PHOTOSYNTHESISEnergy 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 & HETEROTROPHS• 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

PHOTOSYSTHESIS- THE BIG PICTURE

inpu

inputs outputs

ENERGY IN THE CELL

• Energy comes in many forms• Biochemical energy is stored in

• CARBS AND LIPIDS

1 MOLECULE OF C6H12O6= 90x the chemical energy of ATP

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

ATP AND ADPAdenosine---p-----p +energy from glucose+ pADP

Adenosine----p----p------p

Adenosine triphosphateLots of energy (originally from glucose is stored in this bond

Adenosine diphosphate

ATP

ADP adenosine + ribose sugar+2 phosphate groups

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

SITE OF PHOTOSYNTHESIS

In addition to O2 and H2O 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 fallThese pigments do not absorb light well in the green region of the light spectrum which is why most plants are green

SITE OF PHOTOSYNTHESIS• 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”

sun

energy

chloroplast

Co2 + water

Sugar and oxygen

Electron chauffeur

STRUCTURE OF A CHLOROPLAST

• 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 stages1. Light dependent reactions

2 Light independent reactions (Calvin Cycle)

Light dependent light independent reactions reactions

Take place in the thylakoid membranes

Take place in the stroma

Occurs only in light Occurs only in the absence of light

PHOTOSYNTHESIS AS A BIOCHEMICAL PATHWAY

LIGHT DEPENDENT REACTIONSLIGHT DEPENDENT REACTIONS

TAKE PLACE WHERE? Chloroplast in the thykaloid

REQUIRE WHAT? Sunlight, and water H2O

inputs outputs

•H2O

•Light energy•ATP•- NADPH•O2

LIGHT DEPENDENT REACTIONS PH II

• 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

LIGHT DEPENDENT REACTIONS- PH II

• 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 re-

energized by light and be carried by NADPH back to the electron transfer chain

A by-product of this reaction is O2 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 re-energized 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

• Light independent reactions• Take place where?

• Require what?• Also called the Calvin Cycle of “Dark Reactions”

inputs outputs

-- --Products of light dependent rxn’s

LIGHT INDEPENDENT REACTIONS

• Calvin cycle• 6 CO2 molecules enter the cycle from the atmosphere