PHOTOSYNTHESIS

PHOTOSYNTHESIS F Photosynthesis is ability of a plant to turn sunlight, air, and water into sugar (energy). F The overall reaction is: light chlorophyll CO 2 + H 2 O > CH 2 O + O 2 F 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

Light F Photosynthesis uses visible light. –Only visible light with intermediate wavelengths has enough energy to cause chemical change without destroying biological molecules. F What are the colors of the visible spectrum? F Why does a leaf look green?

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

Stages of Photosynthesis

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

The Dark Reactions F The dark reactions take place outside the thylakoid membrane. F 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.

F Intensity of light F Scarcity of water What controls photosynthesis What controls photosynthesis?

Ecological Aspects F 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. F 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!

Vocabulary F Glossary of terms –blade –stipules –petiole –vein –midrib

carotenoids chlorophyll electromagnetic spectrum granum NADP + NADPH photon photosystem photosystem I photosystem II pigment stroma thylakoid Vocabulary