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8.3 The Process of Photosynthesis
8.3 The Process of Photosynthesis
Light-Dependent Reactions: ATP and NADPH
The light-dependent reactions occur in the thylakoids of chloroplasts.
Light-Dependent Reactions: ATP and NADPH
The light-dependent reactions occur in the thylakoids of chloroplasts.
Photosystems - groups of chlorophyll and proteins in the thylakoid. Absorb sunlight and generate high energy electrons that are used to make sugars.
Photosystem II● Water molecules provide new electrons to chlorophyll. ● Enzymes break up the water molecules into 2 electrons, 2 Hydrogen
atoms, and 1 oxygen atom.
Photosystem II● Oxygen is released into the air. ● The H+ ions are released inside the thylakoid.
Electron Transport ChainElectron transport chain - a system that carries high-energy electrons during ATP-generating reactions.
Electron Transport ChainElectron transport chain takes energy from the electrons and uses it to pump H+ ions from the stroma into the thylakoid space.
Electron Transport Chain
Photosystem I - pigments use energy from light to re-energize the electrons
At the end of a short second electron transport chain, NADP+ molecules in the stroma pick up the high-energy electrons and H+ ions at the outer surface of the thylakoid membrane to become NADPH.
The difference in both charge and H+ ion concentration across the membrane creates a gradient, or build up, of hydrogen inside the thylakoid. The H+ now wants to diffuse out of the thylakoid.
ATP synthase spans the thylakoid membrane and allows H+ ions to pass through it, while creating ATP as result. This is called chemiosmosis.
Light-Independent Reactions: Producing Sugars
Light-independent reactions aka the Calvin cycle - plants use the energy that ATP and NADPH contains to build stable high-energy carbohydrate compounds that can be stored for a long time.
Light Independent Reactions
Summary of the Calvin CycleCalvin cycle - 6 CO2 → 1 6 carbon sugar.
The energy for the reactions is supplied by compounds produced in the light-dependent reactions.
Temperature, Light, and Water● The reactions of photosynthesis are made possible by enzymes that function best
between 0°C and 35°C.● High light intensity increases the rate of photosynthesis.● After the light intensity reaches a certain level, however, the plant reaches its
maximum rate of photosynthesis, as is seen in the graph.
Photosynthesis Under Extreme Conditions● In order to conserve water, most
plants under bright, hot conditions close the small openings in their leaves that normally admit carbon dioxide.
● This causes carbon dioxide within the leaves to fall to very low levels, slowing down or even stopping photosynthesis.
● C3 Plants, like soy, oats, wheat and rice, when the climate is hot and dry, these plants close their stomata. This prevents CO2 from entering the plant cells.
● Photorespiration is where no ATP and no sugar is made in the plant cell due to the fact that carbon dioxide is depleted and oxygen is building up.
C4 Plants, like corn and sugarcane keep their stomata closed most of the time to conserve water. They are able to prevent photorespiration by using special enzymes that continue photosynthesis even when carbon dioxide levels are low.
CAM plants, like cacti and pineapples, conserve water by opening their stomata and admitting CO2 only at night. The plant is then able to bank a large amount of CO2 to continue photosynthesis during the day.
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Lab Report Notes
● Show examples ● Discuss the importance of photosynthesis in your conclusion. ● Create a table or a graph of the results. ● Discuss the specific data, the numbers! ● Capitalize “i” ● Reference section - cite at least one source in APA format.
Plant Plant 1 (control)
Plant 2 (sealed with bromothymol blue)
Plant 3 (not sealed with bromothymol blue)
Color change?
None Yes, to yellow.
None
Lab Report
Conclusion● Review your results. Discuss your actual results (color
changes!). ● Review your hypothesis. Discuss how you could change it. ● Review how you performed the experiment. What would you
change? What improvements could you make? Analysis ● Answer the three questions on the handout.
Lab Report
Analysis ● Answer the three questions on the handout. References ● Cite two sources in APA format. ● Example - Charles Law. (2012). Retrieved from http://www.chemteam.info/GasLaw/Gas-Charles.html
Website heading.
YearCopy of the website link.
