Chap. 6 : PhotosynthesisChap. 6 : PhotosynthesisPhotosynthesisPhotosynthesis – involves a series of – involves a series of chemical reactions where the products of one chemical reactions where the products of one become the reactants of another …. called become the reactants of another …. called biochemical pathwaysbiochemical pathways..

I.I. Light Absorption (light reactions)Light Absorption (light reactions)--- occur in chloroplast--- occur in chloroplast

A. Composition of LightA. Composition of Light

ROY G BIV – each color is a certain wavelength ROY G BIV – each color is a certain wavelength of light. The wavelength decreases left to right.of light. The wavelength decreases left to right.

-- When light hits an object it is either :-- When light hits an object it is either : reflected, transmitted, or absorbedreflected, transmitted, or absorbed ( will see it) (won’t see it)( will see it) (won’t see it)Ex. Sky is blue because blue light is reflected while Ex. Sky is blue because blue light is reflected while

all others are absorbed.all others are absorbed.

B. Chloroplast PigmentsB. Chloroplast Pigments

chlorophyll a -- main pigmentchlorophyll a -- main pigment chlorophyll bchlorophyll b carotenoids carotenoids

accessory pigments – help chlorophyll a absorb more wavelengths of light.

II. Electron TransportII. Electron Transport A. Photosystem (PS) – cluster of pigments in A. Photosystem (PS) – cluster of pigments in thylakoids.thylakoids.

Process of Photosynthesis Process of Photosynthesis

Electron replacement into photosystem IIElectron replacement into photosystem II

water splitting moleculePhotosystem II

2H2O O2

4 H+

4 e-

light

2 H2O 4 H+ + 4e- + O2

PS II

YouTube - Light (Dependant) Reactions of Photosynthesis Animation.urlInside Thylakoid

III. ChemiosmosisIII. Chemiosmosis -- making of ATP from creating a concentration gradient -- making of ATP from creating a concentration gradient

of p+( H+). Proton concentration greater inside the of p+( H+). Proton concentration greater inside the thylakoid than outside in stroma so this creates potential thylakoid than outside in stroma so this creates potential energy. This energy is used by enzyme ATP synthase energy. This energy is used by enzyme ATP synthase molecule to change ADP to ATPmolecule to change ADP to ATP

--- end result of light reactions inside the thylakoids is : --- end result of light reactions inside the thylakoids is : ATP and NADPH moleculesATP and NADPH molecules

IV. IV. Calvin CycleCalvin Cycle (light independent reactions)– (light independent reactions)– production of organic compounds using energy production of organic compounds using energy stored in ATP and NADPH from the light reactionsstored in ATP and NADPH from the light reactions

A. Steps of Calvin CycleA. Steps of Calvin Cycle - CO- CO22 is “fixed” – changing the carbon is “fixed” – changing the carbon

from COfrom CO22 into a carbon used by organisms into a carbon used by organisms (organic carbon)(organic carbon)

- occurs in the stroma of chloroplast- occurs in the stroma of chloroplast 1. CO1. CO22 binds with RuBP (5-carbon sugar) to binds with RuBP (5-carbon sugar) to

create a 6 carbon sugar which immediately create a 6 carbon sugar which immediately splits into 2 PGA s (3-carbon molecules)splits into 2 PGA s (3-carbon molecules)

2. Each PGA releases a phosphate group to 2. Each PGA releases a phosphate group to become PGAL. Also ADP and NADP+ is become PGAL. Also ADP and NADP+ is released to fuel the light reactions.released to fuel the light reactions.

3.Most PGAL is converted back to RuBP to 3.Most PGAL is converted back to RuBP to continue the Calvin Cycle but some PGAL continue the Calvin Cycle but some PGAL will be released to become organic will be released to become organic compounds.compounds.

--- It takes 2 cycles through to make 1 --- It takes 2 cycles through to make 1 glucoseglucose

--- Plants that “fix” carbon using only the --- Plants that “fix” carbon using only the Calvin Cycle are called CCalvin Cycle are called C33 plants. plants.

Calvin Cycle (Dark Reactions)Calvin Cycle (Dark Reactions)

Goes through cycle twice so end result is 1 glucose molecule Goes through cycle twice so end result is 1 glucose molecule (C6H12O6)(C6H12O6)

Occurs in stroma of chloroplast

YouTube - The Calvin Cycle or Dark Reactions (Photosynthesis).url

YouTube - The Photosynthesis Song!!.url

*** All 3 parts together ( light dependent / *** All 3 parts together ( light dependent / chemiosmois/ and calvin cycle)chemiosmois/ and calvin cycle)

NADPH and ATP form from the light reactions and provide the energy to NADPH and ATP form from the light reactions and provide the energy to fuel the light independent reactions (dark reactions/calvin cycle)fuel the light independent reactions (dark reactions/calvin cycle)

*** Overall reaction for photosynthesis :*** Overall reaction for photosynthesis :

6CO6CO2 2 + 6H+ 6H22O + light → CO + light → C66HH1212OO6 6 + 6O + 6O22

B. Alternative PathwaysB. Alternative Pathways -- some plants due to their environment (mostly hot and -- some plants due to their environment (mostly hot and

dry) cannot fix carbon like C3 plants because they would dry) cannot fix carbon like C3 plants because they would lose too much water when their stomata(pores in leaf ) lose too much water when their stomata(pores in leaf ) opens to take in CO2opens to take in CO2

1. C4 plants – fix CO2 into a 4-carbon molecule instead of 1. C4 plants – fix CO2 into a 4-carbon molecule instead of 3-carbon one. Allows stomata to open less therefore 3-carbon one. Allows stomata to open less therefore losing less water. Ex. Corn and sugar canelosing less water. Ex. Corn and sugar cane

2. CAM plants2. CAM plants -- open stomata at night and collect -- open stomata at night and collect

CO2 which they then use during the day in CO2 which they then use during the day in the Calvin Cycle. Will not grow very big. the Calvin Cycle. Will not grow very big. Conserves water in hot tropical and desert Conserves water in hot tropical and desert areas.areas.

ex. Cacti and pineappleex. Cacti and pineapple