Photosynthesis: (Overview)
Utilization of light energy and inorganic compounds (carbon dioxide and water) to create organic compounds (carbohydrates, proteins and lipids).Light energy is converted to chemical energy
Absorption of sunlight:
Sunlight is made up of a variety of wavelengths of visible light. These wavelengths make up the different colors.Pigments are chemical substances used within photosynthesis. Pigments absorb light and reflect others. For example, a pigment that reflects the green wavelength and absorbs all the other colors will appear green. In photosynthesis, chlorophyll is the main pigment that is used. It appears to be green.
Light and Photosynthesis:
Chlorophyll absorbs light energy which is used in some integral components of photosynthesis:ADP and a phosphate group are joined to form ATP
Photolysis, which is the separation of molecules with light, is used to release hydrogen and oxygen from split water molecules. The oxygen is released into the atmosphere as a waste product while the hydrogen is later used to make carbohydrates.
The intensity of the light can also increase the rate of photosynthesis. The rate can rise until another factor prevents the rate of photosynthesis from increasing. This factor is called the limiting factor. When a limiting factor is converged upon, the rate simply plateaus and remains the same. So increasing light intensity beyond the limiting factor really has no effect on the rate of photosynthesis that have reach a plateau.
Carbon dioxide and Photosynthesis:
When the concentration of carbon dioxide is low, the rate of photosynthesis rises. When the concentration of carbon dioxide is high, any increases will not affect the rate of photosynthesis since it has already reached a plateau.Carbon dioxide provides the carbon used to make organic molecules within photosynthesis. Carbon fixation is the conversion of carbon dioxide into solid or liquid carbon compounds used in photosynthesis. This also requires ATP to provide energy and hydrogen from photolyzed water. Shortages of hydrogen will occur during darkness because photolysis can not occur. This will stop carbon fixation.
Temperature and Photosynthesis:
The rate of photosynthesis is extremely low during cooler temperatures. As the temperature rises, so does the rate photosynthesis until it reaches a maximum point and the rate will actually decrease f the temperature continues to rise.When the temperature is too high, the enzymes used to catalyze the process of carbon fixation will denature and become unusable.
The optimal temperature for most plants is between 25 and 35 degrees Celsius
Action Spectra:
Chlorophyll in plants can only absorb certain wavelengths of light. An absorption spectrum graph will portray the percentage of each wavelength that is absorbed by pigments. The action spectrum, in turn, describes each wavelength of light in relativity to the rate of photosynthesis.Limiting Factors:
Light intensity, temperature and carbon dioxide concentration are all factors that affect the rate of photosynthesis. The factor that is furthest from its most ideal point will be the limiting factor. This is the factor that is withholding the rate of photosynthesis. For example, to build a desktop computer, you will need a monitor, a system unit and a keyboard. If there are 4 monitors, 6 system units and 3 keyboards then how many fully intact computers can you build? The answer would be 3. The number of computers built is limited by the component that has the lowest number of parts. The limiting factor, therefore, would the 3 keyboards.Light Dependent and Independent Reactions:
Photosynthesis generally consists of a two step process. The first step is dependent on light to convert light energy into chemical energy. The second step does not require light. This step creates organic molecules using the chemical energy made in the light dependent reactionLight Dependent Reactions
The light dependent reactions takes place on the thylakoid membrane. It involve a cyclic or non-cyclic processes.Non-cyclic Photophosphorylation:
Light is absorbed by the chlorophyll in photosystems I and II. This causes electrons within the chlorophyll to become excited. This is known as photoactivation.The excited electrons from photosystem II enter the electron transport chain which is made up of a series of carriers. This produces ATP via chemiosmosis (the movement of ions down their electrochemical gradient and across a selectively permeable membrane). As electrons move through the carriers they release energy which helps in the production of ATP. Some of the energy released is used to pump H+ ions into the thylakoid space from the stroma. The H+ ions then flow back into the stroma through another carrier called the ATP synthase to produce the ATP by binding ADP with an inorganic phosphate (P). ATP synthase acts as a ATP generator in which H+ is the energy that cranks and powers the generator.
The now low energy electrons continue onto photosystem I where they are re-energized by the sun's energy. A second electron acceptor receives the energized electrons and they are used to reduce NADP+. The NADP+ combines with the electron and a H+ from the stroma (the H+ was pumped out of the ATP synthase in photosystem II) to create NADPH. The NADPH and the ATP created from both photosystems will be used in the light independent reactions of photosynthesis.
