BIO UNIT 4 STUDY GUIDE

What is energy?

Energy is the ability to do work; it can be converted from one form to another.

What is potential energy?

Energy of position — such as chemical energy in bonds or electrochemical gradients.

What is kinetic energy?

Energy of motion — like moving particles or molecules.

What are catabolic reactions?

Reactions that break large molecules into smaller ones, releasing energy.

What are anabolic reactions?

Reactions that build larger molecules from smaller ones, requiring energy.

What is a spontaneous reaction?

A reaction that is energetically favorable; products have lower Gibbs free energy (ΔG < 0).

What is a nonspontaneous reaction?

A reaction that is energetically unfavorable; products have higher Gibbs free energy (ΔG > 0).

What is ΔG = ΔH – TΔS?

The Gibbs free energy equation, relating energy, heat, and entropy changes.

What is an exergonic reaction?

A reaction that releases energy (ΔG < 0).

What is an endergonic reaction?

A reaction that requires a net input of energy (ΔG > 0).

What is the 1st Law of Thermodynamics?

Energy cannot be created or destroyed, only converted between forms.

What is the 2nd Law of Thermodynamics?

The entropy (disorder) of the universe tends to increase.

What is ATP?

The main energy currency of the cell; composed ribose (a sugar), adenine (a nitrogenous base), and three phosphate groups

What are the 3 types of work powered by ATP?

1. Chemical work – building molecules. 2. Transport work – moving substances across membranes. 3. Mechanical work – moving cellular structures or muscles.

What do enzymes do?

They catalyze (speed up) reactions by lowering activation energy (Eₐ).

How do enzymes lower activation energy?

Bind substrates in the active site, stabilize the transition state, orient reactants properly, and sometimes form temporary covalent bonds.

What happens to enzymes after a reaction?

They are not consumed; they can be reused.

What are general characteristics shared by all enzymes?

Not changed or used up in reactions; usually proteins (some are ribozymes); have active sites specific to substrates; work best at optimal pH and temperature.

What makes different enzymes unique?

Shape, size, function, substrate specificity, and optimal pH/temperature.

What happens to glucose during glycolysis?

During glycolysis, glucose is oxidized — it loses electrons and breaks down into smaller molecules.

What does oxidation mean?

Oxidation is the loss of electrons (completely or partially) from a molecule.

What does reduction mean?

Reduction is the gain of electrons (completely or partially) by a molecule.

What is released during oxidation/reduction reactions?

The transfer of electrons releases energy stored in organic molecules.

In glycolysis, what happens to glucose and NAD+?

Glucose is oxidized, and high-energy electrons are transferred to NAD+, reducing it to NADH.

What is the function of NAD+ in cellular respiration?

NAD+ acts as an electron carrier that accepts electrons and becomes NADH during glycolysis, pyruvate oxidation, and the citric acid cycle.

What is the function of NADH in cellular respiration?

NADH transports high-energy electrons to the electron transport chain for oxidative phosphorylation.

What happens when NADH donates its electrons to the electron transport chain?

NADH is oxidized back to NAD+, allowing the cycle to continue.

What is the role of coenzymes like NAD+/NADH in cellular respiration?

They act as electron shuttles that carry energy between metabolic reactions.

What is the main goal of aerobic respiration?

To produce ATP by oxidizing glucose and transferring energy through redox reactions.

Where does glycolysis occur?

In the cytoplasm.

Where do the citric acid cycle and oxidative phosphorylation occur?

In the mitochondria.

What are the main stages of aerobic respiration?

Glycolysis, oxidation of pyruvate, citric acid cycle, and oxidative phosphorylation (electron transport chain and chemiosmosis).

What is substrate-level phosphorylation?

The direct formation of ATP from ADP and a phosphorylated intermediate.

What is oxidative phosphorylation?

The production of ATP using energy from electrons transferred through the electron transport chain.

What is chemiosmosis?

The process by which ATP is generated as protons flow through ATP synthase down their electrochemical gradient.

What are cytochromes?

Electron carrier proteins found in the electron transport chain.

What is the role of the electron transport chain?

To transfer electrons from NADH and FADH₂ to oxygen, creating a proton gradient used for ATP synthesis.

What is the final electron acceptor in aerobic respiration?

Oxygen (O₂), which combines with electrons and hydrogen ions to form water (H₂O).

How is most ATP generated in aerobic respiration?

By oxidative phosphorylation through the electron transport chain and chemiosmosis.

Summary equation for photosynthesis

6 CO₂ + 12 H₂O + light energy → C₆H₁₂O₆ + 6 O₂ + 6 H₂O

Similarities between photosynthesis and cellular respiration

Both involve energy transformations and redox reactions; both occur in double-membrane organelles; both generate ATP using chemiosmosis.

Cellular respiration characteristics

Catabolic, exergonic, spontaneous; occurs in mitochondria; oxidizes glucose to make ATP; occurs in heterotrophs and autotrophs.

Photosynthesis characteristics

Anabolic, endergonic, nonspontaneous; requires sunlight; occurs in chloroplasts; reduces CO₂ to produce sugars; occurs only in photoautotrophs.

Chloroplast

Double-membrane organelle where photosynthesis occurs; contains DNA and ribosomes; evolved by endosymbiosis.

Thylakoid

Membrane-bound structures inside chloroplasts containing chlorophyll; site of the light reactions.

Stroma

Fluid-filled interior of chloroplast; site of the Calvin cycle.

Granum

A stack of thylakoid membranes.

Stomata

Leaf pores allowing CO₂ in and O₂ + water vapor out.

Chlorophyll

Pigment in thylakoid membranes that absorbs blue & red light and reflects green; captures solar energy.

Photosystems

Protein–pigment complexes

Photosystem II (PS II) functions first and is best at absorbing a wavelength of 680 nm

Photosystem I (PS I) is best at absorbing a wavelength of 700 nm

• The reaction-center chlorophyll a of PS I is called P700

Reactants of light-dependent reactions

NADP⁺, H₂O, ADP + Pi, light

Products of light-dependent reactions

O₂, NADPH, ATP

Reactants of the Calvin cycle

CO₂, NADPH, ATP

Products of the Calvin cycle

NADP⁺, ADP + Pi, G3P (3-carbon sugar)

In glycolysis, a major portion of the energy remains in the final product, which is called

pyruvate

All of the reactions of cellular respiration that occur after glycolysis take place in what part of the eukaryotic cell?

mitochondria

What stage of cellular respiration can occur in human cells with or without oxygen present?

Glycolysis

What oxidizing agent is used to temporarily store high energy electrons harvested from glucose molecules in a series of gradual steps in the cytoplasm?

NAD+

What aspect of cellular respiration occurs in the cytoplasm in eukaryotic cells?

Glycolysis

The splitting of water and the generation of oxygen occur where?

Photosystem II