Charging the Battery: Light Dependent Reactions Explained

If electrons are energized and sent down an electron transport chain, then the original source (the photosystem) loses them. If the photosystem must remain functional, then it needs replacement electrons. If water is split (photolysis) to provide these electrons, then the statement is true.

If a proton gradient is built up inside the thylakoid space, then those protons will want to flow back to the stroma. If they flow through the enzyme ATP Synthase to generate energy for bonding a phosphate to ADP, then this process is correctly called chemiosmosis.

If a pigment molecule absorbs a photon of light, then that energy is transferred to an electron. If that electron moves from a stable ground state to a high-energy "excited" state to begin the light dependent reactions, then the statement is true.

If the entire process relies on the absorption of photons to move electrons, then light is a mandatory reactant. If you remove the light, then the electrons are never excited, and the production of ATP and NADPH will cease entirely.

If a pigment absorbs a color, then that color's energy is used for the reaction. If chlorophyll absorbs red and blue light but allows green light to bounce off, then our eyes perceive the reflected green light. Therefore, the statement is true.

If water is split at the start, then the electrons begin at PS II. If they then travel through proteins to PS I to be re-energized, then they finally end up on the carrier NADPH. This makes the sequence PS II -> ETC -> PS I -> NADPH the only logical path.

If light energy must be captured by pigments like chlorophyll, then the reaction must happen where those pigments are located. If chlorophyll is embedded in the disc-like membranes of the thylakoid, then the light dependent reactions take place in the thylakoid membranes.

If the first stage of photosynthesis captures energy, then it must store that energy in temporary "batteries." If ATP and NADPH are the molecules that carry chemical energy and electrons respectively, then they are the products sent to power the next stage.

If electrons lose energy as they are pumped across the membrane, then they need a second "boost" from sunlight. If Photosystem I provides this second boost, then it allows the electrons to have enough energy to be added to NADP+, creating NADPH.

If protons are pumped into the thylakoid, then a gradient is created. If they flow back out through ATP Synthase, they produce ATP. If they eventually join with electrons and NADP+, then they help form NADPH. They do not become oxygen gas.

If water (H2O) is split to harvest electrons, then the hydrogen ions and oxygen atoms are separated. If the oxygen atoms are not used to make ATP or NADPH, then they pair up to form O2. If O2 is released from the plant, then oxygen is the byproduct of this stage.

If scientists name things based on the order they find them rather than the order they work, then the numbers may be confusing. If Photosystem I was found first but actually appears later in the light dependent reactions, then PS II is the logical starting point despite its name.

If there are more protons in one area than another, then a difference in density exists. If the light dependent reactions use the energy from electrons to pump these protons into a tight space, then they are building a concentration gradient.

If the stage captures solar energy and stores it in molecules while producing oxygen as waste, then those are the key events. Building sugar (C) happens in the Calvin Cycle, and while reflecting light happens (E), it is not a "goal" or event of the chemical process itself.

If the word "photo" means light and "lysis" means to break apart, then the term describes using light to split a substance. If water is being broken apart at the start of the light dependent reactions, then the scientific name for this process is photolysis.

If carbon dioxide is used to build the physical structure of a sugar molecule, then it is needed for the synthesis stage. If the light dependent reactions are only focused on converting light into temporary chemical energy (ATP/NADPH), then CO2 is not required yet, making the statement false.

If a plant needs to absorb specific wavelengths of light to excite electrons, then it must use a pigment. If chlorophyll a is the specific molecule that absorbs red and blue light to trigger the electron transport chain, then it is the key pigment in the light dependent reactions.

If a photosystem is a functional unit designed to catch light, then it must have pigments like chlorophyll and a place to funnel that energy (reaction center). ATP Synthase is a separate enzyme, and the stroma is the fluid outside the membrane.

If energy is being transferred step-by-step through a membrane, then it acts like a bucket brigade. If this "brigade" consists of protein complexes that use electron energy to move protons, then it is called the electron transport chain.

If the cell needs to convert a proton gradient into chemical energy, then it needs a mechanical-like enzyme. If ATP synthase is the specific protein that spins as protons move through it, then it is the enzyme responsible for creating the cell's energy currency.