BIO 221: Photosynthesis

Photosynthesis equation

6CO2 + 6H2O + light energy --> C6H12O6 + 6O2

Energy transformation

the process of changing one form of energy to another

Why is photosynthesis energy transformation?

takes radiation energy and turns it into chemical energy

What groups can conduct photosynthesis?

plants, algae, and some bacteria (purple bacteria, cyanobacteria)

Photoautotrophs

use light as energy source and CO2 as carbon source

Heterotrophs

use organic organisms as energy and carbon sources

Diffrence between oxygenic and anoxygenic photosynthesis

oxygenic produces O2 while anoxygenic does not

Why are heterotrophs dependent on phototrophs?

phototrophs create organic molecules which heterotrophs need

Why do plants have green pigments?

pigments collect wavelengths of light efficiently for photosynthesis

Mesophyll cell

a plant cell type found in leaves that contain large amounts of chloroplasts where photosynthesis takes place

Chloroplast structure

two membrane cell in packed together in mesophyll's with thylakoids granums surrounded by stroma inside each

Where do light reactions occur?

thylakoids

Where do dark reactions (Calvin cycle) occur?

stroma

How does the light rxn support the dark rxn?

products from the light rxn fuel the dark rxn

What occurs during the light rxn?

radiant energy is captured by leaf pigments in thylakoids creating PMF feeding into the ETC creating ATP

How is radiant energy captured?

thylakoid pigments

Why is the ETC a part of photosynthesis?

to make ATP through PMF in the light rxn

Why is PMF a part of photosynthesis?

to promote ATP synthesis

What occurs during the dark rxn (Calvin cycle)?

chemical energy from the light rxn is used to power glucose synthesis from CO2

What is carbon fixation?

making organic material from CO2

Electromagnetic spectrum

the complete range of electromagnetic waves placed in order of increasing frequency

How are energy and wavelengths related?

the shorter the wavelength, the higher the energy within the photons

What is the visible light spectrum?

the portion of the electromagnetic spectrum that is visible to the human eye (380-740 nm)

What are the highest and lowest energy colors?

purple has the highest and red has the lowest

What are pigments?

molecules that absorb wavelengths of light and reflect others

What happens when pigments absorb photons?

electrons become excited and you can see the absorbed color

What occurs in a pigment in the ground and excited state?

e- move from ground to excited state when photon is absorbed, when returning to ground state, energy is released and can be used for other cellular processes

What happens to excited electrons in photosynthsis?

they move through the ETC through electron carriers losing energy as they are trasnferred

What group do photosynthetic pigments belong to?

porphyrins

Two major groups of photosynthetic pigments

chlorophylls and carotenoids (lipids)

What colors to photosynthetic pigments absorb and reflect?

absorb blue/purple and reflect green/yellow

Light reaction in plants and algae phases

Light -> PS2 -> PS1 -> NADP + reductase -> ATP synthase

What happens in photosystem II (PS2)?

light is absorbed exciting e- releasing them into the ETC, H2O is broken apart providing PMF for ATP

Why must PS2 split water?

replace e- in PS2, provides the system with more oxygen and hydrogen which promotes PMF for ATP

What happens when electrons are passed from PS2 to PS1?

they release energy into the system for PMF

Noncyclic flow from PS2 to PS1

loss of energy occurs which requires more light energy which adds energy back and the e- leave the cell going to a new cell

What is the energy level of e- entering PS1?

moderate energy level due to energy lose between systems

What happens when PS1 e- absorb light?

they are put into the ETC being donated to NADP+ to from NADPH for ATP

What is the function of NADP+ reductase?

catalyzes e- from PS1 into NADPH (electron carriers)

What is the function of ATP synthase?

takes H+ from all steps (PS2, PS1, NADP+ reductase)

Photophosphorylation

the attachment of a phosphate group to ADP to form ATP driven by light absorbed during photosynthesis

What factors contribute to formation of PMF?

energy released from e- in the light rxn cause PMF and photophosphorylation

Cyclic e- flow through PS1

uses e- to create proton electrochemical gradient's through the PS1 only

Results of cyclic e- flow

equal amounts of ATP, NADPH, and O2

Why is cyclic flow needed?

allows for plants to generate additional ATp without producing NADPH

What causes noncyclic flow?

low levels of NADPH

What causes cyclic flow?

low levels of ATP

Phases of the Calvin cycle

carbon fixation, reduction, regeneration of CO2 acceptors

Is light needed in the Calvin cycle?

no since the Calvin cycle only needs CO2 to start

What enzyme participates in carbon fixation in the calvin cycle?

rubisco

What does rubisco do in carbon fuxation?

6 CO2 are fixed to organic molecules becoming 12 3-phosphoglycerate

How much ATP and NADPH is used to fix six CO2?

18 ATP and 12 NADPH

Why does photosynthetic organisms make carbs?

to store energy from sunlight to be used later

Is glucose really the product of the Calvin cycle?

No it makes Glyceraldehyde 3-phosphate which is carb building block to make other sugars like sucrose

What organisms perform anoxygenic photosynthesis?

photosynthetic bacteria

C3 plant

CO2 is fixed to a 3-carbon compound where they are more susceptible to photorespiration, and enters into the Calvin cycle

C4 plant

CO2 is fixed into a 4-carbon compound in mesophyll cells, the 4-carbon is transported to bundle sheath cells where CO2 is released and enters Calvin cycle

How is the C4 plant structured?

the C4 cycle occurs in one pocket while the Calvin cycle occurs in a separate pocket called the Bundle Sheath cell

How are C4 and C3 plants different?

C4 uses 4 carbon molecules which releases into a seperate pocket for the Calvin cycle, C3 has it all in one place and uses 6 carbon molecules

CAM plants

At night, the stomata open to fix CO2 and store ATP/NADPH in vacuoles. At daytime, stomata close to reserve water, CO2 is released to use in Calvin cycle

How does photosynthesis occur in CAM plants?

at night pores on the plant open collecting CO2 stockpiling ATP and NADPH, at day the pores close and the Calvin cycle takes place