AP Biology Unit 3

What is the First Law of Thermodynamics?

Energy can’t be created or destroyed: only transformed

• FALSE: “cells produce energy”

• TRUE: “cells converted …”

What is the Second Law of Thermodynamics?

Every transformation of energy increases the entropy of the universe

• Organisms can decrease their internal entropy by using free energy, but they release heat and waste back into their surroundings, increasing total universal entropy

What is entropy?

A thermodynamic measure of randomness, disorder, or unusable energy in a system

• High entropy = high disorder / energy spread out

• Low entropy = high order / free energy

What is free energy?

Energy available to perform work

• ▵G = ▵H – T▵S

What is the main, immediately usable energy-carrying molecule in a cell?

ATP (Adenosine Triphosphate)

• How it works: hydrolysis breaks the high-energy bond holding the third phosphate group on ATP, producing ADP + Pi and releasing energy that powers cellular work

What are the two types of systems?

• Open system: can exchange both energy and matter with its surroundings

  • EX) Living organisms taking in nutrients and releasing heat/waste

• Closed system: cannot exchange energy or matter with its surroundings

  • EX) A sealed thermos, the universe

What are the different types of reactions (in terms of energy)?

• Exergonic: reactions that have a net release of free energy (▵G < 0)

• Endergonic: reactions that have a net absorption of free energy (▵G > 0)

What are the different types of metabolic pathways (in terms of matter)?

• Catabolic: larger, complex molecules are broken down into smaller, simpler ones

• Anabolic: smaller, simpler molecules are synthesized into larger, complex ones

What is a metabolic pathway?

A series of interconnected chemical reactions in a cell that builds or breaks down a specific molecule

When is ATP hydrolyzed?

Whenever a cell needs energy to perform immediate work

• Endergonic reactions

• Active transport

• Mechanical work

• Signal transduction

When ATP is hydrolyzed, what two molecules does it become?

ATP + H2O → ADP + Pi + Energy

What is energy coupling?

Using an energy-releasing (exergonic) process to drive an energy-requiring (endergonic) process.

What is reaction coupling?

A specific chemical process to accomplish energy coupling. Two separate reactions are physically linked together by a shared intermediate or enzyme.

What is a spontaneous reaction?

A chemical reaction that occurs naturally without requiring a continuous input of external energy, moving the system toward a lower, more stable energy state

• ▵G < 0 ← exergonic

What is an endotherm?

A thermo-regulator that relies on internal heat generated by its own metabolic processes to maintain a stable body temperature

• Energy source: internal metabolic activity

• Thermal strategy: shivering, hibernation, etc.

What is an ectotherm?

An thermo-conformer that relies primarily on external environmental heat sources to determine and regulate its body temperature

Endotherm vs. ectotherm

• Range of temp: ectotherms have a wider range of temperature

• Lasting: endotherms have energy that lasts longer

• Energy: endotherms have more energy

What is chemiosmosis?

The process of using energy stored in a proton (H+) electrochemical gradient across a membrane to drive the synthesis of ATP.

Name one main electron carrier molecule used in cellular energy pathways.

NADH or NAD+