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Chapter 8
Photosynthesis
Autotrophs vs. Heterotrophs
Autotrophs are organisms that can make their
own food
◦ Use light energy from the sun to produce
◦ Plants are an example
 Heterotrophs cannot use the sun’s energy
directly
◦ Obtain energy from the foods they eat
◦ Animals and mushrooms are examples

Autotrophs vs. Heterotrophs
Energy

ATP – Adenosine triphosphate – is the
molecule cells use to store and release energy.
Be able to draw it. Energy is released when the
bond is broken between the last two
phosphates.
Adenosine
ADP – Adenosine diphosphate
 AMP – Adenosine monophosphate

Energy
Energy

Adding a phosphate group to ADP allows the
organism to store energy
◦ ATP is like a fully charged battery
◦ ADP is like a partially charged battery
Energy
Energy is used for:
1. Active transport: Na+ is pumped out and
K+ into the cell
2. Motor proteins that move organelles
3. Synthesis of proteins, nucleic acids, lipids…
4. Produce light (firefly)
5. Cell reproduction and more
Energy
Glucose is better for long term storage than
ATP
 A single molecule of glucose stores 90 times
the chemical energy of a molecule of ATP
 Most cells only have a small amount of ATP, only
enough to last for a few seconds of activity

What is Photosynthesis?

Photosynthesis is the process in which light,
water, and carbon dioxide (CO2) is made into
sugar and oxygen (O2)

Carbon dioxide + water

6CO2 + 6H2O
sugar + oxygen
C6H12O6 + 6O2
Photosynthesis

Chlorophyll a and
Chlorophyll b are
pigments in the
chloroplast that
absorb light of the
visible spectrum,
except for green light.
They reflect green,
thus the leaf looks
green.
Photosynthesis

Photosynthesis takes place in the chloroplasts
◦ Chloroplasts have stacks of thylakoids (saclike
photosynthetic membranes)
◦ Proteins in thylakoids organize chlorophyll
and other pigments into photosystems, which
are the light-collecting units
Light-dependent reactions
Take place in the thylakoid membranes
 Convert light energy to ATP and NADPH
 Split H2O and release O2
 Electron transport chain connects the two
photosystems to make an H+ gradient across
the thylakoid membrane (ATP synthase uses this
force to make ATP). Uses a proton (H+) pump.

Light-dependent reactions
Calvin cycle reactions
Take place in the stroma
 Use ATP and NADPH to convert CO2 to sugar
 Return ADP, inorganic phosphate, and NADP+
to the light reactions

Calvin cycle reactions
Photosynthesis
Factors affecting photosynthesis
Water (required raw material)
◦ Plants in dry climates have a waxy coating to
prevent water loss
 CO2 concentration (required raw material)
 Temperature: enzymes function best between 0o
C and 35o C
 Light intensity
◦ Plants can reach a maximum rate of
photosynthesis with light intensity (varies
between plant type)

Chapter 9
Cellular Respiration
Chemical Energy

How much energy is in food?
◦ One molecule of glucose contains 3811
calories of heat energy
◦ A calorie is the amount of energy needed to
raise the temperature of one gram of water
one degree Celsius
◦ The Calorie (food labels) is actually 1000
calories
Chemical Energy

The beginning of turning food into energy is
glycolysis (produces small amount of energy)

If oxygen is present 2 other pathways occur to
produce more energy

If oxygen is not present, 1 different pathway
occurs
Energy Pathways
Aerobic – requires oxygen
◦ Also called cellular respiration
 Anaerobic – does not need oxygen
◦ Fermentation – name for anaerobic
pathway following glycolysis (if oxygen is not
present). (The term fermentation includes
glycolysis).

What is Cellular Respiration?
Cellular Respiration (video)
 Cellular respiration - the process that
releases energy by breaking down glucose and
other food molecules in the presence of
oxygen.


Glucose + oxygen  carbon dioxide +
water + energy

C6H12O6 + 6O2  6CO2 + 6H2O + ATP
What is Cellular Respiration?
Oxygen
Carbon
dioxide
Carbon
dioxide
Water
Cellular Respiration
Steps of cellular respiration:
1. Glycolysis – one glucose is broken in half to
make 2 pyruvic acids. Anaerobic. Occurs in
cytoplasm.
2. Krebs cycle – pyruvic acid is broken down
into CO2 and energy. Aerobic. Occurs in
mitochondrion. Also called citric acid cycle.
3. Electron transport chain – using a series
of proteins, the electrons from the Krebs
Cycle and glycolysis to convert ADP to ATP.

Glycolysis

NADH passes energy from glucose to the
electron transport chain
Energy Pathways
Aerobic – requires oxygen
◦ Also called cellular respiration
 Anaerobic – does not need oxygen
◦ Fermentation – name for anaerobic
pathway following glycolysis (if oxygen is not
present). (The term fermentation includes
glycolysis).

Fermentation
Two types of fermentation:
 Alcoholic fermentation: yeasts and some
bacteria
Pyruvic acid + NADH  alcohol + CO2 + NAD+


Lactic acid fermentation: most organisms
including us and many bacteria

Pyruvic acid + NADH  lactic acid + NAD+

Both processes regenerate NAD+
Lactic Acid Fermentation
Kreb’s Cycle and ETC
During the Kreb’s cycle pyruvic acid is broken
down into carbon dioxide
◦ Occurs in the mitochondrion
◦ NADH and ATP is produced
 In the electron transport chain (ETC) high
energy electrons (NADH, FADH2) is converted
into ATP
◦ Hydrogen ions are pumped across membrane
◦ ATP synthase – enzyme (protein) that
makes ATP using H+ gradient

Cellular Respiration

1 glucose results in the production of 36 ATP
net
◦ 34 more ATP than anaerobic processes
◦ 38% of the total energy in glucose, the other
62% is “lost” through heat
◦ More efficient than an automobile (25%-30%)
70-75% is lost to heat
Energy Pathway
Glycolysis
No Oxygen
Anaerobic respiration
Fermentation
2 ATP, lactate or
alcohol, and CO2
Oxygen
Aerobic respiration
Cellular respiration
36 ATP
Cellular Respiration
Cellular Respiration
Energy Pathway
Comparing photosynthesis, cellular respiration, & fermentation:
Photosynthesis
Cellular
Fermentation
Respiration
Function
Energy storage
Energy release
Energy release
Location
Chloroplasts
Mitochondria
Cytoplasm
Reactants CO2 and H2O
Glucose and O2
Glucose & NAD
Products
CO2 and H2O &
ATP
Alcohol & CO2 &
ATP or
Lactic acid & ATP
Glucose and O2