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Photosynthesis. = Process by which light energy is converted into chemical energy stored in organic compounds. Important Terms:. Autotroph = Organisms that make their own food. - Ex. Plants, cyanobacteria and algae. Heterotroph = Organisms that cannot make their own food.
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Photosynthesis = Process by which light energy is converted into chemical energy stored in organic compounds.
Important Terms: • Autotroph = Organisms that make their own food. • - Ex. Plants, cyanobacteriaand algae. • Heterotroph = Organisms that cannot make their own food. • - Ex. Animals (including humans), fungi, some protista –like protozoa (paramecium amoeba). • Biochemical Pathway = A series of reactions in which the product of one is a reactant in the next reaction.
Light= Electromagnetic radiation in the form of a wave. • If you pass white light through a prism, you break it up into its’ different wavelengths and you see the ROYGBIV rainbow. • Different colors in the rainbow have different wavelengths and frequencies. Ex. purple have a short wavelength and red have long wavelengths.
Wavelength Frequency • The distance between similar points on consecutive waves. • The number of waves to pass a certain point in a specific amount of time (usually 1 second).
The highest percentage of visible light is yellow – green (tennis ball green) Why do you think plants have green pigments
Waves can be: • Absorbed = Taken in by what they strike. Different pigments absorb different colors • Reflected = Sent back from what they strike. • Refracted = Bent to head in a different direction (like looking at a spoon in a glass of water). • The colors we see are the reflected colors
The general equation for photosynthesis is: CO2 + H2O + light E --- (CH2O) + O2 • The specific equation for the production of glucose during photosynthesis is: 6CO2 + 6H2O + light E --- C6H12O6 + 6O2
Stage 1 – Light Reactions • Takes place in the thylakoid membranes of the chloroplasts in the plant cell.
Pigments of Photosynthesis: • Chlorophyll a, chlorophyll b, and carotenoids are pigments in thylakoid membranes. • Chlorophyll looks green because these wavelengths of light are reflected and the reds, etc. are absorbed. • Chlorophyll a = main pigment of photosynthesis. • Chlorophyll b and the carotenoids are accessory pigments and allow the cell to use additional wavelengths of light. • The accessory pigments pass the E along to chlorophyll a.
Photosystems: • A cluster of pigments is called a photosystem. • There are two photosystems in the cell, abbreviated PSI and PSII.
Electrons in the chlorophyll a of PSI and PSII get excited to higher E levels when light E is absorbed. • When this happens, Chlorophyll a is oxidized as it loses energized e-. • These e- are replaced in chlorophyll by the splitting of water by an enzyme as follows: • 2H2O - 4H+ + 4e- + O2
Electron Transport Chain • = Aseries of molecules in the membrane that pass along e-. • As the e- are passed, they lose E which is used to perform active transport and move H+ into the thylakoid membranes. • After moving down the e- transport chain, the e- are moved to the stroma where they combine with H+ and reduce NADP+ to NADPH.
NADPH • NADPH carries E. • It is used in Stage 3 of photosynthesis called the Dark Reactions.
Stage 2 – Chemiosmosis • = A process that uses the H+gradient and ATP synthase to make ATP by adding a phosphate group to ADP. • ATP synthase is a membrane protein in the thylakoid membrane that functions as both a channel and an enzyme. • As H+ diffuses back out of the thylakoid through this enzyme/channel, ATP is made when a phosphate is added to ADP. • ATP carries E and is used in Stage 3 of photosynthesis called the Dark Reactions.
Stage 3 – Dark Reactions • This set of reactions is called the Calvin Cycle. • “Carbon Fixation” is what happens here as CO2 is incorporated into organic compounds. • This stage happens in the stroma. • CO2 diffuses into the stroma and is combined with other carbon containing compounds. • These C compounds are changed using NADPH and ATP made in Stages 1 and 2 respectively. • All starting materials are recycled in this process. • Some of the C compounds made go out of the cycle to make carbohydrates such as glucose.
Different Types of Photosynthesis: • 1. C4 plants: • They live in hot, dry climates and so close their stomata = pores on the leaf through which gases are exchanged, so that they lose less water. • Consequently, they have a low concentration of CO2 available for photosynthesis and a high concentration of O2 around. • They have special enzymes that fix the CO2 into a 4-carbon molecule, even when CO2 is low. These 4-C molecules release CO2and eventually enter the Calvin cycle. • Corn and grass are C4 plants.
2. CAM Pathway • Some plants keep their stomata open at opposite times then what is usual; they are open at night and closed during the day. • Such plants use CO2 to carbon fix at night, then, during the day the CO2 is released from these compounds and enters the Calvin cycle. • Such plants grow slower but lose less water. • Examples : pineapple and cactus.
Factors affecting the rate of photosynthesis: • Light intensity : As this increases, so does the rate of photosynthesis until a plateau is reached where all the pigment molecules are being used. • CO2 Concentration : As this increases, so does the rate of photosynthesis until a plateau is reached where all the chlorophyll molecules, enzymes, resources of the cell are being used maximally. • Temperature : Enzymes that catalyzes all these reactions are temperature dependent and so the rate of photosynthesis will increase to a certain point then decline since the enzymes are denaturing.
