Chapter 10

The last idea in this challenging concept is how chemiosmosis works in photosynthesis. Describe four ways that chemiosmosis is similar in photosynthesis and cellular respiration.

1. Both use an electron transport chain 2. ATP synthase phosphorylates ADP 3. Protons are pumped into one side 4. Those protons diffuse back through ATP synthase complexes

List the three places in the light reactions where a proton-motive force is generated.

1. water split by photostem II 2. as Pq transfers e- to the cytochrome complex, 4 H+ are translocated across the membrane into the thylakoid space 3. hydrogen ions removed from the stroma when taken up by NADP+

Examine Figure 10.18 in your text while we tally carbons. This figure is designed to show the production of one net G3P. That means the Calvin cycle must be turned three times. Each turn will require a starting molecule of ribulose bisphosphate (RuBP), a five-carbon compound. This means we start with __ carbons distributed in three RuBPs. After fixing three molecules of CO2 using the enzyme ________ , the Calvin cycle forms six G3Ps with a total of _____ carbons. At this point the net gain of carbons is ____ , or one net G3P molecule.

15, rubisco, 18, 3

how many turns of the calvin cycle make one G3P

3, one turn per CO2

how many carbon are in glucose

6

equation for photosynthesis

6CO2 (carbon dioxide) + 6H2O (water) +light energy-------> C6H12O6 (glucose) + 6O2 (oxygen)

The net production of one G3P requires __ molecules of ATP and ___ molecules of NADPH.

9,6

To summarize, note that the light reactions store chemical energy in ________ and _____ , which shuttle the energy to the carbohydrate-producing ____ cycle.

ATP, NADPH, Calvin

Use this same figure to explain the correlation between an absorption spectrum and an action spectrum.

Absorption spectrum is the absorption of light by different chloroplast pigments (chlorophyll a, b, and carotenoids) at different wavelengths. Action spectrum is the rate of photosynthesis (O2 release) at different wavelengths.

spectrophotometer

An instrument that measures the proportions of light of different wavelengths absorbed and transmitted by a pigment solution.

chloroplast

An organelle found in plants and photosynthetic protists that absorbs sunlight and uses it to drive the synthesis of organic compounds from carbon dioxide and water.

Define autotrophs and heterotrophs. Which are the producers of the ecosystem? Which are the consumers? Give an example of each group.

Autotrophs don't eat anything derived from other living beings. They are considered the producers of the biosphere because they are the ultimate sources of organic compounds for all nonautotrophic organisms. Heterotrophs are consumers, they eat other organisms because they are unable to make their own food.

C4 plants vs CAM plants

C4 plants close stomata because of temp/dryness CAM plants close stomata at night

Explain the Calvin cycle, using the term carbon fixation in your discussion.

CO2 from the air and organic molecules in the chloroplast incorporate in a process called carbon fixation. The calvin cycle reduces the fixed carbon to carbohydrate by adding electrons. This is powered by NADPH and ATP (from the light reactions section). The Calvin cycle makes sugar

Explain the important events that occur in the carbon fixation stage of the Calvin cycle.

Each CO2 molecule is attached to RuBP which is a five carbon sugar. The enzyme rubisco catalyzes this. The product is a six-carbon intermediate that splits in half because it is unstable and forms two molecules of 3-phosphoglycerate.

Notice the colors and their corresponding wavelengths. Explain the relationship between wavelength and energy.

Each chlorophyll absorbs a different wavelength of light. This means that each one absorbs certain colors because each color has a different wavelength. Higher wavelength light has less energy.

In this reduction stage, the low-energy acid 1,3-bisphosphoglycerate is reduced by electrons from NADPH to form the three-carbon sugar _____ .

G3P

what happens during the second phase of the calvin cycle

G3P production

As electrons fall from photosystem II to photosystem I, the cytochrome complex uses the energy to pump ___ ions. This builds a proton gradient that is used in chemiosmosis to produce what molecule? ___

H+, ATP

What compound is the source of electrons for linear electron flow?

H2O

Study Inquiry Figure 10.9 on p. 194 which describes the classic experiment of Theodor W. Englemann. Describe how he determined an action spectrum long before the invention of a spectrophotometer.

He exposed different areas of alga to different wavelengths. He used this to determen which wavelengths caused the alga to release the most O2.

chlorophyll a performs what function in plants

It absorbs red and blue light that is used to make energy

Explain the role of PEP carboxylase in C4 plants, including key differences between it and rubisco.

It adds CO2 to PEP, forming the four-carbon product oxaloacetate. It has a much higher affinity for CO2 than rubisco.

mesophyll

Leaf cells specialized for photosynthesis. in C3 and CAM plants, mesophyll cells are located between the upper and lower epidermis; in C4 plants, they are located between the bundle-sheath cells and the epidermis

What is the source of energy that excites the electron in photosystem II?

Light photons

Cyclic electron flow can be visualized in Figure 10.15 in your text. Cyclic electron flow is thought to be similar to the first forms of photosynthesis to evolve. In cyclic electron flow no water is split, there is no production of _____ , and there is no release of _____ . (The Big Picture: Why did oxygen not accumulate in the atmosphere until cyclic electron flow evolved?)

NADP, oxygen

In phase two, the reduction stage, what molecule will donate electrons, and therefore is the source of the reducing power?

NADPH

In photosystem I, NADP+ reductase catalyzes the transfer of the excited electron and H+ to NADP+ to form

NADPH

Explain how photorespiration can be a problem in agriculture.

Photorespiration drains away as much as 50% of the carbon fixed by the carbon cycle. If photorespiration could be reduced in certain plant species without otherwise affecting photosynthetic productivity, crop yields and food supplies can increase.

Use two key differences to explain how chemiosmosis is different in photosynthesis and cellular respiration.

Photosynthesis uses water as the source of electrons instead of glucose. Photosynthesis uses light energy while cellular respiration uses food molecules.

what happens during the 3rd phase of the Calvin cycle

RuBP is regenerated

The absorption spectrum of chlorophyll a alone underestimates the effectiveness of certain wavelengths in driving photosynthesis. Explain why this is so.

The absorption spectrum of chlorophyll a alone underestimates the effectiveness of certain wavelengths in driving photosynthesis because accessory pigments with different absorption spectra - including chlorophyll b and carotenoids - broaden the spectrum of colors that can be used for photosynthesis. Slight structural differences between chlorophyll a and b is enough to cause the two pigments to absorb at slightly different wavelengths in the red and blue parts of the spectrum.

Three turns of the Calvin cycle nets one G3P because the other five G3Ps must be recycled to three RuBPs. Explain how the regeneration of RuBP is accomplished.

The carbon skeletons of five molecules of G3P are rearranged into three molecules of RuBP. It does this using 3 molecules of ATP.

NADP+

The oxidized form of nicotinamide adenine dinucleotide phosphate, an electron carrier that can accept electrons, becoming NADPH. NADPH temporarily stores energized electrons produced during the light reactions.

What is the source of O2 in the atmosphere?

The oxygen atom from water splitting combined with another one from water splitting to form O2

Explain what is meant by a C4 plant.

The preface the Calvin cycle with an alternate mode of carbon fixation that forms a four-carbon compound as its first product

absorption spectrum

The range of a pigment's ability to absorb various wavelengths of light. also a graph of such a range

NADPH

The reduced form of nicotinamide adenine dinucleotide phosphate; temporarily stores energized electrons produced during the light reactions. NADPH acts as "reducing power" that can be passed along to an electron acceptor, reducing it.

Explain this statement: "Only the green cells of a plant are the autotroph while the rest of the plant is a heterotroph."

The rest of the plant depends on organic molecules exported from leaves through veins.

Conceptually, it is important to know that the C4 pathway does not replace the Calvin cycle but works as a CO2 pump that prefaces the Calvin cycle. Explain how changes in leaf architecture (Figure 10.19) help isolate rubisco in regions of the leaf that are high in CO2 but low in O2.

The structure and biochemical functions of the leaves of C4 plants are an evolutionary adaptation to hot, dry climates. This adaptation maintains a CO2 concentration in the bundle-sheath cells that favors photosynthesis over photorespiration.

Explain what occurs in the light reactions stage of photosynthesis. Be sure to use NADP+ and photophosphorylation in your discussion.

Water is split, providing electrons, protons, and O2. Light absorbed by chlorophyll drives a transfer of the electrons and hydrogen ions from water to NADP+. Solar energy is used to reduce NAD+ to NADPH by adding a pair of electrons and an H+. ATP is generated using chemiosmosis to phosphorylate ADP to ATP. NADH and ATP are the products.

Using 18O as the basis of your discussion, explain how we know that the oxygen released in photosynthesis comes from water.

We used 18O as a tracer and found that the O2 produced by plants was only labeled with it if water was the source of the tracer. It didn't appear if CO2 was used.

reaction-center complex

a complex of proteins associated with a special pair of chlorophyll a molecules and a primary electron acceptor. located centrally in a photosystem, this complex triggers the light reactions of photosynthesis. excited by light energy, the pair of chlorophylls donates an electron to the primary electron acceptor, which passes an electron to an electron transport chain

thylakoid

a flattened, membranous sac inside a chloroplast. thylakoids often exist in stacks called grana that are interconnected; their membranes contain molecular "machinery" used to convert light energy to chemical energy

action spectrum

a graph that profiles the relative effectiveness of different wavelengths of radiation in driving a particular process

chlorophyll

a green pigment located in membranes with the chloroplasts of plants and algae and in the membranes of certain prokaryotes. chlorophyll a participates directly in the light reactions, which convert solar energy to chemical energy

photosystem I (PS I)

a light-capturing unit in a chloroplast's thylakoid membrane or in the membrane of some prokaryotes; it has two molecules of P700 chlorophyll a at its reaction center

photosystem

a light-capturing unit located in the thylakoid membrane of the chloroplast or in the membrane of the chloroplast or in the membrane of some prokaryotes, consisting of a reaction-center complex surrounded by numerous light-harvesting complexes. there are two types of photosystems, I and II; they absorb light best at different wavelengths

photorespiration

a metabolic pathway that consumes oxygen and ATP, releases carbon dioxide, and decreases photosynthetic output. Photorespiration generally occurs on hot, dry, bright days, when the stomata close and the O2 : CO2 ratio in the leaf increases, favoring the binding of O2 rather than CO2 by rubisco

stoma

a microscopic pore surrounded by guard cells in the epidermis of leaves and stems that allows gas exchange between the environment and the interior of the plant

chlorophyll a

a photosynthetic pigment that participates directly in the light reactions, which convert solar energy to chemical energy

C4 plants

a plant in which the Calvin cycle is preceded by reactions that incorporate CO2 into a four-carbon compound, the end product of which supplies CO2 for the Calvin cycle

CAM plant

a plant that uses crassulacean acid metabolism, an adaption for photosynthesis in arid conditions. in this process CO2 entering open stomata during the night is converted to organic acids, which release CO2 for the Calvin cycle during the day, when stomata are closed

C3 plant

a plant that uses the calvin cycle for the initial steps that incorporate CO2 into organic material, forming a three-carbon compound as the first stable intermediate

photon

a quantum, or discrete quantity, of light energy that behaves as if it were a particle

linear electron flow

a route of electron flow during the light reactions of photosynthesis that involves both photosystems (I and II) and produces ATP, NADPH, and O2. the net electron flow is from H2O to NADP+

cyclic electron flow

a route of electron flow during the light reactions of photosynthesis that involves only one photosystem and that produces ATP but not NADPH or O2

glyceraldehyde 3-phosphate (G3P)

a three-carbon carbohydrate that is direct product of the calvin cycle; it is also an intermediate in glycolysis

chlorophyll b

an accessory photosynthetic pigment that transfers energy to chlorophyll a

carotenoid

an accessory pigment, either yellow or orange, in the chloroplasts of plants and in some prokaryotes. by absorbing wavelengths of light that chlorophyll cannot, carotenoids broaden the spectrum of colors that can drive photosynthesis

crassulacean acid metabolism (CAM)

an adaption for photosynthesis in arid conditions, first discovered in the family Crassulaceae. in this process, a plant take sup CO2 and incorporates it into a variety of organic acids at night; during the day, CO2 is released from organic acids for use in the Calvin cycle

PEP carboxylase

an enzyme that adds CO2 to phosphoenolpyruvate (PEP) to form oxaloacetate in mesophyll cells of C4 plants. It acts prior to photosynthesis

heterotroph

an organism that obtains organic food molecules by eating other organisms or substances derived from them

autotroph

an organism that obtains organic food molecules without eating other organisms without eating other organisms or substances derived from other organisms. autotrophs use energy from the sun or from oxidation of inorganic substances to make organic molecules from inorganic ones

Is the Calvin cycle catabolic or anabolic?

anabolic (builds carbohydrates from smaller molecules and consumes energy)

what happens during the 1st phase of the calvin cycle

carbon fixation

where does light reaction take place

chloroplast thylakoid membrane

how is water turned into sugar in plants

electron chain that increases in potential energy instead of decreasing like cellular respiration. it requires energy which is provided by light

is photosynthesis endergonic or exergonic

endergonic

The carbohydrate produced directly from the Calvin cycle is not glucose, but the three-carbon compound _________ . Each turn of the Calvin cycle fixes one molecule of CO2; therefore, it will take ___ turns of the Calvin cycle to net one G3P.

glyceraldehyde 3-phosphate, 3

decomposers

heterotrophs that consume the remains of other organisms and organic litter such as feces, fallen leaves

bundle-sheath cell

in C4 plants, a type of photosynthetic cell arranged into tightly packed sheaths around the veins of a leaf

primary electron acceptor

in the thylakoid membrane of a chloroplast or in the membrane of some prokaryotes, a specialized molecule that shares the reaction-center complex with a pair of chlorophyll a molecules and that accepts an electron from them

photosystem II (PS II)

one of two light-capturing units in a chloroplast's thylakoid membrane or in the membrane of some prokaryotes; it has two molecules of P680 chlorophyll a at its reaction center

photoautotrophs

organisms that use light as a source of energy to synthesize organic substances (plants)

explain what happens when a pigment molecule absorbs a photon

pigment molecule absorbs photon, energy is then transferred between pigment molecules within a light-harvesting complex until it is passed to the pair of chlorophyll a molecules in the reaction-center complex.

what are the colors of the visible spectrum

red, orange, yellow, green, blue, violet

what happens during the calvin cycle

rewatch video

rubisco

ribulose biphosphate (RuBP) carboxylase-oxygenase, the enzyme that normally catalyzes the first step of the Calvin cycle (the addition of CO2 to RuBP). When excess O2 is present or CO2 levels are low, rubisco can bind oxygen, resulting in photorespiration

The enzyme responsible for carbon fixation in the Calvin cycle, and possibly the most abundant protein on Earth, is _______ .

rubisco

where does the calvin cycle take place

stroma

where does the carbon cycle take place

stroma

pigments

substances that absorb visible light

visible light

that portion of the electromagnetic spectrum that can be detected as various colors by the human eye, ranging in wavelength from about 380 nm to about 740 nm

photosynthesis

the conversion of light energy to chemical energy that is stored in sugars or other organic compounds; occurs in plants, algae, and certain prokaryotes

stroma

the dense fluid within the chloroplast surrounding the thylakoid membrane and containing ribosomes and DNA; involved in the synthesis of organic molecules from carbon dioxide and water

wavelength

the distance between crests of waves, such as those of the electromagnetic spectrum

electromagnetic spectrum

the entire spectrum of electromagnetic radiation, ranging in wavelength from less than a nanometer to more than a kilometer

light reactions

the first of two major stages in photosynthesis (preceding the calvin cycle). these reactions, which occur on the thylakoid membranes of the chloroplast or on membranes of certain prokaryotes, convert solar energy to the chemical energy of ATP and NADPH, releasing oxygen in the process

carbon fixation

the initial incorporation of carbon from CO2 into an organic compound by an autotrophic organism (a plant, another photosynthetic organism, or a chemoautotrophic prokaryote)

endosymbiont theory

the original chloroplast was a photosynthetic prokaryote that lived inside an ancestor of eukaryotic cells

photophosphorylation

the process of generating ATP from ADP and phosphate by means of chemiosmosis, using a proton-motived force generated across the thylakoid membrane of the chloroplast or the membrane of certain prokaryotes during the light reactions of photosynthesis

calvin cycle

the second of the two major stages in photosynthesis (following the light reactions), involving fixation of atmospheric CO2 and reduction of the fixed carbon into carbohydrate

where are the photosystems in the linear electron flow

thylakoid membranes of chloroplasts

excited state

when a molecule absorbs a photon of light, one of the molecule's electrons is elevated to an orbital where it has more potential energy. it then quickly drops back down to its ground state orbital, releasing excess energy as heat

ground state

when an electron is in its normal state