Ch 10 Flashcards
photosynthesis
the capture of light energy from the sun and its conversion to chemical energy that is stored in organic molecules like sugars
autotrophs
self-feeders
photoautotrophs
organisms that use light as a source of energy to synthesize organic substances
heterotrophs
live on compounds produced by other organisms
all green parts of a plant have
chloroplasts
mesophyll
the tissue in the interior of the leaf where most chloroplasts are found
stoma
greek for mouth
stomata
microscopic pores where oxygen leaves and CO2 enters
-main avenues of transpiration; the evaporative loss of water from leaves
veins in plants
- water from roots takes to leaves
- exports sugar from leaves to nonphotosynthetic parts of plants
thylakoids
a membrane system suspended in the stroma made up of sacs which segregate the stroma from the thylakoid space inside the sacs
chloroplast
- two envelopes surrounding a dense fluid called the stroma
chlorophyll
- resides in the thylakoid membrane of the chloroplasts
- gives plants green color
- absorbs the light that drives photosynthesis
grana (singular granum)
stacks of thylakoids
photosynthesis formula for green plants
6CO2+12H20+ light energy=C6H12O6+6O2+6H2O or sans H2O 6CO2+6H20+ light energy=C6H12O6+6O2 then divided by 6 CO2+H20+ light energy=(CH2O)+O2
photosynthesis is __gonic, and explain
ender-, electrons increase in potential energy, water is split, and electrons are transferred along with hydrogen ions from water to CO2 reducing it to sugar, energy boost is provided by light
the two stages of photosynthesis
light reactions and the calvin cycle
light reactions (summary)
- convert solar energy to chemical energy
- water is split providing e- and protons (hydrogen ions, H+)
- light absorbed by chlorophyll drives a transfer of electrons and H+ from water to an acceptor called NADP+
- solar power reduces NADP+ to NADPH by adding a pair of electrons along with AN H+
- phosphorylation
- two chemical energy products ATP and NADPH
photophosphorylation
generation of ATP using chemiosmosis to power the addition of a phosphate group to ADP
calvin cycle
-begins by incorporating CO2 from air via carbon fixation
-
carbon fixation
- initial incorporation of carbon into organic compounds
- reduces the fixed carbon to carbohydrates by the addition of e-, reducing power is NADPH
- what makes sugars
- known as dark reactions or light-independent reactions
- needs ATP and NADPH
wavelength
distance between crests of electromagnetic waves
electromagnetic spectrum
entire range of radiation nanometer (for gamma rays) to more than a kilometer (radio waves)
visible light
most important to life, can be detected by human eye
photons
“particles” of light, not tangible, have fixed energy quantity
atmosphere and light
filters out some radiation, not visible light
pigments
substances that absorb light
-different pigments absorb different wavelengths
spectrophotometer
machine that measures the ability of a pigment to absorb various wavelengths of light, it directs beam of light of different wavelengths through a solution of a pigment and measures the fraction of the light transmitted at each wavelength
absorption spectrum
a graph plotting a pigment’s light absorption versus wavelength
3 types of pigments in chloroplasts
- chlorophyll a-participates directly in light reactions works best with red and blue-violet light while green is worst-is blue green
- chlorophyll b-accessory pigment absorbs blue green-is olive green
- carotenoids- a group of accessory pigments, absorbs violet and blue green are yellow and orange
active spectrum
- profiles the relative effectiveness of different wavelengths of radiation in driving the process
- prepared by illuminating chloroplasts with light of different colors and then plotting wavelengths against some measure of photosynthetic rate such as CO2 consumption or O2 emission
photoprotection
- important function of at least some carotenoids
- absorption and dissipation of excessive light energy that would otherwise damage chlorophyll or react with oxygen
- also are protective in human eyes
2 parts of chlorophyll
porphyrin ring: light absorbing “head” of molecule; magnesium atom center
hydrocarbon tail: interacts with hydrophobic regions of proteins inside thylakoid membranes of chloroplasts; H atoms not shown
differences between chlorophyll a and b
a: CH3
b: CHO
phyton
greek for plant
phyochemicals
-things plants can synthesize these antioxidants but we must consume them
what occurs when a pigment is struck by a light
- starts in ground state (electron in normal orbital)
- absorption of photon boosts electron to higher orbital ; in an excited state (this state is unstable)
- only photons absorbed are those whose energy is exactly equal to the difference between the ground state and the excited state
- normally orbital re-drops and releases heat and sometimes light
- chlorophyll will emit light when isolated
photosytem
composed of a reaction-center complex surrounded by several light-harvesting complexes
- is able to harvest light over larger area and spectrum than any individual pigment due to its array of pigments
- when photon is absorbed by a pigment the energy travels from pigment to pigment to the reaction-center complex
- there are two types
reaction-center complex
an organized association of proteins holding a special pair of chlorophyll a molecules
- has the primary electron acceptor
- has pair of special chlorophyll a molecules which can transfer electrons to the primary electron acceptor in a redox reaction
light harvesting complex
various pigment molecules (which may consist of chlorophylls a and b and carotenoids) bound to proteins
primary electron acceptor
a molecule capable of accepting electron and becoming reduced
two types of photosystems
PS II: (comes first) reaction-center chlorophyll a of is P680,as that is what it is best at absorbing, 680nm (red part)
PS I :reaction-center chlorophyll a of is P700,as that is what it is best at absorbing, 700nm (far red part)
linear electron flow
flow of electrons through photosystems and other components in the thylakoid membrane
steps of linear electron flow
- photon strikes a pigment in a light harvesting complex of PS II boosting one of its electrons, as it drops another pigment’s e- goes up, continues until P680 pair is reached in reaction center complex of PS II, exciting an e- in this pair
- e- is transferred from P680 to the primary electron receptor, leaving it P680+
- an enzyme catalyzes the splitting of water into 2 e-, 2 H+, and an Oxygen atom. The electrons are supplied one by one to P68+ to replace the e- it just gave up. the H+ are released into thylakoid lumen, oxygen joins another one into O2
- each excited electron then passes to PS I via an etc made of the e- carrier plastoquinone (Pq), a cytochrome complex, and plastocyanin (Pc) protein
- fall of electrons to lower energy level, provides energy for ATP synthesis. As e- pass through cytochrome complex, H+ are pumped into thylakoid lumen contributing to proton gradient in chemiosmosis
- meanwhile light energy is transferred to PS1’s P700 pair, e- then transferred to PS I’s primary electron receptor, leaving it P700+
- e- are passed in redox reactions from the primary e- receptor down a second etc through the protein ferredoxin (Fd) (chain does not produce ATP)
- enzyme NADP+ reductase catalyzes the transfer of electrons from Fd to NADP+. 2 electrons are needed for its reduction to NADPH. molecule has higher energy level than water; more suitable for calvin cycle, removes H+ from stroma
cyclic electron flow
alternate path which uses photosystem I but not II.
- Fd contributes e- and begins cytochrome complex; repeats cycle from there; produces ATP but not NADPH
- vestigial, but beneficial for low light environment
chemiosmosis in photosynthesis differences
- source of electrons is water
- phosphorylation is different
- remember that ATP is produced as well
- gradient maintained by Photosyetem II and Cytochrome
calvin cycle is __bolic
ana-
carbon enters calvin cycle enters as CO2
and leaves as as sugar
what does the calvin cycle use
- it spends ATP as an energy source
- consumes NADPH as reducing power for adding high energy elcectrons to make the sugar
products directly from calvin cycle and how many times must the cycle run for it
-NOT glucose but a 3-carbon sugar: glyceraldehyde 3-phosphate (G3P); 3 times ; fixing 3 molecules of CO2
-9ADP
-6 inorganic phosphate
-6NADPH
(REMEBER ALL THESE NUMBERS ARE FOR 3 GLUCOSE)
3 phases of calvin cycle
- carbon fixation
- reduction
- regeneration of the CO2 acceptor (RuBP)
Carbon fixation in calvin cycle
calvin cycle incoroporates each CO2, one at a time, by attaching it to a 5-carbon sugar called ribulose biphosphate (RuBP) catalyzed by an enzyme called RuBP carboxylase (rubisco). (most abundant protein on earth) the product is a 6-carbon sugar so unstable it immediately splits in half into two molecules of 3-phosphoglycerate (for each CO2)
Reduction in calvin cycle
each 3-phosphoglycerate receives a phosphate group from ATP becoming 1,3 biphosphoglycerate . Next a pair of electrons donated from NADPH reduces a carboxyl group on 1,3 biphosphoglycerate to the aldehyde group of G3P. G3P is a 3 carbon sugar. 1 G3P leaves but 5 must stay (for 3 CO2)
Regeneration of the CO2 acceptor (RuBP)
in a series of reactions, the carbon skeletons of five molecules of G3P are rearranged by the last steps of the calvin cycle into three molecules RuBP. This spends 3 more ATP. The RuBP is now ready for more CO2 and to repeat the cycle
photosynthesis is an ___property of the intact chloroplast
emergent
on hot dry days most plants
close their stomata
C3 plants
product is a 3 carbon compound, 3 phosphoglycerate
most plants
on hot days photorespirate
photorespiration
- O2 used instead of CO2
- no ATP produced
- consumes ATP
- no sugar produced
- decreases photosynthetic output
- reduces damage to excess light
- may be vestigial
plant adaptations to hot environments
- C4 photosynthesis
- crassulacean acid metabolism (CAM)
C4 plants
- forms 4 carbon product
- two types of cells; bundle-sheath and mesophyll
bundle sheath cells
arranged in tightly packed sheaths around the veins in the leaf,
- mesophyll cells are between bundle sheaths and veins
- calvin cycle confined to bundle-sheath cells but is preceded by incorporation of CO2 into organic compounds in the mesophyll cells
C4 pathway
- in mesophyll cells, the enzyme PEP carboxylase adds CO2 to PEP
- a four carbon compound conveys the atoms of the CO2 into a bundle-sheath cell via plasmodesmata
- in bundle-sheath cells CO2is released and enters the Calvin cycle , extra ATP needed comes from cyclic electron flow
crassulacean acid metabolism (CAM)
- many succulents (water storing plants) open their stomata during the night and close them at night
- incorporate CO2 from night into organic acids
- organic acids stored in vacuoles of mesophyll cells
CAM cycle
1.preliminary incorporation of CO2 into organic acids
2.transfer of CO2 to the calvin cycle
(all occurs in same cell, other than that though, identical to C4 pathway)
