BIG IDEA IIBiological systems utilize free energy and molecular building blocks

to grow, to reproduce and to maintain dynamic homeostasis.

Enduring Understanding 2.AGrowth, reproduction and maintenance of the organization

of living systems require free energy and matter.

Essential Knowledge 2.A.1All living systems require a constant input of free energy.

Essential Knowledge 2.A.1: All living systems require a constant input of free energy.

• Learning Objectives:– (2.1) The student is able to explain how biological systems

use free energy based on empirical data that all organisms require constant energy input to maintain organization, to grow and to reproduce.

– (2.2) The student is able to justify a scientific claim that free energy is required for living systems to maintain organization, to grow or to reproduce, but that multiple strategies exist in different living systems.

– (2.3) The student is able to predict how changes in free energy availability affect organisms, populations and ecosystems.

Fig. 9-2

Lightenergy

ECOSYSTEM

Photosynthesis in chloroplasts

CO2 + H2O

Cellular respirationin mitochondria

Organicmolecules+ O2

ATP powers most cellular work

Heatenergy

ATP

Life Requires a Highly Ordered System

• The living cell is a chemical factory in miniature, where thousands of reactions occur within a microscopic space.– Order is maintained by constant free energy input into the system.– Loss of order or free energy flow results in death.– Increased disorder and entropy are offset by biological processes

that maintain or increase order.• The concepts of metabolism help us to understand how matter

and energy flow during life’s processes and how that flow is regulated in living systems.

Metabolism

• Metabolism is the totality of an organism’s chemical reactions:– An organism’s metabolism transforms matter and energy,

subject to the laws of thermodynamics.• Metabolism is an emergent property of life that arises from

interactions between molecules within the cell.• A metabolic pathway begins with a specific molecule and ends

with a product, whereby each step is catalyzed by a specific enzyme.

• Bioenergetics is the study of how organisms manage their energy resources.

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Enzyme 1 Enzyme 2 Enzyme 3

DCBAReaction 1 Reaction 3Reaction 2

Startingmolecule

Product

Overview: A Metabolic Pathway

• Catabolic pathways release energy by breaking down complex molecules into simpler compounds:– Cellular respiration, the breakdown of glucose in the

presence of oxygen, is an example of a pathway of catabolism.

• Anabolic pathways consume energy to build complex molecules from simpler ones:– The synthesis of protein from amino acids is an

example of anabolism.

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Catabolism and Anabolism

Forms of Energy

• Energy is the capacity to cause change.• Energy exists in various forms, some of which can perform work:

– Kinetic energy is energy associated with motion.– Heat (thermal energy) is kinetic energy associated with random

movement of atoms or molecules.– Potential energy is energy that matter possesses because of its

location or structure.– Chemical energy is potential energy available for release in a

chemical reaction.

• Energy cannot be created or destroyed, but can be converted from one form to another.

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Climbing up converts the kineticenergy of muscle movementto potential energy.

A diver has less potentialenergy in the waterthan on the platform.

Diving convertspotential energy tokinetic energy.

A diver has more potentialenergy on the platformthan in the water.

The Laws of Energy Transformation

• Thermodynamics is the study of energy transformations.

• A closed system, such as that approximated by liquid in a thermos, is isolated from its surroundings.

• In an open system, energy and matter can be transferred between the system and its surroundings.

• Organisms are open systems.

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The First Law of Thermodynamics

• According to the first law of thermodynamics, the energy of the universe is constant: – Energy can be transferred and transformed, but it

cannot be created or destroyed• The first law is also called the principle of

conservation of energy.

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The Second Law of Thermodynamics

• During every energy transfer or transformation, some energy is unusable, and is often lost as heat.

• According to the second law of thermodynamics: – Every energy transfer or transformation increases the

entropy (disorder) of the universe.

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(a) First law of thermodynamics (b) Second law of thermodynamics

Chemicalenergy

Heat CO2

H2O

+

Biological Order and Disorder

• Cells create ordered structures from less ordered materials.

• Organisms also replace ordered forms of matter and energy with less ordered forms.

• Energy flows into an ecosystem in the form of light and exits in the form of heat.

• The evolution of more complex organisms does not violate the second law of thermodynamics.

• Entropy (disorder) may decrease in an organism, but the universe’s total entropy increases.

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Free-Energy Change, G

• The free-energy change of a reaction tells us whether or not the reaction occurs spontaneously.

• Biologists often want to know which reactions occur spontaneously and which require input of energy.

• To do so, they need to determine energy changes that occur in chemical reactions.

• A living system’s free energy is energy that can do work when temperature and pressure are uniform, as in a living cell.

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• The change in free energy (∆G) during a process is related to the change in enthalpy, or change in total energy (∆H), change in entropy (∆S), and temperature in Kelvin (T):

∆G = ∆H – T∆S• Only processes with a negative ∆G are

spontaneous.• Spontaneous processes can be harnessed to

perform work.

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Free-Energy Change, G

Free Energy, Stability, and Equilibrium

• Free energy is a measure of a system’s instability, its tendency to change to a more stable state.

• During a spontaneous change, free energy decreases and the stability of a system increases.

• Equilibrium is a state of maximum stability.• A process is spontaneous and can perform work

only when it is moving toward equilibrium.

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(a) Gravitational motion (b) Diffusion (c) Chemical reaction

• More free energy (higher G)• Less stable• Greater work capacity

In a spontaneous change• The free energy of the system decreases (∆G < 0)• The system becomes more stable• The released free energy can be harnessed to do work

• Less free energy (lower G)• More stable• Less work capacity

Free Energy and Metabolism

• The concept of free energy can be applied to the chemistry of life’s processes:– An exergonic reaction proceeds with a net release of

free energy and is spontaneous (∆G is negative).– An endergonic reaction absorbs free energy from its

surroundings and is nonspontaneous (∆G is positive).

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Reactants

Energy

Fre

e e

ne

rgy

Products

Amount ofenergyreleased(∆G < 0)

Progress of the reaction

(a) Exergonic reaction: energy released

Products

ReactantsEnergy

Fre

e e

ne

rgy

Amount ofenergyrequired(∆G > 0)

(b) Endergonic reaction: energy required

Progress of the reaction

(a) An isolated hydroelectric system

∆G < 0 ∆G = 0

(b) An open hydroelectric system ∆G < 0

∆G < 0

∆G < 0

∆G < 0

(c) A multistep open hydroelectric system

H2O

ATP & Energy Coupling

Energetically favorable exergonic reactions, such as ATPADP, that have negative change in free energy can be used to maintain or increase order in a system by being coupled with reactions that have a positive free energy exchange.

Inorganic phosphate

Energy

Adenosine triphosphate (ATP)

Adenosine diphosphate (ADP)

P P

P P P

P ++

H2O

i

(b) Coupled with ATP hydrolysis, an exergonic reaction

Ammonia displacesthe phosphate group,forming glutamine.

(a) Endergonic reaction

(c) Overall free-energy change

PP

GluNH3

NH2

Glu i

GluADP+

PATP+

+

Glu

ATP phosphorylatesglutamic acid,making the aminoacid less stable.

GluNH3

NH2

Glu+

Glutamicacid

GlutamineAmmonia

∆G = +3.4 kcal/mol

+2

1

(b) Mechanical work: ATP binds noncovalently to motor proteins, then is hydrolyzed

Membrane protein

P i

ADP+

P

Solute Solute transported

Pi

Vesicle Cytoskeletal track

Motor protein Protein moved

(a) Transport work: ATP phosphorylates transport proteins

ATP

ATP

Energy Related Pathways in Biological Systems

• Energy-related pathways in biological systems are sequential and may be entered at multiple points in the pathway:– Glycolysis– Krebs cycle– Calvin cycle– Fermentation

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Use of Free Energy

• Organisms use free energy to maintain organization, grow and reproduce. Illustrative Examples include:– Strategies to regulate body temperature– Strategies for reproduction & rearing of offspring– Metabolic rate and size– Excess acquired free energy– Insufficient acquired free energy

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• Animals use the chemical energy in food to sustain form and function.

• All organisms require chemical energy for growth, repair, physiological processes, regulation, and reproduction.

• The flow of energy through an animal, its bioenergetics, ultimately limits the animal’s behavior, growth, and reproduction – which determines how much food it needs.

• Studying an animal’s bioenergetics tells us a great deal about the animal’s adaptations.

Bioenergetics of Animals

Bioenergetics of an Animal

• An animal’s metabolic rate is the amount of energy it uses in a unit of time.

• An animal’s metabolic rate is closely related to its bioenergetic strategy – which determines nutritional needs and is related to an animal’s size, activity, and environment:– The basal metabolic rate (BMR) is the metabolic rate of a non-growing,

unstressed endotherm at rest with an empty stomach.– The standard metabolic rate (SMR) is the metabolic rate of a fasting, non-

stressed ectotherm at rest at a particular temperature.– For both endotherms and ectotherms, size and activity has a large effect

on metabolic rate.

Quantifying Energy Use

Organisms use various strategies to regulate body temperature and metabolism.

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Elevated Floral Temperature in Some Plant Species

Different organisms use various reproductive strategies in response to energy availability.

Seasonal Reproduction in Plants

• There is a relationship between metabolic rate per unit body mass and the size of multicellular organisms – generally, the smaller the organism, the higher the metabolic rate.

• Larger animals have more body mass and therefore require more chemical energy.

• Remarkably, the relationship between overall metabolic rate and body mass is constant across a wide range of sizes and forms.

Metabolic Rate and Size of Organisms

Metabolic Rate and Size of Organisms

• Changes in free energy availability can result in changes in population size and disruption to an ecosystem.

• Change in the producer level can affect the number and size of other trophic levels.

• Change in energy resource levels such as sunlight can affect the number and size of the trophic levels.

Changes in Free Energy Availability

Changes in Free Energy Availability