Photosynthesis Photosynthesis is a producer Photosynthesis nourishes most
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Photosynthesis
Photosynthesis is a producer • Photosynthesis nourishes most organisms on earth • Plants and other autotrophs are producers • Autotrophs produce their own food • Heterotrophs feed on organic material
2 Types 1. Anoxygenic: does NOT produce O 2 Bacteria 2. Oxygenic: produces O 2 Cyanobacteria, algae, and land plants Both use pigments but differ in function of pigments.
Chloroplast: photosynthetic organelles 3 Processes occur here: 1. Capture light energy 2. Use energy to make ATP and reduce NADP+ to NADPH 3. Use ATP and NADPH to power the synthesis of organic molecules from CO 2
2 Stages of Photosynthesis 1. Light-dependent reactions: Light energy stored in ATP and NADPH. Needs light. 2. Light-independent reactions: cycles that form organic molecules using CO 2 in a process called carbon fixation. Does NOT need light.
Equation 6 CO 2 + 12 H 2 O + light energy C 6 H 12 O 2 + 6 H 2 O + 6 O 2 Carbon Water Glucose Water Oxygen Dioxide Generally, opposite of cell respiration
The Chloroplast • The chloroplast is the site of photosynthesis in a cell • Contains a pigment called chlorophyll • Chloroplasts are found mainly in the Mesophyll (leaf tissue) • CO 2 and O 2 enter the leaf via the stomata
Structure of Chloroplast • Like mitochondria, chloroplasts have an internal and external membrane. • Thylakoids are structures made of the inner membranes. A stack of thylakoids is called granum (grana plural). • Thylakoid membranes contain pigments like chlorophyll.
Structure of Chloroplast (cont’d) • The photosynthetic pigments are clustered together to form photosystems which capture energy packets called photons. • Surrounding the grana is a semiliquid called stroma which houses the enzymes that make organic molecules.
Discovery of Photosynthetic Processes Some bacteria use hydrogen sulfide(H 2 S) instead of water for photosynthesis Thus, the general formula for photosynthesis is: CO 2 + 2 H 2 X CH 2 O +2 X By using O 2 isotopes, C. B. Van Niel proved that the O 2 produced came from the splitting of water
Tracking Atoms through Photosynthesis
Pigments • Molecules that absorb light energy in the visible range.
Light is a form energy • Visible light is made of various colors which are different due to their wavelength. • Visible light is a small part of the electromagnetic spectrum.
Photons • Particle of light acting as a bundle of energy. • Light has a dual nature as it is both waves and energy.
Photoelectric Effect • When light or photons transfer energy to electrons, the electrons are removed from molecules and create an electric current. • Chloroplasts act as photoelectric devices.
Absorption Spectrum • The electrons that absorb energy jump to higher energy levels. The shorter the wavelength of light the greater the energy absorbed. • To boost electrons to discrete energy levels, specific atoms can only absorb specific photons of light relative to the atoms energy levels. The range of photons a molecule can absorb is called the absorption spectrum.
Action spectrum • Relative effectiveness of different wavelengths of light for photosynthesis.
Chlorophyll a and Chlorophyll b • Chlorophyll a is the main pigment that can directly convert light energy to chemical energy. • Chlorophyll b is a secondary or accessory pigment that helps to absorb a greater range of wavelengths of light. • Both absorb red and blue-violet light. Thus they reflect green light giving a green appearance.
Structure of Chlorophylls • Chlorophylls are made of a porphyrin ring (rings w/ single and double bonds) a Mg atom at the center, a hydrocarbon chain, and a side chain.
Carotenoid • Pigment that absorbs mostly blue and green ranges of light capturing energy from wavelengths of light not absorbed by chlorophyll. • Play protective role. • May contain beta-carotene which is helpful for vision.
Phycobiloproteins • Pigment found in cyanobacteria and algae which absorbs green light.
Photosystem Organization (8. 4) • 1 molecule of O 2 for every 2500 molecules of chlorophyll. • Light absorbed by a cluster of pigment molecules in a photosystem. • Each photosystem had 2 parts: antenna complex and a reaction center.
Antenna Complex “Light-harvesting” • Made of different pigments like chlorophyll which absorb photons of light and pass the energy from one pigment molecule to the next in the thylakoid membrane. • Eventually the energy is passed to the reaction center.
Reaction Center • When a chlorophyll molecule in the reaction center absorbs a photon of light, an electron is excited and moves the an electron acceptor quinone. • Quinone then passes the e- to another acceptor. • Water donates e- to chlorophyll and is oxidized to form H+ and O 2 a product.
• http: //www. sumanasinc. com/webcontent/a nimations/content/harvestinglight. html
LIGHT-DEPENDENT REACTIONS 4 Parts to Reactions 1. Primary photoevent: photon captured by pigment and e- excited. 2. Charge separation: energy of e- transferred to acceptor molecule at reaction center. 3. Electron transport: e- move along carrier molecules until they reduce NADP+ to NADPH and H+ moves across membrane to generate a gradient. 4. Chemiosmosis: H+ diffuses back across membrane through ATP synthase to generate ATP.
Bacteria use 1 photosystem • In sulfur bacteria, e- absorb photons and are boosted from the reaction center to an eacceptor which happens to be H+ and together they form an H atom.
• e- are recycled as they are used to make ATP and return back to chlorophyll molecules. This is called cyclic photophosphorylation.
Chloroplasts have 2 Photosystems 1. Photosystem I (PS I): has absorption peak of 700 nm so we call it P 700. Transfers e- to NADP+ to make NADPH. 2. Photosystem II (PS II): has an absorption peak of 680 nm, we call it P 680. e- lost in PS I are replaced by e- from water generated in PS II. ** Systems are connected by cytochrome/b 6 -f complex of e- carriers.
Photosystem
How do they work together?
Noncyclic photophosphorylation • e- do not return to photosystems, instead they are used to make NADPH. 2 main products of PS I and PSII are ATP and NADPH.
NOW DRAW IT
Light-Dependent Reactions • http: //highered. mcgrawhill. com/olcweb/cgi/pluginpop. cgi? it=swf: : 5 35: : 535: : /sites/dl/free/0072437316/120072 /bio 13. swf: : Photosynthetic%20 Electron%2 0 Transport%20 and%20 ATP%20 Synthesis
• Plants will carry out cyclic phosphorylation when they run low on ATP. • Cyclic phosphorylation only generates ATP, (no NADPH or oxygen is made). The e- will leave PS I and return to the b 6 -f complex.
Carbon Fixation: Calvin Cycle (8. 6) • Occurs day or night but depends on NADPH and ATP for energy to make sugar. • Produces PGAL (phosphoglycerate) a 3 C molecule used to make glucose and other sugars. Thus it is called C 3 photosynthesis. • 6 turns of cycle produces 2 PGAL or 1 sugar. • Occurs in the stroma.
NOW DRAW IT • http: //www. sinauer. com/cooper/4 e/animati ons 0305. html
Photorespiration and Other Processes (8. 7)
Photorespiration • Normally rubisco uses CO 2 in the Calvin cycle. • However during photorespiration, the stomata are closed increasing O 2 levels and decreasing CO 2 levels in the leaf. • Rubisco will sometimes binds with O 2 instead of CO 2. • ATP is used, CO 2 is made and No sugar is formed. • This generally occurs when temperatures are high or it is dray and the stomata are closed
C 4 Photosynthesis • Assists plants that live in hot, dry areas such as corn, crabgrass, and sugar cane. • (Phosphoenolpyruvate) PEP carboxylase joins CO 2 and PEP to produce oxaloacetate (OAA) in the mesophyll cells. • Now in an organic form, CO 2 is transferred to the bundle sheath cells and there it is used in the Calvin cycle. • The advantage is reducing photorespiration.
• What is similar? • What is different?
CAM plants • CAM = crassulacean acid metabolism • Adaptation to dry areas. • At night plants open their stomata to capture CO 2 using PEP carboxylase and store it in organic compounds. • During the day, they use light energy and the CO 2 to produce sugar. • All reactions occur in the mesophyll cells.
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