Ms. Whipple
Brethren Christian High School
4A-1 Energy Relationships

 Organism’s depend on many conditions in their
environment and the most important of these is a constant
supply of energy. An Organism’s primary need is
ENERGY!!
 Cells use and reuse different substances (amino acids,
sugars, lipids, etc.) but energy must be constantly
supplied as every time it is used, some is lost and
becomes unusable (2nd law of thermodynamics)
 Cells store energy in the bonds of large stable organic
molecules (starch, fat, sugar) and need energy to make
these bonds.
4A-1 Energy Relationships

 Organisms are in constant battle to maintain a
supply of energy because it is difficult to store, is
used and never reused, and escapes constantly as
entropy (2nd law of thermodynamics)
4A-1 Energy Relationships

 Obtaining energy!! There are two classifications of organisms
based on how they obtain energy.
 Autotrophs (Producer): Organisms that make their own food by
photosynthesis. Plants, Algae, and some other organisms capture light
energy to produce their own food. (Photosynthesis). The process of
photosynthesis uses CO2 and H2O in the presence of sunlight to make
Glucose and O2.
Reactants
Equation for Photosynthesis: 6CO2 + 6H2O
Products
C6H12O6 + 6O2
 Heterotrophs (Consumer and Decomposers): Organisms that
depend on other organisms for their energy. Humans, animals, fungi
and bacteria must rely on the energy of other organisms for their food.
To obtain energy, Glucose is broken down into CO2 and H2O
releasing the energy to make ATP (cellular energy).
Reactants
Equation for Cellular Respiration: C6H12O6 + 6O2
Products
6CO2 + 6H2O
4A-1 Energy Relationships

Heterotroph
(Koala)
Autotroph
(tree)
4A-1 Energy Relationships

 The Food Chain: linear consequence of links in a
food web (non-linear web of food relationships
between species) starting from producers and ends
at decomposers.
4A-1 Energy Relationships

 ATP: The Energy Currency of Cells
 To use energy, it must be in an easily accessible form.
Many molecules that store energy, like starch and
lipids, have too much energy to be used at one time
(and that could potentially be destructive!). So, the
energy from these molecules must be converted into
smaller units. In all know organisms this small unit is
the molecule ATP (Adenosine Triphosphate).
4A-1 Energy Relationships

 Structure of ATP
 An ATP molecule consists of Ribose (5-carbon sugar
backbone), Adenine (one of the bases from DNA), and
a chain of three Phosphate Groups.
4A-1 Energy Relationships

 Using ATP: ATP stores energy in the bonds between
the phosphate groups. When these bonds are broken
a small unit of energy is released and can be
immediately used for a cellular function.
 In most reactions, the third phosphate group is broken
off to release energy. This leaves a molecule of ADP
(Adenosine Diphospate) , a free phosphate group,
and energy.
ATP
ADP + P + Energy!
4A-1 Energy Relationships

 Once ATP has been converted to ADP and the
energy used, an enzyme takes it and combines it
with a phosphate group and energy to make ATP
again. In this way it is a reusable energy source.
ADP + P + Energy
ATP
 This cycle of breaking down ATP to use energy and
then rebuilding it with energy is how we stay alive.
It is very much like a prepaid debit card, once you
use the money from the card (break the bond) you
must put more money in to use it again (reform the
bond).
4A-1 Energy Relationships

4A-3 Cellular Respiration

 Respiration is commonly thought to be breathing,
but breathing is really only the first step in
respiration (obtaining oxygen).
 Cellular Respiration: breaking down of food
substances into usable cellular energy in the form of
ATP. This occurs in the mitochondria.
 There are 2 types of cellular respiration: Aerobic
(requiring oxygen) and Anaerobic (not requiring
oxygen).
4A-3 Cellular Respiration

 Aerobic Respiration: Requires Oxygen!! Most cells
require oxygen to break down sugar and release heat in
much the same way that a match needs oxygen to light
and will go out if deprived air.
 In aerobic respiration, cells use a series of enzymes with a
little activation energy to break glucose into energy, CO2
and H2O. Therefore, it can be seen as the opposite of
Photosynthesis (which uses CO2 and water to make
glucose).
 Chemical Equation of Aerobic Respiration
𝐶6 𝐻12 𝑂6 + 6𝑂 2
6𝐻2 𝑂 + 6𝐶𝑂2 + ATP (energy)
4A-3 Cellular Respiration

 The Process of Aerobic Respiration
 Every process of cellular respiration begins with Glycolysis
in the cytoplasm. It does not require oxygen but it is
involved in both aerobic or anaerobic pathways.
 Glycolysis (Stage I): Takes place in the cytoplasm. converts
glucose C6H12O6 into pyruvate, CH3COCOO− + H + . To start
this process, 2 ATP are put into the reaction (energy
investment). In the second stage, the free energy release
forms 4 ATPs (net gain: 4 – 2 = 2 ATP) and 2 NADH
 NET GAIN:




2 PYRUVATE
2 H2O
2 ATP
2 NADH + 2H+

4A-3 Cellular Respiration

 Aerobic Respiration (after glycolysis): Divided into
2 phases: the Citric Acid Cycle (Kreb’s Cycle) and the Hydrogen
and Electron transport chain.
 Citric Acid Cycle (or Kreb’s Cycle) (Stage II): Occurs in the
matrix of the mitochondria. An enzyme breaks the pyruvic
acid from glycolysis into acetyl coA, C𝑂2 , Hydrogen ions, ATP,
and electrons. The CO2 is releases as waste out of the cell and
the hydrogen and electrons move on the next phase. For every
1 molecule of glucose, the Citric Acid Cycle turns twice!
 NET GAIN:




8 NADH
2 FADH2
2 ATP
6 CO2 (waste!)

4A-3 Cellular Respiration

 Hydrogen and Electron Transport Chain (Stage III):
Occurs along the membrane of the inner mitochondrial
membrane (cristae). The energy from NADH and FADH2
are used to pump H+ into the outer compartment of the
mitochondria. This creates a chemiosmotic gradient
which is used to produce ATP. ATP is generated as H+
moves down its concentration gradient through a special
enzyme called ATP synthase.
 NET GAIN:
 32 ATP
 H2O
4A-3 Cellular Respiration

4A-3 Cellular Respiration

 So, altogether the
output of aerobic
respiration:
 Glycolysis: 2 ATP
 Citric Acid Cycle: 2
ATP
 Hydrogen and
Electron Transport
Chain: 32 ATP
 Total: 36 ATP from 1
molecule of glucose
4A-3 Cellular Respiration

 The Process of Anaerobic Respiration:
 Some organisms live in environments without oxygen
and even our bodies are sometimes put into a
anaerobic situation (during exercise when the blood
cannot carry oxygen to the muscles fast enough), so
we must use anaerobic respiration.
 Fermentation: The process of breaking down food
without oxygen. This process does not produce as
much usable energy (ATP) but is used by many
organisms. There are 2 different pathways:
Alcoholic Fermentation and Lactic Acid Fermentation.
4A-3 Cellular Respiration

 Alcoholic Fermentation: The process is carried out
by many bacteria and yeast. The yeast that are used
in making bread rise use this process. During this
process, the pyruvic acid from glycolysis is changed
into ethyl alcohol. The net gain of this process is 2
ATP.
Fizzy bubbles
and bread rising!!
4A-3 Cellular Respiration

 Lactic Acid Fermentation: This process is carried out by
many bacteria, including the bacteria found in cottage
cheese and yogurt. This is also the process animals cells
will use if necessary. During this process the pyruvic acid
from glycolysis is converted into lactic acid, which can
cause cramping in muscle cells. The net gain from this
process is 2 ATP.
4A-2 Photosynthesis

 All energy for living organisms comes from the sun.
However, to be usable this solar energy must be
converted into chemical energy. The process of
converting light energy into chemical energy is
called Photosynthesis, carried out by green plants
and algae.
 Photosynthesis is important to life because it
provides glucose but also, it produces oxygen. This
oxygen is needed for many organisms (including us!)
to survive.
4A-2 Photosynthesis

 Equation of Photosynthesis:
12 H2O + 6CO2 + Light Energy
CHLOROPHYLL
C6H12O6 + 6H2O + 6O2
 Chlorophyll: A green pigment which is the primary
catalyst for photosynthesis. It is found in the
membranes of the thylakoids in the chloroplasts..
4A-2 Photosynthesis

 There are a few different types of chlorophyll. Each
designed to absorb and reflect different colors. When
an object reflects a color, it is absorbing all other
colors. For example, a red sweater is reflecting red
and absorbing all the other colors. White light has
wavelengths of all the colors of light.
4A-2 Photosynthesis

 Chlorophyll a: a blue-green pigment that reflects
blues and greens and absorbs violets and reds.
 Chlorophyll b: a yellow green that reflects yellows
and greens while absorbing blues and reds.
 By having different types of chlorophyll the plant is
able to successfully absorb more colors from the
spectrum.
4A-2 Photosynthesis

 The Process of Photosynthesis:
 Photosynthesis takes place
on the thylakoid
membranes in clusters of
chlorophyll molecules.
 There are 2 separate and
distinct phases of
photosynthesis:
The Light Dependent Phase
and the Light Independent
Phase.
4A-2 Photosynthesis

 Light Dependent Phase

1.
2.
3.
4.

An Electron Transport Chain!! Occurs in the grana (stacks of thylakoids) on the
membrane of the thylakoids. There are 4 main protein complexes assisting in this
process: : Photosystem II (PSII), Cytochrome b6f complex, Photosystem I (PSI), and
ATP synthase.
A Photon (light energy) is absorbed by PSII and the energy is used to excite an
electron and split a molecule of water. This releases 2H+ (protons) into the inside of
the thylakoid (lumen) and Oxygen is released as waste.
The energized electron leave PSII and go to Cytochrome b6f complex which pumps
more H+ into the lumen, creating a chemiosmotic gradient (more H+ inside the
thylakoid than outside)
The depleted electron flows to PSI. It is re-energized with another photon (light
energy) and that energy is used to convert NADP+ to NADPH, a energy-carrying
molecule.
ATP Synthase makes ATP from H+ ions rushing back through the membrane into
the stroma.
Net Reaction of Light Dependent Phase:
2H2O + 2NADP++ 3ADP + 3Pi → O2 + 2NADPH + 3ATP
4A-2 Photosynthesis

4A-2 Photosynthesis

Light Independent Phase (or dark phase)
 Also called the Dark Phase, Calvin Cycle, or Carbon Fixation Cycle.
 Occurs in the stroma, the fluid-filled area of a chloroplast outside of the thylakoid membranes:
1.
The enzyme RuBisCo takes a molecule of CO2 and binds it to a 5-carbon sugar
called ribulose biphosphate (RuBP).
2. The energy from ATP and NADPH (from the light dependent reactions) are
used to convert RuBP into a 3-carbon sugar called phosphoglyceraldehyde
(PGAL)
3. Some of the PGAL molecules are then connected to make glucose while others
form more RuBP to continue the cycle.
Net Equation for Light Independent Reaction:
3CO2+6NADPH+5H2O+9ATP → glyceraldehyde-3-phosphate(G3P/PGAL)+2 H++6NADP++9ADP+8 Pi
(Pi = inorganic phosphate)
4A-2 Photosynthesis

4A-2 Photosynthesis

 PUTTING IT ALL TOGETHER!!!
4A-2 Photosynthesis

 Proper Conditions for Photosynthesis:
 For Photosynthesis to be successful it must have the right
conditions:
1.
2.
3.
4.
Right Temperature: Proper temps vary from plant to plant
but for most it is room temperature (21℃). When it is very
hot or freezing most plants shut down photosynthesis as
the function of chlorophyll is temp. dependent.
Adequate Light: Plants must receive the proper amount of
wavelengths and intensity of light. If plants cannot absorb
enough energy, their chlorophyll a molecules will not
become sufficiently energized.
Sufficient CO2: Plant cells must be able to absorb enough
CO2 but this can be a problem as it makes up only .03% of
the atmosphere.
Adequate Water: Plants must have enough water absorbed
from the roots to support photosynthesis.
4A-2 Photosynthesis

Photorespiration Problem
:
 In all plants CO2 is fixed by the enzyme Rubisco. It catalyzes that
reaction where CO2 combines with RuBP leading to two molecules of
3-phosphoglycerate which later become PGAL.
 Unfortunately, instead of CO2, Rubisco can also fix oxygen to RuBP
resulting in one molecule each of 3-phosphoglycerate and 2phosphoglycolate. Phosphoglycolate has no known metabolic purpose
and in higher concentrations it is toxic for the plant!!!
 This Phosphoglycolate has to be processed (gotten rid of) by a
metabolic pathway called photorespiration. Photorespiration is not
only energy demanding, but furthermore leads to a net loss of CO2.
Thus the efficiency of photosynthesis can be decreased by 40% under
unfavorable conditions including high temperatures and dryness.
 The unfavorable reaction of Rubisco with O2 is thought to be a relic of
the evolutionary history of this enzyme, which is thought to have
evolved more than 3 billion years ago when atmospheric CO2
concentrations were high and oxygen concentrations low.
 Plants in harsh environments developed different ways to cope with
this problem.
4A-2 Photosynthesis

 The CAM Pathway
 Plants like Cacti and Pineapples use the CAM
pathway of photosynthesis. They open their stomata
during to night and keep them closed all day. As the
plants take in CO2 at night, they bind the CO2 to
special organic molecules. These molecules release the
CO2 during the day to keep Photosynthesis running.
4A-2 Photosynthesis

 The C4 Pathway.
 Plants like corn and crabgrass use the C4 pathway.
They only partially close their stomata during the
hottest part of the day. They have special enzymes to
fix CO2 in cells closer to the surface of the leaf. This
CO2 is then moved to lower bundle sheath cells within
the leaf, away from O2.