AP Biology Chapter 8 Photosynthesis

Photosystem 2

a light reaction in which ATP and NADPH are formed (comes 1st) One of two light-harvesting units of a chloroplast's thylakoid membrane; uses absorbed light energy to split water into protons and oxygen and to produce ATP. P680

Because the electrons increase in potential energy as they move from water to sugar, this process requires energy—in other words, is ______________. This energy boost is provided by ___________.

endergonic; light

Calvin uses CO2 to yield

glucose through many steps

ATP and NADPH

high energy products made by the light reactions and used in the Calvin cycle

P700

reaction center of photosystem I

P680

reaction center of photosystem II

RuBP

ribulose biphosphate; a five-carbon carbohydrate that combines with CO2 to form two molecules of PGA in the first step of the Calvin Cycle

thylakoid space

site of proton gradient built up in photosynthesis

Review of Photosynthesis

The light reactions capture solar energy and use it to make ATP and transfer electrons from water to NADP+, forming NADPH. The Calvin cycle uses the ATP and NADPH to produce sugar from carbon dioxide. The energy that enters the chloroplasts as sunlight becomes stored as chemical energy in organic compounds.

ATP and NADPH during Light Reactions

The light reactions regenerate the ATP and NADPH.

Explain how the Calvin Cycle uses the energy molecules of the light reactions (ATP and NADPH) to produce carbohydrates (G3P) from CO2

In plants, carbon dioxide (CO2) enters the leaves through stomata, where it diffuses over short distances through intercellular spaces until it reaches the mesophyll cells. Once in the mesophyll cells, CO2 diffuses into the stroma of the chloroplast

An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle.

In the chloroplast, the thylakoid membranes are the sites of the light reactions, whereas the Calvin cycle occurs in the stroma. The light reactions use solar energy to make ATP and NADPH, which supply chemical energy and reducing power, respectively, to the Calvin cycle. The Calvin cycle incorporates CO2 into organic molecules, which are converted to sugar.

The Calvin cycle

The cycle begins by incorporating CO2 from the air into organic molecules, carbon fixation. The Calvin cycle then reduces the fixed carbon to carbohydrate by the addition of electrons. The reducing power is provided by NADPH, which acquired its cargo of electrons in the light reactions. During this stage, the Calvin cycle also requires chemical energy in the form of ATP, which is also generated by the light reactions. Thus, it is the Calvin cycle that makes sugar, but it can do so only with the help of the NADPH and ATP produced by the light reactions.

Photon

a particle of light

Phase 2 of Calvin Cycle

Reduction. After several steps of modification during the reduction phase (uses ATP and NADPH), one carbon atom is released at the end of the phase. After 6 cycles, glucose is made.

Produce the summary equation for the net reactants and products of photosynthesis and identify the source and fate of each reactant and product

12H20 + 6CO2 + light energy = C6H12O6 + 6H2O + 6O2 - The water molecules on the reactants side are split to release electrons and O2 atoms (6 O2) - Water is also a product of photosynthesis. This water is produced from the oxygen atoms in the carbon dioxide molecules. - CO2 and light energy is absorbed from the plants surroundings - Glucose is the product of the Calvin Cycle

light-harvesting complex

A complex of proteins associated with pigment molecules (including chlorophyll a, chlorophyll b, and carotenoids) that captures light energy and transfers it to reaction-center pigments in a photosystem. A photon of light strikes one of the pigment molecules in a light-harvesting complex of PS II, boosting one of its electrons to a higher energy level.

Thylakoid

A flattened membrane sac inside the chloroplast, used to convert light energy into chemical energy.

action spectrum of photosynthesis

A graph that profiles the relative effectiveness of different wavelengths of radiation in driving photosynthesis

Chlorophyll

A green pigment located in membranes within 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.

Carotenoids

An accessory pigment, either yellow or orange, in the chloroplasts of plants. By absorbing wavelengths of light that chlorophyll cannot, carotenoids broaden the spectrum of colors that can drive photosynthesis.

Explain how leaf and chloroplast anatomy relate to the events of photosynthesis

An envelope of two membranes encloses the stroma, which is a dense fluid filled area. Within the stroma is a network of membranous sacs called thylakoids. They thylakoids; they segregate the stroma from another compartment, the thylakoid space. The exterior of the lower epidermis of a leaf contains tiny pores called stomata where carbon dioxide enters and oxygen and water vapor leave.

Compare photosynthesis with cellular respiration

Both processes involve redox reactions. During cellular respiration, energy is released from sugar when electrons associated with hydrogen are transported by carriers to oxygen, forming water as a by-product . The electrons lose potential energy as they "fall" down the electron transport chain toward electronegative oxygen, and the mitochondrion harnesses that energy to synthesize ATP. Photosynthesis reverses the direction of electron flow. Water is split, and electrons are transferred along with hydrogen ions from the water to carbon dioxide, reducing it to sugar.

Phase 1 of Calvin Cycle

Carbon Fixation. The cycle has an input of 3 CO2 molecules, one at a time, by attaching it to a five-carbon sugar RuBP (ribulose bisphosphate).

How does carbon enters and leave the Calvin cycle?

Carbon enters the Calvin cycle in CO2 and leaves in sugar

Explain how the formation of a proton gradient in the light reactions is used to form ATP from ADP and Pi by ATP synthase

During chemiosmosis, the free energy from the series of redox reactions that make up the electron transport chain is used to pump hydrogen ions (protons) across the membrane. The uneven distribution of H+ ions across the membrane establishes both concentration and electrical gradients (thus, an electrochemical gradient) owing to the hydrogen ions' positive charge and their aggregation on one side of the membrane .

Summarize the light reactions.

Electron flow pushes electrons from water, where they are at a low state of potential energy, ultimately to NADPH, where they are stored at a high state of potential energy. The light-driven electron flow also generates ATP. Thus, the equipment of the thylakoid membrane converts light energy to chemical energy stored in ATP and NADPH. (Oxygen is a by-product.) Let's now see how the Calvin cycle uses the products of the light reactions to synthesize sugar from CO2.

chemiosmosis in photosynthesis

H+ ions and ATP Synthase changing the concentration of H+ ions - H+ ions moving from a heavily concentration gradient in the thylakoid to a lower concentration gradient in the stroma

Where the O2 given off by plants is derived from?

H2O and not from CO2

the overall photosynthetic equation of photosynthesis

In the presence of light, the green parts of plants produce organic compounds and oxygen from carbon dioxide and water. 6CO2+6H2O+Lightenergy→C6H12O6+6O2 (12 molecules of water are consumed and 6 molecules are released, leaving a net reactant of 6 H2O molecules)

Photosystem

In their native environment of the thylakoid membrane, chlorophyll molecules are organized along with other small organic molecules and proteins into complexes called photosystems. A light-capturing unit located in the thylakoid 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.

Explain how the linear electron flow in the light reaction results in the formation of ATP, NADPH, and O2

Light drives the synthesis of ATP and NADPH by energizing the two photosystems embedded in the thylakoid membranes of chloroplasts through the flow of electrons through the photosystems and other molecular components built into the thylakoid membrane. When solar energy reaches plant cells and excites chlorophyll molecules, they release high-energy electrons. The electrons flow throughout each photosystem and through an ETC. The last molecule to form and hold the electrons in this chain is NADPH. The excited chlorophyll molecule's electrons need to be replaced, and these electrons come from water. With the help of enzymes and solar energy, water is split (photolysis) into electrons, protons (H+), and O2 molecules. The electrons go to the chlorophyll, while the protons contribute to a proton gradient that is used to power the synthesis of a second energy-carrying molecule, ATP.

Water is used in the light dependent reaction to yield

O2

What happens on the outside of the thylakoids during light reactions?

On the outside of the thylakoids, molecules of NADP+ and ADP pick up electrons and phosphate, respectively, and NADPH and ATP are then released to the stroma, where they play crucial roles in the Calvin cycle.

Photosystem 1 (PS1)

One of two light-capturing units 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.

Autotroph

Producer; An organism that makes its own food

Phase 3 of calvin cycle

Regeneration of the CO2 acceptor (RuBP). In a complex series of reactions, the carbon skeletons of five molecules of G3P are rearranged by the last steps of the Calvin Cycle into three molecules of RuBP. To accomplish this, the cycles spends three more ATPs. The RuBP is then prepared to receive CO2 again, and the cycle continues.

Stomata

Small openings on the underside of a leaf through which oxygen and carbon dioxide can move

ATP and NADPH during Calvin Cycle

The cycle spends ATP as an energy source and consumes NADPH as reducing power for adding high-energy electrons to make sugar. During the reduction phase of the Calvin Cycle, ATP and NADPH are used to reduce the PGA to G3P. During the regeneration phase of the Calvin Cycle, ATP is used to drive reactions that regenerate the molecule RuBP. For the net synthesis of one G3P molecule, the Calvin cycle consumes a total of nine molecules of ATP and six molecules of NADPH

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.

Identify the ways in which the light reactions and the Calvin cycle contribute to the summary reaction of photosynthesis and involve the cycling of ADP/ATP and NADP+/NADPH

The light reactions are the steps of photosynthesis that convert solar energy to chemical energy. Light energy is a reactant absorbed by chlorophyll drives a transfer of electrons and hydrogen from water to an acceptor called NADP+, which temporarily stores the energized electrons. Water is also a reactant and is split in the process, and thus it is the light reactions of photosynthesis that give off O2 molecules as a by-product. The light reactions also generate ATP by powering the addition of a phosphate group to ADP, a process called photophosphorylation. Thus, light energy is initially converted to chemical energy in the form of two compounds: NADPH, a source of energized electrons ( "reducing power"); and ATP, the versatile energy currency o that the light reactions produce no sugar; that happens in the second stage of photosynthesis, the Calvin cycle. The Calvin cycle begins by using the reactant CO2 from the air during carbon fixation. This also results in the formation of water molecules (from the CO2 molecules). The Calvin cycle then reduces the molecule by the addition of electrons. The reducing power is provided by NADPH, which acquired energized electrons in the light reactions. (***REDOX RXN***) The Calvin cycle also requires chemical energy in the form of ATP during this phase, which is also generated by the light reactions. Thus, it is the Calvin cycle that makes glucose, but it can do so only with the help of the NADPH and ATP produced by the fight reactions.

Photophosphorylation

The process of generating ATP from ADP and phosphate by means of a proton-motive force generated by the thylakoid membrane of the chloroplast during the light reactions of photosynthesis.

absorption spectrum

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

The internal photosynthetic membranes of some prokaryotes are also called __________________________

Thylakoid membranes

Location of the 2 major steps of Photosynthesis

Thylakoid membranes, especially those of the grana, are the sites of the light reactions, whereas the Calvin cycle occurs in the stoma

The light dependent reactions summary

Water is split, providing a source of electrons and protons (hydrogen ions, H+) and giving off O2 as a by-product. Light absorbed by chlorophyll drives a transfer of the electrons and hydrogen ions from water to an acceptor called NADP+ (nicotinamide adenine dinucleotide phosphate), where they are temporarily stored. The light reactions use solar energy to reduce NADP+ to NADPH by adding a pair of electrons along with an H+. The light reactions also generate ATP, using chemiosmosis to power the addition of a phosphate group to ADP, a process called photophosphorylation. Thus, light energy is initially converted to chemical energy in the form of two compounds: NADPH and ATP. NADPH, a source of electrons, acts as "reducing power" that can be passed along to an electron acceptor, reducing it, while ATP is the versatile energy currency of cells. Notice that the light reactions produce no sugar; that happens in the second stage of photosynthesis, the Calvin cycle.

What exactly happens when chlorophyll and other pigments absorb light?

When a molecule absorbs a photon of light, one of the molecule's electrons is elevated to an electron shell where it has more potential energy

Is the Calvin cycle anabolic or catabolic?

anabolic, building carbohydrates from smaller molecules and consuming energy.

Calvin cycle is also known as

light independent reactions

Compare the process of chemiosmosis in the mitochondrion and the chloroplast, explain how the H+ gradient is established, and describe the role of the ATP synthase molecule

noteworthy differences between photophosphorylation in chloroplasts and oxidative phosphorylation in mitochondria: both work by way of chemiosmosis, but in chloroplasts, the high-energy electrons dropped down the transport chain come from water, whereas in mitochondria, they are extracted from organic molecules (which are thus oxidized). Chloroplasts do not need molecules from food to make ATP; their photosystems capture light energy and use it to drive the electrons from water to the top of the transport chain. In other words, mitochondria use chemiosmosis to transfer chemical energy from food molecules to ATP, whereas chloroplasts use it to transform light energy into chemical energy in ATP. similarities in the two: The inner membrane of the mitochondrion pumps protons from the mitochondrial matrix out to the intermembrane space, which then serves as a reservoir of hydrogen ions. The thylakoid membrane of the chloroplast pumps protons from the stroma into the thylakoid space (interior of the thylakoid), which functions as the H+ reservoir. The thylakoid space and the intermembrane space are comparable spaces in the two organelles, while the mitochondrial matrix is analogous to the stroma of the chloroplast. In the mitochondrion, protons diffuse down their concentration gradient from the intermembrane space through ATP synthase to the matrix, driving ATP synthesis. In the chloroplast, ATP is synthesized as the hydrogen ions diffuse from the thylakoid space back to the stroma through ATP synthase complexes, whose catalytic knobs are on the stroma side of the membrane. Thus, ATP forms in the stroma, where it is used to help drive sugar synthesis during the Calvin cycle.

Heterotroph

organism that obtains energy from the foods it consumes; also called a consumer

Describe how the photosystems convert solar energy to chemical energy

solar energy is converted into chemical energy in the form of two energy-transporting molecules, ATP and NADPH. When solar energy reaches plant cells and excites chlorophyll molecules, they release high-energy electrons. The electrons move throughout each photosystem and through an ETC. The last molecule to form and hold the electrons in this chain is NADPH. The excited chlorophyll molecule's electrons need to be replaced, and these electrons come from water. With the help of enzymes and solar energy, water is split (photolysis) into electrons, protons (H+), and oxygen. The electrons go to the chlorophyll, while the protons contribute to a proton gradient that is used to power the synthesis of a second energy-carrying molecule, ATP.

The light reactions are the steps of photosynthesis that convert _______________________________.

solar energy to chemical energy

During photosynthesis, water is _______, and electrons are transferred along with hydrogen ions from the _____________ to ____________, releasing O2 molecules.

split; water to carbon dioxide

Calvin cycle occurs in the

stroma of the chloroplast

Rubisco

the enzyme that catalyzes the first step of the Calvin cycle (the addition of CO2 to RuBP, or ribulose bisphosphate).

These two stages of photosynthesis are known as

the light reactions (the photo part of photosynthesis) and the Calvin cycle

Grana

the stacks of thylakoids embedded in the stroma of a chloroplast.

sites of light reactions

the thylakoids

mesophyll

the tissue in the interior of the leaf where chloroplasts are mainly found

endosymbiotic theory

theory that eukaryotic cells formed from a symbiosis among several different prokaryotic organisms