Chapter 8 Photosynthsis

What are three ways the proton gradient in the chloroplast is maintained?

1. Splitting H2O molecules 2. ETC transport of H+ 3. NAD+ reduced to NADH

How many photons does it take to fully reduce one molecule of NADP+ to NADPH?

2

Which statement correctly describes carbon fixation? A the conversion of CO2 into an organic compound B the use of RuBisCO to form 3-PGA C the production of carbohydrate molecules from G3P D the formation of RuBP from G3P molecules E the use of ATP and NADPH to reduce CO2

A the conversion of CO2 into an organic compound

Label the chloroplast diagram

A - Intermembrane space B - Outer membrane C - Innermembrane D - Thylakoid Membrane X E - Granum X F - Stroma G - Thylakoid Space (Lumen) X

Compare and contrast the ETCs associated with Photosystem I and Photosystem II. What is the function of each?

A photon of light hits an antenna molecule in photosystem II, and the energy released by it travels through other antenna molecules to the reaction center. The energy causes an electron to leave a molecule of chlorophyll a to a primary electron acceptor protein. The electron travels through the electron transport chain and is accepted by a pigment molecule in photosystem I.

Which of the following structures is not a component of a photosystem? A ATP synthase B antenna molecule C reaction center D primary electron acceptor

ATP synthase

Which order of molecular conversions is correct for the Calvin cycle? A) RuBP + G3P → 3-PGA → sugar B) RuBisCO → CO2 → RuBP → G3P C) RuBP + CO2 → [RuBisCO] 3-PGA → G3P D) CO2 → 3-PGA → RuBP → G3P

C) RuBP + CO2 → [RuBisCO] 3-PGA → G3P

Which molecule must enter the Calvin cycle continually for the light-independent reactions to take place?

CO2

Using the energy carriers formed in the first steps of photosynthesis, the light-independent reactions, or the Calvin cycle, take in

CO2 from the environment.

Pigments in Photosynthesis

Chlorophyll a Chlorophyll b Beta-Carotene

H+ gradient is maintained by:

First ETC pumps H+ from the stroma to the thylakoid space Water is split in the thylakoid space, producing 2H+ H+ in the stroma and electrons from the Second ETC reduces NADP+ to NADPH

Photosynthesis as a redox reaction

Has a ΔG = +686 kcal/molEndergonic Not spontaneous Requires energy Products have higher free energy than reactants

What is going on in photosynthesis? Hypothesis 1: Carbon atoms from the carbon dioxide combine with the water to make glucose and the remaining oxygen from the carbon dioxide is released as a byproduct Hypothesis 2: Water is split. The hydrogens from the water combine with the carbon dioxide to make glucose and the oxygen from the water is released as a byproduct.

Hypothesis 2: Water is split. The hydrogens from the water combine with the carbon dioxide to make glucose and the oxygen from the water is released as a byproduct. Photosynthesis splits water!!!

What is the role of ATP in photosynthesis?

In light independent stage the energy carrier for the reaction that take place in the light dependent stage. ATP is also passed from light dependent stage to the dark stage to be used as energy in that process as well.

Which of the following statements is true? A In photosynthesis, oxygen, carbon dioxide, ATP, and NADPH are reactants. G3P and water are products. B In photosynthesis, chlorophyll, water, and carbon dioxide are reactants. G3P and oxygen are products. C In photosynthesis, water, carbon dioxide, ATP, and NADPH are reactants. RuBP and oxygen are products. D In photosynthesis, water and carbon dioxide are reactants. G3P and oxygen are products.

In photosynthesis, water and carbon dioxide are reactants. G3P and oxygen are products.

Which part of the light-independent reactions would be most immediately affected if the cell could not produce the enzyme Rubisco?

It wouldn't happen at all. RuBisCO is necessary in fixing carbon dioxide. It catalyzes the reaction between carbon dioxide and RuBP at the start of the cycle.

Which is the chloroplast that correctly represents the proton gradient in the chloroplast from the diagram?

Low to high

What is the role of NADPH in photosynthesis?

NADPH is simply an NAD carrier molecule carrying both P (Phosphorus) and H (Hydrogen) ions to a different stage of the photosynthesis reaction where ions will be used and NAD will be left over.

The Calvin Cycle Phase 1

Phase 1 - Carbon fixation CO2 incorporated into RuBP using rubisco Reaction product is a six-carbon intermediate that splits into two 3-phosphoglycerate molecules (3PGA)

Calvin Cycle Phase 2

Phase 2 - Reduction and carbohydrate production ATP is used to convert 3PG into 1,3-bisphosphoglycerate (1,3-BPG) NADPH electrons reduce it to glyceraldehyde-3-phosphate (G3P) 3 CO2 → 6 G3P Only 1 G3P molecules used for carbohydrates 5 G3P molecules must be used for regeneration of RuBP

The Calvin Cycle Phase 3

Phase 3 - Regeneration of RuBP 5 G3P are converted into 3 RuBP using ATP

Which complex is not involved in the establishment of conditions for ATP synthesis? A photosystem I B ATP synthase C photosystem II D cytochrome complex

Photosystem II

Which statement about thylakoids in eukaryotes is not correct? A Thylakoids are assembled into stacks. B Thylakoids exist as a maze of folded membranes. C The space surrounding thylakoids is called stroma. D Thylakoids contain chlorophyll.

Thylakoids exist as a maze of folded membranes.

What is the source of electrons for the chloroplast electron transport chain?

Water

Like cellular respiration, photosynthesis creates

a proton gradient between the thylakoid space and stroma

Photosystem I absorbs

a second photon, which results in the formation of an NADPH molecule, another energy and reducing power carrier for the light-independent reactions.

The closing of stomata reduces

access to CO2 and causes O2 to build up. These conditions favor an apparently wasteful process called photorespiration.

chlorophyll b

accessory pigment that absorbs blue and red-orange light and consequently has a yellowish-green tint

In photorespiration, rubisco

adds O2 instead of CO2 in the Calvin cycle, producing a two-carbon compound

The electromagnetic spectrum is the range of

all possible frequencies of radiation. The difference between wavelengths relates to the amount of energy carried by them.

A photon strikes the

antenna pigments of photosystem II to initiate photosynthesis. The energy travels to the reaction center that contains chlorophyll a to the electron transport chain, which pumps hydrogen ions into the thylakoid interior. This action builds up a high concentration of ions.

thylakoid lumen

aqueous space bound by a thylakoid membrane where protons accumulate during light-driven electron transport

Photosynthesis uses carbon dioxide and water to

assemble carbohydrate molecules and release oxygen as a waste product into the atmosphere.

An enzyme, RuBisCO, does what?

catalyzes a reaction with CO2 and another molecule, RuBP.

The ions flow through ATP synthase via

chemiosmosis to form molecules of ATP, which are used for the formation of sugar molecules in the second stage of photosynthesis.

Where in eukaryotic cells does the Calvin cycle take place?

chloroplast stroma

Which of the following components is not used by both plants and cyanobacteria to carry out photosynthesis? A chloroplasts B chlorophyll C carbon dioxide D water

chloroplasts

Eukaryotic autotrophs, such as plants and algae, have organelles called

chloroplasts in which photosynthesis takes place, and starch accumulates.

On hot, dry days, plants

close stomata, which conserves H2O but also limits photosynthesis.

reaction center

complex of chlorophyll molecules and other organic molecules that is assembled around a special pair of chlorophyll molecules and a primary electron acceptor; capable of undergoing oxidation and reduction

light harvesting complex

complex that passes energy from sunlight to the reaction center in each photosystem; it consists of multiple antenna proteins that contain a mixture of 300-400 chlorophyll a and b molecules as well as other pigments like carotenoids

thylakoid

disc-shaped, membrane-bound structure inside a chloroplast where the light-dependent reactions of photosynthesis take place; stacks of thylakoids are called grana

wavelength

distance between consecutive points of equal position (two crests or two troughs) of a wave in a graphic representation; inversely proportional to the energy of the radiation

photon

distinct quantity or "packet" of light energy

photoact

ejection of an electron from a reaction center using the energy of an absorbed photon

Photosystem I accepts

electron from the ETC and uses light energy to excite them again. The electrons fall down a second ETC to NADP+, which combined with two H+ from the stroma make NADPH.

The light reaction produce a proton gradient using

energy from an ETC. ATP Synthase uses the potential energy in the gradient to make ATP.

Photosynthesis in desert plants has

evolved adaptations that conserve water.

light-dependent reaction

first stage of photosynthesis where certain wavelengths of the visible light are absorbed to form two energy-carrying molecules (ATP and NADPH)

Three carbon dioxide molecules are

fixed (added to RuBP) into the Calvin cycle by the enzyme Rubisco to form 3PGA, a three carbon molecule.

stroma

fluid-filled space surrounding the grana inside a chloroplast where the light-independent reactions of photosynthesis take place

chlorophyll a

form of chlorophyll that absorbs violet-blue and red light and consequently has a bluish-green color; the only pigment molecule that performs the photochemistry by getting excited and losing an electron to the electron transport chain

electron transport chain

group of proteins between PSII and PSI that pass energized electrons and use the energy released by the electrons to move hydrogen ions against their concentration gradient into the thylakoid lumen

photosystem

group of proteins, chlorophyll, and other pigments that are used in the light-dependent reactions of photosynthesis to absorb light energy and convert it into chemical energy

cytochrome complex

group of reversibly oxidizable and reducible proteins that forms part of the electron transport chain between photosystem II and photosystem I

Energy from ATP and electrons from NADPH are used to

in the reduction phase to produce G3P, a three carbon sugar. One molecule of G3P leaves the cycle and can be used to build many different organic molecules. Two turns of the Calvin cycle would be required to make glucose.

photosystem I

integral pigment and protein complex in thylakoid membranes that uses light energy to transport electrons from plastocyanin to NADP+ (which becomes reduced to NADPH in the process)

photosystem II

integral protein and pigment complex in thylakoid membranes that transports electrons from water to the electron transport chain; oxygen is a product of PSII

Pigment molecules absorb

light energy, exciting electrons to higher energy states.

Photoautotrophs use

light to make food (Plants, algae, and a group of bacteria called cyanobacteria)

Calvin cycle

light-independent reactions of photosynthesis that convert carbon dioxide from the atmosphere into carbohydrates using the energy and reducing power of ATP and NADPH

In prokaryotes, such as cyanobacteria, the process is less

localized and occurs within folded membranes, extensions of the plasma membrane, and in the cytoplasm.

mesophyll

middle layer of chlorophyll-rich cells in a leaf

Heterotrophs:

must obtain organic materials form photoautotrphs (animals, fungi, and most other bacteria

stoma

opening that regulates gas exchange and water evaporation between leaves and the environment, typically situated on the underside of leaves

chloroplast

organelle in which photosynthesis takes place

photoautotroph

organism capable of producing its own organic compounds from sunlight

chemoautotroph

organism that can build organic molecules using energy derived from inorganic chemicals instead of sunlight

Photorespiration occurs when

oxygen, a byproduct of the light reactions, enters the Calvin Cycle instead of carbon dioxide. This wastes energy and materials.

carotenoid

photosynthetic pigment that functions to dispose of excess energy

From which component of the light-dependent reactions does NADPH form most directly?

photosystem I

antenna protein

pigment molecule that directly absorbs light and transfers the energy absorbed to other pigment molecules

primary electron acceptor

pigment or other organic molecule in the reaction center that accepts an energized electron from the reaction center

carbon fixation

process of converting inorganic CO2 gas into organic compounds

Photosystems are complexes of

proteins and pigments molecules in the thylakoid membrane that absorb solar energy.

electromagnetic spectrum

range of all possible frequencies of radiation

absorption spectrum

range of wavelengths of electromagnetic radiation absorbed by a given substance

P700

reaction center of photosystem I

P680

reaction center of photosystem II

The last stage of the Calvin cycle

regenerates RuBP using ATP to restart the cycle.

light-independent reaction

second stage of photosynthesis, though which carbon dioxide is used to build carbohydrate molecules using energy from ATP and NADPH

CAM plants temporally

separate the two processes, fixing carbon dioxide at night.

C4 plants:

spatial separation of photosynthesis to reduce photorespiration.

C4 plants limit photorespiration by

spatially separating the carbon fixation from the light reactions.

Photosystem II is able to

split water, because p680+ is the strongest biological oxidizing agent we know of. O2 is released as a byproduct, while the electrons from water then flow down an electron transport chain.

granum

stack of thylakoids located inside a chloroplast

The remaining G3P molecules

stay in the cycle to be regenerated into RuBP, which is then ready to react with more CO2.

Plants must open their

stomata to let in CO2 for photosynthesis and let oxygen out.

In which compartment of the plant cell do the light-independent reactions of photosynthesis take place?

stroma

What two main products result from photosynthesis?

sugars/carbohydrates and oxygen

Chemoautotrophs

synthesize sugars, not by using sunlight's energy, but by extracting energy from inorganic chemical compounds;

CAM plants:

temporal separation of photosynthesis to reduce photorespiration.

heterotroph organism

that consumes organic substances or other organisms for food

NADPH and ATP from the light reactions are needed in

the Calvin cycle.

C4 plants (sugarcane, corn) minimize

the cost of photorespiration by incorporating CO2 into four-carbon compounds in mesophyll cells This step requires the enzyme PEP carboxylase

After three cycles, a

three-carbon molecule of G3P leaves the cycle to become part of a carbohydrate molecule.

Photosynthesis requires two Photosystems located in the

thylakoid membrane

open stomata also

wastes water as it is evaporated.

Photosynthesis absorbs

wavelengths of visible light.