Biology Chapter 10: Photosynthesis

What is photosynthesis?

the conversion of light energy to chemical energy

What is an autotroph?

an organism capable of producing their own food from simple substances in their surroundings

What is a heterotroph?

an organism incapable of producing their own food so they must rely on other organisms for fuel

Where was photosynthesis originated from?

prokaryotic organisms

What is cyanobacteria?

an early prokaryote that oxygenated the atmosphere of early Earth through photosynthesis

What is the foundation of Eukaryotic photosynthesis?

prokaryotic photosynthetic pathways

What is the primary location for photosynthesis in plants?

leaves

Which organelle does photosynthesis take place?

chloroplast

Chloroplasts are found in mesophyll; what is mesophyll?

the cells that make up the interior tissues of the leaf

What is the stomata?

pores in the leaves that allow CO2 in and O2 out

Do chloroplasts have double membranes or single membranes?

double membranes

What is the stroma?

aqueous internal fluid

What are thylakoids?

“plates” that form stacks called grana

What is chlorophyll?

green pigment in thylakoid membranes

What is the simplified formula for photosynthesis?

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

What are the reactants of photosynthesis?

6CO2 and 12H2O

What are the products of photosynthesis?

C6H12O6 and 6H2O and 6O2

Which molecule experiences a reduction in photosynthesis?

6CO2 gets reduced to C6H12O6

Which molecule experiences oxidation in photosynthesis?

6H2O gets oxidized into 6O2

What is a redox reaction?

a reaction where one or more electron partially or completely transfers from one reactant to another

Photosynthesis splits H2O into what?

H and O

Where does the electron transferred with the H+(from split H2O) go?

It is transferred to CO2 and reduced to sugar

What is OIL?

oxidation is loss (of electrons)

What is RIG?

reduction is gain (of electrons)

What are the two stages of photosynthesis?

light reactions and calvin cycle

What is light?

electromagnetic energy that travels in waves and is made up of particles called photons

What is a wavelength?

the distance from the crest of one wave to the crest of the next

What is the electromagnetic spectrum?

the entire range of wavelengths; 380nm to 750nm is visible light

The shorter the wavelengths the higher the energy therefore the longer the wavelengths the __________

lower the energy

What are the different ways light interacts with matter?

reflected, transmitted, absorbed

The color we see is from the _____________ wavelengths

reflected

What is chlorophyll a?

primary blue/green pigment involved in light reactions

What is chlorophyll b?

accessory yellow/green pigment

What are carotenoids?

yellow/orange pigment that broadens the spectrum of colors that drive photosynthesis

What is the purpose of photoprotection?

it prevents damage from chlorophyll or interactions with oxygen by using carotenoids to absorb and dissipate light energy

What do light reactions do?

convert solar energy into chemical energy

Where do light reactions take place?

in the thylakoid membrane in the photosystems

idk wtf this is but it’s important so learn it

What are the two forms of chemical energy?

NADPH and ATP

The cell converts light energy to chemical energy by using photons to _________________________

excite electrons

what is this

this is what happens when a chlorophyll absorbs a photon of light

an electron gets excited and becomes unstable so it goes back to ground state which releases heat and emits photons

What is a photosystem?

a reaction center and light capturing complexes

What is a reaction center?

a complex of proteins associated with chlorophyll a and an electron acceptor

What is a light capturing complex?

pigments associated with proteins; it’s like the antenna for the reaction centers

What are the two photosystems in the thylakoid membrane in order of function?

photosystem II

photosystem I

What is photosystem II?

a reaction center at P680 and absorbs light at 680nm

What is photosystem I?

a reaction center at P700 and absorbs light at 700nm

What happens in step 1 of photosystem II?

a photon will make an electron repeat going from an excited state to ground state until it reaches the P680

What happens in step 2 of photosystem II?

The electron is transferred to a primary electron acceptor which then forms P680+

What happens in step 3 of photosystem II?

H2O is split into 2 electrons which reduce P680+, 2 H+ which is released into thylakoid space, and 1 oxygen atom which immediately bonds to another oxygen atom.

What happens in step 4 of photosystem II?

all excited electrons will pass from PSII to PSI through the electron transport chain; this is called linear electron flow

What happens between PS II and PS I to provide energy to form ATP?

the “fall” of electrons

The H+ gradient is a form of ____________ energy

potential

What does ATP synthase do?

it couples the diffusion of H+ to the formation of ATP

What happens in the first step of photosystem I?

light energy excites electrons in the P700 chlorophyll molecules and becomes P700+

What happens in the second step of photosystem I?

electrons go down a second transport chain

What happens in the third step of photosystem I?

NADP+ reductase catalyzes the transfer of electrons from Fd to NADP+

What are the inputs of light reactions?

H2O

ADP

NADP+

What are the outputs of light reactions?

O2

ATP

NADPH

What is the calvin cycle

cyclic electron flow

What does the calvin cycle do?

it uses ATP and NADPH to reduce CO2 to sugar (G3P)

For the net synthesis of 1G3P the cycle must take place __________ times.

3

What are the three phases of the calvin cycle?

carbon fixation

reduction

regeneration of RuBP

What happens in the carbon fixation in the calvin cycle?

CO2 gets incorporated into the cycle one at a time and attaches itself to RuBP (ribulose bisphosphate) which gets catalyzed by the enzyme rubisco and forms 3-phosphoglycerate (PGA)

What happens in the reduction in the calvin cycle?

All the PGA gets phosphorylated by 6 ATP and becomes one PGA and 6NADPH donates electrons to the PGA to reduce it to G3P; there are 6 G3P formed but only a net gain of 1 because the rest were used to generate RuBP

What happens in the regeneration of RuBP in the calvin cycle?

Use 5 G3P and 3 ATP to regenerate 3 RuBP and the cycle repeats to take in CO2 again.

wtf is this

the calvin cycle

What are the inputs of the Calvin cycle?

3 CO2

9 ATP

6 NADPH

What are the outputs of the calvin cycle?

1 G3P

9 ADP

6 NADP+

What is photorespiration?

plants close their stomata to stop water loss on very hot days

Why is photorespiration bad for C3 plants?

There is less CO2 and more O2 so rubisco binds to the O2 and uses ATP producing more CO2 and no sugar

How did C4 plants adapt to combat photorespiration?

the stomata partially close to conserve water and mesophyll cells fix CO2 into a 4-C molecule and transfer it to sheath cells which releases CO2 to be used in the Calvin Cycle

What are CAM plants?

they open stomata at night and close during the day

What happens because of how CAM plants open their stomata?

CO2 is incorporated into organic acids and stored in vacuoles and then during the day, light reactions occur and CO2 is released from the organic acids and incorporated into the Calvin cycle