PHOTOSYNTHESIS

PHOTOSYNTHESIS Photosynthesis is ability of a plant to turn sunlight, air, and water into sugar (energy). The overall reaction is: light chlorophyll 6CO2 + 6H2O -------> C6H12O6 + 6O2

Photosynthesis is vital to life for two reasons 1. The oxygen in the air comes from photosynthesis. The plants continue to replenish the oxygen in the air. 2. All of our food comes directly or indirectly from photosynthesis.

Parts of a leaf Stomata palisade layer spongy layer veins chloroplast thylakoids grana stroma

The Reactions of Photosynthesis Remember it all occurs in the chloroplast. Thylakoids – sac-like photosynthetic membranes inside chloroplasts, arranged in stacks called grana Photosystems – clusters of pigments in thylakoid Stroma – region outside of the thylakoid membrane (Calvin Cycle takes place)

Light Photosynthesis uses visible light. Only visible light with intermediate wavelengths has enough energy to cause chemical change without destroying biological molecules. What are the colors of the visible spectrum? Why does a leaf look green? A wavelength is from the top of a crest to the top of another crest. The electromagnetic spectrum ranges from gamma rays to radio waves. The visible light spectrum is from about 400 to 750 manometers (1 billionth of a meter). The short high frequency waves of gamma rays have too much energy and break the hydrogen bonds. The longer waves of heat, microwaves and radio waves do not have enough and are absorbed by the water in the plant.

Pigments Light is captured by pigments. The main photosynthetic pigment is chlorophyll. There is chlorophyll a, b and c. Chlorophyll a is the major photosynthetic pigment and is found in all photosynthetic plants, protist, and cyanobacteria.

Carotenoids Accessory pigments found in all green plants. They absorb blue and green wavelengths and give a plant a yellow or orange color. In the fall when chlorophyll breaks down, it is the accessory pigments which give colors of fall.

Accessory Pigments The red color of some autumn leaves is due to the anthocyanin pigments. These are not photosynthetic.

Stages of Photosynthesis

Putting it all together CO2 H2O C6H12O6 O2 light energy  + H2O CO2 Plants make both: energy ATP & NADPH sugars sunlight ADP NADP Energy Building Reactions Sugar Building Reactions NADPH ATP O2 sugars

The Energy-Capturing Reactions Light absorption Chlorophyll a and b are antennae pigments Electron transport Electrons lost by chlorophyll a end up at NADP Produce oxygen Chemiosmotic ATP synthesis Powered by H ion reservoir

The Dark Reactions The dark reactions take place outside the thylakoid membrane. Carbon fixation - The carbon dioxide is incorporated into an organic molecule (1C + 5C = 6C). This 6 carbon structure is unstable and immediately splits into 2, 3 carbon molecules. These molecules go through a series of reactions known as the CALVIN CYCLE.

What controls photosynthesis? Intensity of light Scarcity of water

Ecological Aspects C4 PLANTS - Use more ATP but at high temperatures they can photosynthesize faster -allowing plants to grow and reproduce faster. These include many weeds and important crops such as corn. A special variation of C4 plants are the CAM plants. These are mostly desert plants. These plants keep the stomata closed during the day and open at night. They must conserve water!

Energy cycle ATP Photosynthesis Cellular Respiration sun CO2 O2 H2O even though this equation is a bit of a lie… it makes a better story sun Energy cycle Photosynthesis CO2 H2O C6H12O6 O2 light energy  + H2O plants CO2 glucose O2 animals, plants CO2 H2O C6H12O6 O2 ATP energy  + Cellular Respiration ATP The Great Circle of Life,Mufasa!