Fig (a) Plants (c) Unicellular protist 10 µm 1.5 µm 40 µm (d) Cyanobacteria (e) Purple sulfur bacteria (b) Multicellular alga Photosynthesis occurs in plants, algae, certain other protists, and some prokaryotes –These organisms feed not only themselves but also most of the living world BioFlix: Photosynthesis BioFlix: Photosynthesis
Structures of Photosynthesis Chloroplasts are structurally similar to and likely evolved from photosynthetic bacteria Leaves are the major locations of photosynthesis Their green color is from chlorophyll, the green pigment within chloroplasts CO 2 enters and O 2 exits the leaf through microscopic pores called stomata
Fig. 10-3a 5 µm Mesophyll cell Stomata CO 2 O2O2 Chloroplast Mesophyll Vein Leaf cross section Chloroplasts are found mainly in cells of the mesophyll, the interior tissue of the leaf –A typical mesophyll cell has 30– 40 chloroplasts Thylakoid Grana Stroma
The Photosynthesis Equation 6 CO H 2 O + Light energy C 6 H 12 O O H 2 O
Reactants: Fig CO 2 Products: 12 H 2 O 6 O 2 6 H 2 O C 6 H 12 O 6
Light- dependent reactions –Occurs in Thylakoid –Used H 2 O and light to produce ATP, NADPH, and O 2 –NADPH is an electron carrier Calvin cycle –Occurs in stroma – uses carbon dioxide, ATP, and NADPH to produce sugars
The Goal of Photosynthesis is to form high energy sugars. This requires transforming light energy into usable chemical energy (ATP) ATP is form by the process of: Photophosphorylation – –The production of ATP using energy derived from the redox reactions of an electron transport chain.
Redox Reactions A chemical reaction involving the transfer of one or more elections from one reactant to another; also called oxidation/reduction reactions In oxidation, a substance loses electrons, or is oxidized In oxidation, a substance loses electrons, or is oxidized In reduction, a substance gains electrons, or is reduced (the amount of positive charge is reduced)In reduction, a substance gains electrons, or is reduced (the amount of positive charge is reduced)
The Two Stages of Photosynthesis: A Preview The light reactions (in the thylakoids): –Split H 2 O –Release O 2 –Reduce NADP + to NADPH –Generate ATP from ADP by photophosphorylation The Calvin cycle (in the stroma) forms sugar from CO 2, using ATP and NADPH The Calvin cycle begins with carbon fixation, incorporating CO 2 into organic molecules Photosynthesis consists of the light reactions (the photo part) and Calvin cycle (the synthesis part)
Light Fig H2OH2O Chloroplast Light Reactions NADP + P ADP i +
Light Fig H2OH2O Chloroplast Light Reactions NADP + P ADP i + ATP NADPH O2O2
Light Fig H2OH2O Chloroplast Light Reactions NADP + P ADP i + ATP NADPH O2O2 Calvin Cycle CO 2
Light Fig H2OH2O Chloroplast Light Reactions NADP + P ADP i + ATP NADPH O2O2 Calvin Cycle CO 2 [CH 2 O] (sugar)
The Nature of Sunlight Light is a form of electromagnetic energy The electromagnetic spectrum is the entire range of electromagnetic energy, or radiation Visible light consists of wavelengths (including those that drive photosynthesis) that produce colors we can see Wavelength is the distance between crests of waves Wavelength determines the type of electromagnetic energy
Light and Pigments Pigments – light absorbing chemicals Chlorophyll – principle pigment in plants –Chlorophyll a –Chlorophyll b –Carotenoids –Xanthophyll
Why do leaves change colors? Chlorophyll a Chlorophyll b
Component of a Chloroplast Thylakoid – Saclike photosynthetic membranes –Light-dependent reactions occur here Granum – Stack of thylakoidsGranum – Stack of thylakoids Stroma – Region outside the thylakoid membraneStroma – Region outside the thylakoid membrane –Reactions of the Calvin Cycle occur here
The Light-Dependent Reactions Photophosphorylation is the process of creating ATP using a Proton gradient created by the Energy gathered from sunlight. Chemiosmosis is the process of using Proton movement to join ADP and Pi. This is accomplished by enzymes called ATP synthases or ATPases.Chemiosmosis is the process of using Proton movement to join ADP and Pi. This is accomplished by enzymes called ATP synthases or ATPases.
NADP + + e - + Energy NADPH NADP+ (Nicotinamide adenine dinucleotide phosphate) –Electron, hydrogen, and energy carrier
1. Photosystem II Chlorophyll absorbs lightChlorophyll absorbs light Electrons on a chlorophyll molecule (p680) absorb energy from light and become “energized”Electrons on a chlorophyll molecule (p680) absorb energy from light and become “energized” High-energy (“energized”) electrons are passed on to the electron transport chainHigh-energy (“energized”) electrons are passed on to the electron transport chain –Electrons are passed to pheophytin molecule then to plastoquinone Qa then to plastoquinone Qb then to ETC. Chlorophyll’s electrons are replenished by the breakdown of H 2 OChlorophyll’s electrons are replenished by the breakdown of H 2 O H 2 O is broken down into 2H+ ions, O 2, and 2 e-. Electrons are used to replenish chlorophyll’s lost electrons.H 2 O is broken down into 2H+ ions, O 2, and 2 e-. Electrons are used to replenish chlorophyll’s lost electrons.
2. Electron Transport Chain The molecules of the electron transports chain use high-energy electrons to push H+ ions from the stroma into the inner thylakoid space.
3. Photosystem I Chlorophyll absorbs light-energy and re- energized the electrons from photosystem II.Chlorophyll absorbs light-energy and re- energized the electrons from photosystem II. NADP+ picks up these high-energy electrons and H+ to become NADPH.NADP+ picks up these high-energy electrons and H+ to become NADPH.
4. Hydrogen Ions ChemiosmosisChemiosmosis Electrochemical GradientElectrochemical Gradient Hydrogen ions build up inside the thylakiod membrane.Hydrogen ions build up inside the thylakiod membrane. –High concentration of H+ inside the membrane (Strong Positive Charge) –Low concentration of H+ outside the membrane (Negative Charge) –Provides the energy to form ATP
5. ATP formation H+ work to reach equilibrium.H+ work to reach equilibrium. Pass through the ATPsynthasePass through the ATPsynthase Movement of H+ ions through the ATPsynthase powers ATP productionMovement of H+ ions through the ATPsynthase powers ATP production
Do Now… What is the function of NADPH?What is the function of NADPH? How is light energy converted into chemical energy during photosynthesis?How is light energy converted into chemical energy during photosynthesis? Can the complete process of photosynthesis take place in the dark? Explain your answer.Can the complete process of photosynthesis take place in the dark? Explain your answer. Explain what happens to a molecule of water in the light dependant phase of photosynthesis.Explain what happens to a molecule of water in the light dependant phase of photosynthesis. If O 2 is a waste/byproduct of photosynthesis, track where it came from to where it exits the plant.If O 2 is a waste/byproduct of photosynthesis, track where it came from to where it exits the plant.
The Calvin Cycle 1.6 CO 2 molecules enter the cycle. 2.Enzyme “rubisco” combines 6 5-carbon (RuBp) molecules with the carbon from CO 2 and forms them into 12 3-carbon molecules 3.12 ATP and 12 NADPH form the 12 3-carbon molecules into 12 High-energy 3-carbon molecules (G3P) 4.2 (G3P)of the 12 3-carbon molecules are combined to form a 6-carbon sugar 5.6 ATP molecules are used to convert the 10 remaining 3-carbon molecules back into the 6 5-carbon molecules the cycle began with (RuBp)
Factors Affecting Photosynthesis Water supply Amount of sunlight Temperature
Types of Photosynthesis C3 Photosynthesis C4 Photosynthesis CAM Photosynthesis
C3 Photosynthesis : C3 plants. Called C3 because the CO2 is first incorporated into a 3- carbon compound. Stomata are open during the day. RUBISCO, the enzyme involved in photosynthesis, is also the enzyme involved in the uptake of CO2. Photosynthesis takes place throughout the leaf. Adaptive Value: more efficient than C4 and CAM plants under cool and moist conditions and under normal light because requires less machinery (fewer enzymes and no specialized anatomy).. Most plants are C3.
C4 Photosynthesis : C4 plants. Called C4 because the CO2 is first incorporated into a 4-carbon compound. Stomata are open during the day. Uses PEP Carboxylase for the enzyme involved in the uptake of CO2. This enzyme allows CO2 to be taken into the plant very quickly, and then it "delivers" the CO2 directly to RUBISCO for photsynthesis. Photosynthesis takes place in inner cells (requires special anatomy called Kranz Anatomy) Adaptive Value: Photosynthesizes faster than C3 plants under high light intensity and high temperatures because the CO2 is delivered directly to RUBISCO, not allowing it to grab oxygen and undergo photorespiration. Has better Water Use Efficiency because PEP Carboxylase brings in CO2 faster and so does not need to keep stomata open as much (less water lost by transpiration) for the same amount of CO2 gain for photosynthesis. C4 plants include several thousand species in at least 19 plant families. Example: fourwing saltbush pictured here, corn, and many of our summer annual plants.
CAM Photosynthesis : CAM plants. CAM stands for Crassulacean Acid Metabolism Called CAM after the plant family in which it was first found (Crassulaceae) and because the CO2 is stored in the form of an acid before use in photosynthesis. Stomata open at night (when evaporation rates are usually lower) and are usually closed during the day. The CO2 is converted to an acid and stored during the night. During the day, the acid is broken down and the CO2 is released to RUBISCO for photosynthesis Adaptive Value: –Better Water Use Efficiency than C3 plants under arid conditions due to opening stomata at night when transpiration rates are lower (no sunlight, lower temperatures, lower wind speeds, etc.). –May CAM-idle. When conditions are extremely arid, CAM plants can just leave their stomata closed night and day. Oxygen given off in photosynthesis is used for respiration and CO2 given off in respiration is used for photosynthesis. This is a little like a perpetual energy machine, but there are costs associated with running the machinery for respiration and photosynthesis so the plant cannot CAM-idle forever. But CAM-idling does allow the plant to survive dry spells, and it allows the plant to recover very quickly when water is available again (unlike plants that drop their leaves and twigs and go dormant during dry spells). CAM plants include many succulents such as cactuses and agaves and also some orchids and bromeliadscactuses