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ENERGY
Life depends on energy, which is stored in the chemical bonds
of energy storing compounds. One of the most important
energy compounds is ATP (adenosine triphosphate).
I.
ATP
A. made of a sugar, adenine, and 3 phosphates
1. ATP releases chemical energy whenever a bond
holding a phosphate is broken
A
A
S
P
P
P
Energy released when
bond is broken
Adenine
2. The result is ADP – adenosine diphosphate
A
Adenine
A
S
P
P
B. ATP is used for doing work in the cell
1. provides energy for the mechanical functions of cells
2. provides energy for active transport of molecules
and ions across the cell membrane
3. used in making and breaking down large molecules
C. Because cells are constantly at work, they need an
endless supply of ATP
1. ATP comes from attaching a phosphate to an ADP
2. The cycle of making and breaking down ATP
molecules occurs constantly in cells
 10 million new ATP molecules are made
EVERY SECOND in the cell
II. Sources of Energy
Organisms are classified into 2 groups according to how
they get food: autotrophs and heterotrophs
A. Autotrophs: can make their own food
Ex. green plants use CO2 , water, and sunlight to make
food
1. the foods made by autotrophs are mainly
carbohydrates such as glucose
2. autotrophs are called producers because they
produce their own food
3. producers are vital to the world: they are a source
of food for all other organisms, directly or
indirectly
B. Heterotrophs: organisms that can’t make their own
food
1. must eat, or consume, other organisms for food
2. heterotrophs are called consumers
I.
Photosynthesis
Photosynthesis is the process by which autotrophs convert
sunlight into a usable form of energy
A. autotrophs that perform photosynthesis contain
pigments
1. pigment: molecule that absorbs certain wavelengths
of light and reflects others
 whatever wavelength is reflected is the
color you see
2. chlorophyll: pigment that is used in photosynthesis
 absorbs blue, violet, and red light
 reflects green light, gives the green color of
many plants
B. In many autotrophs, the pigments (including
chlorophyll) are in specialized organelles
 chlorophyll is located in the chloroplasts
II. Photosynthesis in a Nutshell
A. 6 CO2 + 6 H2O
carbon
dioxide
water
Light
energy
C6H12O6 + 6 O2
glucose
oxygen
1. The energy stored in glucose is used later to
produce ATP.
B. Photosynthesis does NOT happen all at once. There
are 2 distinct stages.
1. The first stage is called the light dependent
reactions.
a. begins with light hitting the chloroplast
b. water is split into hydrogen ions, oxygen,
and excited electrons
 oxygen diffuses out of the chloroplast
 NADPH and ATP are produced
(NADPH is another energy storing molecule)
LIGHT REACTIONS OCCUR IN THE THYLAKOID.
2. The second stage of photosynthesis is called the
Calvin Cycle. (also called the “dark reactions”)
a. the ATP and NADPH from the light dependent
reactions are used in the Calvin cycle
b. the Calvin cycle uses CO2 to produce sugar
(glucose is a type of sugar)
III. Details: The Light Reactions
A. occur in different areas of the thylakoid called
Photosystem I and Photosystem II, which are light
collecting units of the chloroplast
1. Sunlight comes into Photosystem II and splits water
into H+ ions (hydrogen ions), oxygen (O2), and
energized electrons (e-- ).
2. The excited e— go through the electron transport
chain to Photosystem I.
 carrier molecules (of the e— transport chain)
use the electrons’ energy to actively
transport H+ ions from the stroma to the
thylakoid
IV. Calvin Cycle – Details (a.k.a. Dark Reactions)
A. The Calvin Cycle :
1. Requires the products of the light dependent
reactions
2. Requires the input of CO2
3. Takes place in the stroma of the chloroplast
B. Process:
1. CO2 is used to build molecules of glucose
2. ATP and NADPH are used for energy and
hydrogen (from light dependent reactions)
3. 1 molecule of glucose is made for every 6
molecules of CO2 in the cycle
V. Now what?
A. Photosynthesis gets glucose from the energy of the sun
1. autotrophs and heterotrophs convert glucose to
ATP and use the ATP for energy
2. any glucose not used by the autotrophs right away is
stored as starch
3. when autotrophs are consumed by heterotrophs, the
starch is broken down into glucose
4. glucose is broken down to release energy in the
process of CELLULAR RESPIRATION
Cellular Respiration
*** All organisms rely on cellular respiration for the energy
they need to carry out life functions.
I.
Cellular Respiration
A. process of getting ATP molecules from glucose
B. usually occurs in the mitochondria
II. 2 types of cellular respiration: Aerobic and Anaerobic
A. Aerobic respiration  requires oxygen
1. produces 36 ATP molecules from each glucose
molecule
2. has 3 distinct phases:
a. glycolysis
glucose
2 pyruvate + 2 ATP
b. Krebs Cycle
pyruvate Acetyl-CoA
Krebs Cycle
CO2 + NADH + FADH2 + ATP
 NADH and FADH2 are energy storing molecules.
Since you get 2 pyruvate from each glucose, the
Krebs cycle gets 2 more ATP.
*** So far, glycolysis and the Krebs cycle have gotten 4 ATP.
3. Electron Transport: transfers energy in the
electrons of NADH and FADH2 to ATP
a. this is the part of aerobic cellular respiration
that requires oxygen
b. electron transport generates 32 ATP molecules
**Aerobic respiration generates a total of 36 ATP molecules.
B. The other type of cellular respiration is anaerobic
respiration (also known as fermentation).
1. releases energy from food molecules in the absence
of oxygen
2. 2 types of anaerobic respiration:
a. alcoholic fermentation
b. lactic acid fermentation
3. In both types of anaerobic fermentation, only 2
ATP molecules are made from each molecule of
glucose.
C. Alcoholic Fermentation – Steps
1. glycolysis (just as in aerobic respiration)
glucose
2 pyruvate + 2 ATP
2. pyruvate
ethanol + CO2
This process is used to raise bread, make wine, and brew
beer by using yeasts which perform alcoholic
fermentation.
D. Lactic Acid Fermentation
1. Animal cells can’t perform alcoholic fermentation,
but some animal cells can convert pyruvate to lactic
acid.
Example: muscle cells switch to anaerobic
respiration when there isn’t enough O2 from
breathing, such as during strenuous exercise.
Muscle fatigue and soreness is from a build up of
lactic acid.
2. Steps of Lactic Acid Fermentation
a. glycolysis: just like in aerobic respiration and
alcoholic fermentation
b. pyruvate + NADH
lactic acid + NAD+