1-1 Honors Biology Chapter 8 Photosynthesis John Regan Wendy Vermillion Columbus State Community College Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Overview of photosynthesis Flowering plants as photosynthesizers –Photosynthesis occurs in the green parts of plants –Water is taken up by roots and transported to leaves by veins –Carbon dioxide enters through openings in the leaves called stomata –Light energy is absorbed by photopigments in thylakoids of chloroplasts

Chloroplast Anatomy Double membrane on outside Inner membrane-thylakoids –Stacks of thylakoids- grana –Chlorophyll and other pigments in thylakoid membranes –Absorbs light Stroma- space between grana –Carbohydrates made here 1-3

1-4 Plants as photosynthesizers Fig 8.2

1-5 Overview of photosynthesis cont’d. Photosynthetic reaction Solar energy + 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 –Carbon dioxide is reduced to form glucose, therefore oxygen in glucose comes from CO 2 –Water is oxidized to form oxygen, therefore the oxygen given off by photosynthesis comes from water Two set of reactions –Photosynthesis consists of 2 sets of reactions –The light reactions occur first followed by the Calvin cycle –NADP + carries hydrogens from the light reactions to the Calvin cycle –ATP formed in the light reactions is used in the Calvin cycle

1-6 Overview of photosynthesis Fig 8.3

Solar energy capture Visible light –Visible light is a part of the electromagnetic spectrum –Visible light includes the colors violet,blue green, yellow, orange, and red –Blue-violets have the shortest wavelengths and the highest energy content –Photopigments chlorophyll a and b and carotenoids absorb specific portions of the light spectrum –Blue, violet, and red are best absorbed –Green is reflected

1-8 The electromagnetic spectrum and visible light Fig 8.4

1-9 Photosynthetic pigments and photosynthesis Fig 8.5

1-10 Solar energy capture cont’d. Light reactions –2 types of photosystems (PS I and PS II) composed of photopigments –Composed of chlorophyll a and b and carotenoids –Reaction center of each photosystem is chlorophyll a –Electrons of chlorophyll a absorb light energy and move to an electron acceptor molecule –Electrons then pass down one of 2 paths- noncyclic or cyclic

1-11 Solar energy capture cont’d. The noncylic pathway –Produces ATP and NADPH –Light energy is absorbed by chlorophyll a in PSII –Excited electrons are removed –Those electrons are replaced by splitting a water molecule 2H 2 O  4H + + 4e - + O 2 –High energy electrons removed from PSII pass down an ETC releasing energy to build a chemiosmotic gradient –ATP is produced –Electrons are picked up by NADP + to make NADPH –Electrons lost by PSI chlorophyll a can be replaced by those from PSII

1-12 The light reactions: the noncyclic electron pathway Fig 8.6

1-13 Solar energy capture cont’d. Cyclic pathway –Generates only ATP –PSI absorbs solar energy and electrons from chlorophyll a are removed –Electrons pass down an ETC –Energy released is stored in an electrochemical gradient for chemiosmosis –ATP is produced

1-14 The light reactions: the cyclic electron pathway Fig 8.7

1-15 Solar energy capture cont’d. Organization of thylakoid –Thylakoid space acts as reservoir of hydrogen ions –Hydrogen ions flow down gradient through an ATP synthase complex in thylakoid membrane to produce ATP –Thylakoid membranes contain the following complexes: PS I and II ETC ATP synthase complexes

1-16 Organization of the thylakoid Fig 8.8

Light Reaction In/Out Table In Out H 2 O O 2 NADP+ NADPH ADP + P ATP 1-17

Carbohydrate synthesis Stages of the Calvin cycle 1.Carbon fixation carbon fixation occurs when a reaction occurs that attaches CO 2 to an organic compound Ribulose biphosphate (RuBP) combines with CO 2 to form a 6C molecule Enzyme which catalyzes this reaction is RuBP carboxylase

1-19 The Calvin cycle reactions Fig 8.9

1-20 Stages of the Calvin Cycle 2. Reduction of carbon dioxide –6C molecule breaks into 2 3C 3PG molecules –Each undergoes reduction to G3P in a 2 step process –CO2 is reduced to a carbohydrate and NADPH is oxidized to NADP + –ATP provides the energy –Every 3 turns of the Calvin cycle produce 6 G3P; one molecule leaves the pathway to synthesize carbohydrates

1-21 Stages of Calvin Cycle 3. Regeneration of RuBp –Constant supply of RuBP needed to keep the Calvin cycle turning –For every 3 turns of the Calvin cycle 5 G3P molecules are used to reform RuBP –This reaction also requires energy from ATP

Calvin Cycle In/Out Table In Out NADPH NADP+ ATP ADP + P CO 2 Glucose 1-22

1-23 Carbohydrate synthesis cont’d. Importance of the Calvin cycle –G3P is the Calvin cycle product that can be converted to glucose phosphate –Glucose phosphate can then be converted into many different organic molecules Glucose phosphate Glucose and starches Amino acids Fatty acids and glycerol

Photosynthesis versus cellular respiration Photosynthesis vs cell respiration –Both plant and animal cells carry out cell respiration –Only plant cells photosynthesize –Both processes utilize an electron transport chain and chemiosmosis for ATP production –Photosynthesis reduces CO 2 to carbohydrates and releases O 2 –Respiration utilizes O 2 and gives off CO 2

1-25 Photosynthesis vs cell respiration Fig 8.12

Objectives Chapters 7 1.Know the equation for aerobic cellular respiration. 2. Know the 4 stages of aerobic respiration and where each happens. 3.Know the terms oxidation, reduction. 4.Know how many ATPs are made from NADH and FADH 2 in ETC. 5.Know the 2 categories of metabolism and whether they are exergonic or endergonic. 6.Know the efficiencies of aerobic and anaerobic respiration. 7.Know the 2 types of fermentation. 1-26

Objectives Chapter 8 1.Know the equation for photosynthesis. 2.Know what colors of light have the most energy. 3.Know what colors of light are absorbed the best by chlorophyll. 4.Know the structure of a chloroplast. 5.Know the source of oxygen released by photosynthesis. 6.Know the 2 stages of Photosynthesis. 7.Know the reactants and products of the light reaction and Calvin cycle. 8.Know the differences between the cyclic and noncyclic electron pathways. 9.Know how RuBP is used in the Calvin cycle. 10.Compare photosynthesis and cellular respiration. 1-27