Chapter 4: Photosynthesis Flashcards
where do heterotrophs get their energy from?
from the food they eat
where do autotrophs get their energy from?
from the food they make themselves
where do phototrophs get their energy from?
through photosynthesis
what do photoautotrophs do in photosynthesis?
take light energy and convert it to chemical energy
what are the three main functions of photosynthesis?
reduce atmospheric carbon, release oxygen, create chemical energy that can be transferred through food chains
what is the purpose of photons in photosynthesis?
to synthesize sugars (glucose)
what is carbon fixation?
process by which inorganic carbon (CO2) is converted into an organic molecule (glucose)
what is photolysis?
the process of splitting water molecules
what does photosynthesis do with electrons released from photolysis?
excites them using solar energy
what occurs after electrons are excited through solar energy?
they are used to power carbon fixation
in terms of their overall reactions, what process are photosynthesis and cellular respiration, to each other?
they are reverse processes of each other
what is the reaction of photosynthesis?
6CO2+6H2O —(solar energy)–> C6H12O6 + 6O2
as opposed to cellular respiration, what type of reaction is photosynthesis and why?
endergonic, non-spontaneous, because it produces glucose after an INPUT of solar energy
as opposed to photosynthesis, what type of reaction is cellular respiration and why?
exergonic, spontaneous, because it breaks down glucose to GENERATE energy in the form of ATP
what is the epidermis?
an outer layer of cells that provides protection and prevents water loss
what are palisade mesophyll cells?
cells located right below the upper epidermis, has MANY chloroplasts, MOST photosynthesis occurs here
what are spongy mesophyll cells?
cells found at bottom of leaf where there is space for gas exchange, space allows these cells to facilitate movement of gases within the leaf, has SOME chloroplasts for MODERATE amounts of photosynthesis
what are stomata?
pores on underside of leaf where gas can enter and exit
what are guard cells?
surround stomata and control their opening/closing
what are chloroplasts?
organelles found in plants and photosynthetic algae, but not in cyanobacteria; similar to mitochondria
what are the structures of chloroplasts, from outermost to innermost?
outer membrane, intermembrane space, inner membrane, stroma, thylakoids, thylakoid lumen
what is the outer membrane of chloroplasts made of?
phospholipid bilayer
what is the intermembrane space of chloroplasts?
space between the outer and inner membranes
what is the inner membrane of chloroplast made of?
phospholipid bilayer
what is stroma in chloroplasts?
fluid material that fills the area inside the inner membrane
where does the calvin cycle occur in chloroplasts?
stroma
what are thylakoids in chloroplasts?
organelle suspended within the stroma; individual layers are thylakoids while entire stack is granum
what reactions occur in the thylakoids?
light dependent reactions
what is the thylakoid lumen in chloroplasts?
the interior of the thylakoid; H+ ions accumulate here, making it acidic
what do light dependent reactions do?
harness light energy to produce ATP and NADPH (electron carrier) to be used ONLY in the calvin cycle
what do photosystems contain?
special pigments, chlorophyll and carotenoids, that absorb photons
what does chlorophyll do that gives plants their green color?
absorb red and blue lights, which reflects green light
what is the reaction center?
in photosystems; holds a special pair of chlorophyll molecules in the center and a primary electron acceptor
what is the structure of the head of a chlorophyll molecule?
porphyrin ring structure with a magnesium atom bound in its center
what photosystems are used in photosynthesis?
photosystem II (P680) and photosystem I (P700)
what is non-cyclic photophosphorylation carried out by?
light-dependent reactions
non-cyclic photophosphorylation 1st step
photolysis: photosystem II absorbs photons to photolyze water into 2 e-, 2 protons (H+), and 1 oxygen atom; H+ released into the thylakoid lumen
non-cyclic photophosphorylation 2nd step
power up electrons: e- passed to reaction center of photosystem II (P680), photons excite e-, high energy e- then passed to primary electron acceptor
non-cyclic photophosphorylation 3rd step
use ETC to harness energy: primary electron acceptor sends excited e- to ETC in thylakoid membrane; energy released from e- pumps H+ from the stroma to thylakoid lumen
non-cyclic photophosphorylation 4th step
chemiosmosis intermission: water photolysis and protons pumps created an electrochemical gradient in the thylakoid lumen; protons flow down gradient from lumen back to stroma through ATP synthase, generates ATP for calvin cycle
non-cyclic photophosphorylation 5th step
rinse and repeat: e- leave ETC and are passed to photosystem I reaction center (P700); photons again excite pigments in photosystem I, energizing e- to be passed to another primary electron acceptor
non-cyclic photophosphorylation 6th step
generate e- carrier: e- are sent to a second, short ETC that ends with NADP+ reductase to produce NADPH
what is NADP+ reductase?
an enzyme that reduces NADP+ into NADPH using electrons and protons
what occurs in cyclic photophosphorylation?
photosystem I passes its electrons back to the first ETC instead of the second ETC, causing more proton pumping and more ATP production, while no NADPH is generated
what is the calvin cycle made up of and why?
reactions known as light-INdependent reactions; because they do NOT directly use light energy, BUT can only occur if the light-dependent reactions are providing ATP and NADPH
light-dependent reactions are also known as?
dark reactions
what exactly does the calvin cycle do in the stroma of plant mesophyll cells?
fixes carbon dioxide that enters stomata
calvin cycle 1st step
carbon fixation: carbon dioxide combines with 5-carbon RuBP (ribulose-1,5-biphosphate) to form 6-carbon molecules, which quickly breaks down into 3-carbon PGA (phosphoglycerates), which occurs by being catalyzed by RuBisCo
calvin cycle 2nd step
reduction: PGA is phosphorylated by ATP and subsequently reduced by NADPH to form G3P (glyceraldehyde-3-phosphate)
calvin cycle 3rd step
regeneration: most of the G3P is converted back to RuBP
calvin cycle 4th step
carbohydrate synthesis: some of the G3P is used to make glucose
what is the chemical reaction of light independent reactions?
6CO2 + 18ATP + 12NADPH + H+ → 18ADP + 18Pi + 12NADP+ + 1glucose
in addition to fixing carbon dioxide into RuBP, what else can RuBisCo (enzyme) do?
cause oxygen to bind to RuBP in a process called photorespiration
where does photorespiration occur and what does it produce?
occurs in the stroma; produces a two-carbon molecule phosphoglycolate that is shuttled to peroxisomes and mitochondria for conversion into PGA
what happens to fixed carbon during photorespiration?
gets lost as carbon dioxide
what are the overall products of photorespiration?
net loss of fixed carbon atoms and no new glucose
what else is photorespiration known as and why?
C2 photosynthesis; because it produces two-carbon phosphoglycolate
photorespiration during hot and dry climate
stomata are closed to minimize water loss, leads to oxygen accumulation inside the leaf while carbon dioxide is used up, RuBisCo then binds with oxygen instead of carbon dioxide, leading to photorespiration
what occurs in C3 photosynthesis (alternative photosynthetic pathway) and what is produced?
normal photosynthesis, where three-carbon PGA is produced
what is produced in C4 photosynthesis (alternative photosynthetic pathway) and in what climate?
produces four-carbon oxaloacetate; occurs in plants living in hot environments
what happens to carbon dioxide in C4 photosynthesis?
carbon dioxide is spatially isolated to prevent photorespiration
C4 photosynthesis 1st step
PEP carboxylase fixes CO2 into a three-carbon PEP molecule, producing oxaloacetate, which is converted into malate in the mesophyll cell
C4 photosynthesis 2nd step
malate is transferred to bundle sheath cells, which have lower concentrations of oxygen
C4 photosynthesis 3rd step
Malate is decarboxylated → inorganic CO2, spatially isolating where CO2 is fixed by RuBisCo; only drawback is pyruvate is also produced and needs to be shuttled back to mesophyll cells via ATP hydrolysis
C4 photosynthesis 4th step
pyruvate is converted back into PEP
what does crassulacean acid metabolism (CAM) photosynthesis use and for what?
uses temporal isolation of carbon dioxide to prevent photorespiration in hot environments
CAM photosynthesis 1st step
during the day: stomata are closed to prevent transpiration (evaporation of water from plants)
CAM photosynthesis 2nd step
during the night: stomata are open to let carbon dioxide in; PEP carboxylase will fix CO2 into PEP, producing oxaloacetate and then malate; however, malate is stored in vacuoles instead of being shuttled to bundle sheath cells
CAM photosynthesis 3rd step
during next day: stomata closed again and malate converted back into oxaloacetate, which releases CO2 and PEP; CO2 will accumulate in the leaf for use in the calvin cycle through temporal isolation
