Energy and Life
Living things depend on Energy
We need energy to play soccer, go fishing and even sleep. On a cellular level, we also need energy for active transport, growth and repair, and reproduction of cells.

• Autotrophs: organisms that are able to produce their own food
• What are some examples?
• Heterotrophs: organisms that are Not able to produce their own food
• Most autotrophs use PHOTOSYSTHESIS to produce their own food
WHAT IS PHOTOSYNTHESIS

inputs
PHOTOSYSTHESIS- THE BIG PICTURE outputs inpu

• Energy comes in many forms
• Biochemical energy is stored in
• CARBS AND LIPIDS
Cells metabolize these compounds in a form it can use called ATP
ATP is the energy currency of the cell the only energy the cell recognizes
1 MOLECULE OF C
6
H
12
O
6
= 90x the chemical energy of ATP

Adenosine---p-----p +energy from glucose+ p
ADP Adenosine diphosphate
ADP adenosine + ribose sugar+2 phosphate groups
Adenosine----p----p------p
ATP
Lots of energy (originally from glucose is stored in this bond
Adenosine triphosphate
ATP adenosine+ ribose sugar +3 phosphate groups
Energy stored in ATP is released when ATP is converted to ADP and a phosphate group. When the bond is broken energy is released ATP is like a fully charged battery------ ADP like a battery not fully charged

In addition to O
2 and H
2
O photosynthesis also requires a pigment
What is the PIGMENT found in chloroplasts that is responsible for trapping light energy? ANSWER chlorophyll
There are two types of chlorophyll a (light green) and b (dark green)
Plants also contain other light-absorbing pigments, such as xanthophylls, anthocyanins, and carotenoids (these are referred to as accessory pigments) we know that leaves contain these pigments because of the color of the leaves in the fall
These pigments do not absorb light well in the green region of the light spectrum which is why most plants are green

Co
2
+ water
sun chloroplast energy
Sugar and oxygen
• When chlorophyll absorbs light, the following occurs
• Energy(light)is directly transferred to the electrons in the chlorophyll molecule
• When transferred the energy level in the electron is raised (electrons get
excited)
• Excited electrons have HIGH ENERGY and must have a special chemical carrier called “NADPH”
Electron chauffeur

• Draw a chloroplast • Thylakoid
: bag-like photosynthetic membranes
• Grana : stacked thylakoids
(grannum) single stack
• Stroma : fluid inside the chloroplast but OUTSIDE the thylakoid membrane

PHOTOSYNTHESIS AS A BIOCHEMICAL PATHWAY

PHOTOSYNTHESIS IS A BIOCHEMICAL PATHWAY
Photosynthesis is broken down into 2 stages
1. Light dependent reactions
2 Light independent reactions (Calvin Cycle)
Light dependent reactions
Take place in the thylakoid membranes
Occurs only in light light independent reactions
Take place in the stroma
Occurs only in the absence of light

PHOTOSYNTHESIS AS A BIOCHEMICAL PATHWAY

• H2O inputs
• Light energy
LIGHT DEPENDENT REACTIONS
LIGHT DEPENDENT REACTIONS
TAKE PLACE WHERE? Chloroplast in the thykaloid
REQUIRE WHAT? Sunlight, and water H2O outputs
• ATP
• - NADPH
• O2

• Photosystem II (PH II) Inside the thykaloid
• Discovered AFTER PH I, but in the photosynthetic process
• Pigments absorb light
• Energy from the light “excite” electrons, increasing their energy
• Excited electrons passed through the electron transport chain
• The electron is passed from one molecule to another as it decreases an energy level or step, the energy given off from the electron decreasing an energy level is used to form ATP
• This is the ETC

• Photosystem II (PH II)
• One major problem with PH II is that the electrons are lost
– How does PH II replenish the electrons?
– By splitting the H2O molecule
– Into H+ H+ ions
– These ions will then be pumped back into the thylakoid reenergized by light and be carried by NADPH back to the electron transfer chain
A by-product of this reaction is O
2 which is then released into the atmosphere by the plants for organisms to breathe

LIGHT DEPENDENT REACTIONS– PH I
• Photosystem l (PH I)
• High energy electrons move through the PH II to photosystem I
• Energy from these electrons transports H+ ions from the stroma to the inner thylakoid
Pigments in PH I use energy from light to reenergize the electrons. These reenergized electrons are picked up by NADP+ to form NADPH (the high energy chauffeur) REMEMBER?
So what is NADPH’s role in photosynthesis?
IT IS THE HIGH ENERGY ELECTRON CARRIER

LIGHT DEPENDENT REACTIONS– PH I
• Hydrogen ion movement
• As a result of the H+ ions released during the splitting of H2O and electron transport, the inside of the thylakoid membrane becomes (+) changed while the outside is (-) charged
• This difference in charges provides the energy to make ATP
• ATP synthase:

• Light independent reactions
• Take place where?
--
• Require what?
• Also called the Calvin Cycle of “Dark Reactions” inputs outputs
Products of light dependent rxn’s
--

• Calvin cycle
• 6 CO
2 molecules enter the cycle from the atmosphere