Unit 2 (Week 7 Photosynthesis) Flashcards
What is the process whereby light energy is captured by plant, algal, or photosynthetic bacterial cells and is used to synthesize organic molecules from CO2 and H2O (or H2S)?
Photosynthesis
What is the first of two stages in the process of photosynthesis?
Light reactions.
During the light reactions, photosystem II and photosystem I absorb light energy and produce ATP, NADPH, and O2.
What is the second stage in the process of photosynthesis?
Calvin cycle.
During this cycle, ATP is used as a source of energy and NADPH is used as a source of high-energy electrons, driving the synthesis of carbohydrates using CO2.
What is a major contributor to the mass and size of plants?
CO2
What do some photosynthetic bacteria use instead of water for photosynthesis?
Hydrogen sulfide (H2S). They release sulfur instead of oxygen.
T/F The free-energy change required for the production of 1 mole of glucose from carbon dioxide is endergonic and requires sunlight to drive the synthesis of glucose by making the beginning process exergonic.
True.
T/F The free-energy change required for the production of 1 mole of glucose from carbon dioxide is endergonic and requires sunlight to drive the synthesis of glucose by making the beginning process exergonic.
True.
What is the regions on the surface of the Earth and in the atmosphere where living organisms exist?
Biosphere
What are living organisms categorized as in respect to organic molecules and sustainment?
Heterotrophs and Autotrophs
What is an organism that cannot produce their own organic molecules by using energy from inorganic sources or light; they must obtain one or more organic compounds from their environment?
Heterotroph
What is an organism that has metabolic pathways that use energy from either inorganic molecules or light to make organic molecules?
Autotroph
What is a photoautotroph?
An organism that uses the energy from light to make organic molecules from inorganic sources. This includes plants, algae, and some bacterial species such as cyanobacteria.
What does life in the biosphere rely on?
The key energy cycle that involves the interplay between organic molecules (glucose) and inorganic molecules, namely, O2, CO2, and H2O.
Photosynthesis is a process in which light, CO2, and H2O are used to produce O2 and organic molecules (glucose). The organic molecules are broken down to CO2 and H2O via cellular respiration to supply energy in the form of ATP; O2 is reduced to H2O.
What makes a large portion of the Earth’s organic molecules via photosynthesis by reusing CO2 produced by heterotrophs through cellular respiration to make O2?
Photoautotrophs.
What are semiautonomous organelle found in plant and algal cells that carries out photosynthesis?
Chloroplasts
What is a photosynthetic green pigment found in the chloroplasts of plants, algae, and some bacteria?
Chlorophyll
Where does MOST of the photosynthesis in plants occur?
The leaves.
What is the mesophyll? What is contained within this area located between the two epidermal cell layers of the leaf?
The internal tissue of a plant leaf; the site of photosynthesis. The mesophyll cells.
Where is water taken up by the plant to allow photosynthesis to occur?
The roots.
Where does carbon dioxide enter the plant and where oxygen leaves? Where are these pores located?
Pores in the plant called stomata (singular, stoma or stomate; from the Greek, meaning mouth)
These pores on located within the epidermal layers of the leaf and act as a “antiport” for oxygen and carbon dioxide.
[Review] What parts does the chloroplast consist of within the Mesophyll cell? (8)
Outer membrane, intermembrane space, inner membrane, thylakoid and its membrane, thylakoid lumen, granum, and stroma.
What is a membrane within the chloroplast that forms many flattened, fluid-filled tubules that enclose a single, convoluted compartment. It contains chlorophyll and is the site where the light-dependent reactions of photosynthesis occurs?
Thylakoid membrane
What is a flattened, fluid-filled tubule found in cyanobacterial cells and the chloroplasts of photosynthetic protists and plants; the location of the light reactions of photosynthesis?
Thylakoid
What is the fluid-filled compartment within a thylakoid?
Thylakoid lumen
What is a structure composed of stacked membrane-bound thylakoids within a chloroplast?
Granum
What is the fluid-filled region of the chloroplast between the thylakoid membrane and the inner membrane?
Stroma
How is the term photosynthesis derived?
Photo refers to the light reactions that capture the energy from sunlight.
Synthesis refers to the captured energy used to make carbohydrates that occurs in the Calvin cycle.
Where do the light reactions occur and Calvin occur specifically?
Light reactions occur at the thylakoid membrane while the Calvin cycle happens in the stroma of the chloroplast.
Can the Calvin cycle occur in the dark?
The Calvin cycle can occur in the dark as long as sufficient CO2, ATP, and NADPH are present in the stroma.
What does the light reaction create when storing the energy in the form of covalent bonds?
ATP, NADPH, and O2.
What provides the needed energy and electrons to drive the Calvin cycle?
The energy intermediates created in the light reaction cycle which are ATP and NADPH.
What is NADPH
Nicotinamide adenine dinucleotide phosphate; an energy intermediate that provides the energy and electrons to drive the Calvin cycle during photosynthesis.
How many electrons does the electron carrier, NADPH, accept?
2
What is the difference between NADH and NADPH?
The presence of an additional phosphate group
In regards to the first law of thermodynamics, how does photosynthesis follow this law?
Well, energy cannot be created or destroyed but can be transformed into one form from another.
For photosynthesis, energy in the form of light is sent from the sun to the earth and is captured by a pigment molecule in a photosynthetic organism.
From there, a series of energy transformations occur in which light energy is changed into electrochemical energy and then into energy stored within chemical bonds.
What is a type of electromagnetic radiation, so named because it consists of energy in the form of electric and magnetic fields?
Light
What is the distance from one peak to the next in a sound wave or light wave?
Wavelength
What are all possible wavelengths of electromagnetic radiation, from relatively short wavelengths (gamma rays) to much longer wavelengths (radio waves)?
Electromagnetic spectrum
Since visible light is in the range of wavelengths detected by the human eye, what is the length of the wavelength (range)?
Commonly between 380 and 740 nm in length.
Which has higher energy, gamma rays or radio waves?
Gamma rays have higher energy than radio waves.
What is one of the discrete particles that make up light?
Photons.
A photon is massless and travels in a wavelike pattern. at the speed of light (about 300 million m/sec)
T/F Each photon does not contain a specific amount of energy.
False. They have specific amounts.
What protects organisms on Earth from some, if not most, of the harmful Sun’s ultraviolet (UV) radiation?
The ozone layer.
Gamma rays, x-rays, and UV radiation have very high energy and when molecules absorb such energy, the results can be devastating. This can cause mutations in DNA and lead to cancer.
T/F Visible light is much less intense than gamma, x, and UV rays.
True
What are the three things that can happen when light comes into contact with something?
It may pass straight through.
It may refract or reflect.
It may be absorbed.
What is a molecule that can absorb light energy?
Pigment. Some light waves are absorbed while others are reflected.
Leaves look green to us because of the light energy they reflect back at us in the green region of the visible spectrum.
What reflects practically all visible light energy and what absorbs all visible light energy?
White and black objects, respectively.
In laymen speak, what does it mean for an atom or molecule to absorb light energy?
Light boosts an electron to a higher energy level.
What must an electron receive in order to change energy levels?
The difference of energy of its current orbital and the orbital in which it is going. This specificity of energy is received by a specific photon.
T/F Different pigment molecules have a variety of electrons that can be shifted to different energy levels.
True
What are the states that involve an electron being boosted by a photon?
The ground state to the excited state (a high energy electron photoexcited)
When this happens, an electron is further from its nucleus which makes is less retrained by the positive nucleus allowing it to become unstable.
Describe the four events that can enable a photoexcited electron to become more stable.
To become more stable by dropping down to a lower energy level, a photoexcited electron can release energy in the form of heat, release energy in the form of light, or transfer energy to another electron by resonance energy transfer.
Rather than releasing energy or transferring it to another molecule, an excited electron can be removed from the molecule in which it is unstable and transferred to another molecule where it is stable. When this occurs, the energy in the electron is said to be captured, because the electron does not readily drop down to a lower energy level and release heat or light.
Examples:
For example, on a sunny day, the sidewalk heats up because it absorbs light energy that is released as heat.
Certain organisms, such as jellyfish, possess molecules that make them glow. This glowing is due to the release of light when electrons drop down to lower energy levels, a phenomenon called fluorescence.
What is the process previously talked about by which energy (not an electron itself) can be transferred to adjacent pigment molecules during photosynthesis?
Resonance energy transfer.
What are the two types of chlorophyll pigments?
Chlorophyll a and chlorophyll b.
Where can chlorophyll a be found?
A type of chlorophyll pigment found in plants, algae, and cyanobacteria.
Where can chlorophyll b be found?
A type of chlorophyll pigment found in plants, green algae, and some other photosynthetic organisms.
What do the two chlorophylls consist of?
A porphyrin ring and a phytol tail.
Where is the magnesium ion (Mg2+) bound to?
The center of the porphyrin ring. The electron here is capable of accepting light energy which classifies it as a delocalized electron.
What is the function of the phytol tail?
Since it is a hydrocarbon which makes it hydrophobic, it is an anchor for the pigment to the surface of hydrophobic proteins within the thylakoid membrane of chloroplasts.
What is a type of photosynthetic or protective pigment found in plastids that imparts a color that ranges from yellow to orange to red?
Carotenoids. Found in many fruits, vegetables, and flowers. In leaves, the more abundant chlorophylls usually mask the colors of carotenoids.
In temperate climates where the leaves change colors, the quantity of chlorophyll in the leaf declines during autumn. The carotenoids become readily visible and produce the yellows, oranges, and reds of autumn foliage.
Car-rot-tin-oids
What is a diagram that depicts the wavelengths of electromagnetic radiation that are absorbed by a pigment?
Absorption spectrum.
What is the advantage of having different pigment molecules?
Having different pigment molecules allows plants to absorb a wider range of wavelengths of light.
What is the rate of photosynthesis plotted as a function of the wavelength of light?
Action spectrum
What do the thylakoid membranes of the chloroplast contain in two distinct complexes of proteins and pigment molecules?
Photosystem I (PSI) and photosystem II (PSII)
T/F Photosystem II was discovered first but Photosystem I is the initial step of photosynthesis.
False. PSI was the first step discovered but PSII is the initial step in photosynthesis.
What is a distinct complex of proteins and pigment molecules in chloroplasts that absorbs light and also generates oxygen from water during the light reactions of photosynthesis?
PSII (photosystem 2)
What is a distinct complex of proteins and pigment molecules in chloroplasts that absorbs light during the light reactions of photosynthesis?
PSI (photosystem 1)
Are ATP, NADPH, and O2 produced in the stroma or in the thylakoid lumen?
ATP and NADPH are produced in the stroma of the thylakoid while O2 is produced in the thylakoid lumen.
When the photon excites an electron causing it to excite from PSII, what is used to replenish the lost electron in the reaction center?
Two molecules of water bind to the water-splitting enzyme in the thylakoid lumen that is attached to PSII.
The splitting of the water molecules creates O2 and 4 H+ ions. The electrons released from oxidized water molecules replenish the electrons that are removed from P680.
What is the acceptor of the electron once it leaves PSII?
Plastoquinone (plastic-wi-non). Remember: Ubiquinone (You-Bick-Wi-Noun) is used in animal cells as a electron acceptor in the ETC of ATP creation.
The plastoquinone is reduced and sends the electron to the next membrane complex.
[Bonus] What plays a vital role in electron transport chains?
Quinones
What happens to the b6-f complex when it receives an electron from the plastoquinone?
It causes the complex to pump protons (H+ ions) into the thylakoid lumen from the stroma of chloroplast.
How is ADP and inorganic phosphate phosphorylated into ATP?
The protons must pass through the ATP-synthase channel and released into the stroma. This is known as photophosphorylation.
When light is absorbed by PSI, what happens to the electron when it leaves the system?
The reaction center passes the high energy electron to ferredoxin and then through this reduction, the electron is passed to NADP-reductase where it is attached to NADP+ to create NADPH
How does the reaction center for PSI replace the loss of an electron it used in NADP-reductase in the creation of NADPH?
PSII sends an electron through the b6-f complex to a small protein called Plastocyanin where it is then transported to PSI.
What is another name for the reaction centers in PSII and PSI?
Light-harvesting complex.
What are some of the pigment molecules within in PSII that are electron carriers?
P680, Pheophytin (Pp), Qa, and Qb.
What is the pigment molecule within PSI where a high-energy electron is removed and then transported to an electron acceptor?
P700
How many electrons can the protein called Ferredoxin accept?
- One electron at a time.
What is in the light reactions of photosynthesis, the movement of electrons from PSII to PSI and ultimately to NADP+ to form NADPH?
Linear electron flow
The electrons move linearly from PSII to PSI and ultimately reduce NADP+ to NADPH.
What is the key differences between how PSII and PSI source their electrons received by their respective pigment molecules?
An oxidized pigment in PSII called P680 receives an electron from water. By comparison, an oxidized pigment in PSI called P700 receives an electron from the protein Pc. Therefore, PSI does not need to split water to reduce this pigment and does not generate oxygen.
What is the process via chemiosmosis by which the light reactions of photosynthesis produce ATP?
Photophosphorylation
What are the three ways the gradient in the thylakoid lumen is generated?
The splitting of water places H+ in the thylakoid lumen.
The movement of high-energy electrons along the ETC from photosystem II to photosystem I pumps H+ into the thylakoid lumen.
The formation of NADPH consumes H+ in the stroma.
Now, how are the steps of the light reactions of photosynthesis producing products: O2, NADPH, and ATP?
O2 is produced in the thylakoid lumen by the oxidation of water by photosystem II. Two electrons are removed from water, producing 2 H+ and 1/2 O2. The two electrons are transferred to P680 molecules.
NADPH is produced in the stroma using high-energy electrons that are first boosted to a higher energy level in photosystem II and then are boosted a second time in photosystem I. Two high-energy electrons and one H+ are transferred to NADP+ to produce NADPH.
ATP is produced in the stroma via ATP synthase that uses an H+ electrochemical gradient.
T/F The electron flow within photosynthesis produces roughly the same amount of NADPH and ATP.
True.
However, as we will see later, the Calvin cycle uses more ATP than NADPH.
During photosynthesis, what is a pattern of electron flow in the thylakoid membrane that is cyclic and generates only ATP? Otherwise known as, cyclic electron flow.
Cyclic photophosphorylation.
(1) the path of electrons is cyclic, (2) light energizes the electrons, and (3) ATP is made via the phosphorylation of ADP.
Why does cyclic photophosphorylation provide an advantage to a plant over using only linear electron flow?
How does cyclic photophosphorylation help create more ATP than NADPH?
Linear electron flow produces equal amounts of ATP and NADPH. However, plants usually need more ATP than NADPH. Cyclic photophosphorylation allows plants to make just ATP, thereby increasing the relative amount of ATP.
As electrons travel in this cyclic route, they release energy, and some of this energy is used to transport H+ into the thylakoid lumen. This resulting H+ gradient drives the synthesis of ATP via ATP synthase. When there is low NADP+ and high NADPH, this cycle is favored since there is enough NADPH to power the Calvin cycle later. Linear electron flow is favored when NADPH is low and NADP+ is high. Cyclic is also favored when ATP is low.
What are genes derived from the same ancestral gene that have accumulated random mutations that make their sequences slightly different?
Homologous genes
Explain why the three-dimensional structures of cytochrome b and cytochrome b6 are very similar.
Because these two proteins are homologous, this means that the genes that encode them were derived from the same ancestral gene. Therefore, the amino acid sequences of these two proteins are expected to be very similar, though not identical. Because the amino acid sequence of a protein determines its structure, two proteins with similar amino acid sequences would be expected to have similar structures.
Homologous proteins cytochrome b6 in chloroplasts and cytochrome b in mitochondria both donate electrons to another protein within their complexes, cytochrome f or cytochrome c1 respectively.
Explain why the three-dimensional structures of cytochrome b and cytochrome b6 are very similar.
Because these two proteins are homologous, this means that the genes that encode them were derived from the same ancestral gene. Therefore, the amino acid sequences of these two proteins are expected to be very similar, though not identical. Because the amino acid sequence of a protein determines its structure, two proteins with similar amino acid sequences would be expected to have similar structures.
Homologous proteins cytochrome b6 in chloroplasts and cytochrome b in mitochondria both donate electrons to another protein within their complexes, cytochrome f or cytochrome c1 respectively.
[8.3 Molecular Features of Photosystems]
What are the two main components of PSII and PSI?
Light-harvesting complex and a reaction center.
What is a component of PSII and PSI composed of several dozen pigment molecules that are anchored to proteins in the thylakoid membrane of a chloroplast?
Light-harvesting complex.
