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bio ch. 7
Terms in this set (44)
what does all life on earth depend on?
what do photosynthetic organisms do?
Photosynthetic organisms (algae, plants, and cyanobacteria) transforms solar energy into the chemical energy of carbohydrates.
they are autotrophs
organism that can capture energy and synthesize organic molecules from inorganic nutrients
process, usually occurring within chloroplasts, that uses solar energy to reduce carbon dioxide to carbohydrate
what do photosynthesizers produce>
feed themselves as well as heterotrophs
organism that cannot synthesize needed organic compounds from inorganic substances and therefore must take in organic food
what is the biomass of a tree made from?
○ The biomass (dry weight) of a tree is from the air because carbon dioxide form the air is absorbed by the tree during photosynthesis
what does photosynthesis convert light energy to?
converts light energy to the mechanical energy of food
membrane-bounded organelle in algae and plants with chlorophyll-containing membranous thylakoids; where photosynthesis takes place
what does the structural organization of photosynthetic bacteria cells allow?
§ The structural organization of the photosynthetic bacteria cells allows for the chemical reactions of photosynthesis
where is the major location of photosynthesis in plants?
where does the green color of chloroplasts come from?
what happens in light-dependent reaction?
§ Energy-capturing reactions
§ Chlorophyll absorbs solar energy
§ This energizes electrons
§ Electrons move down an electron transport chain
□ Pumps Hydrogen in to thylakoids
□ Used to make ATP out of ADP and NADPH out of NADP
where do calvin cycle reactions take place?
in the stroma
what happens in the calvin cycle?
® The Calvin cycle uses the products form the light reaction to do its thing.
® Forms sugar (carbohydrates) from CO2, using ATP and NADPH.
® The Calvin Cycle begins with carbon fixation, incorporation CO2 into organic molecules.
® The Calvin cycle produces carbohydrates which gives plants the ability to store energy (use during winter when light reactions can't occur)
® The Calvin Cycle gives the light reactions NADP+ and ADP which the light reactions use as reactants.
what is the equation of photosynthesis?
6CO2 + 6H2O + Light Energy -> C6H12O6 + 6O2
why do chloroplasts split water?
§ Chloroplasts split H2O into H and O, incorporating the electrons of H into sugar molecules and releasing O as a by-product=phytolyses
□ Light is the source of energy used to split the water.
§ The oxygen that is emitted by plants comes from this splitting of water.
what kind of reaction is photosynthesis? what kind of process is it?
a redox reaction
§ It is the opposite of cellular respiration
§ Photosynthesis is an endergonic process; the energy boost is provided by light.
what are the two stages of photosynthesis?
§ Light reactions (the photo part-light dependent) and Calvin Cycle (the synthesis part-light independent)
what do the light reactions do?
reduce NADP+ to NADPH
generate ATP from ADP by phosphorylation
chemicals that absorb certain wavelenghts of light
for photosynthetic pigments, a graph of how much solar radiation is absorbed versus the wavelenght of light
what do pigments in chlorophyll do?
§ Pigments found in chlorophyll absorb various portions of visible light
why is chlorophyll green?
§ Chlorophyll is green because it absorbs much of the reds and blues of white light (if you absorb everything but green, all you see is green).
□ If a pigment absorbs no colors it is white, if a pigment absorbs all light, it is black.
□ Photosynthesis does not absorb green light!!!
□ In fall, the trees absorb the green chlorophyll to use for spring when they make new leaves, and that is why the leaves turn red, yellow, and orange.
what are the noncyclic and cyclic pathways?
two alternate electron pathways of light reactions
photosynthetic unit where solar energy is absorbed and high-energy electrons are generated; contains a pigment complex and an electron acceptor
what do BOTH the cyclic and noncyclic pathways do?
§ Both capture light energy with photosystems
§ Bot occur in the thylakoid membranes
§ Both produce ATP
□ However, the noncyclic pathway also produces NADPH, therefore the cyclic pathway will not go to the Calvin cycle since it does not produce NADPH. So, in the cyclic pathway, we do not make carbohydrates for energy storage (what the Calvin Cycle does).
what are the two types of photosystems in the thylakoid membrane?
□ Two types of photosystems in the thylakoid membrane:
® Photosystem II (PS II) functions first
◊ Best at absorbing a wavelength of 680 nm (red)
◊ The reaction-center of chlorophyll "a" of PS II is called P680
® Photosystem I (PS I)
◊ best at absorbing a wavelength of 700 nm (darker form of red)
The reaction-center of chlorophyll "a" of PS I is called P700
what is the linear electron flow? where does the non-cyclic (linear) electron flow occur?
the primary pathway in light reactions, involves both photosystems and produces ATP and NADPH using light energy.
Happens in PS II
what happens in the linear electron flow?
□ A photon hits a pigment and its energy is passed along until it excited P680.
□ An excited electron from P680 is transferred to the primary electron acceptor (first thing to absorb the electron)
□ H2O is split by enzymes (photolyses) and the electrons are transferred form the hydrogen atoms to P680+ (plus sign because it's been oxidized, so it needs to have an electron to put back when it is reduced).
□ O2 is released as a by-product of this reaction.
□ Each electron from the primary electron acceptor "falls" down an electron transport chain from PS II to PS I.
□ Energy is released by the falling electron (in the form of ATP) which drives the creation of a proton gradient across the thylakoid membrane.
□ Diffusion of (check on slide)
□ In PS I transferred light energy excited P700 which loses an electron to an electron acceptor.
□ P700+ accepts an electron passed down from PS II via the electron transport chain. Each electron ends up getting charged twice by PS II and PS I.
□ Each electron "falls" down another ETC from PS I to the protein ferredoxin (Fd).
□ The electrons are then transferred to NADP+, reducing it to NADPH. The electrons are making NADPH.
® This process also removes an H+ form the stroma.
□ The electrons of NADPH go to the Calvin cycle.
what is the organization of the thylakoid?
§ Photosystems are embedded in the thylakoid membrane.
§ Each time water is oxidized, two H+ remain in the thylakoid space.
§ Protons (H+) are being pumped through the membrane (between the photosystems, during the electron transport chain) and then flow out of the membrane which, that high energy of them flowing out, makes ATP from ADP + Pi=chemiosmosis.
what happens in the cyclic electron flow?
§ Only uses PS I and produces ATP, but does not make NADPH.
§ No oxygen is released=there's no water=no splitting of water=no PS II.
Generates surplus ATP, satisfying the higher demand in the Calvin cycle
how does the cyclic electron flow work?
□ Electron gets excited=goes to electron acceptor,
□ Goes to the electron transport chain that makes ATP (instead of the one that makes NADPH).
how does tropical rain forest destruction affect climate change?
§ Trees take away CO2, slowing global warming.
§ When we cut down trees in the rainforest, CO2 in the atmosphere, can't be taken out.
what are the steps of the calvin cycle?
fixation of carbon dixoide
Reduction of Carbon dioxide
Regeneration of RuBP
what is the calvin cycle
○ A cyclic series of reactions that comes after the light reactions
○ Utilizes CO2 to produce carbohydrates
what is the process of the calvin cycle?
□ RuBP (5-carbon molecule) which is converted by Rubisco into a 6-carbon sugar which is split into 3-carbon sugars.
□ ATP and NADPH are being used and sugar is going to come out.
§ CO2 is now attached to something because it is part of a carbohydrate.
§ Look at diagram on slide 48
§ If CO2 is cut off, the CO2 acceptor will increase because there is nothing to convert it to the new molecule. The reactants will increase and the products will decrease.
how is RuBP regenerated?
§ RuBP is used in CO2 fixation and therefore must be replaced
§ Happens every three turns of the Calvin cycle:
□ Five G3P (a 3-carbon molecule) are used with ATP to remake three RuBP (a 5-carbon molecule)
why will plants start photorepsiration?
§ On hot days, plants close stomata, which conserves water
§ The closing of stomata reduces access to CO2 and causes O2 to build up
Because there's too much oxygen and not enough carbon dioxide, plants will start a process=photorespiration
how does photorespiration work?
in most plants (C3 plants), initial fixation of CO2 via rubisco, forms a three-carbon compound.
in photorespiration, rubisco adds O2 instead of CO2 in the Calvin cycle, producing a 2-carbon compound
photorespiration consumes oxygen and organic fuel and releases CO2 without producing ATP or sugar
on a hot, dry day it can drain as much as 50% of the carbon fixed by the calvin cycle
what is the importance of the Calvin Cycle?
G3P can be converted to many other molecules
the hydrocarbon skeleton of G3P can form
fatty acids and glycerol to make plant oils
starch and cellulose
what do C4 plants do?
§ C4 plants=i.e. sugarcane, minimize the cost of photorespiration by incorporating carbon dioxide into four carbon compounds=this requires the enzyme PEP carboxylase
□ This four carbon compound conserves carbon for a while so when the stoma closes up and carbon dioxide is running low, the plant pulls the extra carbon and combines it with oxygen to form carbon dioxide.
how is C4 plants different from C3 plants?
§ PEP carboxylase has a higher affinity for carbon dioxide than rubisco does; it can fix carbon dioxide even when carbon dioxide concentrations are low.
§ The chloroplasts of C3 plants are not that organized around the stomata while in the C4 plant, they are close to the stomata because they have to take advantage of when its open since it's not always open like in the C3 plants.
what do CAM plants do?
§ Some plants, including succulents, use CAM to fix carbon
§ CAM Plants=open their stomata at night, bringing in the carbon dioxide and incorporating it into organic acids
§ Their stomata close during the day, and CO2 is released from the organic acids and used in the Calvin cycle at night. CO2 is brought in to be used in the calvin cycle ONLY AT NIGHT.
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