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Process whereby plants, algae (which are protists), & certain bacteria transform light energy into chem energy, using carbon dioxide & water as starting materials
In addition to CO2, Photosynthesis requires ______, which is absorbed by plant's roots & transported to leaves, where veins carry it to photosynthetic cells
Chem energy produced via photosynthesis is stored in bonds of what?
Photosynthesis takes place w/in organeles called _____ using gases that are exchanged via pores called ______.
- Light-absorbing organelles that are concentrated in interior cells of leaves
- All green parts of plant/algae contain these & convert sunlight into chem energy in Photosynthesis
- In most plants, however, the leaves have most chloroplasts & are therefore major locations of photosynthesis (about 500,000 per square millimeter of leaf surface)
Chlorophyll (Green color on leaves)
- Selective absorption of other colors while reflecting/transmitting green light
- Light-absorbing pigment in chloroplasts that plays central role in converting solar energy to chem energy
- Tiny pores (singular, stoma, meaning "mouth")
- Carbon dioxide (CO2) enters, & oxygen (O2) exits these
Chloroplasts have a double-membrane envelope, just like a what?
Membranes w/in chloroplast form framework where many of the reactions of......
- A Thick fluid
- Chloroplast's inner membrane encloses compartment filled w/ this fluid
- Interconnected mambranous sacs suspended in stroma
- --- Chlorophyll molecules that capture light energy are built into this
- Stacks where thylakoids are concentrated
- (singular, granum)
Structure of Chloroplast
- Aids its function by providing large surface area for reactions of photosynthesis, w/ its stacks of disks
- Chemical factories powered by the sun
Chem equation: Relationship between Photosynthesis & Cellular respiration
- ---Photosynthesis Reactants: CO2, H2O (are also waste products of cellular respiration)
- ---Photosynthesis produces what Respiration uses: C6H12O6(Glucose) & O2(Oxygen)
- Photosynthesis takes "exhaust" of cellular respiration & rearranges its atoms to produce food & oxygen
- CHEM TRANSFORMATION REQUIRING MUCH ENERGY Provided By SUNLIGHT Absorbed By CHLOROPHYLL
In Photosynthesis, electrons are boosted _______ & added to CO2 to produce sugar, as a pose to cellular respiration causing their electrons to "fall"
- -NEXT: Hydrogen moves along w/ electrons, so.....Redox process: Hydrogen transfer from H2O to CO2; this transfer requires chloroplast to split water molecules into hydrogen & oxygen.
- -THEN: Hydrogen is transfered w/ electrons to CO2 to form sugar
- -FINALLY: Xxygen escaped thru stomata into atmosphere as O2= Wast Product of Photosynthesis
2 Stages of Photosynthesis:
- LIGHT REACTIONS
- Calvin CYCLE
Stage 1 Photosynthesis: LIGHT REACTIONS
- Chlorophyll in thylakoid membranes absorbs solar energy, then is converted to chem energy ATP & NADPH
- Water is split providing a source of electrons & giving off O2 gas as by-product
- NO SUGAR IS PRODUCED IN THIS PROCESS
- Electron carrier in Photosynthesis
- Light drives electrons from chlorophyll to NADP+(oxidized form of carrier), forming NADPH (reduced form of carrier)
- Provides high-energy electrons for reduction of CO2 to sugar in Calvin cycle
Stage 2 Photosynthesis: Calvin CYCLE
- Uses products of light reactions to power production of sugar from CO2
- Enzymes from cycle are dissolved in stroma(thick fluid in chloroplast)
- Indirectly DEPENDS on Light to produce sugar because it Requires: ATP (Sugar Synthesis Energy) & NADPH (High-Energy Electrons for Reduction of CO2 & Glucose) BOTH produced by LIGHT REACTIONS
- Type of energy called Radiation, or Electromagnetic Energy
- Travels thru space as rhythmic waves; Analogous to ripples that are made by pebble dropped into pond
Distance between crests of 2 adjacent waves
- Full range of radiation (From very short wavelengths of gamma rays to very long wavelengths of radio signals)
- Visible light is small fraction of spectrum (Consists of wavelengths our eyes see as diff colors)
When sunlight shines on pigmented material, certain wavelengths (colors) of the visible light are...
- ...absorbed & disappear from light that's reflected by material
- **Ex: Pair of Blue jeans, Pigments in fabric absorb other colors, leaving only light in blue part of spectrum to be reflected from fabric to our eyes
- German biologist OBSERVED that "Certain bacteria living in water tend to cluster in areas w/ higher oxygen concentration" in 1883
- He knew light passed thru PRISM & separated into diff wavelengths (colors)
What did Theodor Engelmann QUESTION?
His info to determine which wavelengths of light work best for photosynthesis
Theodor Engelmann's HYPOTHESIS
Oxygen-seeking bacteria would congragate near regions of algae performing most photosynthesis (Producing most Oxygen)
Theodor Engelmann's EXPERIMENT
- Laid a string of freshwater algal cells w/in a drop of water on microscope slide.
- Then added oxygen-sensitive bacteria to drop
- Next, using prism, created spectrum of light & shined it on slide
- RESULTS: Most bacteria congregated around algae exposed to red-orange & blue-violet light, w/ very few bacteria moving to green light
Other than Theodor Engelmann's Main EXPERIMENT, what did his other experiments verify?
That Chloroplasts absorb light mainly in blue-violet & red-orange part of spectrum & those wavelengths of light are ones mainly responsible for Photosynthesis
Chloroplasts contain how many kinds of pigments?
Chloroplast Pigment: Chlorophyll a
- Absorbs mainly blue-violet & red light
- Participate directly in light reactions
Chloroplast Pigment: Chlorophyll b
- Absorbs mainly blue & orange light
- Doesn't participate directly in light reactions, but it broadens range of light that plant can use by conveying absore energy to chlorophyll a
- It then puts energy to work in light reactions
Chloroplast Pigment: Carotenoids
- Family of yellow-orange which absorb mainly blue-green light
- Some pass energy to chlorophyll a
- **Protective Function of Other Carotenoids: They absorb & dissipate excessive light energy that would otherwise damage chlorophyll (Similar Carotenoids, which we get from carrots & certain other plants, may help protect our eyes from bright light)
The falling autumn temp's cause an increase or decrease in levels of chlorophyll?
- **This allows color of longer-lasting carotenoids to show thru
Chloroplast pigments are all built into thylakoid membranes, which are organized into light-harvesting complexes called?
- Fixed quantity of light energy; Discrete packets of energy
- --The SHORTER the wavelength of light, GREATER the energy of Photon
- **Ex: Photon of Violet light packs nearly 2x as much energy as Red light Photon
When a pigment molecule absorbs a photon, one of pigment's electrons gains energy, & electron has become what?
- -- The electron has been raised from Ground State to an Excited State, which is HIGHLY UNSTABLE; so an Excited Elec. usually loses its excess energy & FALLS BACK to its Ground State almost Immediately
- -- Most pigments merely Release HEAT ENERGY as their light-excited electrons FALL BACK (Black Auto Hood gets HOT on Sunny Day)
The fluorescent light emitted by a glow stick is caused by a chemical reaction that excites electrons of a fluorescent dye. So....
electrons quickly FALL BACK Down to Ground State, releasing energy in form of fluorescent light
- Light-gathering antenna that focuses light energy onto a reaction center
- Has cluster of a few hundred pigment molecules, including chlorophylls a & b & some carotenoids == This cluster of pigment molecules functions as Light-gathering antenna
Photosystem: Reaction Center & Primary Electron Acceptor
When photon strikes 1 of the pigment molecules, energy jumps from molecule to molecule until it arrives at REACTION CENTER: Consists of a chlorophyll a molecule that sits next to another molecule called PRIMARY ELECTRON ACCEPTOR: Traps light-excited electron from chlorophyll a in reaction center.
How Light Reactions Generate ATP & NADPH
- 1.) Photons excite electrons in chlorophyll of water-splitting Photosystem, THEN Photons are trapped by PRIMARY ELECTRON ACCEPTOR. Water-splitting Photosystem replaces its light-excited electrons by extracting electrons from water, which RELEASES O2 during Photosynthesis
- 2.) Energized electrons from water-splitting Photosystem pass down an ETC to NADPH-producing Photosystem, Chloroplast uses energy released by electron "fall" to make ATP
- 3.) NADPH-producing Photosystem transfers its light-excited electrons to NADP+, reducing it to NADPH
- ***2 Types of PHOTOSYSTEMS cooperate in Light Reactions
- --They incorporate carbon from CO2 into 4-Carbon compound before proceeding to Calvin cycle
- When it's hot/dry weather, it keeps its Stomata mostly closed, conserving water
- BUT has enzyme that continues to incorporate carbon even when leaf's CO2 concentration is low (donates CO2 to Calvin cycle to nearby cell)
- **Ex: sugarcane, corn
- CO2 is incorporated into 4-Carbon compound that banks it at Night & releases to Calvin cycle in Same Cell during day, Keeps Photosynthesis Going when Stomata's closed during daytime
- Adapted to VERY DRY weather
- Conserves water by opening stomata & admitting CO2 ONLY at night
- **Ex: Pineapples, cacti, succulent (water-retaining) plants ALOE & JADE
- The first organic compound produced in Calvin Cycle is 3-Carbon molecule
- Widely distributed
- Farmers face issue of growing it cause plants close their stomata on hot, dry days, REDUCING water loss but also prevents CO2 from entering leaves; Sugar Production CEASES
- **Ex(Common Crops): Soybeans, Oats, Wheat, Rice
Location of Light Reactions in Thylakoid Membrane
- 2 Photosystems & ETC that connects them transfer electrons from H2O-->NADP+, reducing it to NADPH
- NOTE: Mechanism of ATP Production during light reacitons VERY SIMILAR to Mechanism in Cell Respir.
- In both cases, An ETC pumps Hydrogen Ions (H+) across a membrane-----Inner Mitochondrial Membrane in the case of Respiration & Thylakoid membrane in Photosynthesis
- ALSO, ATP synthases use energy stored by H+ gradient to make ATP
- MAIN DIFFERENCE: Food provides high-energy electrons in Cell Respir, whereas light-excited electrons flow down Transport Chain during Photosynthesis
Hard-hat Analogy for Light Reacitons
- Light Reactions absorb Solar Energy == Chem energy of ATP & NADPH
- ***PRODUCES NO SUGAR
Calvin Cycle: Makin Sugar from Carbon Dioxide
- Functions like Sugar Factory w/in Stroma of Chloroplast
- INPUTS: CO2 (Using its C) from air, as well as ATP (Using it Energy) & NADPH (Using its High-Energy Electrons)
- Cycle constructs energy-rich sugar molecule====>Output
- OUTPUT: *G3P (Glyceraldehyde 3-Phosphate)
- Plant cell uses G3P as Raw material to make Glucose & other organic compounds (Cellulose, Starch) that it needs
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