Photosynthesis
Converts kinetic energy in light to potential energy in the covalent bonds of glucose
Photosynthetic organisms
- Plants
- Algae
- Some microorganisms
Photosynthesis builds what from what
Builds carbohydrates from carbon dioxide and water
What type of reaction is P/S
Redox
REdox reaction of P/S
Water = oxidized ( looses an electron when split by chlorophyll to replace its own lost electron)
Carbon dioxide = reduced ( gains electron from Nadph)
Why do plants need glucose
- To generate ATP
- nourish non-photosynthetic parts of the plant.
- Produce cellulose
- other biochemicals
Most plants store Excess glucose as
- Starch
2. Sucrose
Explain the evolution of Photosynthesis
Before photosynthesis evolved, organisms were heterotrophs that relied on organic molecules as a carbon source.
The first autotrophs developed the ability to produce their own organic molecules from atmospheric Co2.
Oxygen produced by these organism changed the Earth’s climate
Visible Light
A small part of the Electromagnetic Spectrum
Photons
Packets of energy that move in waves.
Effect of wave length and kinetic energy
The longer the wavelength the less kinetic energy per photon
Photosynthetic pigments do what
Capture Light Energy
2 types of pigments found in chloroplasts
- Chlorophyll a
2. accessory Pigments
Chlorophyl a
The primary photosynthetic pigment– Reaction Center ( along with proteins)
Accessory pigment
absorb wavelengths of light that chlorophyll a cannot absorb, extending the range of wavelengths useful for P/S
Chloroplasts are
The sites of P/S
Stomata
Pores where plant exchange gases with the environment through ( take in co2 and release O2)
Mesophyll
collective term for the internal cells of the plant.
Stroma
gelatinous matrix in the chloroplast ( outside the thylakoid membrane.
Thylakoid membrane
Site of light reaction. assembled in stacks in the the stroma.
Grana ( granum singl. )
Stacks of thylakoid membrane
Where are the pigments embedded
In the Thylakoid membrane
Photosystem
Consists of:
- Antenna Pigments
- Reaction Center ( chlorophyll a)
2 stages of P/S
1st. Light Reaction ( light dependent)
2nd. Carbon Reaction ( Light independent)
The 2 main products of Light Reaction needed by the 2nd stage
- ATP
2. NADPH
The use of ATP and NADPH for Carbon Reaction
They provide energy and electrons for the glucose producing carbon reaction
Photosystem II produces
ATP
Photosystem ! Produces
NADPH
THE 2 STAGES OF LIght Reaction
Photosystem I
Photosystem II
Steps of Photosystem I
- Antenna pigments capture photons from light energy.
- Sends it to the Reaction center ( chlorophyll a)
- chlorophyll a releases an electron into an Electron Transport Chain that joins Photosystem I with Photosystem II
- Electrons from chlorophyll a are replaced by splitting water. O2 is a waste product.
- Energy released in the ETC drives the active transport of protons ( through a proton pump) from the stroma into the thylakoid space.
- Accumulation of protons from water splitting and active transport creates a transport gradient.
- The protons diffuse in ATP Synthase
- Th movement powers the phosphorylation of ADP to ATP
Chemiosmotic Phosphorylation
The coupling of the
- proton gradient
- ATP formation
Steps of Photosystem I
P/s I receives electrons from the electron transport chain
- The electrons are used to reduce NADP to NADPH ( NADP + H)
- Light is captured again to power this process
Carbon Reaction produces
carbohydrates
How does Carbon reaction produce carbohydrates
The carbon reactions use energy from ATP and electrons from NADPH in carbon fixation reactions that incorporate Co2 into organic molecules.
Carbon fixation
reactions that incorporate Co2 into organic compounds. The first of Carbon Reaction
3 names for the 2nd stage of P/S
- Carbon Reaction
- Calvin cycle
- C3 Pathway
Steps of Carbon Reaction
- Rubisco catalyzes the reaction of Co2 with RuBP to yield 2 molecules of PGA.
- PGA Molecules are converted into PGAL
- PGAL later becomes glucose
PGAL
the immediate Carbohydrate of P/S which later becomes glucose.
C3 Pathway
Another name for the Calvin Cycle.
Refers to plants that can only use this pathway to fix carbon ( to two 3 carbon molecules with one phosphate-PGA)
3 pathways plants use to fix carbon
- C3
- C4
- CAM
Photorespiration
wastes carbon and energy when rubisco reacts with O2 instead of CO2
How do C4 pathway plants reduce Photorespiration
By separating the light and carbon reactions into different cells
Light reaction in the Mesophyll cells and Carbon Reactions int the the bundle sheath cell
How do CAM pathway plants reduce Photorespiration
Desert plants such as Cacti open their stomata and take in Co2 at night, storing fix carbon in vacuoles. during the day Light reactions occur
Where does the energy come from to peer P/S
The Sun
P/S is an example of an ——– chemical reaction because ———
Endergonic Reaction because light energy is used to build chemical bonds.
