Photosynthesis Chapter 7 Sections

Figure 7.0_2

Photosynthesis Photo “light”; synthesis “putting together” Light 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 Chlorophyll

7.1 Autotrophs are the producers of the biosphere Autotrophs (self-feeders) – Photoautotrophs: light energy, photosynthesis Producers What products do we get from plants? – Chemoautotrophs: inorganic molecules Heterotrophs (other eaters) – consumers © 2012 Pearson Education, Inc.

Figure 7.1A-D

7.2 Photosynthesis occurs in chloroplasts in plant cells Chloroplasts are the major sites of photosynthesis in green plants. Chlorophyll – A light-absorbing pigment in chloroplasts, – is responsible for the green color of plants – plays a central role in converting solar energy to chemical energy. © 2012 Pearson Education, Inc.

Figure 7.2 Leaf Cross Section Mesophyll CO 2 O2O2 Vein Leaf Stoma Mesophyll Cell Chloroplast Thylakoid Thylakoid space Stroma Granum Inner and outer membranes

7.3 Scientists traced the process of photosynthesis using isotopes Scientists have known since the 1800s that plants produce O 2. But does this oxygen come from carbon dioxide or water? – Research using a heavy isotope of oxygen, 18 O, showed that oxygen produced by photosynthesis comes from H 2 O. (Neil) © 2012 Pearson Education, Inc.

7.3 SCIENTIFIC DISCOVERY: Scientists traced the process of photosynthesis using isotopes Experiment 2: 6 CO 2  12 H 2 O → C 6 H 12 O 6  6 H 2 O  6 O 2 Photosynthesis produces billions of tons of carbohydrate a year. Where does most of the mass of this huge amount of organic matter come from? © 2012 Pearson Education, Inc.

7.4 Photosynthesis is a redox process, as is cellular respiration Photosynthesis, like respiration, is a redox process. – CO 2 becomes reduced to sugar as electrons along with hydrogen ions from water are added to it. – Water molecules are oxidized when they lose electrons along with hydrogen ions. © 2012 Pearson Education, Inc. Becomes reduced Becomes oxidized

7.4 Photosynthesis Summary Requires energy (light) – Endergonic light energy is captured by chlorophyll molecules to boost the energy of electrons, light energy is converted to chemical energy, Light reactions chemical energy is stored in the chemical bonds of sugars. Calvin cycle © 2012 Pearson Education, Inc.

7.5 Photosynthesis Overview Photosynthesis occurs in two metabolic stages. 1.The light reactions occur in the thylakoid membranes. In these reactions water is split, providing a source of electrons and giving off oxygen as a by-product, ATP is generated NADP+ is reduced to NADPH ATP and NADPH are used in the Calvin cycle © 2012 Pearson Education, Inc.

7.5 Photosynthesis Overview 2.The second stage is the Calvin cycle, which occurs in the stroma of the chloroplast. The Calvin cycle is a cyclic series of reactions that assembles sugar molecules using CO 2 and the energy-rich products of the light reactions. (ATP and NADPH) CO 2 is incorporated into organic compounds in a process called carbon fixation. Also called the Light independent reaction or Dark reactions Why? © 2012 Pearson Education, Inc.

Figure 7.5_s3 Light Reactions (in thylakoids) Calvin Cycle (in stroma) Sugar O2O2 NADPH ATP NADP + ADP P H2OH2O CO 2 Light Chloroplast

7.6 Visible radiation absorbed by pigments drives the light reactions Sunlight contains energy called electromagnetic energy or electromagnetic radiation. – Electromagnetic energy travels in waves, and the wavelength is the distance between the crests of two adjacent waves. © 2012 Pearson Education, Inc.

7.6 Visible radiation absorbed by pigments drives the light reactions Light behaves as discrete packets of energy called photons. – A photon is a fixed quantity of light energy. – The shorter the wavelength, the greater the energy of the photon © 2012 Pearson Education, Inc.

Figure 7.6A Increasing energy 10  5 nm 10  3 nm 1 nm 10 3 nm 10 6 nm 1 m 10 3 m 650 nm Wavelength (nm) Visible light Gamma rays Micro- waves Radio waves X-rays UVInfrared

7.6 Visible radiation absorbed by pigments drives the light reactions Plant pigments – Light absorbing molecules – Built into the thylakoid membranes – Blue green and red orange absorbed – Absorb light energy © 2012 Pearson Education, Inc. Animation: Light and Pigments

7.6 Visible radiation absorbed by pigments drives the light reactions Chloroplasts contain several different pigments – Chlorophyll a absorbs blue-violet and red light and reflects green. – Chlorophyll b absorbs blue and orange and reflects yellow-green. – Carotenoids broaden the spectrum of colors that can drive photosynthesis and provide photoprotection – Antioxidant in cells © 2012 Pearson Education, Inc.