I. PhotosynthesisI. Photosynthesis

The process of converting light energy into chemical bond energy in the form of glucose

Supplies energy and oxygen to virtually all living things

II. ChloroplastsII. Chloroplasts

The site of photosynthesis Chloroplasts contain chlorophyll absorb

light use energy to drive photosynthesis Three functional parts inside the

chloroplast

1. Intermembrane Space1. Intermembrane Space

Chloroplasts is a double membrane Intermembrane space separates the two

membranes

2. Thylakoid2. Thylakoid Flattened membrane sacs inside

chloroplast Chlorophyll is found here Light reactions take place here Grana stacks of thylakoids

3. Stroma3. Stroma

Fluid filled space that surrounds grana Reactions that use chemical energy to

convert carbon dioxide to sugar occur here These are called

dark-reactions

III. Light ReactionsIII. Light Reactions Occur in the thylakoid membranes of

chloroplasts Light energy excites a pair of electrons Electrons passed to different “carriers” – they

lose a bit of energy at each step Generate ATP (photophosphorylation) and

NADPH as they give off energy Give off oxygen as a by-product from splitting of

water

IV. Noncyclic Electron FlowIV. Noncyclic Electron Flow

Involve PS I and PS II Occurs in thylakoids Passes electrons continuously from water to

NADP+ Produces ATP Produces NADPH Produces oxygen

V. Cyclic Electron FlowV. Cyclic Electron Flow

Involves only PS I Makes ATP Does not produce NADPH or oxygen

Bottom Line:Bottom Line:

Light reactions take energy from light and hold it for later use Held in ATP and NADPH

VI. Calvin Cycle – the Dark ReactionsVI. Calvin Cycle – the Dark Reactions Carbon-fixation reactions that assimilate 6

Carbons into a carbohydrate Occurs in the stroma ATP and NADPH produced by light reactions are

used in the Calvin cycle to turn carbon dioxide to sugar

NADPH provides the reducing power ATP provides the chemical energy

More Calvin Cycle…More Calvin Cycle…

End product of the Calvin Cycle is a glucose molecule

Uses 18 ATP molecules and 12 NADPH molecules

3 CO2 + 6 NADPH + 5 H2O + 9 ATP → C3H5O3-PO32- + 2 H+ + 6 NADP+ + 9 ADP + 8 Pi

Bottom Line:Bottom Line:

Water donates electrons Light provides energy CO2 provides the

carbons for sugar

Photosynthesis As a ProcessPhotosynthesis As a Process

Water is split, oxygen is released, sugar gets made from CO2

…mmmmm…. sugar

Energy for PhotosynthesisEnergy for Photosynthesis OIL RIG

Oxidation is loss of electrons, reduction is gain of electrons

Photosynthesis is an endergonic process: energy is required to reduce carbon dioxide to sugar

Light provides energy of electrons as they are moved from water to sugar

Energy for Photosynthesis (cont’d)Energy for Photosynthesis (cont’d)

Water is split, electrons are transferred from the water to carbon dioxide (via NADPH), reducing it to sugar

There are two separate parts to photosynthesis Light reactions (the “Photo”) Calvin Cycle (dark reactions) – (the “synthesis”)

IV. Respiration – Returning the EnergyIV. Respiration – Returning the Energy We digest sugar, and energy is released in the

form of ATP. Sugar gets oxidized (loses electrons) and the

energy released makes ATP This happens in all cells of plants, animals, and

bacteria The byproduct is CO2, which is then used to

make new sugar through photosynthesis

PHEW! Take a breather!PHEW! Take a breather!

On with Photosynthesis!!!

III. Photosynthesis As a ProcessIII. Photosynthesis As a Process

Light energy absorbed; CO2 absorbed; O2 released from water; sugar produced

Plants split the water to release Hydrogen to make NADPH

Plants absorb light to energize electrons in the thylakoid membrane

Sugars provide a more useful storage form for the energy in the electrons released from water

IX. The Good Stuff…IX. The Good Stuff… Light reactions take

energy in as light and store it as ATP and NADPH

Dark reactions take the energy stored in ATP and NADPH to make sugar molecules

*****We take glucose in and convert the energy in glucose back to ATP so our bodies can use it*****

X. Three Types of PlantsX. Three Types of Plants C3 plants: These include rice, wheat, beans Most plants are C3 which means 3-

phosphoglycerate is produced

C4 plants: crab grass and sugarcane, plants in hot regions They make a 4 carbon compound prior to the Calvin

Cycle An adaptation for plants that grow in hot regions, when

stomata are closed

X. Three Types of Plants (cont’d)X. Three Types of Plants (cont’d) CAM plants: (crassulacean acid metabolism) Occurs in many desert dwelling plants such as

cacti Open stomata at night instead of during the day.

Carbon gets fixed at night. The only difference in these plants is the time of

carbon fixation; they still all use the Calvin Cycle to produce sugar from CO2