Ch. 10 Photosynthesis Flashcards
big idea here is photosynthesis, which is greatly assisted by knowing how the electron transport chain works. also understand photorespiration and the C3/C4/CAM plants and their differences
what are photosynthetic autotrophs?
organisms that obtain nutrients from non-organic molecules - the sun
what are chemosynthetic autotrophs?
organisms that make their food from inorganic compounds: H2S, CH4, NH3, etc
what are heterotrophs?
organisms that get their food from organic molecules or other organisms: fungi, animals, plants, protists, bacteria, archaea
what is the structure of a chloroplast?
-double membrane enclosing the stroma
-stroma contains grana, which are stacks of thylakoid membranes
-chlorophyll is within the thylakoid membrane
where are chloroplasts located?
within the mesophyll cells of leaves
what are the 3 pigments involved in photosynthesis?
chlorophyll = green [primary]
fucoxanthin = brown
phycoerythrin = red
what is the summary equation for photosynthesis?
6CO2 + 6H20 -> C6H12O6 + 6O2
-H2O gets oxidized
-CO2 gets reduced
how does light travel?
light travels in waves and in packets of particles called photons
what colours does chlorophyll absorb and reflect?
chlorophyll is green, so it absorbs all colours but green and reflects green
what is the absorption spectrum?
the wavelengths of light that a pigment absorbs:
chlorophyll b absorbs around 400-500nm (blue) and 600-660nm (red)
what is an action spectrum?
the effects of wavelengths of light on a specific PROCESS, ie , what wavelengths are useful to the organism
ex - wavelengths between 300-500 & 600-700nm stimulate photosynthesis
how do the electrons of pigmented molecules work?
-electrons of pigment molecules absorb photons corresponding to a specific wavelength
-this energizes them, causing them to jump to another orbital
what 2 things can happen when a pigment electron jumps orbitals?
- electron loses energy and returns to its original position, giving off light and heat
OR - energy is converted to chemical energy = photosynthesis
what are photosystems?
-light harvesting units located in the thylakoid membranes
what are photosystems composed of?
- light harvesting center = collection of accessory pigment molecules
- reaction centers = light energy is transformed to energized electrons, accepted by the primary electron acceptor
what are the two main photosystems in photosynthesis? what is their function?
-photosystem [PS] I and II
-absorb different wavelengths of light and function in light reactions of photosynthesis
-PS II starts the process
what is the flow of electrons through photosystem II?
- light enters PS II and is harvested
- “chlorophyll a” uses harvested light to excite electrons
- electrons are taken in by the primary electron acceptor
- ETC occurs, H+ pumped into thylakoid space, ATP is generated
- electrons used up are replaced by splitting H2O
- ATP created is used in calvin cycle
what is the flow of electrons through photosystem I?
- energy from photon hits PS I
- light is used to excite electrons, which eventually meet the primary electron acceptor
- ETC undergoes like normal, but
- no H+ gradient is made. instead, NADPH is made using NADPH reductase
how does the electron transport chain in photosystem I differ from photosystem II?
-PS I does not generate a H+ gradient
-instead it uses the electron energy to convert NADP+ to NADPH by using the enzyme NADPH reductase
what is the function of cyclic electron flow?
to produce ATP without the synthesis of NADPH in photosystem I
why do plant cells need to use cyclic electron flow?
-the calvin cycle needs 9 ATP for every 6 NADPH
-but NADPH and ATP are made in the photosystems in a 1:1 ratio
-therefore, extra ATP needs to be synthesized
what are the products of the calvin cycle?
-3 Carbon sugar
-9x ADP + Pi
-6x NADP+
what are the reactants of the calvin cycle?
-6x NADPH
-9x ATP
-3x CO2
what is the 2nd phase of the calvin cycle?
-reduction: carbon compounds gain energy [reduction]
-NADPH and ATP lose energy [oxidization]
what is the 1st phase of the calvin cycle?
-carbon fixation: CO2 must be changed from a gas to an organic molecule
-done through binding to RuBP and being catalyzed by the enzyme rubisco
what is the 3rd phase of the calvin cycle?
-regeneration of the CO2 acceptor (RuBP = ribulose biphosphate)
what is photorespiration?
a process in which plants use oxygen for the calvin cycle instead of CO2, generating no sugar and essentially wasting NADPH/ATP
why does photorespiration occur?
when plants keep their stomata closed to save water, CO2 can’t enter and O2 builds up, eventually binding to RuBP and entering the calvin cycle
what are the three types of carbon fixating plants?
C3, C4, and CAM
what are C3 plants? where do they fix carbon?
-plants, usually crops, that fix carbon in the mesophyll of their leaves
-these plants are most affected by photorespiration
what are C4 plants? how do they combat photorespiration?
-C4 plants allow their CO2 to be fixed and stored as malic acid in the mesophyll of their leaves
-calvin cycle occurs in bundle-sheath cells
what are CAM plants?
-plants that open their stomata at night and close them during the day
-CO2 is taken in at night and fixed as organic acids for use during the day
