Chapter 10 Flashcards
Chloroplasts
Organelle where photosynthesis occurs
Autotrophs
“Self-feeders”. The producers of the biosphere that use up CO2. Almost all plants
Heterotrophs
Obtain organic material from other organisms. Consumers. Depend on photoautotrophs for food and O2
Photoautotroph
Organisms that can use light energy to sustain themselves - plants mostly, but can also be multicellular alga, unicellular eukaryotes, cyanobacteria, and Purple Sulphur Bacteria
________ are the major locations of photosynthesis in plants
leaves
mesophyll
Cells where chloroplasts are mainly found, the interior tissue of the leaf
Each mesophyll cell contains ________
30-40 chloroplasts
Stroma
The dense fluid bound inside two membranes of a chloroplast
Stomata
microscopic pores in a leaf where CO2 and O2 enter and exit
Thylakoids
The connected sacs in the chloroplast that compose a third membrane system. These may be stacked in columns called grana
Chlorophyll
The pigment that gives leaves their green color and resides in the thylakoid membranes
Photosynthesis reaction formula
6 CO2 + 12 H2O + Light Energy —> C6H12O6 + 6 02 + 6 H2O
Splitting H2O
Chloroplasts split H2O into hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules and releasing oxygen as a by-product
Photosynthesis as a redox process
Photosynthesis reverses the direction of electron flow compared to respiration. Photosynthesis is a redox process in which H2O is oxidized and CO2 is reduced. Photosynthesis is an endergonic process where the energy boost is provided by light
The Two Stages of Photosynthesis
Light Reactions (photo) and the Calvin Cycle (synthesis)
The light reactions
1) Split H2O
2) Release O2
3) Reduce the electron acceptor NADP+ to NADPH
4) Generate ATP from ADP by photophosphorylation
photophosphorylation
The process of converting light energy into chemical energy, such as ATP, in chloroplasts during photosynthesis
Chemiosmosis
the process where ions, typically hydrogen ions (H+) move across a semipermeable membrane down their electrochemical gradient
Carbon Fixation
The beginning of the Calvin cycle that incorporates CO2 into organic molecules
Light Reactions
Create ATP and NADPH which are then used in the Calvin Cycle
Nature of Sunlight
Electromagnetic Energy; travels in waves that are created by disturbances of electrical and magnetic fields
Photons
A light particle
Electromagnetic Spectrum
The spectrum of light; ranges from less than a nanometer (gamma rays) to more than a kilometer (radio waves); The segment most important to life is 380 nm to 740 nm (visible light)
Spectrophotometer
An instrument that can measure a pigments ability to absorb various wavelengths of light
Absorption spectrum
A graph that plots a pigment’s light absorption versus wavelength
chlorophyll a
the key light-capturing pigments in chloroplasts (green); special because they can transfer an excited electron to a different molecule
chlorophyll b
An accessory pigment that helps absorb light (yellow-green)
Action Spectrum
Profiles the relative effectiveness of different wavelengths of radiation in driving process
Carotenoids
Other accessory pigments in a chloroplast; Hydrocarbons that are usually yellow and orange because they absorb violet and blue-green shades
Excitation
A photon that matches that pigments required wavelength is absorbed by the pigment, exciting an electron and raising it up one or more orbitals. This increases the energy but makes the pigment unstable. When the electron drops back down, it releases energy
photosystem
consists of a reaction-center complex surrounded by light-harvesting complexes
Reaction-center complex
an association of proteins holding a special pair of chlorophyll a molecules and a primary electron acceptor
Light-harvesting complex
consists of pigment molecules (chlorophyll a and b, carotenoids, and xanthophyll b) bound to proteins; transfer the energy of photons to the chlorophyll a molecules in the reaction-center complex
Primary electron acceptor
in the reaction center; accepts excited electrons and is reduced; transfer of an electron from a chlorophyll a molecule to the primary electron acceptor is the first step of light reactions
Photosystem II (PS II)
functions first; The reaction-center chlorophyll a of PS II is called P680 because it is best at absorbing a wavelength of 680 nm
Photosystem I (PS I)
functions second; The reaction-center chlorophyll a of PS I is called P700 because it is best at absorbing a wavelength of 700 nm
Linear electron flow
the primary pathway; involves both photosystems; produces ATP and NADPH using light energy
First step in linear electron flow
A photon hits a pigment in a light-harvesting complex of PS II, and its energy is passed among pigment molecules until it excites P680
Second step in linear electron flow
An excited electron from P680 is transferred to the primary electron acceptor (we now call it P680+)
Third Step in Linear electron flow
H2O is split by enzymes, and the electrons are transferred from the hydrogen atoms to P680+, thus reducing it to P680 (P680+ is the strongest known biological oxidizing agent; The H+ are released into the thylakoid space; O2 is released as a by-product)
Fourth Step in Linear Electron Flow
Each electron “falls” down an electron transport chain from the primary electron acceptor of PS II toPS I. Energy released by the fall drives the creation of a proton gradient across the thylakoid membrane
Fifth Step of Linear Electron Flow
Potential energy stored in the proton gradient drives production of ATP by chemiosmosis
Sixth Step of Linear Electron Flow
In PS I (like PS II), transferred light energy excites P700, which loses an electron to the primary electron acceptor (chlorophyll A0)
Seventh Step in Linear Electron Flow
P700+ (P700 that is missing an electron) accepts an electron passed down from PS II via the electron transport chain
Eighth Step of Linear Electron Flow
NADP+ reductase catalyzes the transfer of electrons to NADP+, reducing it to NADPH (The electrons of NADPH are available for the reactions of the Calvin Cycle; This process also removes an H+ from the stroma)
Glyceraldehyde 3-phosphate
The sugar produced in the Calvin Cycle
