8.2 Photosynthesis: An Overview Lesson Overview 8.2 Photosynthesis: An Overview

Light Photosynthesis Energy from the sun travels to Earth in the form of light. Sunlight is a mixture of different wavelengths visible spectrum- different wavelengths that we differentiate as different colors: red, orange, yellow, green, blue, indigo, and violet.

Chlorophyll molecules absorb blue light & some red light. Pigments pigments- light-absorbing molecules A red apple appears red because the pigment in the apple’s skin absorbs blue light & reflects red. So we see RED Chlorophyll molecules absorb blue light & some red light. Reflect green-so we see GREEN

Pigments Two types of chlorophyll in plants: chlorophyll a & chlorophyll b, absorb light very well in the blue-violet and red regions of the visible spectrum, but not in the green region, as shown in the graph. .

Pigments Plants also contain carotenoids- red, orange, or yellow pigments, and include the familiar compound carotene, which gives carrots their color. accessory pigments-pass their absorbed energy to chlorophyll because can’t transfer energy directly to the photosynthetic pathway

Pigments Most of the time chlorophyll overwhelms the other pigments- as temperatures drop, chlorophyll molecules break down and red and orange pigments appear. In some trees, like maples, glucose is trapped in the leaves after photosynthesis stops. Sunlight and the cool nights of autumn cause the leaves to turn this glucose into a red color. The brown color of trees like oaks is made from wastes left in the leaves.

Chloroplasts Photosynthesis takes place inside chloroplasts. thylakoids- saclike photosynthetic membranes which are interconnected Grana- stacks of thylakoids

Pigments are located in the thylakoid membranes. Chloroplasts Pigments are located in the thylakoid membranes. Stroma- fluid portion outside of the thylakoids

Energy Collection Light is a form of energy Compounds that absorb light absorb energy Chlorophyll absorbs visible light especially well. When chlorophyll absorbs light, a large fraction of the light energy is transferred to electrons. These high-energy electrons make photosynthesis work.

High-Energy Electrons NADP+ (nicotinamide adenine dinucleotide phosphate) is a carrier molecule. NADP+ accepts and holds two high-energy electrons, along with a hydrogen ion (H+). In this way, it is converted into NADPH. The NADPH can then carry the high-energy electrons to chemical reactions elsewhere in the cell.

An Overview of Photosynthesis Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into high-energy sugars and oxygen.

An Overview of Photosynthesis Plants use sugars generated by photosynthesis to produce complex carbohydrates such as starches, and to provide energy for the synthesis of other compounds, including proteins and lipids, cellulose.

Light-Dependent Reactions Photosynthesis involves two sets of reactions. Light-dependent reactions- uses light and light-absorbing pigments to produce ATP and NADPH. reactions take place within the thylakoid membranes

Light-Dependent Reactions Water is required as a source of electrons and hydrogen ions. Oxygen is released as a byproduct.

Light-Independent Reactions Light-independent reactions / Calvin Cycle use CO2 from the atmosphere & ATP and NADPH from the light-dependent reactions to produce high-energy sugars from carbon dioxide.

Light-Independent Reactions No light is required to power the light-independent reactions. The light-independent reactions take place in the stroma.