autotroph

"self-feeders"

sustain themselves without eating anything derived from other organisms

producers

ultimate source of organic compounds

where did photosynthesis first evolve?

prokaryotes

prior to the evolution of photosynthesis...

there was very little oxygen found in Earth's atmosphere

(photosynthesis produces oxygen as a waste product)

heterotroph

consumers

live on compounds produced by other organisms

dependent on the process of photosynthesis for both food and oxygen

chloroplasts

the specific sites of photosynthesis in plant cells

stroma

dense, fluid-filled area

enclosed by an envelope of two membranes

thylakoids

within the stroma

vast network of interconnected membranous sacs

thylakoid space

compartment, segregated from stroma by thylakoids

the thylakoids set up compartments...

separate from the stroma

this allows a proton gradient to be established

chlorophyll

located in the thylakoid membranes

is the light-absorbing pigment that drives photosynthesis

gives plants their green color

stomata

many tiny pores

found in the exterior of the lower epidermis of a leaf

the means through which carbon dioxide enters, and oxygen/water vapor exit the leaf

transpiration

the loss of water through open stomata

overall photosynthesis reaction

6 CO₂ + 6 H₂O + Light Energy -> C₆H₁₂O₆ + 6 O₂

the overall chemical change during photosynthesis is...

the reverse of the one that occurs during cellular respiration

water is split for its electrons...

which are transferred along with hydrogen ions from water to carbon dioxide, reducing it to sugar

an endergonic process, requires energy from the sun

oxygen we breathe is formed...

in the process of photosynthesis when a water molecule is split

photosynthesis occurs in how many stages?

two

light reactions and calvin cycle

the light reactions

occur in the thylakoid membranes

solar energy -> chemical energy

net products of light reactions

NADPH (which stores electrons), ATP, and oxygen

step one of the light reactions

light energy is absorbed by chlorophyll, which drives the transfer of electrons from water to NADP⁺, forming NADPH

step two of the light reactions

water is split, oxygen is released

step three of the light reactions

ATP is generated, using chemiosmosis to power the addition of a phosphate group to ADP, a process called photophosphorylation

calvin cycle

occurs in the stroma

CO₂ from the air is incorporated into organic molecules in carbon fixation

uses the fixed carbon plus NADPH and ATP from the light reactions in the formation of new sugars

carbon fixation

CO₂ from the air is incorporated into organic molecules

light

the primary energy source for life on earth

electromagnetic energy that travels in rhythmic waves

visible spectrum

the portion of light that we can see

consists of the colors red, orange, yellow, green, indigo, and violet

ie. ROY G BIV

photons

light behaves as though it is made up of discrete particles

each of which has a fixed quantity of energy

pigments

substances that absorb light

different pigments...

absorb light of different wavelengths

chlorophyll is a...

pigment

it absorbs violet-blue and red while transmitting and reflecting green light

this is why we see summer leaves as green

absorption spectrum

a graph plotting a pigment's light absorption as a function of wavelength

for chlorophyll, it provides clues to the effectiveness of different wavelengths for driving photosynthesis (confirmed by an action spectrum)

action spectrum

graphs, for photosynthesis, the effectiveness of different wavelengths of light in driving the process of photosynthesis

confirms that plants use energy from red and blue light (which is absorbed) and very little energy from green light (which is reflected)

photons of light are absorbed by...

certain groups of pigment molecules in the thylakoid membrane of chloroplasts

photosystems

the groups of pigment molecules in which photons of light are absorbed in the thylakoid membrane of chloroplasts

consist of two parts: a light-harvesting complex and a reaction-center

light-harvesting complex

made up of chlorophyll and carotenoid molecules of different colors of green and orange/yellow

this arrangement allows the complex to gather light effectively

carotenoid molecules

accessory pigments in the thylakoid membrane

when chlorophyll absorbs light energy in the form of photons...

one of the molecule's electrons is raised to an orbital of higher potential energy

chlorophyll is in an "excited state"

reaction center

where the energy is transferred

consists of two chlorophyll a molecules that donate electrons to the second member of the reaction center

primary electron acceptor

chlorophyll a molecules donate electrons to these

a molecule capable of accepting electrons and becoming reduced

first step of the light reactions

the solar-powered transfer of an electron from the reaction-center chlorophyll a pair to the primary electron acceptor

conversion of light energy to chemical energy

elections donated from the reaction center...

must be replaced

splitting of water is the source of the replacement electrons

the thylakoid membranes contain...

two photosystems that are important to photosynthesis

PS I (Photosystem 1)

sometimes designated P700 - chlorophyll a in the reaction center of this photosystem absorbs red light of this wavelength best

PS II (Photosystem 2)

P680 - absorbs light of this wavelength best

the key to the light reactions is...

the flow of electrons through the photosystems in the thylakoid membrane

STEP ONE, light reactions

PS II absorbs light energy, exciting an electron in the P680 reaction center of two chlorophyll a molecules to a higher energy state

STEP TWO, light reactions

electron is transferred to the primary electron acceptor

reaction-center chlorophyll is oxidized and now requires an electron

STEP THREE, light reactions

enzyme splits a water molecule into two hydrogen (H+) ions, two electrons, and an oxygen atom

electrons are supplied to the P680 chlorophyll a molecules

oxygen immediately combines with another oxygen atom (forms O₂, released in atmosphere)

H⁺ released into thylakoid space

STEP FOUR, light reactions

original excited electron passes from the primary electron acceptor of PS II to PS I through an electron transport chain

energy from the transfer of electrons down the electron transport chain is used to pump protons (H⁺) into the thylakoid space

STEP FIVE, light reactions

H⁺ accumulates in the thylakoid space creating a gradient that is used in chemiosmosis to phosphorylate ADP to ATP

ATP used as energy in the formation of carbohydrates in Calvin cycle

STEP SIX, light reactions

light energy has also activated PS I, resulting in the donation of an electron to its primary electron acceptor

electrons donated by PS I are replaced by the electrons from PS II

STEP SEVEN, light reactions

the primary electron acceptor of PS I passes the excited electrons along to another electron transport chain

STEP EIGHT, light reactions

excited electrons are transmitted to NADP+, then reduced to NADPH

(second of the two important light reaction products)

this process removes H⁺ from the stroma, increasing the proton gradient

high energy electrons of NADPH available for use in Calvin cycle

chemiosmosis

how chloroplasts and mitochondria generate ATP

electron transport chain uses...

flow of electrons to pump protons across the thylakoid membrane

stroma -> thylakoid space

this creates an electrochemical gradient

what is the electrochemical gradient that is created used for?

ATP synthase is able to phosphorylate ADP to ATP

occurs when protons flow out of the thylakoid space, down electrochemical gradient, through ATP synthase, and into stroma

where is proton-motive force generated?

3 places

1) hydrogen ions from splitting of water

2) hydrogen ions pumped across the membrane by cytochrome complex

3) removal of hydrogen ions from the stroma when NADP⁺ is reduced to NADPH

differences between chemiosmosis in cellular respiration and photosynthesis

spatial differences

mitochondria uses chemiosmosis to transfer chemical energy from food molecules to ATP

chloroplasts transfer light energy into chemical energy of ATP

(difference between consumer and a producer)

calvin cycle

carbon enters in the form of CO_2, leaves in the form of a sugar

what does the calvin cycle spend and consume?

ATP as an energy source, NADH for reducing power

to net one molecule of G3P, the calvin cycle must go through...

three rotations, fix three molecules of CO₂

to produce one molecule of glucose, the calvin cycle must go through...

six rotations, fix six molecules of CO₂