Photosynthesis

Bio 100

Tri-County Tec. College

Pendleton, S. C.

What are Pathways?

• Pathways lead from one place to another• Biochemical pathways

– contains reactions that are linked to each other– the products of one reaction serve as the

reactants of the next reaction

• A B C D E• Usually there is an enzyme that catalyzes

each reaction.

The Major Pathways

• Photosynthesis and respiration• Photosynthesis

– occurs in green plants– carbon dioxide and water is converted into

glucose– energy comes from the sun– chlorophyll is necessary– associated with chloroplasts in eukaryotes

The Major Pathways

• Respiration– carried out by all living organisms– glucose is converted to carbon dioxide and the

energy in it is released as ATP– one form requires oxygen (aerobic) – some microorganisms can do respiration w/o

oxygen (anaerobic)– associated with mitochondria in eukaryotes

Autotrophs vs. Heterotrophs

• Autotrophs– use sunlight and inorganic raw materials such

as carbon dioxide to make glucose – green plants

• Heterotrophs– use glucose from autotrophs to obtain energy– humans and other animals

Photosynthesis

• Generalized Reaction– sunlight + 6CO2 + 6H2O C6H12O6 + 6O2

– Green plants in the presence of sunlight take six carbon dioxide molecules and six water molecules and make glucose and six oxygen molecules.

– Involves a light energy conversion stage and a carbon dioxide conversion stage

Let there be light…

• Light is form of electromagnetic energy traveling in waves that are composed of photons (discrete bundles of energy)

• What one sees depends on absorption and/or reflection

• ROY G BIV

• Time to synthesize some information based on what is seen

Light Energy Conversion-1

• 1. Oxidation-Reduction reactions (redox)• 2. Electrons are knocked loose from

chlorophyll by sunlight.• 3. Some of those electrons are jacked up to

a higher energy level and when they fall back the energy is used to make ATP.

• 4. Cytochromes mediate the process.• 5. The electrons return to chlorophyll.

Light Energy Conversion-2

• 5. Some of the excited electrons are captured by NADP which becomes negative and receives a H+ from the breakdown of water.

• 6. The hydroxyl ions from the breakdown of water interact to form water, oxygen and free electrons.

Light Energy Conversion-3

• The oxygen becomes a part of the atmosphere.

• The water becomes a part of the water already in the plant cell.

• The free electrons are accepted by chlorophyll that lost them to begin with.

Light Energy Conversion-4

• The products of the light energy conversion stage--– 1. usable energy as ATP– 2. source of usable hydrogen - NADPH– 3. water– 4. oxygen

• Useful for the carbon dioxide conversion stage

CO2 conversion

• 1. CO2 (1C) is attached to ribulose (5C) using energy from the ATP generated by the LEC reactions resulting in a 6C compound.

• 2. The 6C compound immediately breaks down into two 3C compounds (PGAL).

• 3. Most of the PGAL is rearranged to form ribulose and the other intermediates in the process of photosynthesis.

CO2 Conversion

• 4. Two out of twelve PGAL’s (3C) are used for the production of Glucose (6C) and other substances.

• Light energy conversion reactions take place in the grana of the chloroplasts.

• Carbon dioxide conversion stage takes place in the stroma of the chloroplasts.

What comes from what?

– sunlight + 6CO2 + 6H2O C6H12O6 + 6O2

• Sunlight comes from the sun

• Carbon dioxide --- from animals and plants

• Water -- from soil

• Glucose -- primarily the CO2 conversion reactions

• Oxygen -- light energy conversion react

• C3, C4, and CAM plants

• Cyanobacteria and their contribution