40 terms

Chapter 7 - Photosynthesis

- produce their organic molecules
- source of organic compoundsfor heterotrops
-- producers
-- autorophtic bacteria
- ex. plants, algae, other protists and some prokaryotes
autotrophic bacteria
use CO2 to synthesize organic molecules without solar energy
needs of photoautotrophs
- light energy
- water
- minerals
- CO2
- unable to produce their own organic materials
- consumers
- completely dependent on Photoautotrophs
- the major sites of photosynthesis in green plants
- organelles consisting of photosynthetic pigments, enzymes, and other molecules grouped together in membranes
- found in the cells of the mesophyll
- chlorophyll
- an important light absorbing pigment in chloroplasts
- responsible for the green color of plants
- plays a central role in converting solar energy to chemical energy
- absorbs light energy and drives the synthesis of organic molecules
- interior tissue of the leaf
- 30-40 in a cell
- stroma
- the place where chloroplasts are found
- fluid within the chloroplast
- Pore-like openings in leaves that allow gases (CO2 and O2) and water to diffuse in and out of the leaves
- CO2 enters
- O2 exits
- H2O Roots --> Leaves and SUgar --> Roots/ Other parts (nonphotosynthetic)
photosynthetic equation
[6CO2 + 12H2O + Light Energy --> C6H12O6 + 6O2 + 6 H2O]
- used a heavy isotope of Oxygen
- use isotope to trace Oxygen during the reaction
- Glucose
- 12 H2O consumed, 6 produced
photosynthesis redox process
- photosynthesis, like respiration, is a redox (oxidation/reduction) process
- water molecules are split apart by oxidation
-- they lose electrons along with hydrogen ions
- CO2 is reduced to sugar
-- electrons and hydrogen ions are added to it
energy hill
- in photosynthesis, electrons gain energy when they are pushed up this
- light energy captured by chlorphyll moelcues provides the boost for the electrons
- light energy is converted to chemical energy which is stored in the chemical bonds of sugar molecules
- the sugar produced in photosynthesis is stored for later use or as raw material for biosynthesis of new plant material
light reaction
- linked by ATP and NADPH
-- solar energy --> Chemical energy
--- chlorophyll absorb light
--- water split
--- e-(H+) H2O --> NADP+
---- NADP+ reduced to NADPH (2e- + H+)
---- ADP --> ATP (chemiosmosis)
--- O2 as a byproduct
Calvin Cycle
- often called the dark (or light -independent) reactions
- occurs during daytime in most plant when the light reactions are powering the cycle's sugar assembly line
- carbon fixation
- fixed CO2 reduced (e- added) --> Carbohydrate
-- NADPH reducing power (from light reaction)
- ATP chemical power (from light reaction)
carbon fixation
CO2 from the atmosphere incorporated into existing C compound
light energy
- both electromagnetic energy and radiation
- travels in rhythmic waves
-- measured in wavelength
visible light
- 380 nm - 750 nm
- detected by human eye
- drives photosynthesis
the distance between the crests of two adjacent waves
- light behaves as photons
- particles of light explain light's behavior
- fixed quantity of energy
- energy = 1/wavelength
-- shorter wavelength = greater energy
-- longer wavelength = less energy
discrete packets of energy
pigments/ light receptors
- different pigments absorb light at different wavelengths
- absorbed light disappear
- color seen is reflected or transmitted (spectrophotometer)
- also called galvinometer
- device that measures the fraction of light transmitted at a specific wavelength
- absorption spectrum
absorption spectrum
the spectrum of electromagnetic radiation that has passed through a medium that absorbed radiation of certain wavelengths
- different for each pigment
- light absorption vs Wavelength
action spectrum
- the efficiency with which electromagnetic radiation produces a photochemical reaction plotted as a function of the wavelength of the radiation
- resembles absorbtion spectrum
chlorophyll A
[pigment involved in photosynthesis]
absorbance spectrum
-- violet-blue-red = high
-- green = less efficiently
-- blue-green = transmittance
Chlorophyll B
[pigment involved in photosynthesis]
- accesory pigment
- almost identical to Chlorophyll A but has a slight structural difference
- transmittance = yellow-green
[pigment involved in photosynthesis]
- accessory pigment
- absorb violet and blue-green
- transmit yellow-orange shades
- function mostly in photoprotection
-- antioxidant
- absorbs excess light energy that would damage chlorophyll
- ex. carotenoids
- ex. Carotenoids
- prevents energy from interacting with oxygen to form oxidative molecule
Chlorophyll interaction with light
- color disappears but not energy
- absorbs light photon
- e- elevated to where it has a higher potential energy
-- ground state, excited state
- can absorb only the amount of energy difference in potential energy between ground and excited
- differs between different pigments: why the absorption spectrum differs
- excited (unstable) --> ground; release energy as heat
- isolate chlorophyll also emits light
ground state
- the lowest energy state of an atom
- e- at normal level
excited state
- condition of an atom whose electrons are at higher energy levels than the ones they normally occupy
- e- has higher potential energy
photosystems capture solar power
- the energy released could be lost as heat or light, but rather it is conserved as it is passed from one molecule to another
- all of the components to accomplish this are organized in thylakoid membranes in clusters called photosystems
- light harvesting complexes surrounding a reaction center complex (proteins)
- chlorophyll, small organic compounds, proteins
- reaction center surrounded by light harvesting complexes (complex and reaction center)
protein complex
- pigment bound to proteins
- reaction center in photosystems
-- two special chlorophyll A molecules use energy from light to boost 1 e- to an excited state
-- primary e- acceptor
light reactions
- first step: e- (chlorophyll) is excited by the light energy
- as it drops from this unstable state the energy is passed from molecule to molecule within the photosystem
- finally it reaches the reaction center where a primary electron acceptor accepts these electrons consequently becomes reduced
- this solar powered transfer of an electron from the reaction center pigment to the primary electron acceptor is the first step of the light reaction
- redox reaction
- light energy --> chemical energy --> sugar
- isolated chlorophyll give off light because there is no e- acceptor so the e- drops from excited --> ground state
photosystem I and II
- 2 systems in light reactions
- the chylorophyll are identical but their association with other proteins causes their difference in absorbance
- chlorophyll a P680
- most effective at 680 nm
- chlorophyll a P700
- most effective at 700 nm