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21 Cards in this Set

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Photosynthesis is a metabolic pathway that converts solar energy (electromagnetic) to chemical energy stored in the bonds of glucose

Photosynthesis consists of two stages:


  1. Photophosphorylation/“light reactions”
  2. Calvin cycle/ “light dependent reactions"

The light reactions take place on the thylakoidmembrane inside the chloroplasts. The interior of the thylakoid is called thelumen




Pigments are molecules that absorb light in thevisible spectrum

The purpose of the non-cyclic electron pathway ofphotosynthesis is to produce ATP and NADPH → which will be used in the second stage of photosynthesis


→ In this pathway electrons in photosynthesis II are exited by light energy and taken up by the primary electron acceptor pheophytin1


→ the electrons then pass along an electron transport chain where ATP is produced.

Step 1:Photons strike the photosystem of IIp680


electrons energized (boosts their energy)


→ photolysis (“splitting of water”) occurs: az-enzyme catalyzes the removal of 2 electrons & 2 protons (H+) from water(H20)


→ two H20 molecules are split in order to provide one molecule of 02, which is given off as a waste gas

Step 2: the energized electrons pass to the electron transport chain where they are passed from one molecule to another via a series of redox reactions

Step 3: as electrons pass from Pq to the cytochrome b/f complex, some of their energy is utilized to pump protons (H+) from the stroma into the lumen → The protons are moved via active transport from an area of low concentration (in the stroma) to an area of high concentration (lumen), across the thylakoid membrane- this isthe proton pump.

Step 4: The protons (H+) from photolysis accumulate in the lumen of the thylakoid


→ 02 diffuses out of the cell

Step 5: The protons from the stroma and from photolysis accumulate in the lumen, increasing the concentration of the lumen

Step 6: The protons move back across the membrane (from lumen to stroma) by passing througha channel protein called ATP synthase. → As they do so, their charge provides energy for ATP synthase to catalyze the formation of ATP by adding an inorganic phosphate group (pi) to ADP→ This is photophosphorylation: thephosphorylation of ATP by the enzyme ATP synthase, using energy from the sun

Step 7: Electrons pass from the electron transport chain to the Ip700 photosystem. Solar energy energizes more electrons from this photosystem to higher energy levels.

Step 8: These electrons enter a very short ETC where they eventually pass to NADP reductase, an enzyme that catalyzes the formation of the coenzyme NADPH + H from NADP+ (this molecule is reduced by accepting 2electrons and 2 protons)

Step 9: A carbon atom from atmospheric C02 is fixed to Ribulosebiphosphate (RuBP) by the enzyme RuBP carboxylase (rubisco). The five-carbonRuBP is changed to a 6-carbon unstable intermediate molecule, and this immediately splits into two molecules of 3-phosphoglcerate (PGA-3 carbons each)→ This is carbon fixation

Step 10: PGA is reduced to PGAL (glyceraldehyde-3-photosphate, orG3P) in two steps:


→ the first requires ATP (PGAP, an intermediate molecule is produced) and NADPH in the second. → This is reduction of PGA


→ at this point one molecule of PGAL leaves the Calvin cycle to be used in later metabolic pathways to make glucose and other molecules

Step 11: The remaining PGAL molecules pass through a series of reactions requiring ATP, in order to regenerate RuBP, which is necessary tokeep the calvin cycle running.→ This is regeneration

How many C02molecules are needed per glucose molecule?


→ 6 C02’s per glucose
How many ATP and NADPH molecules are required per glucose molecule?


→ 18 ATP


→ 12 NADP

The water necessary for photosynthesis:


→Provides the electrons to replace lost electronsin photosystem II


The reaction center pigment differs from other pigment molecules oflight harvesting complex in what way?


→The reaction center pigment transfers excited electrons to other molecules

During the light-dependent reactions, the highenergy electron from an excited p680: →eventually moves to NADP+


The Calvin cycle occurs where?


→In the stroma




Starch stored in the cytoplasm of plants is produced from glycerahdehyde-3-photosphate molecules transported from the chloroplasts.

The NADPH is produced during the light-dependent reactions necessaryfor?


→The reduction phase, which produces carbohydrates in the calvin cycle


What is the function of RuBp in the Calvin cycle?


To accept carbon dioxide

Which process in considered redox step? →conversion of NADPH to NADP+


During the first phase of the Calvin cycle, carbon dioxide is incorporated into the ribulosebiphosphate to form what?


→3-phosphoglcerate


The majority of the G3P produced during the reduction and carbohydrate production phase is used to produce what?


→RuBp to continue the cycle

Describe the two distinct phases of photosynthesis, including their reactants and products


Photophosphorylation →H20, light →ATP, NADPH


Calvin cycle → C02, ATP, NADPH →PGAL




Describe the arrangement of pigments andproteins in the thylakoid membranes arranged in photosystems- embedded in the membrane to form ETC

What is the role of each of the structures?Leaf veins: transport water


Stomata: c02 in, oxygen out
Mesophyl: chloroplasts -> mostphotosynthesis Thylakoids: membrane: ETC, ATPproduction Stroma: calvin cycle

Adenosine triphosphate (ATP)


→A nucleotide that serves as the most important energy-transfer molecule in living things.

C4 photosynthesis:


A form of photosynthesis in which carbon dioxide is first fixed into a four-carbon molecule and then transferred to special bundle sheath cells in which the Calvin cycle is undertaken.

Calvin cycle/reaction:


The set of steps in photosynthesis in which an energy-rich sugar is produced by means of two essential processes—the fixing of atmospheric carbon dioxide into a sugar and the energizing of this sugar with the addition of electrons supplied by the light-dependent reactions of photosynthesis.

CAM Photosynthesis:
→A form of photosynthesis, undertaken by some plants in hot, dry climates, in which carbon fixation takes place at night and the Calvin cycle during the day. Practiced by succulent plants in particular, its metabolism allows plants to preserve water by opening their stomata only at night.

chlorophyll a:


The primary pigment of chloroplasts, found embedded in its membranes.




Together with the accessory pigments, it absorbs some wavelengths of sunlight in the first step of photosynthesis.

chloroplast:


The organelle within plant and algae cells that is the site of photosynthesis.

photorespiration:


→A process in which the enzyme rubisco undercuts carbon fixation in photosynthesis by binding with oxygen instead of with carbon dioxide. This wasteful reaction takes place most frequently in C3 plants.

photosystem:


→An organized complex of molecules within a thylakoid membrane that, in photosynthesis, collects solar energy and transforms it into chemical energy.

reaction center:


A molecular complex in a chloroplast that, in photosynthesis, transforms solar energy into chemical energy.

rubisco:


An enzyme that allows plants to incorporate atmospheric carbon dioxide into their own sugars during the process of photosynthesis.

stomata:


Microscopic pores, found in greatest abundance on the undersides of leaves, that allow plants to exchange gases with the atmosphere. (Carbon dioxide moves into plants while oxygen and water vapor move out.)

stroma:


In plants and algae, the liquid material of chloroplasts that is the site of the Calvin cycle.

thylakoid:


→A flattened, membrane-bound sac in the interior of a chloroplast that serves as the site for the light reactions in photosynthesis.


→ where the light-capturing reactions of photosynthesis occur


→ chlorophyll & other pigments are embedded



Name the parts of a chloroplast:


→outer membrane


→inner membrane


→a liquid called the stroma

What is the network of membranes within chloroplasts?


thylakoids


When thylakoids stack on top of each other they form?


→a granum


Any compound that strongly absorbs visible wavelengths of sunlight is called a...


→pigment

first step in photosythesis is called:


→light reaction


second step in photosynthesis is called:


Calvin Cycle


two important things in light reaction step:


1) the splitting of water


2) transformation of solar energy to chemical energy

what step does the oxygen in our atmosphere come from?




1) the water is split


2) the hydrogen atoms are removed from H2O3) the oxygen is left behind and the two oxygen atoms come together and the result is O2

energized sugar that is produced in the calvin cycle?


G3P


What does two molecules of G3P turn into?


→a six-carbon sugar glucose



The energy acquired in the light reactions takes two forms: energetic _____ stored in the carrier _____ and energy stored in the energy transfer molecule _____. An important by-product of the light reactions is the ____ produced when water is split.




→electrons; NADPH; ATP; oxygen

The enzyme rubisco brings together the _______ (from the plant) and _______ (from the atmosphere), creating the product that moves through the Calvin cycle.




→low-energy sugar


→carbon