Metabolic Processes: Cellular Respiration & Photosynthesis

Why is glucose phosphorylated at the beginning of glycolysis

Traps glucose inside the cell and activates it for breakdown in later steps.

What is the net reaction of glycolysis?

Glucose → 2 Pyruvate + 2 ATP (net) + 2 NADH

What happens to glucose in the absence of oxygen?

Undergoes anaerobic respiration (fermentation), producing lactate (animals) or ethanol + CO₂ (yeast).

What is pyruvate and what is meant by pyruvate oxidation?

End product of glycolysis: Pyruvate is converted into Acetyl-CoA, releasing CO₂ and forming NADH.

Net reaction of pyruvate oxidation

2 Pyruvate → 2 Acetyl-CoA + 2 NADH + 2 CO₂

What is the net reaction of the Krebs cycle (citric acid cycle)?"

Each Acetyl-CoA → 3 NADH + 1 FADH₂ + 1 ATP + 2 CO₂ (per turn; happens twice per glucose)

What is oxidized and what is reduced during pyruvate oxidation?

Pyruvate is oxidized to Acetyl-CoA; NAD⁺ is reduced to NADH.

What role do NADH and FADH₂ play in cellular respiration?

They carry high-energy electrons to the electron transport chain (ETC), where they power ATP production.

How does ATP synthase make ATP? Use a dam analogy.

H⁺ ions flow through ATP synthase like water through a dam, turning a rotor and powering ATP formation from ADP + Pi.

What's the difference between oxidative and substrate-level phosphorylation?

Oxidative: ATP formed by ETC + chemiosmosis (in mitochondria)

Substrate-level: Direct phosphate transfer in glycolysis/Krebs

How do light, water, and CO₂ enter a plant for photosynthesis?"

Light: Absorbed by chlorophyll in chloroplasts

Water: Taken up by roots via osmosis

CO₂: Enters through stomata (leaf pores)

Pigment

Molecule that absorbs light (e.g. chlorophyll).

Photosystem

Protein-pigment complex that captures light.

Antenna complex

Group of pigments funneling energy to reaction center.

Connection between light reactions and Calvin Cycle

Light reactions make ATP and NADPH, which fuel the Calvin Cycle to make glucose. Calvin Cycle regenerates ADP and NADP⁺ for light reactions.

Key reactants and products of glycolysis

Glucose → 2 ATP + 2 NADH

Key reactants and products of pyruvate oxidation

2 Pyruvate → 2 NADH + 2 CO₂

Key reactants and products of Krebs cycle

2 Acetyl-CoA → 6 NADH + 2 FADH₂ + 2 ATP + 4 CO₂

Key reactants and products of ETC

NADH/FADH₂ + O₂ → ~34 ATP + H₂O

What are redox reactions?

Reactions involving transfer of electrons — one substance is oxidized (loses e⁻), another is reduced (gains e⁻).

Importance of redox reactions in cellular respiration

They transfer energy from glucose to electron carriers (NADH/FADH₂), which power ATP production in the ETC.