AP Biology Chapter 10 Photosynthesis
Terms in this set (67)
Which color has the shortest wavelength in the visible spectrum?
What would happen is photosynthesis stopped occurring throughout the world?
the extinction of plants and animals
*plants are producers, by which all the energy on earth is provided
Where does photosynthesis commonly take place?
mosses, ferms, algae, leafy plants
NOT in fungi
*fungi are heterotrophs and do not contain chloroplasts
What are needed for photosynthesis to occur?
carbon dioxide, chlorophyll, sunlight, NADP+
*CO2 is required for the Calvin cycle; NADP+ extracts electrons from the light independent reactions; sunlight is required to excite electrons in chlorophyll; O2 is produced in photosynthesis, but not required
What are characteristics of chloroplasts?
-located in the mesophyll tissue of leaves
-bound by a double membrane
-contain chlorophyll molecules
-similar in size and structure to mitochondria
-contained within the plant cell
NOT found in the fluids that surround most plant cells
Where does the oxygen produced in light dependent reactions of photosynthesis come from?
*H2O is split in order to provide electrons to chlorophyll in photosystem II; a byproduct of the spitting of 2H2O molecules is 4H+ ions and one O2
What is the compound that is incorporated into existing organic molecules to build carbohydrates during photosynthesis?
What is the function of the waxy cuticle found on the leaves of many higher plants?
protect the leaf from water loss
*the adaptation of the cuticle serves to avoid dehydration
What is a major purpose of thylakoids that form the grana in chloroplasts?
to provide increased membrane surface area for the reactions in the light phase
*similar to the cristae in mitochondria, the thylakoids increase the surface area for the light dependent reactions to take place
Why are accessory pigments such as chlorophyll b, xanthophyll, and carotenoids important in photosynthesis?
because they are able to absorb wavelengths of light that are not absorbed by chlorophyll a
*accessory pigments are able to absorb different wavelengths when compared to chlorophyll a, the primary photosynthetic pigment
What is the source of the electrons captured and transferred by NADPH?
*H2O is responsible for replenishing electrons "lost" from PSII; an electron source is necessary as the electrons are not recycled; the electrons eventually reside in glucose/starch
Why is ribulose biphosphate (RuBP) important in the light independent reactions?
it is a molecule that combines with carbon dioxide
*with the aid of rubisco, RuBP combines with CO2 at the beginning of the Calvin cycle
How is PGA formed during the Calvin cycle?
through the breakdown of an unstable six-carbon molecule
*RuBP and CO2 combine to form an unstable molecule that will later be broken down into PGA; the photosynthesis of ATP and NADPH both occur in the light dependent reactions
What are glyceraldehyde-3-phosphate (PGAL) molecules used to create?
RUBP and glucose
*two G-3-P molecules will combine to form a glucose
How is the C-4 photosynthesis pathway found in some plants characterized?
by the chemical transfer of ribulose biphosphate from one tissue area to another
*the reactants for the Calvin cycle occur are transferred to the bundle sheath cells during C-4 photosynthesis
What contains chlorophyll molecules imbedded in membranes?
*grana (stacks of thylakoids) contain chlorophyll molecules in the photosynthesis
What are the regions of chloroplasts where light dependent and light independent reactions occur?
grana and stroma
*the light dependent reactions occur on the thylakoids of grana; the light independent reactions occur in the stroma
What becomes activated when expose to certain wavelengths of light?
*electrons in chlorophyll molecules are excited when exposed to the appropriate wavelength of light
What controls gas exchange through leaf surfaces?
*oxygen and carbon dioxide exchange occurs through the stomata
In what conditions is it advantageous to have the adaptation of a C-4 pathway to be able to photosynthesize faster than plants with a typical C-3 pathway?
-high light intensity
-low carbon dioxide concentration
-dry conditions with high temperatures
-areas where plants grow tightly clustered together
NOT high turgor pressure in guard cells that surround stomata
*high turgor pressure in guard cells would imply that stomata are open; when stomata are open, adequate CO2 is entering and O2 is not trapped; C-4 plants specialize in situations of low CO2 concentration
Where does the Clavin cycle take place?
storm of the chloroplast
Where do protons flow from in chemiosmosis in chloroplasts?
thylakoid space to the stroma
What is a direct by-product when oxygen is released as a result of photosynthesis?
splitting water molecules
In a plant cell, where are the ATP synthase complexes located?
thylakoid membrane and inner mitochondrial membranes
Which of the following statements best represents the relationships between the light reactions and the Calvin cycle?
the light reactions provide ATP and NADPH to the Calvin cycle, and the calvin cycle returns ADP, inorganic phosphate, and NADP+ to the light reactions
Which of the following events occurs in the light reactions of photosynthesis?
light is absorbed and funneled to reaction-center chlorophyll a
How do C3 plants compare to C4 plants?
C4 plants can continue to fix CO2 even at relatively low CO2 concentrations and high oxygen concentrations
Which of the following are products of the light reactions of photosynthesis that are utilized in the Calvin cycle?
ATP and NADPH
Where are the molecules of the electron transport chain associated with photophosphorylation located in plant cells?
thylakoid membranes of chloroplasts
What is the primary function of cyclic electron flow?
to produce additional ATP
Where do the reactions that require ATP take place in C3 photosynthesis?
the calvin cycle only
What is true about the relationship between photosynthesis and cellular respiration?
cellular respiration is catabolic and photosynthesis is anabolic
What is the relationship between wavelength of light and the quantity of energy per photon?
they are inversely related
What is directly associated with photosystem I?
receiving electrons from the thylakoid membrane ETC
Where do the enzymatic reactions of the Calvin cycle take place?
stroma of the chloroplast
What is the primary function of the Calvin cycle?
produce simple sugars from carbon dioxide
Where do the reactions that consume CO2 take place?
the calvin cycle
When does the synthesis of ATP by chemiosmosis occur in photosynthetic cells?
both photosynthesis and cellular respiration
Where does the electron transport chain pump protons from in chloroplasts?
stroma to thylakoid space
How do CAM plants keep stomata closed in daytime in order to reduce loss of water?
they fix CO2 into organic acids during the night when temperatures are cooler
What is photosynthesis?
-the process that converts solar energy into chemical energy
-nourishment to the entire living world
-transforms solar light energy trapped by chloroplasts into chemical bond energy of carbohydrates
What are autotrophs?
-able to sustain themselves without eating anything derived from other organisms
What are heterotrophs?
-obtain their organic material from other organisms
-animals that eat plants or other animals
Where did chloroplasts likely evolve from?
What is the site of photosynthesis?
-leaves are the major locations of photosynthesis
Why are leaves green?
because of the chlorophyll, which provides the green pigment within chloroplasts
How do gases enter the leaf?
through microscopic pores called stomata
What are the mesophyll cells?
-the interior tissue of the leaf
-the main location of chloroplasts
-typically contains 30-40 chloroplasts
What is the anatomy of the chloroplast?
-two membranes, an outer and an inner
-chlorophyll is found in the thylakoid; it converts light energy to chemical energy through PSI and PSII
-grana are stacks of thylakoids in the chloroplasts
-stroma is the fluid outside the thylakoids; it uses chemical energy to convert carbon dioxide to sugar through the Calvin cycle
How are water molecules split during photosynthesis?
-oxygen released by plants comes from the splitting of water
-plants split water as a source of hydrogen and release oxygen as a byproduct
What happens in the light dependent reactions? What are the two types?
-light energy is converted to chemical bond energy in ATP and NADPH during energy capturing reactions
-occurs in the thylakoid membrane
-cyclic: uses PSI to generate ATP
-noncyclic: uses PSI and PSII to generate ATP and NADPH
What happens in the light independent reactions? What are the three parts?
-the calvin cycle
-sugars are produced
-occurs in the stroma of the chloroplasts
-light is not directly required
-CO2 is required
-the Calvin Cycle uses ATP and NADPH from the light reactions to convert CO2 to CH2O (CO2 is reduced)
-the Calvin cycle has 3 Parts: carbon fixation, CO2 reduction, and regeneration of RuBP
What are accessory pigments?
-used to expand the range of wavelengths available for photosynthesis
-chlorophyll b: yellow-green pigment
-chlorophyll a: slightly different absorption spectrum
-carotenoids: yellow-orange hydrocarbons
What are photosystems?
-pigments are assembled into photosystems within the thylakoid membrane
-absorbs solar energy and generates high energy electrons
-composed of an antenna complex, a reaction-center chlorophyll, and a primary electron acceptor
-photosystem I P700
-photosystem II P680
What is the cyclic electron pathway?
-generates ATP, no NADPH, and no Oxygen
-uses PS I.
-cyclic because excited electrons leave from the chlorophyll a at the reaction center and return to the reaction center
-cyclic supplements the ATP supply required for the Calvin cycle and other metabolic pathways
-some photosynthetic bacteria use cyclic only, suggesting it may have evolved early
-may be utilized only when CO2 is in limited supply
-photons are absorbed by PS I.
-reaction center releases excited electrons to the electron acceptor
-electrons are passed to ferredoxin
-electrons travel down Electron transport System (ETS); as they move down ETS they pass from higher to lower energy level and the energy released is stored in form of H+ gradient
-when H+ ions flow down their electrochemical gradient through ATP synthase complesxes, ATP is produced
What is the noncyclic electron pathway?
-both PS I and PS II are used
-oxygen, NADPH, and ATP are produced
-occurs in the thylakoid membrane
-electrons move from water through PSII/PSI and then on to NADP+
-PSII takes replacement electrons from water, which splits, releasing O2 and H+ ions
-PSII absorbs light energy and boosts electrons
-electrons are passed to the primary electron acceptor and then to the ETS
-electrons lose potential energy and produce ATP as they move down the ETS and arrive at the PSI
-light excites electrons in PSI and these excited electrons do not return to the reaction center but are stored in NADPH
-again in PSI, excited electrons are passed to an electron acceptor and then to ferredoxin
-ferredoxin passes the electrons to NADP+ to produce NADPH
What is chemiosmosis?
-chemiosmosis is a coupled reaction
-the thylakoid space acts as a reservoir for H+ ions; each time water is split, two H+ remain
-electrons move carrier to carrier, giving up energy to pump H+ from stroma into thylakoid space
-flow of H+ from high to low concentration across thylakoid membrane provides energy to produce ATP from ADP using the ATP synthase enzyme
-in Photosynthesis this process is called photophosphorylation
-ATP is produced on the outside of the thylakoid, depositing it in the stroma for use in the Calvin Cycle
What is the first part of the calvin cycle?
-CO2 fixation is the attachment of CO2 to an organic compound
-RuBP is the 5 carbon molecule that combines with CO2
-enzyme RuBP carboxylase (rubisco) speeds the reaction
-the product of this reaction is an unstable 6 carbon intermediate molecule
What is the second part of the calvin cycle?
Reduction of Carbon Dioxide
-6 carbon intermediate immediately breaks down into 2 PGA molecules (3-phosphoglycerate C3)
-each of two PGA molecules undergoes reduction to PGAL in two steps
-light dependent reactions provide NADPH and ATP to reduce PGA to PGAL (G3P)
-it takes 2 PGAL to make 1 glucose and 6 turns of the Calvin cycle
What is the third part of the calvin cycle?
Regeneration of RuBP
-every 3 turns of the Calvin Cycle, 6 PGAL are produced
-5 PGAL are used to regenerate 3 RuBP and 1 is used to build carbohydrate
-it takes 2 PGAL to build 1 Glucose
-PGAL is the raw material that can be used to synthesize other carbohydrates as well
-to make this glucose 18 ATP and 12 NADPH are used
What is another name for C3 photosynthesis?
The Calvin Cycle because the first molecule created (PGA) is a 3 carbon molecule
What is photorespiration?
-a metabolic pathway that consumes oxygen, evolves CO2, produces no ATP and decreases photosynthesis
-occurs because active site of rubisco can accept O2 as well as CO2
-when O2 concentration in a leaf's air spaces is higher than CO2, rubisco accepts O2 and tranfers it to RuBP
-whether photorespiration is beneficial to plants is not known
-if photorespiration could be reduced in agricultural plants, crop yields and food supplies would increase
-photorespiration is fostered by hot, dry, bright days when plants don't open stomata to reduce water loss
What are the modes of photosynthesis?
-sometimes PGA (a 3 carbon molecule) is not the first molecule created
-C4 plants fix CO2 by forming a C4 molecule prior to the involvement of the Calvin cycle
-CAM plants fix CO2 by forming a C4 molecule at night when the stomato can open without loss of water
How are chloroplasts arranged in C3 plants?
mesophyll cells contain chloroplasts arranged in parallel layers
How are chloroplasts arranged in C4 plants? How does photosynthesis occur in C4 plants?
-bundle sheath cells as well as mesophyll cells contain chloroplasts
-mesophyll cells are arranged concentrically around the bundle sheath cells
-C4 plants use the enzyme PEP carboxylase to fix CO2 to PEP and the end product is oxaloacetate (OAA-a 4 carbon molecule)
-OAA is then converted to malate and the malate is shuttled to bundle sheath cells, where malate is converted to pyruvate and CO2
-pyruvate is then shuttled back to mesophyll cells where one 1 ATP is required to convert the pyruvate back into PEP
-the overall effect is to move CO2 from mesophyll cells to bundle sheath cells
-the purpose of moving CO2 to bundle sheath cells is to increase efficiency of photosynthesis
-very little oxygen reaches bundle sheath cells so when malate delivers CO2 to them rubisco begins the Calvin cycle
-because little oxygen is present here, CO2 can be fixed without competition from O2
-little photorespiration takes place and photosynthesis is more efficient
What are CAM plants?
-crassulacean acid metabolism
-exists in succulent plants adapted to very arid conditions; these plants open their stomata primarily at night and close them during the day
-conserves water during the day but prevents CO2 from entering the leaves
-when stomata are open at night, CO2 is incorporated into a variety of organic acids
-organic acids are stored in vacuoles until morning when the stomata close
-during the day, light reactions supply ATP and NADPH for the Calvin Cycle
-at this time, CO2 is released from the organic acids and used to make sugars
What is chemiosmosis?
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