MIDTERM - RESPIRATION & PHOTOSYNTHESIS Flashcards
Q: What are the reactants and products of photosynthesis? Write the balanced chemical equation.
A: Reactants: Carbon dioxide (CO₂), water (H₂O), and light energy.
Products: Glucose (C₆H₁₂O₆) and oxygen (O₂).
Equation: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂.
Q: What are the two major stages of photosynthesis, and where do they occur?
A: 1. Light-dependent reactions (occur in the thylakoid membranes).
2. The Calvin cycle (light-independent reactions, occur in the stroma of the chloroplast).
Q: Describe the role of chlorophyll in the light-dependent reactions.
A: Chlorophyll absorbs light energy, primarily red and blue wavelengths, and excites electrons to a higher energy state. This energy drives the synthesis of ATP and NADPH.
Main events of the light-dependent reactions
- Photolysis of water provides electrons, releasing O₂ as a byproduct.
- Excited electrons from photosystem II (PSII) pass through the electron transport chain to photosystem I (PSI), creating a proton gradient for ATP synthesis (photophosphorylation).
- Electrons from PSI reduce NADP⁺ to form NADPH.
Explain how ATP is synthesized in the light-dependent reactions.
ATP is synthesized by ATP synthase as protons move down their gradient from the thylakoid lumen into the stroma (chemiosmosis), driven by the energy from electron transport.
What is photolysis, and what role does it play in photosynthesis?
Photolysis is the splitting of water molecules by light energy in photosystem II, producing oxygen, protons (H⁺), and electrons needed for the electron transport chain.
What are the inputs and outputs of the Calvin cycle?
** Inputs: **CO₂, ATP, and NADPH.
**Outputs: **Glucose (C₆H₁₂O₆) and regenerated RuBP (ribulose bisphosphate).
What enzyme is responsible for carbon fixation in the Calvin cycle, and what is its role?
Rubisco (ribulose-1,5-bisphosphate carboxylase-oxygenase) catalyzes the fixation of CO₂ to RuBP, forming 3-phosphoglycerate (3-PGA).
How are ATP and NADPH used in the Calvin cycle?
ATP provides energy, and NADPH provides reducing power (electrons) to convert 3-PGA into glyceraldehyde-3-phosphate (G3P).
How many molecules of G3P are needed to form one molecule of glucose?
Two G3P molecules are needed to form one glucose molecule
Describe the three phases of the Calvin cycle.
- Carbon fixation: CO₂ is fixed to RuBP by rubisco, forming 3-PGA.
- Reduction: ATP and NADPH convert 3-PGA into G3P.
- Regeneration: RuBP is regenerated from G3P using ATP.
What are stomata, and how do they regulate photosynthesis?
Stomata are small openings on leaf surfaces controlled by guard cells. They regulate gas exchange (CO₂ intake and O₂ release) and water loss through transpiration.
What environmental factors influence the rate of photosynthesis?
Light intensity, carbon dioxide concentration, temperature, and water availability.
What is the balanced chemical equation for cellular respiration?
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ~38 ATP.
What are the three main stages of cellular respiration, and where do they occur?
Glycolysis (in the cytoplasm),
Krebs cycle (citric acid cycle) (in the mitochondrial matrix),
Electron transport chain (ETC) and oxidative phosphorylation (in the inner mitochondrial membrane).*
What are the inputs and outputs of glycolysis?
Inputs: Glucose, 2 ATP, 2 NAD⁺.
Outputs: 2 pyruvate, 4 ATP (net gain of 2), 2 NADH, 2 H₂O.
What happens to pyruvate after glycolysis if oxygen is present?
Pyruvate enters the mitochondria, where it is converted to acetyl-CoA, releasing one CO₂ and generating one NADH per pyruvate.
What is the role of acetyl-CoA in the Krebs cycle?
Acetyl-CoA (2 carbon) combines with oxaloacetate (4) to form citrate, initiating the Krebs cycle.
What are the main products of one turn of the Krebs cycle?
1 ATP (or GTP), 3 NADH, 1 FADH₂, and 2 CO₂
What is the total yield of ATP, NADH, and FADH₂ after two turns of the Krebs cycle per glucose molecule?
2 ATP, 6 NADH, 2 FADH₂, and 4 CO₂.
What is the function of NADH and FADH₂ in cellular respiration?
They carry high-energy electrons to the electron transport chain (ETC) for ATP production.
Describe the role of the electron transport chain (ETC) in photosynthesis.
The ETC transfers electrons from NADH and through protein complexes, creating a proton gradient that drives ATP synthesis.
What is the purpose of Cytochrome C in the ETC (cellular respiration)?
It gives electrons to the final electron acceptor, oxygen, which combines with protons to form water (H20).
What is the theoretical maximum yield of ATP from one molecule of glucose in aerobic respiration?
Approximately 36 to 38 ATP.
What is anaerobic respiration, and how does it differ from aerobic respiration?
Anaerobic respiration occurs without oxygen, using a different electron acceptor. In humans, this process results in lactic acid fermentation, producing 2 ATP per glucose.
Explain the importance of oxygen in cellular respiration.
Oxygen is the final electron acceptor in the ETC, allowing the chain to continue functioning and preventing a backup of electrons. Without oxygen, ATP production would cease.
What happens when the mitochondria is exposed to cyanide?
Cytochrome C is inhibited from handing electrons over to oxygen, causes a backup in electrons that would halt ATP synthesis.
