Chapter 6 - Photosynthesis

Photosynthesis Song

I. Capturing the Energy in LightA. 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 CO2 + 6 H20 C6H12O6 + 6 O2

chlorophyll

Carbon dioxide + Water Sugar + Oxygen

Leaf Cells

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

D. Light and Pigments1. Visible Spectrum – range of colors from sunlight; ROYGBIV2. 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 ReactionsSteps 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+ + 2 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.

2H2O 4H+ + 4e- + O2

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 CycleA. 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.

1. 3 CO2 + 3 RuBP three 6 – Carbon

molecules. These split into six 3 – Carbon molecules of PGA.

Carbon Dioxide 1-CRibulose biphosphate 5-CPhosphoglyceric 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 GlucoseGlucose 6-C

E. Balance Sheet1. 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 PathwaysA. Based on water loss, CO2, and O2.

1. Stomata – pores on leaves where water, carbon dioxide, and oxygen enters/leaves a plant.

Stomata

2. Types of Pathwaysa. C3 Plants – use Calvin Cycle; most plants.

b. C4 Plants – combines CO2 with a

4 – Carbon compound; partially closed stomata during hot days low CO2

i.e. corn, sugar cane, crabgrass

c. CAM Pathway – open stomata at night due to hot, dry days. This allows CO2

to enter and make organic compounds; i.e. cactus; pineapple

B. Rate of photosynthesis1. Environmental Factors

a. Light intensityb. Temperaturec. CO2