PHOTOSYNTHESIS

2 Autotrouphs

3 Photosynthesis Anabolic (small molecules combined)Anabolic (small molecules combined) Endergonic (stores energy)Endergonic (stores energy) Carbon dioxide (CO 2 ) requiring process that uses light energy (photons) and water (H 2 O) to produce organic macromolecules (glucose).Carbon dioxide (CO 2 ) requiring process that uses light energy (photons) and water (H 2 O) to produce organic macromolecules (glucose). 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 glucose SUN photons

4 Question: Where does photosynthesis take place?

5 Plants Autotrophs – produce their own food (glucose)Autotrophs – produce their own food (glucose) Process called photosynthesisProcess called photosynthesis Mainly occurs in the leaves:Mainly occurs in the leaves: a.stoma - pores b.mesophyll cells Stoma Mesophyll Cell Chloroplast

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7 Stomata (stoma) Pores in a plant’s cuticle through which water vapor and gases (CO 2 & O 2 ) are exchanged between the plant and the atmosphere. Guard Cell Carbon Dioxide (CO 2 ) Oxygen (O 2 ) Found on the underside of leaves Stoma

8 Question: Why are plants green?

9 Chlorophyll Molecules Located in the thylakoid membranesLocated in the thylakoid membranes Chlorophyll have Mg + in the centerChlorophyll have Mg + in the center Chlorophyll pigments harvest energy (photons) by absorbing certain wavelengths (blue-420 nm and red- 660 nm are most important)Chlorophyll pigments harvest energy (photons) by absorbing certain wavelengths (blue-420 nm and red- 660 nm are most important) Plants are green because the green wavelength is reflected, not absorbedPlants are green because the green wavelength is reflected, not absorbed.

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11 Wavelength of Light (nm) Short waveLong wave (more energy)(less energy)

12 Absorption of Light by Chlorophyll wavelength Absorption violet blue green yellow orange red Chlorophyll absorbs blue-violet & red light best

13 Question: During the fall, what causes the leaves to change colors?

14 Fall Colors In addition to the chlorophyll pigments, there are other pigments presentIn addition to the chlorophyll pigments, there are other pigments present During the fall, the green chlorophyll pigments are greatly reduced revealing the other pigmentsDuring the fall, the green chlorophyll pigments are greatly reduced revealing the other pigments Carotenoids are pigments that are either red, orange, or yellowCarotenoids are pigments that are either red, orange, or yellow

15 Redox Reaction The transfer of one or more electrons from one reactant to another. This allows atoms to be rearranged into new molecules. Two types: 1.Oxidation is the loss of e - 2.Reduction is the gain of e -

16 Question: What do cells use for energy?

17 Energy for Life on Earth Sunlight is the ULTIMATE energy for all life on Earth Plants store energy in the chemical bonds of sugars Chemical energy is released as ATP during cellular respiration

18 Parts of Photosynthesis

19 Photosynthesis Overview Reactants Products 3 carbon sugar (G3P)

20 Two Parts of Photosynthesis Two reactions make up photosynthesis: 1.Light Reaction or Light Dependent Reaction - Produces energy from solar power (photons) in the form of ATP and NADPH. SUN

21 Two Parts of Photosynthesis 2. Calvin Cycle or Light Independent Reaction Also called Carbon Fixation or C 3 FixationAlso called Carbon Fixation or C 3 Fixation Uses energy (ATP and NADPH) from light reaction to make sugar (glucose).Uses energy (ATP and NADPH) from light reaction to make sugar (glucose).

22 Energy Carriers Nicotinamide Adenine Dinucleotide Phosphate (NADP + )Nicotinamide Adenine Dinucleotide Phosphate (NADP + ) NADP + = Oxidized Form (Empty, needs e-)NADP + = Oxidized Form (Empty, needs e-) Picks Up 2 high-energy electrons and H + from the Light Reaction to form NADPH (Full)Picks Up 2 high-energy electrons and H + from the Light Reaction to form NADPH (Full) NADPH formed in the light reactions carries high energy electrons to be passed on to another molecule in the calvin cycle.NADPH formed in the light reactions carries high energy electrons to be passed on to another molecule in the calvin cycle.

23 NADPH

24 Light Reactions

25 STEP 1 – Photosystem II 1.Sun Light hits pigments 2.excites 2 electrons. 3.Electrons jump from pigment to pigment 4.Electrons reach P680 (reaction center – a specialized chlorophyll) 5.Passed to primary electron acceptor (Protein)

26 STEP 2 – Replacement of Electrons 1.Water is split 2. 2 electrons (from H) replace those lost in PS II 2. H+ builds a gradient (High concentration) in Thylakoid space 3. Oxygen gas is released out

27 STEP 3 – Electron Transport Chain Electrons are passed down a series of electron acceptor proteins As electrons are passed down – energy is lost with each transfer Energy is used by to create H+ gradient in thlylakoid for production of ATP

28 STEP 4 - Photosystem I SAME AS PHOTOSYSTEM II Light excites 2 electrons in pigment Electrons are passed until reach reaction center (P700) Electrons are sent to second primary electron acceptor. Electrons from first ETC fill missing space.

29 1.Electrons are passed from Primary acceptor to NADP+ reductase 2.Energy from small ETC is used to add electrons to NADP+ to form NADPH and H+ (electron carrier) STEP 5 – ETC

30 ATP SYNTHESIS Enzyme in thylakoid membrane called ATP Synthase As H+ ions passed through thylakoid membrane, enzyme attaches a free phosphate group to ADP Forms ATP in stroma to be used in CALVIN CYCLE

31 Chemiosmosis Powers ATP synthesisPowers ATP synthesis Takes place across the thylakoid membraneTakes place across the thylakoid membrane Builds H+ (hydrogen ion) gradient (high concentration in thylakoid space)Builds H+ (hydrogen ion) gradient (high concentration in thylakoid space) Uses ETC and ATP synthase (enzyme)Uses ETC and ATP synthase (enzyme) H+ move down their concentration gradient through channels of ATP synthase forming ATP from ADPH+ move down their concentration gradient through channels of ATP synthase forming ATP from ADP

32 Chemiosmosis

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34 Calvin Cycle Light Independent ReactionLight Independent Reaction Uses CO 2 + RuBP (5 C) and an enzyme called RuBISco to carry out Carbon FixationUses CO 2 + RuBP (5 C) and an enzyme called RuBISco to carry out Carbon Fixation C 3 plants (80% of plants on earth) – product is a 3 – carbon sugar called G3PC 3 plants (80% of plants on earth) – product is a 3 – carbon sugar called G3P Occurs in the stroma of chloroplasts Occurs in the stroma of chloroplasts A series of steps modify the molecule RuBP until final product is produced (biochemical pathway)A series of steps modify the molecule RuBP until final product is produced (biochemical pathway) 1 G3P is the product for sugar production; 5 G3P are rearranged to form the starting molecule 3 RuBP1 G3P is the product for sugar production; 5 G3P are rearranged to form the starting molecule 3 RuBP Uses ATP for energy and NADPH for reduction from light reactionUses ATP for energy and NADPH for reduction from light reaction To produce glucose: it takes 6 turns and uses 18 ATP and 12 NADPH.To produce glucose: it takes 6 turns and uses 18 ATP and 12 NADPH.

35 RuBISco: control enzyme RuBP 2 G3P make glucose; It can make any monomer! ATP and NADPH;release ADP, Pi, and NADP +; molecules rearranged and split to form 6 (3C) Carbon dioxide added 1 at a time! 3 turns to make 1 G3P 6 turns to make 1 glucose. ATP used; ADP and Pi released G3P

36 Photorespiration Occurs on hot, dry, bright daysOccurs on hot, dry, bright days Stomates closeStomates close Fixation of O 2 instead of CO 2Fixation of O 2 instead of CO 2 Produces 2-C molecules instead of 3-C sugar moleculesProduces 2-C molecules instead of 3-C sugar molecules Produces no sugar molecules or no ATPProduces no sugar molecules or no ATP

37 Photorespiration Because of photorespiration, plants have special adaptations to limit the effect of photorespiration: 1.C 4 plants 2.CAM plants

38 C 4 Plants Hot, moist environmentsHot, moist environments 15% of plants (grasses, corn, sugarcane)15% of plants (grasses, corn, sugarcane) Photosynthesis occurs in 2 places to prevent oxygen build up.Photosynthesis occurs in 2 places to prevent oxygen build up. –Light reaction - mesophyll cells –Calvin cycle - bundle sheath cells

39 CAM Plants Hot, dry environmentsHot, dry environments 5% of plants (cactus and ice plants)5% of plants (cactus and ice plants) Stomates closed during dayStomates closed during day Stomates open during the nightStomates open during the night –Light reaction - occurs during the day –Calvin Cycle - occurs when CO 2 is present

40 Question: Why do CAM plants close their stomata during the day?

Cam plants close their stomata in the hottest part of the day to conserve water