splash contents chapter introduction organisms and energy 2.1characteristics of organisms 2.2energy...

Chapter IntroductionOrganisms and Energy

2.1 Characteristics of Organisms2.2 Energy and Nutrients2.3 Energy and Ecosystems

Energy Flow2.4 Energy Conversions2.5 Energy and Entropy

Metabolism and Energy Transfer2.6 Enzymes and Energy2.7 Chemical Reactions in Organisms2.8 Energy Transfer and ATP

Digestion2.9 Digestion Inside and Outside Cells2.10 An Overview of Human Digestion2.11 Carbohydrates, Proteins, Fats, and Absorption

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A Discuss why organisms need energy and how they obtain it.

Learning Outcomes

By the end of this chapter you will be able to:

B Describe energy flow through an ecosystem.

C Relate the first and second laws of bioenergetics to their implications for living systems.

D Distinguish between synthesis and decomposition reactions in metabolism.

E Summarize the importance of ATP in cellular energy transfer.

F Describe how digestion breaks food into small molecules.


What is the source of energy that maintains these organisms?

Transport Systems How does this scene

demonstrate the relationship between life, energy, and the biosphere?

An insect from the order Heteroptera feeding on a white fly (Trialeurodes vaporariorum).


Transport Systems• Biologists agree that the ability to absorb and

convert energy is a basic characteristic of life.

• The study of the energy flow and energy transformations among living systems is called bioenergetics.

An insect from the order Heteroptera feeding on a white fly (Trialeurodes vaporariorum).


• Living organisms have the following characteristics:

Organisms and Energy

2.1 Characteristics of Organisms

– Take in and convert materials and energy from the environment; release wastes

– Have a high degree of chemical organization compared to nonliving objects

– Have complex structural organization that is responsible for their appearance and activities

– Contain coded instructions (such as DNA) for maintaining their organization and activities


• Living organisms have the following characteristics:

2.1 Characteristics of Organisms (cont.)


– Sense and react to changes in their environment

– Grow and develop during some part of their lives

– Reproduce others like themselves

– Communicate with similar organisms

– Move under their own power


• Energy, the capacity to do work or to cause change, is needed by all living things.

2.2 Energy and Nutrients

• Organisms store chemical energy in the organic molecules from which the organisms are made.


• The portion of this chemical energy that is available to do work is called free energy.


• Living cells need a constant source of free energy for chemical and mechanical work and for transport.

• Heterotrophs are organisms that obtain energy and nutrients from other organisms, either living or dead.

2.2 Energy and Nutrients (cont.)


• Autotrophs are organisms that obtain energy and nutrients from nonliving sources such as the Sun, minerals, and the air.


• Photoautotrophs are autotrophs that capture energy from sunlight and use it to synthesize organic compounds from carbon dioxide and water in a process called photosynthesis.

• Chemoautotrophs are autotrophs, all of which are bacteria, that use chemosynthesis to capture energy, which is stored as chemical energy and used for cellular work.



• Autotrophs use the organic compounds they make as building blocks for maintenance, growth, and reproduction.


• Heterotrophs consume autotrophs and other heterotrophs as food.

• Autotrophs directly or indirectly supply the energy and organic nutrients needed for the maintenance, growth, and reproduction of all heterotrophs.

• Both autotrophs and heterotrophs carry out chemical reactions, known as cell respiration, that release the free energy of organic compounds.






In the relationship between autotrophs and heterotrophs, energy passes from autotrophs to heterotrophs. Oxygen and carbon dioxide cycle repeatedly between them.


– Autotrophs, which produce food other organisms use, are the producers in a community of living organisms, such as a forest or an ocean.

– Heterotrophs consume plants and other organisms for food; they are the consumers.

– Bacteria, fungi, and other heterotrophs that break down and use dead plants and animals for food are decomposers.

• The need for energy and nutrients links organisms in many complex ways.

2.3 Energy and Ecosystems




• Producers, consumers, and decomposers form a food web in which energy and nutrients flow from the environment through the producers to the consumers and finally to the decomposers.

2.3 Energy and Ecosystems (cont.)


• The organisms in a food web depend on abiotic, or nonliving, factors, such as the soil, minerals, water, and weather.

• The organisms make up the biotic, or living, factors.


2.3 Energy and Ecosystems (cont.)

• The biotic and abiotic components of a particular place make up an ecosystem.

• Within each ecosystem are many habitats, places where particular organisms live.

• All ecosystems combine to make up Earth’s biosphere.


• Energy conversions are described by principles called the laws of thermodynamics.

Energy Flow

2.4 Energy Conversions

• The first law of thermodynamics states that energy cannot be created or destroyed, but it can change form.

• On a broader scale, the first law is called the law of conservation of energy and it states that the total energy of the universe is constant.


• The first law of thermodynamics means that organisms cannot create their own energy, but must obtain it from an outside source.

2.4 Energy Conversions (cont.)

Energy Flow

An important difference between living and nonliving systems is the ability of living systems to conserve and use some of the energy released in chemical reactions.


• The second law of thermodynamics states that systems tend to change in a way that increases the disorder, or entropy, of the system plus its surroundings.

2.5 Energy and Entropy

• Because energy tends to spread out into the surroundings, the free energy in a system is slightly less after each energy conversion than before.

• The world becomes increasingly disordered as free energy is released.

Energy Flow


• Organisms must be well organized to remain alive and to grow.

• Energy is the key to maintaining organization in all living systems.

• In ecosystems, light or chemical energy flows from the environment (the Sun or inorganic chemicals) to producers to consumers to decomposers.

2.5 Energy and Entropy (cont.)

Energy Flow


• As energy flows through food webs, it eventually escapes in the form of heat energy, resulting in a one-way flow of energy.

• Living systems overcome the tendency toward entropy by constantly obtaining energy from their surroundings.

• Organisms stay organized and can function and grow only as the entropy of their surroundings increases.

2.5 Energy and Entropy (cont.)

Energy Flow


Energy flow in an ecosystem

Click the image to view an animated version.


• To release chemical energy to perform work, cells must have a way to break and form chemical bonds.

Metabolism and Energy Transfer

2.6 Enzymes and Energy

• All living cells contain specialized proteins called enzymes that lower the activation energy required to make a reaction proceed.

• Chemicals, such as enzymes, that lower activation energies are called catalysts.


2.6 Enzymes and Energy (cont.)


Consider the starting molecule, S, and the product molecule, P, which can be formed from S through a chemical reaction. To achieve an activated condition S*, S must acquire considerable energy.

In an enzyme-catalyzed reaction, S combines temporarily with the enzyme E, forming a complex ES*, in which S requires less energy to form P (the barrier is lower).


• Each type of enzyme catalyzes only one or a few specific reactions.

– The specific reaction catalyzed by an enzyme depends on a small area of its tertiary structure called the active site.



– The close fit of the starting molecule, called the substrate, into the active site of the enzyme brings the enzyme and substrate close together.

– The resulting interaction lowers the activation energy, which allows the chemical reaction from substrate to product to proceed.


The induced-fit model of enzyme action



• Many reactions catalyzed by enzymes are reversible.

• Each enzyme is most active at a certain temperature and pH.




• Metabolism consists of all the chemical activities and changes that take place continuously in a cell or an organism.

2.7 Chemical Reactions in Organisms

• There are two types of metabolism:


– “building-up” reactions, or synthesis

– “breaking-down” reactions, or decomposition


• Synthesis includes biosynthesis reactions that form larger, more complex biomolecules from small, less complex ones.

• Biosynthesis consumes free energy, because the products are more ordered and contain more chemical energy than the simpler, less ordered reactants.

• Biosynthesis enables organisms to grow and maintain their structure.

2.7 Chemical Reactions in Organisms (cont.)





Biosynthesis requires an input of free energy.

The molecule ATP is used by all organisms as a storage form of cellular free energy. Decomposition of ATP releases some of its stored energy in a way that can perform cellular work, such as adding a glucose molecule to glycogen.


• In decomposition reactions, larger molecules break down into smaller molecules.

• Decomposition reactions release free energy because they produce simple molecules from complex molecules, which increases entropy.

• Cells use some of the free energy and simple molecules released during decomposition for biosynthesis of other macromolecules






In decomposition reactions, free energy, and some heat energy, is released from the breakdown of complex molecules.

An example of decomposition is the breakdown of glycogen in muscle cells. Glucose, from glycogen, also can break down in several steps to carbon dioxide and water. During this process, energy in the form of ATP is released and is used by the cell.


Coupling of synthesis and decomposition



• Free energy is released through a process of decomposition called oxidation, which is the removal of electrons from a molecule.

2.8 Energy Transfer and ATP

• The free energy follows a series of electron transfers and ultimately ends up in a molecule called ATP, adenosine triphosphate.


• The free energy that is released through oxidation is available in chemical form (ATP) to drive the reactions of biosynthesis.


• ATP is a nucleotide consisting of adenine and ribose joined to a chain of three phosphate groups.

• Usually when an ATP molecule is involved in a chemical reaction, the bond between the second and third phosphate groups breaks and free energy is released.

2.8 Energy Transfer and ATP (cont.)



• A molecule that accepts the phosphate group from ATP gains free energy and is activated; it can then react usefully with other molecules in the cell.






ATP is used to synthesize glucose-6-phosphate, an activated form of glucose, or blood sugar. Glucose-6-phosphate added to a chain of glycogen lengthens it by one glucose molecule. Glycogen is a useful way to store glucose. ( P is inorganic phosphate.)


• ATP is continually synthesized and broken down in cells, forming a cycle.

• ATP becomes ADP, adenosine diphosphate, when it gives up one phosphate group.



• ADP must combine with one phosphate group, requiring free energy from the breakdown of organic compounds to form ATP.


• ATP is the principal energy currency of living cells and was probably an energy carrier of primitive organisms.

• ATP is used as an energy carrier in all known living cells—from single-celled heterotrophs to cells of humans and plants.




• Food provides organisms with a source of raw materials and cellular energy, which are essential for growth and maintenance.

• Organisms have digestive systems that are adapted to the type of food the organism obtains.

• A heterotroph must break down large food particles into small molecules that can enter its cells.

• The processes that break down food are known collectively as digestion.

2.9 Digestion Inside and Outside Cells

Digestion


• Digestion consists of two parts:

– physical—the breakdown of large pieces of food into smaller ones to increase surface area

2.9 Digestion Inside and Outside Cells (cont.)

Digestion

In some birds, food is temporarily stored in a sac called a crop. Farther along the digestive tract, a specialized part of the stomach—the gizzard—grinds up food to aid digestion. The walls of the gizzard are thick and muscular, an evolutionary adaptation to grinding. Some birds swallow sand and small pebbles that aid the grinding action.

– chemical—the breaking down of complex food molecules into simpler ones


• Most animals, including humans, rely on extracellular digestion—digestion that takes place outside the cells.

• Most animals secrete digestive enzymes into a digestive cavity, where chemical digestion yields the simpler molecules that are then absorbed by the cells.


Digestion


• Most plants rely on intracellular digestion—digestion that takes place inside the cells with foods the plant has made itself.

• Single-celled organisms, such as Paramecium, also rely on intracellular digestion.


Digestion


• Many organisms, such as Venus flytraps and bread mold produce enzymes that digest food outside the organism itself and then absorb the nutrients into the cells.


Digestion

Venus flytrap (Dionaea muscipula)

Bread mold


• Complex multicellular animals digest food in specialized cavities or digestive tubes with two openings.

• Food enters the mouth at one end of the tube, and material that cannot be digested passes out of the anus at the other end of the tube.


Digestion



Digestion

The earthworm’s system is a complete digestive tube with two openings—the mouth at one end through which food is ingested, and the anus at the other end, through which wastes are eliminated. Digestion occurs extracellularly within the tube.


• The digestive tube of most complex animals is divided into different regions with specialized functions.

• The specialization may depend on the diet of the animal.


Digestion


• Ingestion, the process of taking food into the digestive tract, begins in the oral cavity.

• The chewing action of the teeth begins physical digestion, and the highly muscular tongue mixes food with saliva.

• Saliva is a watery secretion containing digestive enzymes that begin chemical digestion.

2.10 An Overview of Human Digestion

Digestion


2.10 An Overview of Human Digestion (cont.)

Digestion

The human digestive system is a continuous tube with highly specialized organs and tissues along it. It produces some of its own enzymes, and nearby glands supply other enzymes.


• When you swallow food, it passes over the epiglottis, a trapdoor-like tissue that normally prevents food and liquids from entering the trachea (or airway).

• Food then enters the esophagus, a muscular tube connecting the oral cavity to the stomach.

• In a process called peristalsis, wavelike contractions of the muscles of the esophagus move food to the stomach.


Digestion


• The next organ reached is the stomach where contractions of muscles lining the stomach wall break up and mix food with gastric juices, or secretions, from stomach glands.

• A ring of muscle that acts like a valve periodically relaxes, releasing small amounts of partially digested food into the small intestine.


Digestion


• Food then enters the small intestine where chemical digestion is completed and food molecules are absorbed.

• The pancreas and liver contribute digestive juices to the small intestine through ducts.

• Food molecules are absorbed through the intestinal walls into the bloodstream which carries the molecules to all the cells.


Digestion


• Any undigested material eventually passes to the large intestine, where bacteria help produce several vitamins, gases, and other compounds.

• The vitamins and much of the water that was mixed with the food are absorbed through the walls of the large intestine.

• This absorption partly dries out the wastes, called feces, which are then eliminated through the anus.


Digestion


• Carbohydrate digestion begins in the mouth with the action of an enzyme called salivary amylase in the following reaction:

• Carbohydrate digestion is completed in the small intestine.

2.11 Carbohydrates, Proteins, Fats, and Absorption

Digestion


• Protein digestion occurs in the stomach and in the small intestine.

• As food enters the stomach, it stimulates certain cells to release a hormone called gastrin, that stimulates the secretion of hydrochloric acid.

2.11 Carbohydrates, Proteins, Fats, and Absorption (cont.)

Digestion

• Pepsin is the active protein-digesting enzyme in the stomach, which is secreted by stomach gland cells in an inactive form called pepsinogen.


• When food enters the small intestine, pancreatic juice enters the intestine through the pancreatic duct and shifts the pH from acidic to basic.

• The intestinal enzyme trypsin breaks peptide bonds, producing amino acids from polypeptides.

Digestion



Digestion


Acidic food enters the small intestine (1) from the stomach and stimulates secretion of the intestinal hormone secretin (2). The secretin enters the bloodstream (3) and circulates to the pancreas (4). In the pancreas, secretin stimulates production of pancreatic juices (5) that flow into the intestine.


• Fats are prepared for digestion in the small intestine by bile, a substance secreted by the liver and stored in the gallbladder.

• The fat-digesting enzyme lipase, which is secreted in the pancreatic and intestinal juices, splits fats into fatty acids and glycerol.

Digestion


• The end products of digestion are amino acids, simple sugars, fatty acids, and glycerol which pass through the cells lining the small intestine.


• The surface area of the intestinal lining is increased tremendously by millions of small fingerlike projections called villi (singular: villus).

Digestion


• Each villus contains capillaries—tiny, thin-walled blood vessels that serve as entry points to the bloodstream


Digestion


Intestinal villi are shown enlarged in the micrograph (x136) and drawing. The products of digestion enter the blood and the lymph through the villi. Blood passes from arteries to capillaries to veins on its course through each villus.


Summary

• Organisms use free energy to grow, move, reproduce, and maintain internal order.

• Biotic and abiotic components together make up an ecosystem.

• Energy flows in one direction from the Sun and inorganic chemicals to producers and then through a series of consumers and decomposers in the form of food.

• The laws of thermodynamics allow us to predict the flow of energy in organisms and ecosystems since organisms obey these laws.

• All organisms require energy.


Summary (cont.)

• Producers obtain energy from the environment.

• Consumers obtain energy from producers and other consumers.

• Decomposers obtain energy through the decay of dead producers and consumers.

• Metabolism includes all the chemical reactions in an organism. Biosynthesis requires energy. Decomposition releases free energy. ATP connects these processes.

• Energy changes drive metabolism. Enzymes speed up reactions in living cells that otherwise would not occur at adequate rates.

• To stay alive, organisms must maintain and even increase a highly ordered state which requires energy.


Summary (cont.)

• Intracellular digestion takes place in the individual cells that will use the food.

• Most animals break down food by extracellular digestion, which takes place in a tube specialized for digestion. Specific enzymes break down fats, proteins, and polysaccharides in this system.

• The small molecules that are the products of digestion can be absorbed and used by living cells as a source of energy or as nutrients for growth and repair.

• Heterotrophs break down food into molecules small enough to be absorbed and used by individual cells.


Reviewing Key TermsMatch the term on the left with the correct description.

___ abiotic

___ entropy

___ catalyst

___ oxidation

___ heterotrophs

___ autotrophs

a. the loss of electrons from a substance in a chemical reaction

b. a chemical that promotes a reaction between other chemicals by lowering the activation energy that is needed

c. referring to a nonliving component of an ecosystem

d. an organism that forms its own food molecules

e. a measure of the degree of disorder in a system

f. an organism that obtains carbon compounds from other organisms

c

e

b

a

f

d


Reviewing Ideas1. How does the first law of thermodynamics apply

to biological processes?

The first law of thermodynamics means that organisms cannot create their own energy, but must obtain it from an outside source.


Reviewing Ideas2. Why does energy flow only in one direction in

a food web?

As energy flows through food webs, it eventually escapes into the surroundings in the form of heat energy. As a result, there is only a one-way flow of energy through food webs.


Using Concepts3. What differences would you expect to find between the

digestive tracts of a herbivore and a carnivore?

Herbivores, which consume vegetation, may have multi-chambered stomachs, side pockets in their stomachs with microorganisms, or long digestive tracts to handle the hard-to-digest food that they eat. Carnivores consume mostly meat, which is more easily digested than grass. Consequently, a carnivore’s digestive tract is relatively short.


Using Concepts4. In terms of digestion, what is the main reason

to chew your food?

Chewing food begins physical digestion. Physical digestion breaks large pieces of food into smaller pieces, thus increasing the surface area of the food. This allows greater access to the food particles by enzymes, aiding chemical digestion.


Synthesize5. How is ATP a key in evolutionary theory?

All known living cells—from single celled heterotrophs to the cells of humans and plants— use ATP as an energy carrier. This is evidence of a common evolutionary origin.


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Chapter Animations

Energy flow in an ecosystem

The induced-fit model of enzyme action

Coupling of synthesis and decomposition

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