Bio 1080 Chapter 10

Front 1

oxygenic photosynthesis is carried out by

Back 1

cyanobacteria, 7 groups of algae, and all land plants

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6O2 + 12H2O -------> C6H12O6 + 6H2O + 6O2

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photosynthesis

Front 3

in photosynthesis, ____________ becomes reduced

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CO2

Front 4

in photosynthesis, ____________ becomes oxidized

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H2O

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mesophyll

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cells that make up the interior tissue of the leaf

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Each mesophyll contains _________ chloroplasts

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30-40

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stomata

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microscopic pores that allow the entry and exit of CO2 and O2

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photosynthesis is divided into two types of reactions

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light-dependent reactions and carbon-fixation reactions (light-independent reactions)

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light-dependent reactions

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require light, capture energy from sunlight, split H2O, release O2, make APT and reduce NADP+ to NADPH

Front 10

carbon-fixation reactions

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do not require light, use APT and NADPH to synthesize sugar molecules from CO2 (carbon fixation)

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photosynthesis takes place in

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chloroplasts

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thylakoid membrane

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internal membrane arranged in flattened sacs- contain clorophyll and other pigments

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grana

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stacks of thylakoid membranes

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stroma

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semiliquid substance surrounding the thylakoid membranes

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photon

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a particle of light- acts as a discrete bundle of energy, (it's energy content is inversely proportional to the wavelength of the light)

Front 16

the smaller the wavelenghth

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the more energy photons contain

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pigments

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molecules that absorb visible light

Front 18

when a photon strikes a molecule it's energy is either

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lost as heat, or absorbed by the electrons of the molecule

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different __________ absorb different wavelenghts

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pigments

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wavelengths that are not absorbed are

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reflected or transmitted

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chlorophyll makes leaves green because it

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reflects and transmits green light

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two types of pigments used in green plant photosynthesis

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chlorophylls and carotenoids

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chorophyll a

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primary pigment in plants and cyanobacteria, only pigment that can act directly to conver light energy to chemical energy (P680)

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chorophyll a

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absorbs violet-blue and red light

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porphyrin ring

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complex ring structure of chorophyll with magnesium ion at center, photons excite electrons in the ring and they are shuttled away from the ring (has hydrocarbon tail)

Front 26

chlorophyll molecules are embedded in a ______ _______ in the thylakoid membrane

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protein complex

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that which distinguishes chloryphll a from chlorophyll b

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R group in the head of the porphyrin ring (a--CH3, b--- CHO) chorophyll b peak absorption: 700 nm

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accessory pigments

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secondary pigments absorbing light wavelengths other than those absorbed by cholorphyll a (include: chlorophyll b, carotenoids)

Front 29

accessory pigments function

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increase the range of light wavelengths that can be used in photosynthesis, protect chlorophyll by absorbing excessive light

Front 30

photosystem

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consists of a reaction-center complex (a type of protein complex) surrounded by light-harvesting complexes

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light-harvesting complex

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pigment molecules bound to proteins- they transfer the energy of photons to the reaction center

Front 32

at the reaction center, the energy from the antenna complex is transferred to__________ _______

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chloropyll a

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excited electrons are transferred from chloropyll a to an __________ __________

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electron acceptor

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__________ donates an electron to chlorophyll a to replace the excited electron

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water

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electron transport

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step 2 of the light-dependent reaction in which electrons move through carriers to reduce NAPD+ and create a proton gradient

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chemiosmosis

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produces ATP

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NADP+

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electron carrier identical to NAD+ except it has an additional phosphate group

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photosystem II

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reaction center pigment (P680) has a peak absorption at 680 nm

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photosystem I

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reaction center pigment with a peak absorption at 700 nm

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photosystem II acts first

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pigments absorb 2 photons and shuttle energy to the P680 reaction center- 2 excited electrons frmo the P680 are transferred to the electron transport chain, electrons lost from P680 are replaced by electrons released from the splitting of water (byproduct O2)

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electron transport chain

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series of electron carriers embedded in the thylakoid membrane

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cytochrome complex

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pumps protons into the thylakoid space and forms a proton gradient

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chemiosmosis

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the diffusion of H+ (protons) across the thylakoid membrane drives ATP sythesis using ATP synthase

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photosystem I acts second

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by absorbing photons and passes energy to P700 reaction center- excited electrons are transferred to a membrane-bound electron carrier, electrons are used to reduce NADP+ to NADPH

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electrons lost from P700 are replaced from the ________ ________

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cytochrome complex

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cyclic electron flow

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uses only photosystem I and produces ATP, but not NADPH- no oxygen is released- generates surplus ATP satisfying the higher demand in the Calvin cycle

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carbon fixation reactions

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Calvin cycle- to build carbs, cells need energy in the form of ATP from light-dependent reactions, and reduction potential derived from NADPH from photosystem I

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Calvin cycle

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biochemical pathway that allows for carbon fixation, uses ATP and NADPH as energy sources, incorporates CO2 into organic molecules

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Calvin cycle occurs in the _______

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stroma

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carbon fixation

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the incorporation of CO2 into organic molecules, occurs in the first step of the Calvin cycle

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(RuBP) + CO2 --------> 2 (PGA)

5 carbons 1 carbon 3 carbons

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carbon fixation

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rubisco

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catalyzes the carbon fixation reaction

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Calvin cycle is a ___________ reaction

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endergonic, requires massive amount of energy

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energy needed for every 3 CO2 fixed

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9 ATP + 6 NADPH

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end product of the Calvin Cycle

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G3P (glyceraldehyde-3-phosphate)

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3 phases of the Calvin cycle

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1. carbon fixation RuBP+CO2-->2 molecules PGA 2. reduction PGA is reduced to G3P

3. regeneration of RuBP

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__ CO2 must enter the Calvin cycle to produce the __ G3P that will be exported from the chloroplast

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6 , 2

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6 CO2 produces ___ molecules of G3P

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12

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____ GP3 molecules are used to regenerate _____ so that the Calvin Cycle can continue

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10, RuBP

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glucose is produced from ______ which takes place in the ______

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2 G3P molecules, cytoplasm

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energy needed to run the Calvin cycle

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18 ATP molecules, 12 NADPH molecules

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the energy cycle

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photosythesis uses the products of respiration as starting substrates -- respiration uses the products of photosynthesis as starting substrates

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the 2 enzymatic activities of rubisco

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carboxylation (the addition of CO2 to RuBP), and photorespiration (the oxidation of RuBP by the addition of O2)

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photorespiration favored when

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the stomata are closed in hot conditions (low CO2 and high O2), process decreases the efficiency of photosynthesis

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CO2 and O2 compete for the active site on ________ during photorespiration

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rubisco

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the build up of O2

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causes photorespiration, decreasing the efficiency of photosythesis by binding rubisco

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C3 plants

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plants that fix carbon using only C3 photosynthesis (the Calvin Cycle), all reactions take place in mesophyll cells using CO2 that diffuses in through stomata

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some plants can avoid ___________ by using an enzyme other than rubisco

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photorespiration

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PEP carboxylase

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has a higher affinity for CO2 than rubisco, present in C4 plants

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C4 plants

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use PEP carboxylase to capture CO2 which is added to PEP in the mesophyll cell, the resulting 4-carbon compound is moced into a bundle sheath cell (where O2 is low) and the CO2 is released and used in the calvin cycle

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main role of PEP carboxylase

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keeps rubisco saturated with CO2 and isolated from O2

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C4 plants

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corn, sugar cane, many grasses- advantageous in hot dry climates where photorespiration would remove more than half of the carbon fixed by the usual C3 pathway

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cost of C4 pathway

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requires 12 additional ATP compared with the Calvin Cycle to produce a single glucose

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CAM plants

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succulents (cacti, pineapple), keeps stomata open during the night and closed during the day- Fix CO2 using PEP carboxylase during the night to produce a 4 carbon compound

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4 carbon compound in CAM plans

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releases high levels of CO2 during the day, used by rubisco in the Calvin cycle, and minimizing photorespiration (keeps CO2 from running low while stomata are closed)

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C4 vs CAM plants

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both use both C3 and C4 pathways, C4- two pathways occur in different cells, a SPATIAL solution to photorespiration; CAM- C4 pathway at night and the C3 pathway during the day, a TEMPORAL solution to photorespiration