AP Biology Chapter 10 Photosynthesis

Photosynthesis

conversion process in which light energy from the sun is captured by chloroplasts of plants and converted into chemical energy stored in sugar and other organic molecules

autotrophs

self- feeders. they sustain themselves without eating anything derived from other organisms.

photoautotrophs

organisms that use light to synthesize organic substances

heterotrophs

obtain organic material from compounds produced by other organisms

decomposers

consume the remains of dead organisms by decomposing and feeding on organic litter such as carcasses, feces, and fallen leaves

leaves are

major site of photosynthesis in plants

chlorophyll

the color of the leaf is from this. green pigment located within chloroplasts. absorbs light energy that drives the synthesis of organic molecules in the chloroplasts

mesophyll

chloroplasts are found mainly in these cells. it is the tissue that is on the interior of the leaf

stomata

co2 enters the leaf and oxygen exits by way of tehse microscopic pores

water absorbed by roots is delivered to leaves by

veins

stroma

envelope of two membranes encloses this dense fluid within the chloroplast

thylakoids

elaborate system of interconnected membranous sacs that segregate the stroma from another compartment, the interior of the thylakoids, or thylakoid space

grana

thylakoids are stacked in columns called this

chlorophyll resides in

thylakoid membranes

photosynthesis chemical equation:

6 co2 + 12 h20 + light energy > c6h1206 + 6 o2 + 6 h2o

the chloroplasts split

water into hydrogen and oxygen

a result of shuffling of atoms during photosynthesis is the

extraction of hydrogen from water adn its incorporation into sugar

O2

the waste product of photosynthesis in light reactions

reactants of photosynthesis

6 CO2 and 12 H2O

products of photosynthesis

C6H12O6 and 6 H2O and 6 O2

Light reactions

convert solar energy to chemical energy, light powers it, water is split in process, O2 is given off as byproduct, light reactions use light to reduce NADP+ to NADPH by adding a pair of electrons along with a H+

light reactions also

generate ATP using chemiosmosis to power teh addition of a phosphate group to ADP a process called photophosphorylation

light energy is initally converted into

NADPh and ATP

light reactions produces no

sugars. this happens in the calvin cycle

calvin cycle begins by

incorporating CO2 from the air into organic moelcuels already present in the chloroplast

site of light reactions

thylakoids of the chloroplast

calvin cycle occurs in

the stroma

Chloroplast's thylakoids transform

light energy into chemical energy of ATP and NADPH

wavelength

distance between crests of electromagnetic waves

electromagnetic spectrum

the entire range of radiation

segment of light spectrum most important to us is

narrow band between 380 and 750 nm because it is visible light and detectable by human eye

photon

light behaves as though it consists of discrete particles called these, they have a fixed quanitty of energy

the shorter the wavelength of light..

the greater the energy of each photon of that light

pigments

substances that absorb visible light

wavelengths that are absorbed

disappear

spectrophotometer

this machine directs beams of light of different wavelengths through a solution of the pigment and measures the fraction of the light transmitted at each wavelength

absorption spectrum

a graph plotting a pigment's light absorption versus wavelength

chlorophyll a

its absorption spectrum suggests that violet blue adn red light work best for photosynthesis since they are absorbed, while green light is the least effective

action spectrum

profiles the relative effectiveness of different wavelengths of radiation in driving the process.

an action spectrum is prepared by

illuminating chloroplasts with light of different colors and then plotting wavelengths against some measuer of photosynthetic rate, such as co2 consumption or o2 release.

chlorophyll b-

one of the accessory pigments that is another form of chlorophyll. it is almost identical to chlorophyll a but a slight structural difference between them is enough to give the two pigments slightly different absorption spectra

chlorophyll a colors

blue- green

chlorophyll b colors

yellow- green

carotenoids

accessory pigments that are hydrocarbons that are various shades of yellow and orange because they absorb violet and blue- green light

photoprotection

most important function of carotenoids. they absorb and dissipate excessive light energy that would otherwise damage chlorophyll or interact with oxygen, forming reactive oxidative molecules that are dangerous to the cell

what exactly happens when chlorphyll and other pigments absorb light?

the colors corresponding to teh absorbed wavelengths disappear from the spectrum of the transmitted and reflected light, but energy cannot disappear.

photosystem

composed of a reaction center surrounded by a number of light-harvesting complexes

light-harvesting complex

consists of pigment molecules (which may include chlorophyll a, b, and carotenoids) bound to particular proteins

the number and variety of proteins allows a photosystem to

harvest light over a larger surface adn a larger portion of the electromagnetic spectrum than any single protein could alone do

light- harvesting complexes act as an antenna

when a pigment molecule absorbs a photon, the energy is transferred from pigment molecule to pigment molecule within a light- harvesting complex until it is funneled into the reaction center

reaction center

protein complex that includes two special chlorophyll a molecules and a molecule called the primary electron acceptor

the chlorophyll a molecules in the primary electron acceptor are special because

their molecular environment- their location and other molecules with which they are associated- enables them to use the energy from light to boost one of their electrons to a higher energy level

first step in light reactions

solar powered transfer of an electron from a special chlorophyll a molecule to the primary electron acceptor

as soon as the chlorophyll a molecule reaches a higher energy level

the primary electron acceptor captures it

the thylakoid membrane is populated by

two types of photosystems that cooperate in the light reactions of photosynthesis. They are photosystem I and photosystem II. Photosystem II functions first

each photosystem has a

reaction center with a particular kind of primary electron accpetor next to a pair of special chlorophyll a molecules associated with specific proteins

reaction center chlorophyll a of photosystem II

known as p680 because this pigment is best at absorbing light having a wavelength of p680 (red wavelength)

reaction center chlorophyll a of photosystem I

p700 because this pigment is best at absorbing light having a wavelength of p700

the two pigments p700 and p680 are

identical in chlorophyll a molecules. their association with different proteins in the thylakoid membrane affects the electron distribution in teh chlorophyll molecuels and accounts for the slight difference in teh light absorbing proteins

what drives the synthesis of NADPH and ATP by energizing the two photosystems embedded in the thylakoid membrane?

light!

what is the predominant route in light reactions?

noncyclic electron flow

calvin cycle is

anabolic, building sugar from smaller molecules and consuming energy

carbon enters the calvin cycle in the form of

co2 and leaves in the form of sugar. the cycle spends ATP as an energy source and consumes NADPH as reducing power for adding high energy electrons to make the sugar

for every three molecules of co2 synthesized

one molecule of G3P is produced

phase one of the calvin cycle:

carbon fixation- incorporates each CO2 molecule by attachign it to a five carbon sugar named RuBP. the enzyme that catalyzes the raction is Rubisco. product of this reaction is a six carbon intermediate that immediately splits in half to form two molecules of 3- phosphoglycerate

phase 2 of the calvin cycle

reduction- each molecule of 3- phosphoglycerate receives an additional phosophate group from ATP,. next a pair of electrons that originated from NADPH reduces it to G3P.

phase 3 of the calvin cycle

regeneration of the co2 acceptor RuBP- carbon skeletons of five molecules of G3p are rearranged into three molecules of RuBP. the cycle spends three more molecules of G3P.

inputs into the calvin cycle

9 atp 6 nadph 3 co2

outputs

1 g3p 9 adp 6 nadp+