Chapter 6 - Photosynthesis

Photosynthesis Song

I.Capturing the Energy in Light A. Biochemical Pathway – a series of chemical reactions in which the product of one reaction is consumed in the next reaction.

B.Autotrophs/Producers - Photosynthesis light energy 6 CO H 2 0 C 6 H 12 O O 2 chlorophyll Carbon dioxide + Water Sugar + Oxygen

Leaf Cells

C.Chloroplast Anatomy a. Thylakoids – saclike membranes which contain chlorophyll. b. Grana – stacks of thylakoids. c. Stroma – solution surrounding the thylakoids.

D.Light and Pigments 1. Visible Spectrum – range of colors from sunlight; ROYGBIV 2. Wavelength - measurement of light waves  distance between crests; Red (long)  Violet (short)

3. Chloroplast pigments – absorb light. a. Chlorophyll a – directly involved in the light reactions; absorbs more red, less blue. b. Chlorophyll b – accessory pigment (assists in light absorption); absorbs more blue; less red. c. Carotenoids – accessory pigment; i.e. yellow, orange, brown.

E.Light Dependent Reactions Steps of Electron Transport: 1. Light energizes electrons in Photosystem II. 2. Electrons leave chlorophyll a and move to a primary electron acceptor  oxidation reaction (loses electrons).

3.Electrons move through a series of molecules called the electron transport chain where they lose energy. This energy is used to move protons (H + ) into the thylakoid. 4.Light energizes electrons in Photosystem I. They move to a primary electron acceptor.

5.Photosystem I electrons move to a second electron transport chain; a redox reaction occurs (electrons are accepted): NADP + + H e -  NADPH Nicotinamide adenine dinucleotide phosphate

Light Dependent Reactions

Steps of Restoring Photosystem II Electrons: 1.The replacement electrons are produced when an enzyme splits water molecules inside the thylakoid. 2H 2 O  4H + + 4e - + O 2

Steps of Chemiosmosis – the synthesis of ATP: 1.A concentration gradient of protons (H + ) is higher inside the thylakoid than the stroma. 2.These H + provide energy for an enzyme called ATP Synthase. 3. ADP + phosphate + ATP Synthase  ATP

II.The Calvin Cycle A. Light Independent Reaction – does not require light. B. Uses NADPH and ATP from the light dependent reactions. C. Takes place in the stroma.

D.Steps of Calvin Cycle  Carbon atoms are bonded (fixed) into organic compounds CO RuBP  three 6 – Carbon molecules. These split into six 3 – Carbon molecules of PGA. Carbon Dioxide 1-C Ribulose biphosphate 5-C Phosphoglyceric Acid 3-C

2.6 ATP + 6 NADPH + 6 PGA  6 PGAL Phosphoglyceraldehyde 3-C

3a. 5 PGAL remain in the cycle: 5 PGAL + 3 ATP  3 RuBP 3b. 1 PGAL exits the chloroplast and moves into the cytoplasm where it combines with another PGAL to form glucose: PGAL + PGAL  Glucose Glucose 6-C

E.Balance Sheet 1. It takes 3 turns of the Calvin Cycle to produce 1 PGAL; therefore 6 turns to produce 1 Glucose.

2.Energy Yield: * 3 x 2 ATP = 6 ATP Step 2 * 3 x 2 NADPH = 6 NADPH * 3 x 1 ATP = 3 ATP Step 3 Total: 9 ATP 6 NADPH

Calvin Cycle Video

III. Alternative Pathways A. Based on water loss, CO 2, and O Stomata – pores on leaves where water, carbon dioxide, and oxygen enters/leaves a plant.

Stomata

2.Types of Pathways a. C 3 Plants – use Calvin Cycle; most plants. b. C 4 Plants – combines CO 2 with a 4 – Carbon compound; partially closed stomata during hot days  low CO 2 i.e. corn, sugar cane, crabgrass

c. CAM Pathway – open stomata at night due to hot, dry days. This allows CO 2 to enter and make organic compounds; i.e. cactus; pineapple

B.Rate of photosynthesis 1. Environmental Factors a. Light intensity b. Temperature c. CO 2