Chapter 8 Flashcards
Chlorophyll
pigment that gives plants the green color
photosynthesis
energy from light is captured and used to synthesize glucose and other organic molecules
CO2 + H2O + light energy → C6H12O6 + O2 + H2O
- CO2 is reduced
- H2O is oxidized
- Energy from light drives this endergonic reaction
light reactions
Stage 1 of Photosynthesis:
-light energy is absorbed by chlorophyll and converted to chemical energy in the form of two energy intermediates: ATP and NADPH.
- requires light
- produces ATP, NADPH and O2
Photosynthesis powers the biosphere
- Regions on the surface of the Earth and in the atmosphere where living organisms exist
- Largely driven by the photosynthetic power of green plants
- Cycle where cells use organic molecules for energy and plants replenish those molecules using photosynthesis
- Plants also produce oxygen
Calvin Cycle
Stage 2 of Photosynthesis:
ATP and NADPH are used to drive the synthesis of carbohydrates
- no requirement for light
- fixes CO2 into an organic molecule
Biosphere
the regions on the surface of the earth and in the atmosphere where living organisms exist.
Heterotrophs
must consume food- organic molecules from their environment- to sustain life
-most species of bacteria, protist, fungi and
animals
Heterotrophs are the Consumers of the environment
- Heterotroph - other feeding
- Require complex organic molecules from other organsims.
- Decomposers - live on “organic litter”
- a nice way to say - decaying animal or plant matter
- carcasses, feces, other debris (plant or animal)
- a nice way to say - decaying animal or plant matter
- Everything not an autotroph, IS a heterotroph
Autotrophs
sustain themselves by producing organic molecules from inorganic sources such as CO2 and H2O
Photoautotrophs
they are autotrophs that use lift as a source of energy to make organic molecules
-including green plants, algae, and some bacterial species such as cyanobacteria
Autotrophs are the Producers of the environment
- Autotroph - self feeding
- Require only raw materials (water, minerals and a carbon source) to make their own food
- Photoautotrophs
- Green plants, algae, cyanobacteria
- They need only water, minerals and CO2 + light
Plants FIX CO2
- Plants use light energy to synthesize complex organic molecules
- HOW???
- By FIXing the gas CO2 into sugar molecules
- Start with 1C molecule and make 6C molecules - The process of Photosynthesis
Green tissue is Photosynthetic
- Photosynthesis occurs in the green parts of plants, leaves, stems etc.
- Inside cells, inside the chloroplasts, in the thylakoid membranes
Chloroplast
-Organelles in plants and algae that carry out photosynthesis
- Chlorophyll- green pigment protein
- Majority of photosynthesis occurs in leaves in mesophyll
-Stomata- carbon dioxide enters and oxygen exits leaf
Chloroplast Anatomy
- Outer and inner membrane
- Intermembrane space
- 3rd membrane - thylakoid membrane contains pigment molecules
- Forms thylakoids
- Enclose thylakoid lumen
- Granum- stack of thylakoids
- Stroma- fluid filled region between thylakoid membrane and inner membrane
Mesophyll
- tissue in the internal part of the leaf
- contains cells with chloroplast
- for photosynthesis to occur, the cell must obtain water and carbon dioxide
thylakoid membrane
- contains pigment molecules, including chlorophyll
- forms thylakoids
thylakoids
- flattened, fluid filled tubules
- encloses thylakoid lumen
thylakoid lumen
a single, convoluted compartment
granum
formed when thylakoids stack on top of each other
stroma
fluid-filled region of the chloroplast between the thylakoid membrane and the inner membrane
Light Reactions
- in the Thylakoid membranes
- Take place only when light is present
- Split water to form ATP, NADPH, and O2
Dark Reactions (Calvin Cycle)
- in the Stroma
- Can take place with or without light being present
- Takes ATP and NADPH from light reactions + CO2 to make sugar (CH2O)
Light as a wave
- Electromagnetic Energy, radiation
- Travels in waves
- similar to what you see if you drop a rock into a pond - The distance between the tops of the waves = wavelength
- The wavelengths can vary enormously
- 1 nanometer - 1 kilometer - Visible light has wavelengths from 350nm- 750nm!
- ROY G BIV
Light as a particle
- But light also behaves as a particle
- Called photons - Photons act like particles, but aren’t
- Each photon has a fixed quantity of energy
- The amount of energy in a photon is inversely proportional to its wavelength.
- The shorter the wavelength, the more energy
- Violet photons have 2x the energy of red photons
wavelength
distance between the peaks in a wave pattern
electromagnetic spectrum
encompasses all possible wavelengths of electromagnetic radiation, from relatively short wavelengths
photons
massless particles traveling in a wavelike pattern and moving at the speed of light
Light receptors
- When light hits matter it can be
- Reflected
- Absorbed
- Refracted
- Chlorophyll absorbs red and blue light
- Electrons are EXCITED!
- But it reflects green light
- So leaves look green - The color of an object is dependent on absorption and reflection
pigment
a molecule that can absorb light energy
-ex: leaves looking green because of radiant light reflection
It’s about electrons
- Photosynthetic pigments absorb some light energy and reflect others
- Absorption boosts electrons to higher energy levels
- Wavelength of light that a pigment absorbs depends on the amount of energy needed to boost an electron to a higher orbitalAfter an electron absorbs energy, it is in an excited state and usually unstable
- Releases energy as
- Heat
- Light
- Excited electrons in pigments can be transferred to another molecule or “captured”
- Captured light energy can be transferred to other molecules to ultimately produce energy intermediates for cellular work
Photosynthetic Pigments
-Chlorophyll a and accessory pigments are the big players in absorbing light and getting the light reactions started - blue green in color
-One of the accessory pigments is Chlorophyll b (almost identical to chlorophyll a) - yellow green in color
other accessory pigments are carotenoids - yellow orange (carrots!)
-often are photoprotective
carotenoids
- another type of pigment found in chloroplasts
- color ranges from yellow to orange to red
- found in flowers and fruits
Absorption
- wavelengths that are absorbed by different pigments in the plant
- absorption spectrum is a graph that plots a pigment’s light absorption as a function of wavelengths
action spectrum
-rate of photosynthesis by a whole plant at specific wavelengths
Photoexcitation of Chlorophyll
- A photon can be absorbed only if its energy is exactly the same as the energy it takes for the e- to go from ground state to excited state
- Electrons that are in an excited state have lots of potential energy and are unstable
- The electrons have a tendency to emit the absorbed energy or transmit the energy to something else
- If the electrons don’t have something to pass the energy off to . . .
- The energy will be emitted as light (fluorescence) and heat
- This is FAST 0.000000001 seconds
Chlorophyll in a Thylakoid Membrane
- Chlorophyll in a thylakoid membrane is organized along with proteins and other organic molecules into photosystems
- They have antenna complexes that gather the light and pass it along to the reaction center
- a particular chlorophyll a molecule
- where the first light-driven reaction of photosynthesis starts
- The reaction center chlorophyll a passes an electron in the excited state to
- The primary electron acceptor accepts the excited electron
- This is a redox reaction
- the chlorophyll a looses an electron to the primary acceptor - By trapping the excited electron, primary electron acceptor prevents the rapid decay of the excited state electron to ground state
Photosystems
- Thylakoid membrane
- Photosystem I (PSI)
- Photosystem II (PSII)
Photosystem II
- 2 main components
- Light-harvesting complex or antenna complex
- Directly absorbs photons
- Energy transferred via resonance energy transfer
- Light-harvesting complex or antenna complex
- 2 main components
- Reaction center
- A redox machine
- P680 →P680*
- Relatively unstable
- Transferred to primary electron acceptor
- Removes electrons from water to replace oxidized P680
- Oxidation of water yields oxygen gas
- Reaction center
- Light excites pigment molecules in PSII and PSI
- PSII - excited electrons travel to PSI
- Water is oxidized- generates O2 and H+
- Releases energy in electron transport chain
- Energy used to make H+ electrochemical gradient
- PSI – primary role to make NADPH
- Addition of H+ to NADP contributes to H+ electrochemical gradient
- PSII - excited electrons travel to PSI
Photosystem I (PSI)
- Key role to make NADPH
- Light striking light-harvesting complex of PSI transfers energy to a reaction center
- High energy electron removed from P700 and transferred to a primary electron acceptor
- NADP+ reductase
- NADP+ + 2 electrons + H + → NADPH
- P700+ replaces its electrons from the ETC (plastocyanin)
- No splitting water, no oxygen gas formed
- ATP synthesis
- Chemiosmotic mechanism
- Driven by flow of H+ from thylakoid lumen into stroma via ATP synthase
- H+ gradient generated by
- ↑H+ in thylakoid lumen by splitting of water
- ↑H+ by ETC pumping H+ into lumen
- ↓H + from formation of NADPH in stroma
Summary
- O2 produced in thylakoid lumen by oxidation of H2O by PSII
- 2 electrons transferred to P680+
- NADPH produced in the stroma from high-energy electrons that start in PSII and boosted in PSI
- NADP+ + 2 electrons + H + → NADPH - ATP produced in stroma by H+ electrochemical gradient
- Splitting of water places H+ in the lumen
- High-energy electrons move from PSII to PSI, pumping H+ into the lumen
- Formation of NADPH consumes H+ in the stroma
