• Plants have special organelles to capture light
energy called chloroplasts.
• Once the energy is captured, two energy
storage molecules, NADPH and ATP, are
produced to be used in the light-independent
reaction.
Chloroplasts
• Large organelles
that are used to
capture light
energy in
photosynthetic
organisms.
• In plants,
chloroplasts are
found mainly in
the cells of their
leaves.
Disk-shaped organelles that
contain two main
compartments important for
photosynthesis.
1. The Thylakoid
• Flattened, saclike
membranes that are
arranged in stacks (Grana).
• Location where lightdependent reactions take
place.
2. The stroma
• Fluid like space that Is
outside of the grana.
• Location where Lightindependent reactions
take place in phase 2.
• Light-absorbing colored molecules called pigments
are found within the thylakoid membranes of
chloroplasts.
• The major light-absorbing pigments in plants are
called chlorophylls. (most common are chlorophyll A
and B.
• Different pigments absorb different wavelengths of
light.
• Chlorophylls absorb most strongly in the violet-blue
region of the visible light spectrum.
• This is why plants appear Green to the human eyes.
Electron Transport
• The Structure of the thylakoid
membrane is the key to efficient
transfer during electron
transport.
• Thylakoid membrane has a large
surface area, which provides
space to hold large numbers of
electron transporting molecules
and photosystems (electrontransporting molecules.)
Photosystem 1 and 2
contain light absorbing
pigments and proteins
that play major roles in
the light reaction
phase.
How exactly
does this
work?
First, the light
energy excites
electrons in
photosystem 2 and
causes water
molecules to split,
releasing an electron
into the electron
transport system.
+
• hydrogen ion (𝐻 )
are released into
the thylakoid space
and oxygen (𝑂2 ) as
a waste product.
* This break down
of water is essential
for photosynthesis
to occur.
The excited
electrons move
from photosystem
2 to an electron
acceptor
molecule in the
thylakoid
membrane.
The electronacceptor molecule
transfers the
electrons along a
series of electroncarriers in
photosystem 1.
• In the presence of light,
photosystem 1
transfers the electrons
to a protein called
ferrodoxin.
• The electrons lost by
photosystem 1 are
replaced by electrons
shuttled from
photosystem 2.
Finally, ferrodoxin
transfers the
electrons to the
+
carrier 𝑁𝐴𝐷𝑃 ,
forming 𝑁𝐴𝐷𝑃𝐻.
• ATP is produced in
conjunction with
electron transport by
the process of
chemiosmosis.
• The 𝐻+ released
during the electron
transport acclimated in
the interior of the
thylakoid (causing a
high concentration in
the interior and a low
in the exterior)
• 𝐻+ protons will diffuse
down their
concentration gradient
out of the thylakoid
interior into the stroma
through a channel
spanning the
membrane (enzymes
called ATP synthases)
• As 𝐻+ moves through
the ATP synthase,
ATP is formed in the
stroma.
Section 2:
Photosynthesis
Phase # 2
RECAP!
The end products for
the first phase of
photosynthesis were
ATP and NADPH.
Phase 2: The Calvin Cycle
ATP and NADPH are able to provide the
cell with a large amount of energy but
they are not stable enough to store
chemical energy for a long period of time.
This is when the second phase of
photosynthesis comes into play!
The Calvin Cycle!
• Also referred to as Light-independent
reactions.
• Stores energy in organic molecules, such
as glucose.
How exactly
does this
work?
The first step is called
carbon fixation.
Six carbon dioxide
molecules (𝐶𝑂2 ) combine
with six 5-carbon
compounds to form
Twelve 3-Carbon
molecules called 3phosphoglycerate(3PGA).
In the second step, the
chemical energy stored in
ATP and NADPH is
transferred to the 3-PGA
molecules to form highenergy molecules called
glyceraldehyde 3-phosphate
(G3P).
ATP provides the phosphate
groups, which NADPH
supplies the hydrogen ions
and electrons.
In the third step, two
G3P molecules leave
the cycle to be used
for the production of
glucose and other
organic molecules.
In the final step, an
enzyme called rubisco
converts the remaining
G3P molecules into 5carbon molecules called
Rubisco 1,5bisphosphate (RuBP).
These molecules
combine with new
carbon dioxide
molecules to
continue the
cycle.