From the Sun to Food

PHOTOSYNTHESIS1. Photosynthesis is ability of a plant to

turn sunlight, carbon dioxide, and water into sugar (food for energy storage).

2. The overall reaction is: light chlorophyll

6CO2 + 6H2O -------> C6H12O6 + 6O2

Photosynthesis3. Photosynthesis is vital to life for

two reasonsa. The oxygen in the air comes

from photosynthesis. The plants continue to replenish the oxygen in the air.

b. Almost all energy on Earth and all of our food comes directly or indirectly from photosynthesis.

Stages of Photosynthesis4. Photosynthesis occurs in three stages:

a. Stage 1: Energy is captured from sunlight

b. Stage 2: Light energy is converted to chemical energy (temporarily stored as ATP and NADPH)

c. Stage 3: The chemical energy in the ATP and NADPH powers the formation of organic compounds (food) using CO2.

5. Stage 1: Pigments capture light

a. Light energy captured by chlorophyll (main photosynthetic pigment) and carotenoids (fall colors).

b. Together they allow more wavelengths of light to be captured.

5. Stage 1i. When light strikes these pigments,

energy is transferred to their electrons causing the electrons to jump to their next energy level (they get excited).

ii. Excited electrons jump from chlorophyll to nearby molecules.

iii. Those electrons must be replaced so special enzymes split water molecules, taking electrons from the H leaving H+ and O2 (gas).

6. Stage 2 – Conversion of Light Energy

a. The excited electrons that leave the chlorophyll jump through a series of molecules like a fire line

b. There are two series or electron transport chains which pass down these electrons.

The Electron Transport Chains

7. The Products of the ETCsa. One ETC provides energy to make ATPb. The other ETC provides energy to make

NADPHc. Both of these compounds provide

temporary chemical storage of the energy from the sunlight.ETC ETC

ATP NADPHStore Chem. Energy from

sun

8. The Light Reactionsa. Stage 1 and Stage 2 both require light to

occur…

9. Stage 3 – Energy Storage(The Calvin Cycle – The Dark Reactions)

a. The dark reactions take place outside the thylakoid membrane in the stroma.

b. Calvin Cycle converts CO2 to sugar in a three phase process.

The Calvin Cycle (continued)

2. Carbon fixation – CO2 is incorporated into an organic molecule (1C + 5C = 6C) called RuBP by the enzyme Rubisco. This 6 carbon structure is unstable and immediately splits into 2, 3 carbon molecules.

2. Reduction – Each 3 carbon molecule is phosphorylated by ATP and NAPH. One of the 3 carbon sugars is used to make starches or sugars.

3.3. Regeneration of CORegeneration of CO2 2 acceptoracceptor – The other 3 carbon sugars are used to regenerate the initial 5 carbon compound…completing the cycle.

10. What factors affect photosynthesis?a.a. Intensity of Intensity of lightlight

b.b. Scarcity of Scarcity of waterwater

c.c. TemperatureTemperature

d.d. Amount of Amount of carbon dioxide carbon dioxide