CELL ENERGY:
PHOTOSYNTHESIS
ACADEMIC: CHAPTER 8
HONORS: CHAPTER 7
ENERGY AND LIFE
• Energy- Ability to do work
• No energy = no life
• Laws of thermodynamics
• First law- energy can be converted from one form to
another, but it cannot be created nor destroyed.
• Second law- energy cannot be converted without the
loss of useable energy (thermal energy/heat)
• Example : Food chains
Forms of Energy
Energy comes in many forms:
Light
Heat
Electricity
 . . . Energy can also be stored
in the bonds of chemical
compounds.
AUTOTROPHS AND HETEROTROPHS
• Autotrophs- organisms that make their own food from
energy from the sun or other sources
• Known as producers
• Heterotrophs- organisms that need to ingest or consume
food to obtain energy
• Known as consumers
• ALL organisms have to release the energy in sugars and other
compounds to live.
• Metabolism- all of the chemical reactions in a cell
• Photosynthesis- light energy from the sun is
converted into chemical energy for use by the cell
• Cellular respiration- Organic molecules are broken
down to release energy for use by the cell.
CHEMICAL ENERGY AND ATP
• ATP- Adenosine Triphosphate- Energy for the cell
• Made of adenosine, ribose and three phosphates
• ATP releases energy when the bond between the second
and third phosphate groups is broken, forming a molecule
called adenosine diphosphate (ADP) and a free phosphate
• ADP + P
CHEMICAL ENERGY AND ATP (NOT IN NOTES)
• Storing energy- when bonds are formed, energy is
stored
• ADP- Adenosine diphosphate is similar to ATP, but
with two phosphates instead of three
• Energy is stored when another phosphate is added to
ADP
RELEASING ENERGY
• Energy is released when bonds are broken
• When a phosphate is removed from ATP, energy is
released
• As many as two phosphates can be removed from ATP
• Remove one phosphate = ADP
• Remove two phosphates = AMP (Adenosine Monophosphate)
USING BIOCHEMICAL ENERGY
• 1. Cells use ATP for active transport, to move organelles in
the cell, and to synthesize proteins and nucleic acids
• 2. Cells do not keep large amounts of ATP in the cell. The cell
can regenerate ATP from glucose as needed
• Cellular Respiration
• 3. ATP is great for transferring energy, but not for storing it.
Where do trees get their mass from?
Veritasium Video
Video from: http://www.youtube.com/watch?v=2KZb2_vcNTg
PHOTOSYNTHESIS OVERVIEW
• Photosynthesis- The process by which plants use sunlight to
convert water and carbon dioxide into sugar
• The photosynthesis equation:
• 6 CO2 + 6 H20  C6H12O6 + 6 O2
• Carbon dioxide and water  sugar and oxygen
• What are the products and the reactants?
PHOTOSYNTHESIS REQUIRES LIGHT
• Light is a mixture of wavelengths – ROY G BIV
• Pigments- light absorbing molecules- there are different types of pigments
• Chlorophyll- principal pigment that absorbs light in the blue-violet and red
regions, but not the green
• There are accessory pigments: like carotenoids (think carrot)
• Chlorophyll is found in the chloroplasts of leaves
• This is why chloroplasts look green
Chlorophyll a & b
Blue and red
Chlorophyll is best at absorbing ____________
Green and yellow
Does not absorb ______________________
BLACKEST SUBSTANCE
PHOTOSYNTHESIS REACTIONS
Photosynthesis occurs within the
chloroplasts of specialized cells
within the leaves of plants.
PARTS OF THE
CHLOROPLAST
Stroma –
Liquid inside the chloroplast.
Surrounds the thylakoid
membranes.
Grana – (granum plural)
Stacks of thylakoid membranes
Thylakoid –
Membranes containing
photosystems
Photosystems –
Light capturing systems
DRAW THIS IN YOUR NOTES
TWO PROCESSES OF PHOTOSYNTHESIS
1. Light Dependent Reaction
2. Calvin Cycle (Light Independent Reaction)
THE LIGHT REACTION
• Takes place in the membrane of the thylakoids
STEPS TO THE LIGHT REACTION: THYLAKOID MEMBRANE
• 1. Photons of light strike photosystem II in the thylakoid membrane
• Light dependent
• 2. This causes water to split H2O  H+ AND O
• The hydrogen's are now positive (protons) because the e- (electron)
that they had are now “excited” and move to the Electron Transport
Chain- ETC
• ETC- think of a frying pan to move hot coal……
• As the e- travels through the ETC, the energy is used to pump more
H+ into the thylakoid space
• The oxygen leaves out the stomata (pores in the leaf)
• The H+ remain in the inside of the thylakoid
• 3. The e- travels through the ETC until it reaches photosystem I
where it is re-excited with another photon of light
• 4. The re-excited electron is used to convert NADP+ into NADPH
• NADP+ is an electron carrier that will take the electrons into the
second phase of photosynthesis
• 5. The H+ (protons) that are now in a HIGH concentration in the
thylakoid space are now used to create ATP from ADP.
• As they flow through to the stroma they pass through a
protein that adds a phosphate to ADP (ADP + P = ATP)
• 6. The ATP and the NADPH now head to the Calvin Cycle to act
as the energy to drive the reaction
• Summary: Reactants- H20 and Light
Products – O2 ( as waste), ATP and NADPH
THE CALVIN CYCLE
• Takes place in the stroma (empty space)
STEPS TO THE CALVIN CYCLE: STROMA
• The ATP and NADPH from the light reaction are used to “fuel “ the Calvin Cycle
• 1. (6) CO2 enter through the stomata (pores in the leaf)
• 2. CO2 combines with a (6) 5-carbon sugar Ribulose (1+5=6)
(6) 6-carbon sugars!
• 3.The 6 carbon sugars are then broken down into 12 3-carbon sugars
• Because they were unstable
• 4. The 2 3-carbon sugars leave to make Glucose
• 5. The remaining 3-carbon sugars continue in the cycle for the next round
WHAT IT REALLY LOOKS LIKE
SUMMARY OF THE CALVIN CYCLE
Reactants- ATP, NADPH , and CO2
Products: Glucose
SUMMARY OF PHOTOSYNTHESIS
• Two step process
• 1. Light Dependent Reaction in the Thylakoid
membrane
• 2. Light Independent Reaction (Calvin Cycle) in the
Stroma
• The reactants : CO2 and H2O
• The products: C6H12O6 AND O2
WHAT EFFECTS THE RATE OF PHOTOSYNTHESIS?
•Temperature
•CO2
•Light
•Water