Photosynthesis is the process by which plants use sunlight, carbon dioxide, and water to produce oxygen and energy in the form of sugar. It occurs in two stages: the light-dependent reactions in the chloroplasts absorb sunlight and split water, producing oxygen and energized molecules. The Calvin cycle then uses this energy to fix carbon from carbon dioxide into organic compounds like glucose. Chlorophyll and other pigments capture sunlight and transfer the energy through electron transport chains to produce ATP and NADPH, which power the Calvin cycle to reduce carbon dioxide into sugars.

1. Photosynthesis The Sun is the main source of energy for life on earth

2. Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water AN OVERVIEW OF PHOTOSYNTHESIS

3. During Photosynthesis… Organisms (plants  ) absorb light energy from the sun and store it in organic compounds. Energy is crucial to all life, without it work could not be done.

4. An example of basic photosynthesis…

5. Photosynthesis consists of two stages Light dependent reactions Take place in the chloroplasts Depends on sunlight for activation energy Responsible for the absorbing of light in Photosynthesis Water is split, giving off oxygen H2O O2 + ATP + NADPH2 Non-light dependent (dark) reactions Takes place in the Stroma Includes the Calvin cycle Does not literally occur in the dark, but requires no light to occur Separated into three steps Carbon dioxide is split, providing carbon to make sugars ATP + NADPH2 + CO2 C6H12O6

6. Chloroplasts The site of Light Dependent Reactions These organelles are surrounded by a double membrane and contain an inner membrane separate into disk like sacs called thylakoids Thylakoid are arranged into granum , or neat stacks Each thylakoid contains the green pigment chlorophyll The light absorbing pigments are organized into photosystems , which transfer energy during the light reactions

8. Pigments in chloroplasts Chloroplasts absorb all other color pigments, leaving green to be reflected resulting in a plant’s color. Chlorophyll a and b are two are the 2 most common types of chlorophyll Chlorophyll b absorbs colors or light energy NOT absorbed by chlorophyll a Light Reflected light Absorbed light Transmitted light Chloroplast

9. The Calvin Cycle – Step one CO2 diffuses into the stroma from surrounding cytosol An enzyme combines a CO2 molecule with a five-carbon carbohydrate called RuBP The six-carbon molecule produced then splits immediately into a pair of three-carbon molecules known as PGA

10. The Calvin Cycle – Step two Each PGA molecule receives a phosphate group from a molecule of ATP This compound then receives a proton from NADPH and releases a phosphate group producing PGAL These reactions produce ADP, NADP+, and phosphate which are used again in the Light Reactions

11. The Calvin Cycle – Step three Most PGAL is converted back to RuBP to keep the Calvin cycle going Some PGAL leaves the Calvin Cycle and is used to make other organic compounds including amino acids, lipids, and carbohydrates PGAL serves as the starting material for the synthesis of glucose and fructose Each turn of the Calvin cycle fixes One CO2 molecule so it takes six turns to make one molecule of glucose

12. Photosystems & Electron Transport Chain Only 1 in 250 chlorophyll molecules (chlorophyll a ) actually converts light energy into usable energy; these molecules are called reaction-center chlorophyll Antenna pigments - the other molecules (chlorophyll b, c, & d and carotenoids) tha absorb light energy and deliver it to the reaction-center molecule Photosystem- unit of several hundred antenna pigment molecules plus a reaction center There are 2 types of photosystems- photosystem I & photosystem 2 Light is absorbed by the antenna pigments of photosystems II and I NADPH is used in the Calvin cycle

13. Chemiosmosis Synthesis of ATP (energy) Depends on the concentration gradient of protons ( H+) across the thylakoid membrane Protons (H+) are produced from the splitting of water in Photosystem II Concentration of Protons is HIGHER in the thylakoid than in the stroma Enzyme, ATP synthetase in the thylakoid membrane, makes ATP by adding a phosphate group to ADP

14. Alternate Pathways C3 Plants are the most common users of the Calvin Cycle Stomata are small openings on the underside of leaves used for gas exchange (O2 & CO2) Guard cells help to open and close the stomata Plants also lose H2O through stoma so they are closed during the hottest part of the day

15. Review: Photosynthesis uses light energy to make food molecules Sugar used for  Cellular respiration  Cellulose  Starch  Other organic compounds Chloroplast Light Stack of thylakoids ADP + P NADP  Stroma Light reactions Calvin cycle