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Photosynthesis!. Obtaining NRG. Autotrophs Use NRG from the sun to make organic compounds Heterotrophs Must get NRG from food instead of directly from sunlight. ATP=NRG!. ATP= adenosine triphosphate ATP is the molecule that DIRECTLY provides NRG to do cellular work
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Obtaining NRG • Autotrophs • Use NRG from the sun to make organic compounds • Heterotrophs • Must get NRG from food instead of directly from sunlight
ATP=NRG! • ATP= adenosine triphosphate • ATP is the molecule that DIRECTLY provides NRG to do cellular work • Chemical NRG from organic molecules is transferred to ATP
ATP • ATP is made up of five parts: • The sugar= ribose • The base= adenine • 3 phosphate groups
ATP cont. • When ATP loses the 3rd phosphate: • NRG is released • This NRG is used by the cell • ADP is left
Obtaining NRG • PHOTOSYNTHESIS • Converts light NRG from sun into chemical NRG • Series of reactions known as biochemical pathways
Photosyn. Overview • The oxygen (O2) and some organic compounds produced by photosynthesis are used by cells in process called cellular respiration.
Chloroplasts • Chloroplasts have double membranes • Outer Membrane • Separates chloroplast from cytoplasm • Thylakoids • Inner membranes • Numerous • Grana • Stacks of thylakoids • Stroma • Fluid-like space
Overview cont. • Photosynthesis can be divided into two stages: • LIGHT REACTIONS • Light NRG is converted to chemical NRG • Temporarily stored in ATP and the NRG carrier molecule NADPH (nicotinamide adenine dinucleotide phosphate-oxidase) • CALVIN CYCLE • Organic compounds are formed using CO2 and the chemical NRG stored in ATP and NADPH
Capturing Light NRG • The light reactions begin with the absorption of light in chloroplasts • Found in cells of plants, some bacteria, and algae
Capturing Light NRG • Light and Pigments • White light from the sun is composed of an array of colors called the visible spectrum • Pigments: • Absorb certain colors of light and reflect or transmit the other colors
Capturing Light NRG • Chloroplast Pigments: • Located in the membrane of the thylakoids are several pigments: • 1. Chlorophylls: chlorophyll a and chlorophyll b • 2. Carotenoids: yellow, orange, and brownish
Light NRG to Chemical NRG • PHOTOSYSTEM: • Grouped clusters of a few hundred pigment molecules in the thylakoid membrane • By absorbing light, pigment molecules in the photosystems (I and II) acquire some of the NRG carried by the light
Steps 1 and 2 • In each photosystem, the acquired NRG is passed quickly to other pigment molecules until it reaches a specific pair of chlorophyll a molecules. • The acquired NRG forces electrons to enter a higher NRG level in the two chlorophyll a molecules of photosystem II • These excited electrons now have NRG to leave the chlorophyll a.
Step 3 • The acceptor of these electrons from photosystem II is called the primary electron receptor, which donates the electrons to the electron transport chain. • Electrons move from molecule to molecule, losing most of the acquired NRG! • The NRG they lose is used to move H+ into the thylakoid
Step 4 • Light is absorbed by photosystem II at the same time it is absorbed by photosystem I. • Electrons move from chlorophyll a to another primary electron receptor. • Electrons lost from chlorophyll a are replaced by electrons that have passed through the electron transport chain from photosystem II.
Step 5 • Electrons are then donated to another chain, which brings the electrons to the side of the thylakoid membrane that faces the stroma. • In the stroma, the electrons combine with a proton and NADP+. This causes the NADP+ to be reduced to NADPH.
Electron Replacement • Electrons from photosystem II replace electrons that leave photosystem I. • Replacement electrons are provided by the splitting of water molecules • For every two water molecules that are split, four electrons become available
Products? • Oxygen produced when water molecules are split diffuses out of the chloroplast and leaves the plant!
Light to Chemical NRG • Making ATP in Light Reactions: • Light reactions produce ATP through chemiosmosis! • During chemiosmosis, the movement of protons through ATP synthase into the stroma releases NRG, then used to produce ATP.
Carbon Fixation • CALVIN CYCLE • The ATP and NADPH produced in the light reactions drive this stage • CARBON FIXATION • CO2 is incorporated into organic compounds, a process called carbon fixation
Carbon Fixation • CALVIN CYCLE • Occurs in the stroma • Assisted by enzymes to produce three carbon sugars • Most three carbon sugars (PGAL) generated in the Calvin Cycle are converted to five carbon sugars (RUBP). • Some of the three carbon sugars leave the cycle and are used to make organic compounds that are stored as NRG for later
Factors Affecting Photosynthesis • Light Intensity • Rate increases as light intensity increases • More electrons get excited in both photosystems! • Once all electrons are excited, the rate levels off.
Factors Affecting Photosynthesis • Carbon Dioxide Levels • Increasing levels of CO2 also stimulate photosynthesis until the rate levels off.
Factors Affecting Photosynthesis • Temperature • As temperature increases, photosynthesis increases to a maximum and then decreases with further increases in temperature. • Too high of a temperature will denature key enzymes!
