AP Bio Unit 3

where are most chloroplasts found?

where are most chloroplasts found?

mesophyll (interior tissue of leaf)

where does CO2/O enter and exit the leaf?

stomata

how many chloroplasts does a typical mesophyll cell have?

30-40

general photosynthesis equation

6CO₂ + 6H₂O+Light energy → C₆H₁₂O₆ + 6O₂

is photosynthesis endergonic or exergonic?

endergonic

2 stages of photosynthesis

• light reactions

• calvin cycle

outputs of light reactions

• ATP

• NADPH

what happens when light hits matter?

it is reflected, transmitted, or absorbed

pigments

• substances that absorb visible light

• different pigments absorb lights of different wavelengths—> colors

spectrophotometer

machine to measure ability of pigment to absorb different wavelengths of light by directing a beam of light through different solutions and measure fraction transmitted

absorption spectrum

graph that plots pigment absorption vs. wavelength

chlorophyll a

key light capturing pigment in light reactions

chlorophyll b

accessory pigment in light reactions

action spectrum for photosynthesis

• first demonstrated by Engelmann in 1883

• suggests that violet blue/red light work best for photosynthesis, while green works worst

carotenoids

group of accessory pigments that are various shades of yellow/orange

function of carotenoids

• may broaden the possible color spectrum for photosynthesis

• photoprotection

photoprotection

process of absorbing or dissipating excess light that could damage chlorophyll or O2

what happens when photons hit electrons?

they move to a higher energy level (excited)

photosystem composition

• reaction center complex in center

• light harvesting complex around

reaction center complex

proteins holding pair of chlorophyll a and primary electron acceptor

light harvesting complex

various pigment molecules bound to proteins

what is the path of light/energy through the photosytems?

photon→pigment→waves from pigment to pigment→chlorophyll a pair is excited→donates electrons to primary electron acceptor

difference between photosystem I and photosystem II

• PS II has P680 rxn center complex (accepts 680 nm)

• PS I has 700 rxn center complex (accepts 700 nm)

how are the electrons from photosystem II replaced?

an enzyme catalyzes the splitting of H2O, which creates 2 electrons for photosystem II and hydrogen protons for the gradient

proton gradient

there is a high H+ concentration in the thylakoid space and they diffuse into the low concentration stroma

where does the calvin cycle take place?

stroma

what carbohydrate is produced by the calvin cycle?

glyceraldehyde 3-phosphate (G3P)

how many times does the cycle take place to make one G3P? one glucose?

• 3 times to make 1 G3P

• 6 times to make 1 glucose

first phase of calvin cycle

carbon fixation

• CO2 and a 5 carbon sugar RuBP are combined by enzyme rubisco

• forms unstable 6 carbon sugar, which splits into 2 3-phosphoglycerates

second phase of calvin cycle

reduction

• each 3-phosphoglycerate receives a phosphate group from ATP

• reduced by NADPH and loses phosphate group to make 6-carbon G3P

third phase of calvin cycle

RuBP regeneration

• one carbon of G3P leaves cycle, the remaining 5 carbon are rearranged using ATP to become RuBP

C3 plants

use rubisco for carbon fixation; when stomata close on hot days simply less sugar is produced

photorespiration

evolutionary baggage in which O2 enters the calvin cycle instead of CO2 when levels are low, this decreases photosynthetic output

C4 plants

CO2 is concentrated into mesophyll cells where a 4 carbon compound is fixated. that 4 carbon compound travels to bundle sheath cells where carbon can enter the calvin cycle

CAM plants

• open stomata in night, close in day

• the calvin is stored in organic compounds for its use in the day