Question

In chloroplasts, ATP is synthesized from ADP plus inorganic phosphate (Pi) in a reaction catalyzed by ATP synthase molecules that are embedded in the thylakoid membrane. Which of the following statements provides evidence to support the claim that no ATP will be synthesized in the absence of a proton gradient across the thylakoid membrane?

Answer 1

Explanation:

Complete Question:

A. Blocking electron flow from one carrier to the next in the electron transport chains blocks formation of a proton gradient in the thylakoid.

B. Increasing the proton concentration difference across the thylakoid membrane is not associated with a parallel increase in the rate of ATP synthesis.

C. No ATP is synthesized when channel proteins that allow the free passage of protons are inserted into the thylakoid membrane.

D. No ATP is synthesized while the Calvin cycle is synthesizing carbohydrates and using ATP and NADPH at a high rate.

Correct: C. No ATP is synthesized when channel proteins that allow the free passage of protons are inserted into the thylakoid membrane.

Photophosphorylation describes a process in which the H+ made in previous steps of photosynthesis, and free electrons are used to obtain energy stored as ATP; in the electron transport chain move down the chain the energy they release is used in pumping protons out of the thykaloid space.

The high concentration of  H+ from photolysis, outside the leads to increased H+ concentration within the thykaloid space, due to its high permeability.  This forms a gradient where there is a differential in the number of protons on either side of the membrane the protons flow into the stroma through the enzyme ATP synthase, which makes the energy storage molecules of ATP from the reduction of ADP and inorganic phosphate, Pi. NAD+ functions as the terminal electron acceptor and is reduced to NADPH.

Thus:

• a H+ concentration gradient is required for oxidative phosphorylation in the electron transport chain of the chloroplast, and thus the production of ATP
• the H+ ion gradient must favor the flow of electrons into the stroma

The free flow of H+ disrupts the gradient, and H+ cannot flow into ATP synthase to produce ATP.

Further Explanation:

Photosynthesis is a chemical pathway that’s integral to producing energy in plants and other primary producers. Energy in the form of molecules of glucose is produced from light, water and carbon dioxide while oxygen is released. This occurs in several complex steps, photosynthesis is a rate limited reaction, depends on several factors including carbon dioxide concentration, ambient temperature and light intensity; the energy is retrieved from photons, I.e. particles of light, and water is used as a reducing agent. This occurs in the thykaloids, where pigment molecules like chlorophyll reside.

The chloroplast is a membrane bound organelle found in plants. It contains several invaginations of a plasma membrane called the thylakoid membrane. This contains chlorophyll pigments, in stacks called granum, while the internal spaces of the organelle are called the lumen. Liquid surrounds the granum, forming the stroma.

During the light reaction:

• Light is absorbed by pigments in phosystem II (PSII). This energy is transferred among pigments til it gets to the reaction center, and is transferred to P680; this promotes an electron to a higher energy level where it then goes to an acceptor molecule.
• Water supplies the chlorophyll in plant cell with replacement electrons for the ones removed from photosystem II. Additionally, water (H2O) split by light during photolysis into H+ and OH- acts as a source of oxygen along with functioning as a reducing agent.
• the electron moves down an electron transport chain (to PS I)where it experiences continuous energy loss. This energy fuels the pumping of H+ from the stroma to thykaloid, leading to the formation of a gradient. The H+ move along their gradient and cross through ATP synthase, into the the stroma.
• ATP synthase converts ADP and Pi to the energy storage molecule ATP.
• The electron gets to photosystem I where it goes to pigments at P700. It absorbs light energy, the electron is promoted to a higher energy level, and passed to an electron acceptor. This leaves a space for another electron which is then replaced by one from photosystem II.
• in the ETC, the molecule NADP is reduced to NADPH by providing H+ ions. NADP and NADPH are integral to the Calvin cycle where monosaccharides or sugars like glucose are produced after the modification of several molecules.

Learn more about photosynthesis at brainly.com/question/4216541

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