AP BIO- Cellular Energetics

Krebs Cycle

3rd step in cell respiration; breaks down glucose in the mitochondria (Note

Aerobic

Uses oxygen

Anaerobic

Doesn't use oxygen

Oxidative Phosphorylation

• Happens in: Inner mitochondrial membrane

• Uses:

  • Electron Transport Chain (ETC)

  • Chemiosmosis (proton gradient + ATP synthase)

• Requires oxygen as the final electron acceptor.

• Makes a lot of ATP (~26–28 ATP per glucose).

• Process:
  Electrons → ETC → proton gradient → ATP synthase → ATP

Alcohol Fermentation

Produces NAD+ & releases CO2.

Acetyl CoA

Coenzyme A & is easily converted for Krebs cycle.

Cellular Respiration

Anaerobic and Aerobic respiration $\rightarrow$ breaks down organic molecules & uses ETC to make ATP.

Redox reactions

Gains/Loss of an electron (transfer of e).

ATP synthase

An enzyme to make ATP, uses chemiosmosis (H+gradient energy).

Substrate-level Phosphorylation

Making ATP in glycolysis.

Lactic Acid Fermentation

Regenerates NAD+ into reducing CO2

Oxidation

Complete or partial loss of e.

Glycolysis

Breaks down glucose -> pyruvate, starting point for fermentation or cell respiration.

Catabolism

Breaking molecules, releases energy.

Reduction

Gaining electrons in redox reaction.

Chemiosmosis

Diffusion of ions across a membrane, causes ADP to pick up H+ so it can now change to ATP synthase to make ATP

NAD+/NADH

{NAD}+= oxidized -> can take e -> NADH= e holder

Proton motive force

The proton motive force is the energy stored when protons (H⁺) are pumped across a membrane during cellular respiration or photosynthesis. Because there are more protons on one side than the other, they want to flow back across—like water behind a dam.

Proton gradient

when there are more protons (H⁺) on one side of a membrane than the other.

Photosynthesis

Light energy to Chemical energy.

Non-cyclic photophosphorylation

the normal “one-way” flow of electrons in the light reactions of photosynthesis. It uses Photosystem II → Photosystem I to make ATP, NADPH, and oxygen.

Autotrophs

Organisms that make their own food.

Cyclic electron flow

During photosynthesis, when electrons cycle only through Photosystem I (not PSII) to make extra ATP but no NADPH or oxygen.

Heterotrophs

Eat other organisms for energy.

Cyclic photophosphorylation

a light reaction where electrons cycle only through Photosystem I to make extra ATP.

Chlorophyll

Green pigment in chloroplasts.

Absorption spectrum

Range of pigments ability to absorb light.

Mesophyll cells

Leaf cells specialized for photosynthesis.

Chlorophyll a

Directly participates in light reactions.

Rubisco (RuBP Carboxylase)

Enzyme that initiates the Calvin cycle by catalyzing the reaction of CO₂ + RuBP → C₆H₁₂O₆. Takes carbon from air.

Carbon Spectrum

Determines how effectively plants absorb wavelengths of light.

C₃ Plants

Use the Calvin cycle as their first step to convert CO₂ → organic material.

Stroma

Dense fluid within chloroplasts.

Chlorophyll b

Transfers energy to chlorophyll a.

Photrespiration

Rubisco binds to oxygen instead of carbon, causing energy waste.

Light Reactions

1st step of photosynthesis. Converts solar energy → chemical energy (NADPH + ATP).

Accessory Pigments

Light-absorbing compounds that work with chlorophyll a.

C₄ Plants

Physically separate carbon fixation from Calvin cycle. Supply CO₂ for Calvin cycle using PEP; use 2 different cell types.

Calvin Cycle

RUBISCO fixes CO₂ → C₆H₁₂O₆. 2nd major step of photosynthesis.

Bundle Sheath Cells

Photosynthetic cells surrounding vascular bundles.

Reaction Center

Triggers light reactions by exciting electrons.

Photophosphorylation

Making ATP from ADP using solar-derived energy.

Carbon Fixation

Incorporation of carbon from CO₂ into organic molecules.

PEP Carboxylase

Enzyme in C₄ and CAM plants; fixes carbon before photosynthesis. Does not bind O₂.

Photosystem I

Light-capturing units acting as a reaction center.

Photosystem II

Light-capturing units contributing electrons to the chain.

CAM Plants

Separate carbon fixation from Calvin cycle by time.

Night

Stomata open → CO₂ enters & stored.

Day

Calvin cycle occurs.

Thylakoid Membrane

Inside chloroplast; converts light energy → chemical energy.