Chlorophyll α By far the most common photosynthetic pigment in plants, photosynthetic protists, and cyanobacteria. Chlorophyll α absorbs violet and red light, so it appears green. Most types of photosynthetic organisms use a mixture of pigments for photosynthesis. In leaves of typical plants, chlorophyll is usually abundant that it masks the colors of all the other pigments. Thus, giving the green color.

Only light between 380 – 750 nm drive photosynthesis. Electromagnetic Spectrum

Chemical Energy ATP Energy comes in many forms including light, heat, and electricity. Energy can be stored in chemical compounds, too. An important chemical compound that cells use to store and release energy is adenosine triphosphate, abbreviated ATP. ATP is used by all types of cells as their basic energy source. ATP consists of: adenine ribose (a 5-carbon sugar) 3 phosphate groups Adenine Ribose 3 Phosphate groups

Storing Energy ADP has two phosphate groups instead of three. A cell can store small amounts of energy by adding a phosphate group to ADP. Fully charged battery + Adenosine Triphosphate (ATP) Partially charged battery Adenosine Diphosphate (ADP) + Phosphate

Releasing Energy Energy stored in ATP is released by breaking the chemical bond between the second and third phosphates. ADP 2 Phosphate groups

What is the role of ATP in cellular activities? The energy from ATP is needed for many cellular activities, including active transport across cell membranes, protein synthesis and muscle contraction. ATP’s characteristics make it exceptionally useful as the basic energy source of all cells. Most cells have only a small amount of ATP, because it is not a good way to store large amounts of energy. Cells can regenerate ATP from ADP as needed by using the energy in foods like glucose.

Engelmann’s Experiment Botanist Theodor Engelmann designed his experiment to test his hypothesis that the color of light affects photosynthesis. It had long been known that photosynthesis releases oxygen, so Engelmann used the amount of oxygen released by photosynthetic cells as a measure of how much photosynthesis was occurring in them.

Engalmann directed light through a prism so that bands of colors crossed a water droplet on a microscope slide. The water held a strand of Chladophora and oxygen-requiring bacteria. The bacteria clustered around the algal cells that were releasing the most oxygen – the ones that were most actively engaged in photosynthesis. Those cells were under red and violet light.

Absorption spectra ROY G BIV Engelmann’s experiment allowed him to correctly identify the colors of light most efficient at driving photosynthesis. His results constituted an absorption spectrum – a graph that shows how efficiently the different wavelengths of light are absorbed by a substance. Peaks in the graph indicate wavelengths of light that the substance absorbs best.

Chloroplast An organelles that specializes in photosynthesis in plants and many protists. Plant chloroplast have two outer membranes , and are filled with a semifluid matrix call the stroma. Stroma contains the chloroplast’s DNA, some ribosomes, and an inner, much-folded thylakoid membrane. The folds of a thylakoid membrane typically forms stacks of disks that are connected by channels. The space inside all of the disks and channels is a single, continuous compartments. Many thylakoids together make a granum.

6CO2 + 6H2O C6H12O6 + 6O2 Light

Photosynthesis Photosynthesis is actually a series of many reactions that occur in two stages. Light-dependent Light-independent

Light-dependent Reaction First stage; the energy of light gets converted to the chemical bond energy of ATP. Typically, the co-enzyme NADP+ accepts electrons and hydrogen ions, thus becoming NADPH. Oxygen atoms released escape from the cells as O2. NADP+ accepts and holds 2 high-energy electrons along with a hydrogen ion (H+). This converts the NADP+ into NADPH.

Light-Dependent Reactions The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. The light-dependent reactions take place within the thylakoid membranes of chloroplasts. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Photosynthesis begins when pigments in photosystem II absorb light, increasing their energy level. Photosystem II The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. The light-dependent reactions take place within the thylakoid membranes of chloroplasts. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall These high-energy electrons are passed on to the electron transport chain. Photosystem II Electron carriers High-energy electron Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Enzymes on the thylakoid membrane break water molecules into: Photosystem II 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. Electron carriers High-energy electron Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall hydrogen ions oxygen atoms energized electrons Photosystem II + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. Electron carriers High-energy electron Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The energized electrons from water replace the high-energy electrons that chlorophyll lost to the electron transport chain. Photosystem II + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. High-energy electron Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall As plants remove electrons from water, oxygen is left behind and is released into the air. Photosystem II + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. The light-dependent reactions take place within the thylakoid membranes of chloroplasts. High-energy electron Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The hydrogen ions left behind when water is broken apart are released inside the thylakoid membrane. Photosystem II + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. High-energy electron Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Energy from the electrons is used to transport H+ ions from the stroma into the inner thylakoid space. Photosystem II + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall High-energy electrons move through the electron transport chain from photosystem II to photosystem I. Photosystem II + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. Photosystem I Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Pigments in photosystem I use energy from light to re-energize the electrons. + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. Photosystem I Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall NADP+ then picks up these high-energy electrons, along with H+ ions, and becomes NADPH. + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 2 NADP+ 2 2 NADPH Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall As electrons are passed from chlorophyll to NADP+, more H+ ions are pumped across the membrane. + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 2 NADP+ 2 2 NADPH Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Soon, the inside of the membrane fills up with positively charged hydrogen ions, which makes the outside of the membrane negatively charged. + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 2 NADP+ 2 2 NADPH Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The difference in charges across the membrane provides the energy to make ATP + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 2 NADP+ 2 2 NADPH Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall H+ ions cannot cross the membrane directly. ATP synthase + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 2 NADP+ 2 2 NADPH Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The cell membrane contains a protein called ATP synthase that allows H+ ions to pass through it ATP synthase + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 2 NADP+ 2 2 NADPH Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall As H+ ions pass through ATP synthase, the protein rotates. ATP synthase + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 2 NADP+ 2 2 NADPH Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall As it rotates, ATP synthase binds ADP and a phosphate group together to produce ATP. ATP synthase + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. ADP 2 NADP+ 2 2 NADPH Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Because of this system, light-dependent electron transport produces not only high-energy electrons but ATP as well. ATP synthase + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. ADP 2 NADP+ 2 2 NADPH Copyright Pearson Prentice Hall

Light-independent Reaction/Calvin Cycle Second stage; runs on energy delivered by the ATP and NADPH formed in the first stage. That energy drives the synthesis of glucose and other carbohydrates from carbon dioxide and water. The Calvin cycle uses ATP and NADPH from the light-dependent reactions to produce high-energy sugars. Because the Calvin cycle does not require light, these reactions are also called the light-independent reactions (aka dark reactions).

Copyright Pearson Prentice Hall Six carbon dioxide molecules enter the cycle from the atmosphere and combine with six 5-carbon molecules. CO2 Enters the Cycle The Calvin cycle uses ATP and NADPH to produce high-energy sugars. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The result is twelve 3-carbon molecules, which are then converted into higher-energy forms. The Calvin cycle uses ATP and NADPH to produce high-energy sugars. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The energy for this conversion comes from ATP and high-energy electrons from NADPH. Energy Input 12 12 ADP 12 NADPH The Calvin cycle uses ATP and NADPH to produce high-energy sugars. 12 NADP+ Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Two of twelve 3-carbon molecules are removed from the cycle. Energy Input 12 12 ADP 12 NADPH The Calvin cycle uses ATP and NADPH to produce high-energy sugars. 12 NADP+ Copyright Pearson Prentice Hall

The molecules are used to produce sugars, lipids, amino acids and other compounds. 12 12 ADP 12 NADPH The Calvin cycle uses ATP and NADPH to produce high-energy sugars. 12 NADP+ 6-Carbon sugar produced Sugars and other compounds Copyright Pearson Prentice Hall

The 10 remaining 3-carbon molecules are converted back into six 5-carbon molecules, which are used to begin the next cycle. 12 12 ADP 6 ADP 12 NADPH 6 The Calvin cycle uses ATP and NADPH to produce high-energy sugars. 12 NADP+ 5-Carbon Molecules Regenerated Sugars and other compounds Copyright Pearson Prentice Hall

The two sets of photosynthetic reactions work together. The light-dependent reactions trap sunlight energy in chemical form. The light-independent reactions use that chemical energy to produce stable, high-energy sugars from carbon dioxide and the hydrogen from water.