Biology Flashcards: Explain Light To Chemical Energy

What this deck covers

This deck focuses on Explain Light To Chemical Energy, giving you a quick way to review the definitions, rules, and examples that matter most for Biology.

How to use these flashcards

Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: What is the overall purpose of the Calvin cycle?

Answer: Use ATP and NADPH to fix $CO_2$ into sugars. Energy carriers from light reactions power $CO_2$ reduction to carbohydrates.

Flashcard 2: Which photosystem is used in cyclic electron flow?

Answer: Photosystem I. Only PSI participates in the cyclic pathway.

Flashcard 3: What 5-carbon molecule does Rubisco attach $CO_2$ to at the start of the Calvin cycle?

Answer: RuBP (ribulose-1,5-bisphosphate). Five-carbon acceptor molecule for $CO_2$ in the Calvin cycle.

Flashcard 4: What is the role of the electron transport chain in the light reactions?

Answer: Create an $H^+$ gradient to drive ATP synthesis. Proton pumping creates the gradient needed for ATP synthesis.

Flashcard 5: What organelle converts light energy into chemical energy during photosynthesis?

Answer: Chloroplast. Contains thylakoids where light reactions occur and stroma for the Calvin cycle.

Flashcard 6: What is the immediate energy conversion when chlorophyll absorbs a photon?

Answer: Light energy excites an electron to a higher energy level. Photon energy elevates electrons to higher energy states.

Flashcard 7: What are the three direct products of water splitting (photolysis) in chloroplasts?

Answer: Electrons, $H^+$, and $O_2$. Water splitting provides electrons, protons, and releases oxygen gas.

Flashcard 8: What is the name of the stack of thylakoids in a chloroplast?

Answer: Granum. Stacked thylakoids increase surface area for light-capturing reactions.

Flashcard 9: What is cyclic electron flow primarily used to produce in chloroplasts?

Answer: ATP (without NADPH production). Generates extra ATP when more is needed than NADPH.

Flashcard 10: Which molecule provides the reducing power to convert 3-PGA into G3P?

Answer: NADPH. Provides electrons and hydrogen for reducing carbon compounds.

Flashcard 11: Identify the direct source of the $O_2$ released in photosynthesis: $CO_2$ or $H_2O$?

Answer: $H_2O$. Oxygen atoms in released $O_2$ come from split water molecules.

Flashcard 12: What is the balanced overall equation for oxygenic photosynthesis?

Answer: $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$. Overall reaction showing $CO_2$ and water converting to glucose and oxygen.

Flashcard 13: What is the main carbon-fixing enzyme of the Calvin cycle?

Answer: Rubisco. Catalyzes the attachment of $CO_2$ to RuBP in carbon fixation.

Flashcard 14: What molecule is split to replace electrons lost by Photosystem II?

Answer: $H_2O$. Water splitting provides electrons to replace those lost by chlorophyll.

Flashcard 15: What chloroplast membrane system contains the light-dependent reactions?

Answer: Thylakoid membrane. Contains photosystems and electron transport chains for light-dependent reactions.

Flashcard 16: What pigment primarily absorbs light energy for photosynthesis in plants?

Answer: Chlorophyll $a$. Most abundant photosynthetic pigment that directly participates in light reactions.

Flashcard 17: Which photosystem directly reduces NADP$^+$ to NADPH?

Answer: Photosystem I. PSI provides electrons to reduce NADP$^+$ to NADPH.

Flashcard 18: What molecule is split to replace electrons lost by Photosystem II?

Answer: $H_2O$. Water splitting provides electrons to replace those lost by chlorophyll.

Flashcard 19: What process splits water during the light-dependent reactions?

Answer: Photolysis. Light-driven water splitting releases electrons, protons, and oxygen.

Flashcard 20: What is the reaction center chlorophyll pair in Photosystem I called?

Answer: $P700$. Absorbs light at 700 nm wavelength in PSI reaction center.

Flashcard 21: In which direction do protons flow through ATP synthase in chloroplasts?

Answer: From thylakoid lumen to stroma. Protons flow down their gradient through ATP synthase channels.

Flashcard 22: What is the name of the protein complex that transfers electrons and pumps protons after PSII?

Answer: Cytochrome $b_6f$ complex. Links PSII and PSI while pumping protons across the membrane.

Flashcard 23: What is the main chemical form in which light energy is stored after photosynthesis?

Answer: Chemical energy in sugars (such as glucose). Light energy is converted into stable chemical bonds in carbohydrates.

Flashcard 24: What is the name of the stack of thylakoids in a chloroplast?

Answer: Granum. Stacked thylakoids increase surface area for light-capturing reactions.

Flashcard 25: What 3-carbon molecule is the direct carbohydrate product that exits the Calvin cycle?

Answer: G3P (glyceraldehyde-3-phosphate). Three-carbon sugar that can be used to make glucose.

Flashcard 26: What is the reaction center chlorophyll pair in Photosystem II called?

Answer: $P680$. Absorbs light at 680 nm wavelength in PSII reaction center.

Flashcard 27: What are the two main stages of photosynthesis called?

Answer: Light-dependent reactions and Calvin cycle. First stage captures light energy, second uses it to make sugars.

Flashcard 28: What organelle converts light energy into chemical energy during photosynthesis?

Answer: Chloroplast. Contains thylakoids where light reactions occur and stroma for the Calvin cycle.

Flashcard 29: Which stage of photosynthesis can proceed without light if ATP and NADPH are available?

Answer: Calvin cycle. Can operate independently if energy carriers are available.

Flashcard 30: Which stage of photosynthesis can proceed without light if ATP and NADPH are available?

Answer: Calvin cycle. Can operate independently if energy carriers are available.

Flashcard 31: What is the term for incorporating inorganic $CO_2$ into an organic molecule?

Answer: Carbon fixation. Conversion of inorganic carbon into organic molecules.

Flashcard 32: Choose the correct pairing: PSI reaction center is $P680$ or $P700$?

Answer: PSI is $P700$. PSI contains $P700$ chlorophyll reaction center.

Flashcard 33: Choose the correct pairing: PSII reaction center is $P680$ or $P700$?

Answer: PSII is $P680$. PSII contains $P680$ chlorophyll reaction center.

Flashcard 34: What chloroplast fluid region contains the Calvin cycle (light-independent reactions)?

Answer: Stroma. Fluid matrix where $CO_2$ fixation and sugar synthesis occur.

Flashcard 35: What is the name of the enzyme that makes ATP using a proton gradient?

Answer: ATP synthase. Uses proton gradient energy to phosphorylate ADP into ATP.

Flashcard 36: What reduced electron carrier is produced when NADP$^+$ gains electrons and $H^+$?

Answer: NADPH. Carries electrons and protons to power Calvin cycle reactions.

Flashcard 37: Which photosystem is used in cyclic electron flow?

Answer: Photosystem I. Only PSI participates in the cyclic pathway.

Flashcard 38: Identify the direct source of the $O_2$ released in photosynthesis: $CO_2$ or $H_2O$?

Answer: $H_2O$. Oxygen atoms in released $O_2$ come from split water molecules.

Flashcard 39: Choose the correct pairing: PSI reaction center is $P680$ or $P700$?

Answer: PSI is $P700$. PSI contains $P700$ chlorophyll reaction center.

Flashcard 40: What is the term for ATP production powered by light-driven electron transport in chloroplasts?

Answer: Photophosphorylation. ATP synthesis driven by light energy through electron transport.

Flashcard 41: What molecule is the final electron acceptor in the light-dependent reactions?

Answer: NADP$^+$. Accepts electrons from PSI to become reduced to NADPH.

Flashcard 42: What is the overall purpose of the light-dependent reactions?

Answer: Convert light energy to ATP and NADPH. Transform light energy into chemical energy carriers for the Calvin cycle.

Flashcard 43: What are the two main stages of photosynthesis called?

Answer: Light-dependent reactions and Calvin cycle. First stage captures light energy, second uses it to make sugars.

Flashcard 44: What 3-carbon molecule is the direct carbohydrate product that exits the Calvin cycle?

Answer: G3P (glyceraldehyde-3-phosphate). Three-carbon sugar that can be used to make glucose.

Flashcard 45: What is the name of the pathway describing electron flow from PSII to PSI to NADP$^+$?

Answer: Noncyclic (linear) electron flow. Standard pathway from water to NADP$^+$ producing ATP and NADPH.

Flashcard 46: What is the balanced overall equation for oxygenic photosynthesis?

Answer: $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$. Overall reaction showing $CO_2$ and water converting to glucose and oxygen.

Flashcard 47: What is the name of the protein complex that transfers electrons and pumps protons after PSII?

Answer: Cytochrome $b_6f$ complex. Links PSII and PSI while pumping protons across the membrane.

Flashcard 48: Which molecule provides the energy input to phosphorylate intermediates in the Calvin cycle?

Answer: ATP. Powers the phosphorylation reactions in the Calvin cycle.

Flashcard 49: What gas is released as a byproduct when water is split in photosynthesis?

Answer: $O_2$. Oxygen is released when water is split to provide electrons.

Flashcard 50: Which photosystem directly reduces NADP$^+$ to NADPH?

Answer: Photosystem I. PSI provides electrons to reduce NADP$^+$ to NADPH.

Flashcard 51: Where do protons ($H^+$) accumulate during the light-dependent reactions?

Answer: Thylakoid lumen. Interior space where protons accumulate to create the gradient.

Flashcard 52: What gas is released as a byproduct when water is split in photosynthesis?

Answer: $O_2$. Oxygen is released when water is split to provide electrons.

Flashcard 53: Identify the correct location for Rubisco activity: thylakoid lumen, thylakoid membrane, or stroma.

Answer: Stroma. Calvin cycle enzymes operate in the chloroplast's fluid matrix.

Flashcard 54: What is the immediate energy conversion when chlorophyll absorbs a photon?

Answer: Light energy excites an electron to a higher energy level. Photon energy elevates electrons to higher energy states.

Flashcard 55: What are the two main energy-rich products of the light-dependent reactions?

Answer: ATP and NADPH. Energy carriers that power $CO_2$ fixation in the Calvin cycle.

Flashcard 56: What are the three direct products of water splitting (photolysis) in chloroplasts?

Answer: Electrons, $H^+$, and $O_2$. Water splitting provides electrons, protons, and releases oxygen gas.

Flashcard 57: Choose the correct pairing: PSII reaction center is $P680$ or $P700$?

Answer: PSII is $P680$. PSII contains $P680$ chlorophyll reaction center.

Flashcard 58: What is the name of the enzyme that makes ATP using a proton gradient?

Answer: ATP synthase. Uses proton gradient energy to phosphorylate ADP into ATP.

Flashcard 59: In which direction do protons flow through ATP synthase in chloroplasts?

Answer: From thylakoid lumen to stroma. Protons flow down their gradient through ATP synthase channels.

Flashcard 60: What is the role of accessory pigments such as carotenoids in photosynthesis?

Answer: Absorb additional wavelengths and transfer energy to chlorophyll. Expand the range of light wavelengths captured for photosynthesis.

Flashcard 61: Which photosystem acts first in the light reactions: Photosystem I or II?

Answer: Photosystem II. PSII initiates the electron transport chain in linear electron flow.

Flashcard 62: Which photosystem acts first in the light reactions: Photosystem I or II?

Answer: Photosystem II. PSII initiates the electron transport chain in linear electron flow.

Flashcard 63: What is the name of the pathway describing electron flow from PSII to PSI to NADP$^+$?

Answer: Noncyclic (linear) electron flow. Standard pathway from water to NADP$^+$ producing ATP and NADPH.

Flashcard 64: What is the reaction center chlorophyll pair in Photosystem II called?

Answer: $P680$. Absorbs light at 680 nm wavelength in PSII reaction center.

Flashcard 65: What is the main carbon-fixing enzyme of the Calvin cycle?

Answer: Rubisco. Catalyzes the attachment of $CO_2$ to RuBP in carbon fixation.

Flashcard 66: What is cyclic electron flow primarily used to produce in chloroplasts?

Answer: ATP (without NADPH production). Generates extra ATP when more is needed than NADPH.

Flashcard 67: What is the term for ATP production driven by a proton gradient across a membrane?

Answer: Chemiosmosis. ATP synthesis powered by proton gradient across membrane.

Flashcard 68: What is the term for incorporating inorganic $CO_2$ into an organic molecule?

Answer: Carbon fixation. Conversion of inorganic carbon into organic molecules.

Flashcard 69: What is the reaction center chlorophyll pair in Photosystem I called?

Answer: $P700$. Absorbs light at 700 nm wavelength in PSI reaction center.

Flashcard 70: What is the role of the electron transport chain in the light reactions?

Answer: Create an $H^+$ gradient to drive ATP synthesis. Proton pumping creates the gradient needed for ATP synthesis.

Flashcard 71: What chloroplast fluid region contains the Calvin cycle (light-independent reactions)?

Answer: Stroma. Fluid matrix where $CO_2$ fixation and sugar synthesis occur.

Flashcard 72: Which molecule provides the reducing power to convert 3-PGA into G3P?

Answer: NADPH. Provides electrons and hydrogen for reducing carbon compounds.

Flashcard 73: What process splits water during the light-dependent reactions?

Answer: Photolysis. Light-driven water splitting releases electrons, protons, and oxygen.

Flashcard 74: What reduced electron carrier is produced when NADP$^+$ gains electrons and $H^+$?

Answer: NADPH. Carries electrons and protons to power Calvin cycle reactions.

Flashcard 75: What are the two main energy-rich products of the light-dependent reactions?

Answer: ATP and NADPH. Energy carriers that power $CO_2$ fixation in the Calvin cycle.

Flashcard 76: What is the immediate 3-carbon product formed after $CO_2$ fixation and splitting of the 6-carbon intermediate?

Answer: 3-PGA (3-phosphoglycerate). First stable product formed after $CO_2$ combines with RuBP.

Flashcard 77: Identify the correct location for Rubisco activity: thylakoid lumen, thylakoid membrane, or stroma.

Answer: Stroma. Calvin cycle enzymes operate in the chloroplast's fluid matrix.

Flashcard 78: What is the main chemical form in which light energy is stored after photosynthesis?

Answer: Chemical energy in sugars (such as glucose). Light energy is converted into stable chemical bonds in carbohydrates.

Flashcard 79: Which molecule provides the energy input to phosphorylate intermediates in the Calvin cycle?

Answer: ATP. Powers the phosphorylation reactions in the Calvin cycle.

Flashcard 80: What is the name for chlorophyll and accessory pigments that capture light in a photosystem?

Answer: Light-harvesting complex (antenna complex). Network of pigments that collect and funnel light energy.

Flashcard 81: What is the overall purpose of the Calvin cycle?

Answer: Use ATP and NADPH to fix $CO_2$ into sugars. Energy carriers from light reactions power $CO_2$ reduction to carbohydrates.

Flashcard 82: What is the immediate 3-carbon product formed after $CO_2$ fixation and splitting of the 6-carbon intermediate?

Answer: 3-PGA (3-phosphoglycerate). First stable product formed after $CO_2$ combines with RuBP.

Flashcard 83: What pigment primarily absorbs light energy for photosynthesis in plants?

Answer: Chlorophyll $a$. Most abundant photosynthetic pigment that directly participates in light reactions.

Flashcard 84: What is the term for ATP production driven by a proton gradient across a membrane?

Answer: Chemiosmosis. ATP synthesis powered by proton gradient across membrane.

Flashcard 85: What is the name for chlorophyll and accessory pigments that capture light in a photosystem?

Answer: Light-harvesting complex (antenna complex). Network of pigments that collect and funnel light energy.

Flashcard 86: What 5-carbon molecule does Rubisco attach $CO_2$ to at the start of the Calvin cycle?

Answer: RuBP (ribulose-1,5-bisphosphate). Five-carbon acceptor molecule for $CO_2$ in the Calvin cycle.

Flashcard 87: What molecule is the final electron acceptor in the light-dependent reactions?

Answer: NADP$^+$. Accepts electrons from PSI to become reduced to NADPH.

Flashcard 88: What is the role of accessory pigments such as carotenoids in photosynthesis?

Answer: Absorb additional wavelengths and transfer energy to chlorophyll. Expand the range of light wavelengths captured for photosynthesis.

Flashcard 89: What chloroplast membrane system contains the light-dependent reactions?

Answer: Thylakoid membrane. Contains photosystems and electron transport chains for light-dependent reactions.

Flashcard 90: Which stage of photosynthesis directly requires photons to proceed?

Answer: Light-dependent reactions. Light is directly needed to drive photosystem reactions.

Flashcard 91: What is the term for ATP production powered by light-driven electron transport in chloroplasts?

Answer: Photophosphorylation. ATP synthesis driven by light energy through electron transport.

Flashcard 92: Which stage of photosynthesis directly requires photons to proceed?

Answer: Light-dependent reactions. Light is directly needed to drive photosystem reactions.

Flashcard 93: Where do protons ($H^+$) accumulate during the light-dependent reactions?

Answer: Thylakoid lumen. Interior space where protons accumulate to create the gradient.

Flashcard 94: What is the overall purpose of the light-dependent reactions?

Answer: Convert light energy to ATP and NADPH. Transform light energy into chemical energy carriers for the Calvin cycle.