Section 2 Photosynthesis Chapter 8 Section 2 Photosynthesis

Main Idea LIGHT energy is trapped and converted into CHEMICAL energy by autotrophs during photosynthesis

Overview of Photosynthesis

Photosynthesis occurs in two phases. Light-dependent reactions (Phase - One) light energy is absorbed and then converted into chemical energy (ATP) Light-independent reactions (Phase -Two) GLUCOSE is made using the chemical energy formed in phase 1

Phase One: Light-dependent Reactions The ABSORPTION of light is the first step in photosynthesis Large organelles called CHLOROPLAST capture light energy. Occurs in the THYLAKOID

Photosynthesis Structures

Chloroplasts Chloroplasts are found in the LEAVES of plants that contain 2 main compartments THYLAKOIDS – flattened, saclike membranes arranged into stacks called grana (site of light- DEPENDENT reactions) STROMA – fluid filled space outside the grana (site of light-INDEPENDENT reactions)

Pigments Light absorbing colored molecules found in the THYLAKOIDS ) membrane CHLOROPHYLL are the major pigments in plants, which generally absorb most strongly in the VIOLET- BLUE region of the visible light spectrum and reflect light in the GREEN region ACCESSORY PIGMENTS allow plants to trap additional light energy from other parts of the visible spectrum

Chemiosmosis The mechanism by which ADP is converted to ATP with the help of ATP sythetase.

Phase Two: Light-independent Reactions The chemical energy produced in phase-one is used to produce organic molecules such as GLUCOSE. Glucose = Energy Storage Phase Two is also called the Calvin Cycle Occurs in the STROMA

The Calvin Cycle

Alternative Pathways Plants living in HOT & DRY environments have alternative photosynthesis pathways to minimize WATER LOSS without sacrificing CARBON DIOXIDE uptake

C4 pathway Plants Plants use this when in Hot environment Example: Corn & Sugarcane Plants keep stomata (pores) closed during the day Fix CO2 into 4 carbon compound instead of 3 Carbon Compound CO2 is released into the Calvin Cycle through specialized cells

CAM pathway Plants Plants use this when in Dry environment, or when conserving water Plants make live in Desert or Salt Marsh where water is limited Example: Cacti, orchids, pineapple Fix CO2 at night rather than during the day Then release CO2 to the Calvin Cycle during the day.