Photo Own notes

PHOTOSYNTHESIS

  • Directly or indirectly, photosynthesis nourishes almost the entire living world.

  • It is an Endergonic Process; the energy boost is provided by light.

  • Its a complex of series of reactions that can be summarized as: 6 CO2 + H2O + Light Energy (sun) – (produces) – C6H12O6 + 6 O2

  • Things capable of going through photosynthesis:

    • plants

    • algae

    • protist (unicellular eukaryotes)

    • Cyanobacteria (prokaryotes)

    • Purple sulfur bacteria (prokaryotes)

A REDOX REACTION

  • Photosynthesis is a redox process where H2O is oxidized (removing electrons) and CO2 is reduced (adding electrons).

    • Electron carrier NADPH is reduced.

    • Electrons move down the Electron Transport Chain from protein to protein.

    • NADPH is the final electron acceptor.

      Electron Carriers:

    • NADPH – made in the light-dependent reactions in photosynthesis. accepts electrons and hydrogen ions to form NADP+, which is used in the Calvin cycle for synthesizing glucose.

    Protirens that ar awpart of the ETC

    • Plastoqiuone - moves electrons from photosystem II to the cytochrome b6f complex.

    • Pastocyanin - transfers electrons from plastoquinone to photosystem I,

    • Ferredoxin– facilitates the transfer of electrons from photosystem I to NADP+.

  • The overall chemical change in photosynthesis is the reverse of cellular respiration.

Photosynthesis and Cellular Respiration:

  • Both contain an Electron Transport Chain.

  • In photosynthesis, it produces ATP an Electron Carrier.

    • Produces less ATP than Cellular Respiration.

Photosynthesis formula:
6 CO2 + H2O + Light Energy (sun) – produces – C6H12O6 + 6 O2 (carbon dioxide + water + light energy = Glucose + Oxygen)

  • Substrates produce products.

  • Building bonds – (carbon fixation).

  • Requires energy / endergonic reaction.

LOCATION OF OCCURRENCE:

  • Photosynthesis usually takes place in the chloroplast in eukaryotic cells.

    • The chloroplast is a membrane-bound organelle.

  • Photosynthesis can also take place in bacteria (prokaryotic cells).

    • Since it lacks a chloroplast, it takes place in the cytoplasm.

CHLOROPLAST:
Structure of the chloroplast: The site of photosynthesis in plants

  • Made of an outer and inner membrane (the phospholipid bilayer).

  • Inside of the chloroplast are Thylakoids (3rd sets of membranes).

  • It is folded in a way that looks like little discs, referred to as a Grana. (plural).

    • Light-dependent reactions occur in the thylakoid membrane.

    • When light strikes the pigments in the Thylakoid, the pigments transfer energy to an electron.

    • The Electron then moves from protein to protein, etc., beginning the Electron Transport Chain.

  • There’s a fluid outside of the thylakoids referred to as the Stroma.

    • The stroma is the “cytoplasm of the chloroplast.”

  • Leaves are the major locations of photosynthesis in plants.

  • Chloroplasts are located in the Mesophyll (jelly-like substance).

  • Mesophyll is the interior tissue of the leaf.

    • Each mesophyll cell contains 30-40 chloroplasts.

    • CO2 enters, and O2 exists in the leaf through microscopic pores called Stomata.

  • Stomata is the opening of the leaf that’s responsible for the exchange of gases. (where light independat reactions occur.

  • CO2 is taken in by the stomata, and O2 is released.

ELECTRON TRANSPORT CHAIN Electrons moving from protein to protein.
Proteins that participate in the Electron Transport Chain:

  • Photosystem 2 – only protein capable of oxidizing water.

  • Plastoquinone.

  • Cytochrome Complex BCF.

  • Plastocyanin.

  • Photosystem 1.

  • Ferredoxin.

  • NADP Reductase.

Order of the electron transport Chain:

  • Light comes in hitting Chlorophyll A & B and Carotenoids.

  • Energy is transferred to an electron from the Reaction Center to the electron center.

  • Moves from photosystem 2 to Plastoquinone.

  • Passes to the cytochrome complex BCF.

  • Then, it passed to Plastocyanin.

  • Makes its way to Photosystem 1.

  • Then to Ferredoxin to NADP Reductase.

  • Finally the NADPH.

THE TWO STAGES OF PHOTOSYNTHESIS

  • Photosynthesis consists of light reactions (photo) and Calvin Cycle (synthesis).

  • Light Reactions (in the thylakoids):

    • Split H2O (removes electrons).

    • Releases O2.

    • Reduces the electron receptor NADP and produces NADPH.

    • Generates ATP from ADP by Photophosphorylation.p

ATP Synthase is the protein responsible for pumping hydrogen protons from the thylakoid membrane into the stroma.

Calvin Cycle:

  • Building bonds: taking carbon dioxide and making glucose.

  • Requires energy from the ATP and NADPH that was produced in the light-dependent reactions.

  • Takes place in the Stroma.

  • Starts with Carbon Fixation, incorporating CO2 into organic molecules.
    Carbon Fixation: taking smaller molecules and building them into larger molecules.

 

LIGHT-DEPENDENT REACTIONS: takes light energy and outs it into eelctrons

  • Captures sunlight and converts it to ATP and NADPH (electron carriers).

  • An Exergonic reaction (since energy is being released).

  • The pigment inside the thylakoid membrane captures and transfers the energy into an electron.

  • The electron moves from protein to protein and starts the Electron Transport Chain.

    • The Cytochrome Complex pumps hydrogen protons from the stroma into the thylakoid membrane.

    • ATP Synthase pumps out the hydrogen protons, using mechanical energy to produce ATP.

    • The final electron acceptor is NADPH.

    • Since you are building bonds during the Calvin Cycle, you require energy (ATP and NADPH).

  • CO2 binds to molecules to produce sugar (substrate).

    • The electron movement causes a protein to miss an electron.

    • Protein Photosystem 2 oxidizes water (water loses an electron) to replenish the missing electron.

      • Oxidizing water produces oxygen.

      • Oxidizing water is referred to as The Splitting of Water.

      • Chloroplasts take water (H2O) and split it into hydrogen and oxygen. They use hydrogen electrons to make sugar and release oxygen as a byproduct.


        Without water, there is nothing to use to replenish the electron. Therefore, you cannot produce ATP or NADPH, which are both needed to produce the Calvin Cycle.

LIGHT-INDEPENDENT REACTION/ CALVIN CYCLE/ CARBON FIXATION

  • It's an Endergonic reaction (since energy is being consumed).

  • Energy is received from the light-dependent reactions.

    • An exergonic process that drives the completion of endergonic processes is called Energy Coupling.

  • Plants absorb energy from the sun with their chloroplasts and produce organic molecules.

    • CO2 is used to make C6H12O6 (and other carbs).

    • Goes from a one-carbon molecule (CO2) to a six-carbon molecule (C6H12O6 glucose).

    • Taking inorganic molecules to make organic molecules using sunlight.

    • Requires light energy.

1ST step of Calvin Cycle: Carbon Fixation:

  • It takes CO2 (1 carbon), binds it to RuBP (5 carbons), and builds a 6-carbon molecule.

  • The enzyme that’s responsible for binding CO2 to RuBP is called Rubisco.

2ND phase of the Calvin cycle: Reduction

  • When the molecule is generated, we reduce it by adding electrons from NADPH.

3RD phase: Regeneration

  • Regenerates its starting material, (CO2 acceptor) RuBP (Ribulose bisphosphate), after molecules enter and leave the cycle.

  • Once made, repeat the cycle.

  • During this process, a molecule called G3P (Glyceraldehyde 3-phosphate) is generated – a 3-carbon chain.

  • G3P exits the cycle and makes glucose and other organic compounds.

  • Each Calvin Cycle adds a one-carbon molecule (CO2) to produce glucose (6 carbons); the cycle has to be repeated 6x.

 

THE NATURE OF SUNLIGHT

  • Light is electromagnetic energy, also called Electromagnetic Radiation.

  • Sunlight has different radiations (UVA, UVB, and UVC).

  • Wavelength is the distance between crests of electromagnetic waves.

    • Photons travel in waves.

  • Light shines as white light and reflects into all light spectrum colors: ROYGBIV, and each has different wavelengths.

  • Each light energy is measured based on its wavelength.

    • Due to different wavelengths, they have different energy levels.

    • Small wavelengths – higher energy levels.

    • Large wavelengths – lower energy levels.

    • Energy level from smallest to largest: VIBGYOR (rainbow in reverse).

  • Light energy strikes pigments inside of the chloroplast and the energy is converted to help produce glucose molecules.

PIGMENTS

  • The pigments are found within the thylakoid membrane and are involved in light-dependent reactions.

  • Different pigments can absorb and reflect different wavelengths of light.

    • The color you see in an item is reflected; the ones you don’t see are absorbed.

    • In white – all colors are reflected – no energy is absorbed.

    • In black – all colors are absorbed – all energy is absorbed.

  • Plants have molecules that absorb light energy and reflect the color green.

  • Three pigments in green plants:

    • Chlorophyll A – main pigment – the only chlorophyll molecule that can transfer light energy to an electron and reflects green light.

    • Chlorophyll B – accessory pigment – passes energy to Chlorophyll A and reflects green light.

    • Carotenoid – accessory pigment – reflects orange light.

LIVING CATEGORIES

  • Plants are Producers because they can take an inorganic molecule using sunlight to create an organic molecule (it doesn’t really produce energy, it just transfers energy).

    • A producer is an autotroph (or self-feeders).

    • Plant autotrophs use sunlight to make their own food, so they can be categorized as a Photoautotroph.

    • Humans, birds, dogs (all animals) are considered Consumers.

    • Consumers are Heterotrophs (we don’t have chloroplasts, only mitochondria).

    • Cannot make their own food, reliant on producers for food (carbs, glucose) and O2.

  • Decomposers break down dead organic material (amino acids, nucleic acids, monosaccharides) or feces and release it into the environment.

    • Ex: Fungi and bacteria.

  • Since they take energy from another molecule, they are considered Saprobes.

  • Usually rely on decay and matter.

    • Ex: a mushroom is considered a saprobe. Whenever you see a mushroom, there is usually a dead (material) animal or plant that is recycling that energy.

PHOTONS

  • Light energy is photons (tiny beads of light energy).

  • UV Radiation is also found in sunlight.

    • Three types that come from the sun:

    • UVA

      • Is 95% of UV rays that reach the earth’s surface.

      • Penetrates the skin, going into the deeper layers of the tissue (to subcutaneous fat, muscle cells).

      • Ex: an immediate sunburn that’s very bad is because of UVA.

      • Contributes to aging of the skin and is linked to cancer.

    • UVB

      • Medium wavelength, cannot penetrate the skin.

      • Responsible for delayed tanning and burning.

      • Strongest promoter of skin cancer.

    • UVC

      • Strongest of these three energy levels.

      • Stays in the atmosphere, never reaching the ground (therefore, cannot harm humans).

CLIMATE CHANGE:

  • Breathing (breaking bonds) releases CO2 in the air (carbon footprint).

    • Trees take in CO2 and lower the amount of it in the atmosphere.

  • When there’s too much CO2, it produces a layer/cloud above the atmosphere, referred to as The Greenhouse Gases.

    • When the sun’s radiation comes in, it cannot escape the atmosphere and gets stored by greenhouse gases (a blanket on heat).

      Effects:

    • Temperatures keep rising on Earth.

    • When CO2 gets added to water, it creates H2CO3 (carbonic acid).

    • Ex: let’s say water’s pH is 7 (neutral), when more CO2 enters the water, it becomes more acidic, which can result in organisms in the water dying.