Chapter 6Chapter 6PhotosynthesisPhotosynthesis

Section 6.1Section 6.1

Energy Processes for LifeEnergy Processes for Life

Autotrophs manufacture their own food from Autotrophs manufacture their own food from inorganic substancesinorganic substances

Use photosynthesis to convert light energy Use photosynthesis to convert light energy from the sun into chemical energyfrom the sun into chemical energy

Heterotrophs cannot manufacture their own Heterotrophs cannot manufacture their own foodfood

Must obtain food by eating autotrophs or other Must obtain food by eating autotrophs or other heterotrophsheterotrophs

PhotosynthesisPhotosynthesis

Involves a complex series of chemical Involves a complex series of chemical reactions in which the product of one reaction reactions in which the product of one reaction is consumed in the next reactionis consumed in the next reaction

Biochemical pathwayBiochemical pathway

6CO6CO22 + 6H + 6H22O + solar energy O + solar energy C C66HH1212OO6 6 + 6O+ 6O22

Solar energy drives a series of chemical Solar energy drives a series of chemical reactions that require carbon dioxide and waterreactions that require carbon dioxide and water

Light Absorption in ChloroplastsLight Absorption in Chloroplasts

Light reactions- the initial reactions in Light reactions- the initial reactions in photosynthesisphotosynthesis

Begin with the absorption of light in Begin with the absorption of light in chloroplastschloroplasts

ChloroplastsChloroplasts

Each chloroplast is surrounded by a pair of Each chloroplast is surrounded by a pair of membranesmembranes

Inside the membranes are stacks of Inside the membranes are stacks of thylakoidsthylakoids

The stacks are called The stacks are called granagrana

The fluid surrounding the grana is called The fluid surrounding the grana is called stromastroma

Light and PigmentsLight and Pigments

Visible spectrum- white light can be separated Visible spectrum- white light can be separated into an array of colors when passed through a into an array of colors when passed through a prismprism

ROY G. BIVROY G. BIV

LightLight

Light travels in wavesLight travels in waves

The distance from the crest of one wave to the The distance from the crest of one wave to the crest of another wave is called a crest of another wave is called a wavelengthwavelength

Chloroplast PigmentsChloroplast Pigments

Pigments- compounds that absorb lightPigments- compounds that absorb light

Chlorophyll aChlorophyll a – absorbs more red light – absorbs more red light Chlorophyll bChlorophyll b – absorbs more blue light – absorbs more blue light CarotenoidsCarotenoids – absorbs more green light – absorbs more green light

Only chlorophyll a is directly involved in the Only chlorophyll a is directly involved in the light reactions of photosynthesislight reactions of photosynthesis

Chlorophyll b assists chlorophyll a in Chlorophyll b assists chlorophyll a in capturing light energy (accessory pigment)capturing light energy (accessory pigment)

In the leaves of a plant, chlorophylls are In the leaves of a plant, chlorophylls are abundantabundant

In Fall, plants lose their chlorophylls and their In Fall, plants lose their chlorophylls and their leaves take on the color of the carotenoidsleaves take on the color of the carotenoids

Electron TransportElectron Transport

Each cluster of pigment molecules is a Each cluster of pigment molecules is a photosystemphotosystem

Two types of photosystems: photosystem I & Two types of photosystems: photosystem I & photosystem IIphotosystem II

Light ReactionsLight Reactions

1. light energy excites electrons in 1. light energy excites electrons in chlorophyllchlorophyll a a molecules of photosystem IImolecules of photosystem II

2. These electrons move to a 2. These electrons move to a primary primary electron acceptorelectron acceptor

3. The electrons are then transferred along a 3. The electrons are then transferred along a series of molecules called an series of molecules called an electron electron transport chaintransport chain

4. light excites electrons in 4. light excites electrons in chlorophyll achlorophyll a molecules molecules of photosystem I. As these electrons move to another of photosystem I. As these electrons move to another primary electron acceptor, they are replaced by primary electron acceptor, they are replaced by electrons from photosystem IIelectrons from photosystem II

5. The electrons from photosystem I are transferred 5. The electrons from photosystem I are transferred along a second electron transport chain. At the end of along a second electron transport chain. At the end of this chain, they combine with NADPthis chain, they combine with NADP++ and H and H++ to make to make NADPHNADPH

Restoring Photosystem IIRestoring Photosystem II

Replacement electrons come from water Replacement electrons come from water moleculesmolecules

An enzyme inside the thylakoid splits water An enzyme inside the thylakoid splits water molecules into protons, electrons, and oxygenmolecules into protons, electrons, and oxygen

2H2H22O O 4H 4H++ + 4 + 4ee-- + + OO22

ChemiosmosisChemiosmosis

Synthesis of ATPSynthesis of ATP

Depends on a concentration gradient of Depends on a concentration gradient of protons across a thylakoid membraneprotons across a thylakoid membrane

The concentration of protons is higher inside The concentration of protons is higher inside the thylakoidthe thylakoid

ATP synthase makes ATP by adding a ATP synthase makes ATP by adding a phosphate group to ADPphosphate group to ADP

ATP synthase functions as a carrier proteinATP synthase functions as a carrier protein