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Photosynthesis (The earth is solar powered! ((((((((The Nature of Sunlight…

- - - - The Nature of Sunlight :sunny:
        
        chloroplasts are powered by the sun
        
        light is a form of energy known as electromagnetic energy
        
        electromagnetic waves are disturbances of electric and magnetic fields
        
        electromagnetic energy travels in rhythmic waves analogous to those created by dropping a pebble into a pond
        
        wavelength is the distance between the crests of electromagnetic waves
        
        wavelengths range from less than a nanometer (gamma) to more than a kilometer (radio); the entire range of radiation is known as the electromagnetic spectrum
        
        the segment most important to life is about 380 nm to 750 nm in wavelength
        the above band description is known as visible light bc it can be detected as various colors by the human eye
        photons are not tangible, but they make lights behave as though it consists of discrete particles (the particles are photons)
        
        spectrophotometer = the measurement of the ability of a pigment to absorb various wavelengths of light
        
        absorption spectrum = a graph plotting a pigment's light absorption versus wavelength
        
        chlorophyll a = the key light-capturing pigment that participates directly in the light reactions; suggests that violet-blue and red light work best for photosynthesis (since they are absorbed) and green is the least effective color
        chlorophyll b = the accessory pigment
        
        The Two Stages of Photosynthesis
        
        Photosynthesis Equation
        
        6CO2 + 6H2O + Light energy = C6H12O6 + 6O2
        
        the O2 given off by planys is derived from H2O and not from CO2
        
        the chloroplasts split water into hydrogen and oxygen
        
        before the discovery of ^above^, scientists thought that photosynthesis split carbon dioxide and then added water to the carbon
        
        Photosynthesis as a Redox Process
        
        both photosynthesis and cellular respiration have redox reactions
        
        basically, water is split, and its electrons are transferred along with hydrogen ions from the water to carbon dioxide, reducing it to sugar
        because the electrons increase in potential energy as they move from water to sugar, this process requires energy - in other words it is endergonic
        the energy boost that occurs during photosynthesis is provided by light
        
        the two stages of photosynthesis are known as the light reactions (the photo part) and the Calvin cycle (the synthesis part)
        
        Light Reactions
        
        this step convert solar energy to chemical energy
        
        water is split, giving a source of electrons and protons (H ions) and giving off oxygen as a by-product
        light absorbed by chlorophyll drives a transfer of the electrons and H+ ions from water to an acceptor called NADP+ where they are temeporarelly stored
        using solar energy, it converts NADP+ to NADPH by adding a pair of electrons along with an H+
        these reactions also generate ATO (using chemiosmosis to power the addition of a phosphate group to ADP, a process called phosphophorylation
        light energy is initially converted to chemical energy in the form of NADPH and ATP (NADPH acts as 'reducing power' and ATP is the versalitile energy currency of cells
        THIS PART DOES NOT CREATE ANY SUGAR
        
        Calvin Cycle
        
        the cycle begins by using carbon dioxide from the air and incorporating it into organic molecules already present in the chloroplast
        this incorporation of carbon into organic compounds is called carbon fixation
        the Calvin cycle then reduces the fixed carbon to carbohydrate by adding electrons, the reducing power is provided by NADPH (which was acquired during the light reactions)
        to convert the carbon dioxide to carbohydrate, this cycle also requires chemical energy in the form of ATP (also made by the light reactions)
        
        THE CALVIN CYCLE MAKES SUGAR BUT ONLY SO BC OF THE NADPH AND ATP PRODUCED FROM THE LIGHT REACTIONS
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        C4 Plants
        
        these plants preface the Calvin cycle with an alternate mode of carbon fixation that forms 4-carbon compound as its first product
        
        examples of C4 plants are sugarcane and corn (members of the grass family)
        there are two distinct types of photosynthetic cells: bundle-sheath cells and mesophyll cells
        bundle-sheath cells are arranged into tightly packed sheaths around the veins of the leaf. Between the bundle-sheath and the leaf surface are more loosely arranged mesophyll cells, which are closely associated with bundle-sheath cells
        
        The first step is carried out by an enzyme (present in only mesophylls) called PEP carboxylase
        
        this enzyme adds carbon dioxide to phosphoenolpyruvate (PEP) forming the 4-carbon product oxaloacetate
        PEP carboxylase has a higher affinity for CO2 than rubisco which means that PEP carboxylase can fix carbon efficiently when runisco cannot
        
        After the CO2 is fixed in the mesophyll cells, the 4-carbon products are exported to bundle-sheath cells through plasmodesmata
        
        Within the bundle-sheath cells, the 4-carbon compounds release CO2 which is re-fixed into organic materialby rubisco and the Calvin cycle
        
        the same reaction regenerate pyruvate, which is then transferred to the mesophyll cells, There, ATP is used to convert pyruvate to PEP which allows the cycle to continue
      - Photorespiration
      - in most plants, initial fixation of carbon occurs by rubisco
      - these plants are called C3 plants because the first organic product of the carbon fixation is a three-carbon compound (3-phosphoglycerate)
        examples of C3 plants include rice, soy, and wheat
      - photorespiration - instead of fixing carbon dioxide molecules during low photosyntheic points of environments, rubisco starts fixing oxygen instead
      - this process uses ATP rather than generating it
      - this process also produces no sugar ---- this process actually decreases photosynthetic output by siphoning organic material from the Calvin cycle and releasing CO2 that would otherwise be fixed
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        CAM Plants :cactus:
        
        a second photosynthetic adaptation to arid conditions has evolved in many succulent plants, cati, pineapples, and some other plant families
        these plants open their stomata during the night and close them during the day (reverse of other plants)
        closing the stomata helps them conserve water, but it also helps prevent CO2 from entering the leaves
        
        during the night when their stomata are open, the plants take CO2 and incorperate it into different organic acids. This mode of carbon fixation is called crassulacean acid metabolism (CAM)
        the mesophyll cells of these CAM plants store the organic acids in their vacuoles until morning when the stomata closes
        during the day (when light reactions can supply ATP and NADPH for the Calvin cycle) CO2 is released form the organic acids to become incorporated into the sugar in the chloroplasts
      - Linear Electron Flow
      - light drives the synthesis of ATP and NADPH by energizing the two types of photosystems embedded in the thylakoid membranes of chloroplasts
        the key to the above statement is a flow of electrons through the photosystems and other components built into the thylakoid membrane - this is called linear electron flow
        LEF occurs during the light reactions of photosynthesis
        STEPS :ballot_box_with_check:
        
        A photon of light hits one of the pigment molecules in a light-harvesting complex, boosting one of its electrons to a higher energy level. When this electron falls back to its original ground state, an electron nearby goes into its excited stat. This process continues until it reaches the P680 pair of chlorophyll a molecules in the PS II reaction-center complex. It excites an electron in this pair of chlorophylls to a higher energy state
        
        This electron is transferred from the excited P680 to the primary electron acceptor
        
        An enzyme then catalyzes the splitting of water into two electrons, two hydrogen ions (H+), and an oxygen atom. The electrons are then given one by one to the P680 pair, each electron replacing the one transferred to the PER. The hydrogen ions are released into the thylakoid space. The oxygen atom combines with another oxygen atom generated by the splitting of another water molecule. forming O2
      - Each excited electron passes from the primary electron acceptor of PS II to PS I by an electric transport chain
        This chain is made up of the electron carrier plastoquinone, which is a cytochrome complex, and a protein called plastocyanin. Each component carries out redox reactions as electrons flow down the ETC and releasing free energy that is used to pump H+ protons into the thylakoid space, contributing to a proton gradient across the thylakoid membrane
        
        The potential energy stored in the proton gradient is used to make ATP in a process called chemiosmosis
        
        Light energy has been transferred by light-harvesting complex, exciting an electron of the P700 pair of chlorophyll a molecules. The excited electron is then transferred to PS I's PEA and creates an electron "hole" in the P700. Basically, now P700 can act as an electron acceptor, accepting an electron that reaches the bottom of the ETC from PS II
      - Excited electrons are passed through redox reactions from the primary electron acceptor of PS I down a second ETC through the protein ferredoxin (Fd)
        
        The enzyme NADP reductase catalyzes the transfer of electrons from Fd to NADP. Two electrons are required for its reduction to NADPH. Electrons in NADPH are at a higher energy level than they are in water so they're more ready for the reactions of the Calvin cycle
- - - - In mitochondria, organic molecules are broken down by cellular respiration, capturing energy in molecules of ATP which are used to power the work of the cell (such as protein synthesis and active transport)
        
        In chloroplasts, the process of photosynthesis uses the energy of light to convert CO2 and water to organic molecules (with oxygen as a by-product)
      - Light Reactions!
      - are carried out by molecules in the thylakoid membranes
      - convert light energy into chemical energy into ATP and NADPH
        split water and release oxygen into the atmosphere
      - Calvin Cycle Reacions!
      - take place in the stroma
      - use ATP and NADPH to convert CO2 to the sugar G3P
      - return ADP, inorganic phosphate, and NADP to the light reactions