Essential Biology with Physiology, 5e

Essential Biology with Physiology

Fifth Edition

Chapter 15

The Evolution of

Microbial Life

Copyright © 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved


Figure 15.0-1


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Figure 15.0-1d


Biology and Society: Our Invisible

Inhabitants (1 of 2)

• Your body contains trillions of individual cells.

• But microorganisms residing in and on your body,

which primarily live in your skin, mouth, and nasal

passages, outnumber your own cells by 10 to 1.


Figure 15.0 Colorized Scanning Electron

Micrograph of Bacteria on a Human Tongue


Biology and Society: Our Invisible

Inhabitants (2 of 2)

• Scientists hypothesize that disrupting our microbial

communities may

– increase our susceptibility to infectious diseases,

– predispose us to certain cancers, and

– contribute to conditions such as

▪ asthma and other allergies,

▪ irritable bowel syndrome,

▪ Crohn’s disease, and

▪ autism.


Major Episodes in the History of

Life (1 of 5)

• Earth was formed about 4.6 billion years ago.

• Prokaryotes, having cells that lack true nuclei,

– evolved by about 3.5 billion years ago,

– began oxygen production about 2.7 billion years

ago as a result of photosynthesis by autotrophic

prokaryotes,

– lived alone for about 1.7 billion years, and

– continue in great abundance today.


Figure 15.1 Some Major Episodes

in the History of Life (1 of 4)



Life (2 of 5)

• Eukaryotes are composed of one or more cells that

contain

– nuclei and

– many other membrane-bound organelles absent in

prokaryotic cells.



Life (3 of 5)

– Eukaryotes first evolved from a prokaryotic community,

a host cell containing even smaller prokaryotes.

▪ Mitochondria are descendants of smaller prokaryotes, as

are the chloroplasts of plants and algae.

• Multicellular eukaryotes first evolved at least 1.2 billion

years ago.



Life (4 of 5)

• The Cambrian explosion, about 540 million years ago,

resulted in the evolution of

– all major animal body plans and

– all the major groups.

• About 500 million years ago plants, fungi, and insects

began to colonize the land.



Life (5 of 5)

• At the end of the Mesozoic, 65 million years ago,

flowering plants, birds, and mammals, including

primates, began to dominate the landscape.

• The origin of modern humans, Homo sapiens,

occurred roughly 195,000 years ago.


The Origin of Life (1 of 2)

• For the first several hundred million years of its

existence, conditions on the young Earth were so

harsh that it’s doubtful life could have originated,

or if it did it, could not have survived.

• The Earth of 4 billion years ago was still in violent

turmoil.

– Water vapor had condensed into oceans on the

planet’s cooling surface.

– Volcanic eruptions belched gases such as carbon

dioxide, methane, and ammonia and other nitrogen

compounds into its atmosphere.


Figure 15.2 An Artist’s Rendition

of Conditions on Early Earth


The Origin of Life (2 of 2)

• Life is an emergent property that arises from the

specific arrangement and interactions of its molecular

parts.

• To learn how life originated from nonliving substances,

biologists draw on research from the fields of

– chemistry,

– geology, and

– physics.


A Four-Stage Hypothesis for the

Origin of Life (1 of 2)

• According to one hypothesis for the origin of life, the

first organisms were products of chemical evolution in

four stages:

1. the synthesis of small organic molecules, such as

amino acids and nucleotide monomers;

2. the joining of these small molecules into

macromolecules, including proteins and nucleic acids;


A Four-Stage Hypothesis for the

Origin of Life (2 of 2)

3. the packaging of all these molecules into pre-cells,

droplets with membranes that maintained an internal

chemistry different from the surroundings; and

4. the origin of self-replicating molecules that eventually

made inheritance possible.


Stage 1: Synthesis of Organic

Compounds (1 of 4)

• The first stage in the origin of life was the first to be

extensively studied in the laboratory.

– The chemicals in Earth’s early atmosphere, such as

water (H2O), methane (CH4), and ammonia (NH3), are

all small, inorganic molecules.

– In contrast, the structures and functions of life depend

on more complex organic molecules, such as sugars,

fatty acids, amino acids, and nucleotides, which are

composed of the same elements.



Compounds (2 of 4)

• In 1953, Stanley Miller devised an apparatus to

simulate conditions thought to prevail on early Earth.

– A flask of warmed water simulated the primordial sea.

– An “atmosphere”—in the form of gases added to a

reaction chamber—contained hydrogen gas, methane,

ammonia, and water vapor.

– To mimic the prevalent lightning of early Earth,

electrical sparks were discharged into the chamber.

– A condenser cooled the atmosphere, causing water

and any dissolved compounds to “rain” into the

miniature “sea.”


Figure 15.3 Apparatus Used to Simulate

Early-Earth Chemistry in Urey and Miller’s

Experiments



Compounds (3 of 4)

• After the apparatus had run for a week, an abundance

of organic molecules essential for life, including amino

acids, the monomers of proteins, had collected in the

“sea.”

• Many laboratories have since repeated Miller’s

experiment using various atmospheric mixtures

and have also produced organic compounds.



Compounds (4 of 4)

• Scientists are testing other hypotheses for the origin

of organic molecules on Earth, including

– the hypothesis that life may have begun in submerged

volcanoes or deep-sea hydrothermal vents and

– the hypothesis that meteorites were the source of

Earth’s first organic molecules.


Stage 2: Abiotic Synthesis

of Polymers

• Once small organic molecules were present on Earth,

how were they linked together to form polymers such

as proteins and nucleic acids without the help of

enzymes and other cellular equipment?

• Researchers have brought about the polymerization

of monomers to form polymers, such as proteins and

nucleic acids, by dripping solutions of organic

monomers onto hot sand, clay, or rock.


Stage 3: Formation of Pre-Cells

• A key step in the origin of life would have been the

isolation of a collection of organic molecules within a

membrane.

• Researchers have demonstrated that pre-cells could

have formed spontaneously from fatty acids.


Figure 3.11 The Synthesis and Structure

of a Triglyceride Molecule (1 of 3)


Stage 4: Origin of Self-Replicating

Molecules

• Life is defined partly by the process of inheritance,

which is based on self-replicating molecules.

• One hypothesis is that the first genes were short

strands of RNA that replicated themselves without the

assistance of proteins, perhaps using RNAs that can

act as enzymes, called ribozymes.


Figure 15.4 Self-Replication of RNA

“Genes” (1 of 4)


From Chemical Evolution to

Darwinian Evolution

• The gap between pre-cells and even the simplest

of modern cells is enormous.

• But with millions of years of incremental changes

through natural selection, these molecular

cooperatives could have become more and more

cell-like.


Prokaryotes

• Prokaryotes lived and evolved all alone on Earth

for about 2 billion years.

• They have continued to adapt and flourish on a

changing Earth and in turn have helped to modify

the planet.


They’re Everywhere! (1 of 2)

• Prokaryotes

– are found wherever there is life,

– have a collective biomass that is at least ten times that

of all eukaryotes,

– thrive in habitats too cold, too hot, too salty, too acidic,

or too alkaline for any eukaryote, and

– cause about half of all human diseases.


Figure 15.5 A Window to Early Life?


They’re Everywhere! (2 of 2)

• However, prokaryotes also form our microbiota, the

community of microorganisms that live in and on our

bodies, which help to

– supply essential vitamins,

– allow us to extract nutrition from food molecules that we

cannot otherwise digest,

– decompose dead skin cells, and

– guard against disease-causing intruders.

• Prokaryotes also help decompose dead organisms and

other waste materials, returning vital chemical elements

such as nitrogen to the environment.


Figure 15.6 Bacteria on the Point

of a Pin


Structure/Function: Prokaryotes

• Prokaryotic cells

– lack a membrane-enclosed nucleus,

– lack other membrane-enclosed organelles,

– typically have cell walls exterior to their plasma

membranes, and

– display a remarkable range of diversity.


Figure 4.2 A Prokaryotic Cell (1 of 3)


Figure 4.3 An idealized animal cell

and plant cell (1 of 3)


Prokaryotic Forms (1 of 5)

• The three most common shapes of prokaryotes are

1. spherical, called cocci (singular, coccus),

2. rod-shaped, called bacilli (singular, bacillus), and

3. spiral or curved, including spirochetes.


Video: Prokaryotic Flagella

(Salmonella typhimurium) (random)


Figure 15.7 Three common shapes

of prokaryotic cells (1 of 4)



• All prokaryotes are unicellular.

• Some species

– exist as groups of two or more cells,

– exhibit a simple division of labor among specialized

cell types, or

– are giants that actually dwarf most eukaryotic cells.


Video: Cyanobacteria (Oscillatoria)


Figure 15.8 A Diversity of Prokaryotic

Shapes and Sizes (1 of 4)



• About half of all prokaryotes are mobile, and many of

these travel using one or more flagella.

• Many of those that travel have one or more flagella

that propel the cells away from unfavorable places or

toward more favorable places, such as nutrient-rich

locales.



• In many natural environments, prokaryotes attach to

surfaces in a highly organized colony called a biofilm,

which

– may consist of one or several species of prokaryotes,

– may include protists and fungi,

– can show a division of labor and defense against

invaders, and



– can form on almost any type of surface, including

▪ rocks,

▪ metal,

▪ plastic, and

▪ organic material including teeth.


Figure 15.9 Dental Plaque, a Biofilm

that Forms on Teeth


Prokaryotic Reproduction (1 of 2)

• Many prokaryotes can reproduce

– by dividing in half by binary fission and

– at very high rates if conditions are favorable.

• Few prokaryotic populations can sustain exponential

growth for long.

– Environments are usually limiting in resources such as

food and space.

– Prokaryotes also produce metabolic waste products

that may eventually pollute the colony’s environment.


Figure 15.10 Household Sponge Contaminated with

Bacteria (Red, Green, Yellow, and Blue Objects in

This Colorized Micrograph)


Prokaryotic Reproduction (2 of 2)

• Some prokaryotes can survive during very harsh

conditions by forming specialized cells called

endospores, thick-coated, protective cells produced

within the prokaryotic cell that can survive all sorts of

trauma and extreme temperatures.


Prokaryotic Nutrition (1 of 5)

• Like multicellular organisms, prokaryotes obtain

energy and carbon, the two main resources needed

for synthesizing organic compounds, by

– using carbon dioxide and the sun’s energy in the

process of photosynthesis and

– obtaining them from organic matter.


Figure 15.11 Two Methods of

Obtaining Energy and Carbon (1 of 3)



• But the metabolic capabilities of prokaryotes are

far more diverse than those of eukaryotes.

– Some species harvest energy from inorganic

substances such as ammonia (NH3) and hydrogen

sulfide (H2S).



• The metabolic talents of prokaryotes make them

excellent symbiotic partners with animals, plants, and

fungi.

• Symbiosis (“living together”) is a close association

between organisms of two or more species.



– In some cases of symbiosis, both organisms

benefit from the partnership.

– For example, many of the animals that inhabit

hydrothermal vent communities, such as the giant

tube worm shown in Figure 15.12, harbor sulfur

bacteria within their bodies.

▪ The animals absorb sulfur compounds from the

water.

▪ The bacteria use the compounds as an energy

source to convert CO2 from seawater into organic

molecules that, in turn, provide food for their hosts.


Figure 15.12 Giant Tube Worm



• In addition to photosynthesis, many cyanobacteria

are also capable of nitrogen fixation, the process of

converting atmospheric nitrogen (N2) into a form

usable by plants.

– Symbiosis with cyanobacteria gives plants such as

the water fern Azolla an advantage in nitrogen-poor

environments.

– This tiny, floating plant has been used to boost rice

production for more than a thousand years.


Figure 15.13 Azolla (Water Fern,

Inset) Floating in Rice Paddy (1 of 3)


The Ecological Impact of Prokaryotes

• As a result of their nutritional diversity, prokaryotes

perform a variety of ecological services that are

essential to our well-being.


Prokaryotes and Chemical Recycling (1 of 2)

• Life depends on the recycling of chemical elements

between the biological and physical components of

ecosystems.

• Prokaryotes play essential roles in these chemical

cycles.


Prokaryotes and Chemical Recycling (2 of 2)

• Prokaryotes also promote the breakdown of

– organic wastes and

– dead organisms.


Putting Prokaryotes to Work (1 of 2)

• Bioremediation is the use of organisms to remove

pollutants from

– water,

– air, or

– soil.

– One example of bioremediation is the use of

prokaryotic decomposers to treat our sewage.


Figure 15.14 Putting Microbes to

Work in Sewage Treatment Facilities


Putting Prokaryotes to Work (2 of 2)

• Bioremediation has also become an important tool for

cleaning up toxic chemicals released into the soil and

water by industrial processes.

– Naturally occurring prokaryotes capable of degrading

pollutants such as oil, solvents, and pesticides are

often present in contaminated soil, but environmental

workers may use methods of speeding up their activity.

– In Figure 15.15, an airplane is spraying chemical

dispersants on oil from the disastrous 2010 Deepwater

Horizon spill in the Gulf of Mexico.


Figure 15.15 Spraying Chemical

Dispersants on an Oil Spill in the

Gulf of Mexico


The Two Main Branches of Prokaryotic

Evolution: Bacteria and Archaea (1 of 4)

• By comparing diverse prokaryotes at the molecular

level, biologists have identified two major branches

of prokaryotic evolution:

1. bacteria and

2. archaea.

• Thus, life is organized into three domains:

1. Bacteria,

2. Archaea, and

3. Eukarya.




• Archaea are abundant in many habitats, including

places where few other organisms can survive.

– One group of archaea, the extreme thermophiles (“heat

lovers”), live in very hot water.

– Another group is the extreme halophiles (“salt lovers”),

archaea that thrive in such environments as

▪ Utah’s Great Salt Lake,

▪ the Dead Sea, and

▪ seawater-evaporating ponds used to produce salt.


Figure 15.16 Heat-Loving Archaea




• A third group of archaea are methanogens, which live

in anaerobic (oxygen-free) environments and give off

methane as a waste product.

– They are abundant in the mud at the bottom of lakes

and swamps.

– Many municipalities collect this methane and use it as

a source of energy.

– Great numbers of methanogens also inhabit the

digestive tracts of animals.


Figure 15.17 Pipes for Collecting Gas

Generated by Methanogenic Archaea

from a Landfill




• Archaea are also abundant in more moderate

conditions, especially the oceans.

• Archaea are thus one of the most abundant cell types

in Earth’s largest habitat.


Bacteria That Cause Disease (1 of 6)

• Bacteria and other organisms that cause disease are

called pathogens.

• Most pathogenic bacteria cause disease by producing

a poison.

– Exotoxins are proteins that bacterial cells secrete into

their environment.

– Endotoxins are chemical components of the outer

membrane of certain bacteria.


Figure 15.18 Bacteria that Cause

Meningitis



• Sanitation is generally the most effective way to

prevent bacterial disease.

– The installation of water treatment and sewage

systems continues to be a public health priority

throughout the world.

• Antibiotics have been discovered that can cure most

bacterial diseases. However, resistance to widely

used antibiotics has evolved in many of these

pathogens.



• A third defense against bacterial disease is education.

• For example, Lyme disease is caused by a spirochete

bacterium carried by ticks.

– Lyme disease usually starts as a red rash shaped like

a bull’s-eye around a tick bite.



– Antibiotics can cure the disease if administered within

a month of exposure.

– If untreated, Lyme disease can cause

▪ debilitating arthritis,

▪ heart disease, and

▪ nervous system disorders.

– The best defense against Lyme disease is public

education about avoiding tick bites and the

importance of seeking treatment if a rash develops.


Figure 15.19 Lyme Disease, a Bacterial

Disease Transmitted by Ticks (1 of 5)



• The potential of some pathogens to cause serious

harm has led to their use as biological weapons.

– One of the greatest threats is from endospores of the

bacterium that causes anthrax.

▪ When anthrax endospores enter the lungs, they

germinate, and the bacteria multiply, producing an

exotoxin that eventually accumulates to lethal levels in

the blood.



▪ Another bacterium considered to have dangerous

potential as a weapon is Clostridium botulinum.

– Unlike other biological agents, the weapon form of

C. botulinum is the exotoxin it produces, botulinum,

rather than the living microbes.

– Botulinum, the deadliest poison on Earth, blocks

transmission of the nerve signals that cause muscle

contraction, resulting in paralysis of the muscles

required for breathing.

– On the other hand, the minute amount of botulinum in

Botox is used for cosmetic purposes. When the toxin

is injected under the skin, it relaxes the facial

muscles that cause wrinkles.


The Process of Science: Are Intestinal

Microbiota to Blame for Obesity? (1 of 6)

• Our bodies are home to trillions of bacteria that cause

no harm or are even beneficial to our health.

• Because our intestinal microbes are known to be

involved in some aspects of food processing,

researchers speculate that they might be involved in

obesity.




• Using observations from previous studies, the

scientists asked the question: Can microbiota from

an obese person affect the body composition of

another person?

• The scientists formed the hypothesis that intestinal

microbiota of an obese person would increase the

amount of body fat in mice.




• Their prediction was that if the hypothesis was

correct, then lean, germ-free mice that received

transplants of microbes from the intestines of obese

individuals would show a greater increase of body fat

than would germ-free mice that received transplants

of microbes from the intestines of lean individuals.




• The researchers recruited four pairs of female twins

for the experiment.

– One member of each set of twins was obese, and her

twin was lean.

• Microbiota from the feces of each individual were

transplanted into separate groups of germ-free mice.


Figure 15.20 Experiment to Investigate the

Effect of Microbiota on Body Composition




• The results, shown in Figure 15.21, supported the

hypothesis.

– Mice that received microbiota from an obese donor

became more obese.

– Mice that received microbiota from a lean donor

remained lean.


Figure 15.21 Results of Microbiota

Transplantation Experiment




• Is a microbe-based cure for obesity just around the

corner? It’s not likely.

– The experiment described here represents an early

stage of scientific investigation.

– A great deal more research is needed to determine

whether our microbial residents are responsible for

obesity.

– If that proves to be the case, the next challenge

will be figuring out how to safely manipulate the

complex ecosystem within our bodies.


Protists (1 of 6)

• The fossil record indicates that the first eukaryotes

evolved from prokaryotes around 2 billion years ago.

• These primal eukaryotes were

– the predecessors of the great variety of modern

protists and

– also ancestral to all other eukaryotes:

▪ plants,

▪ fungi, and

▪ animals.


Protists (2 of 6)

• The term protists is not a taxonomic category.

– At one time, protists were classified in a fourth

eukaryotic kingdom (kingdom Protista).

– However, recent genetic and structural studies

show that they are not a unified group.

▪ Some protists are more closely related to fungi, plants,

or animals than they are to each other.

▪ Hypotheses about protist phylogeny (and thus

classification) are changing rapidly as new information

causes scientists to revise their ideas.


Protists (3 of 6)

• The only characteristic common to protists is that they

are eukaryotes.

• Protists obtain their nutrition in a variety of ways.

– Algae

▪ are autotrophs, producing their food by photosynthesis,

and

▪ may be unicellular, colonial, or multicellular.


Figure 15.22 Protist Modes of

Nutrition (1 of 4)


Protists (4 of 6)

– Other protists are heterotrophs, acquiring their

food from other organisms.

▪ Some heterotrophic protists eat bacteria or other

protists.

▪ Other protists are fungus-like and obtain organic

molecules by absorption.

▪ Parasites derive their nutrition from a living host,

which is harmed by the interaction. Parasitic

trypanosomes infect blood and cause sleeping

sickness.



Nutrition (2 of 4)


Protists (5 of 6)

• Other protists are mixotrophs, capable of

photosynthesis and heterotrophy.

– Euglena, a common inhabitant of pond water, can

change its mode of nutrition, depending on availability

of light and nutrients.


Video: Euglena Motion



Nutrition (3 of 4)


Protists (6 of 6)

• Protist habitats are also diverse.

– Most protists are aquatic, living in oceans, lakes, and

ponds.

– Some are found almost anywhere there is moisture,

including terrestrial habitats such as damp soil and

leaf litter.

– Others are symbionts that reside in the bodies of

various host organisms.


Protozoans (1 of 7)

• Protists that live primarily by ingesting food are called

protozoans.


Figure 15.23 A Diversity of Protozoans (1 of 7)


Protozoans (2 of 7)

• Protozoans with flagella are called flagellates and

are typically living (nonparasitic), but some are nasty

parasites, such as Giardia, a common waterborne

parasite that causes severe diarrhea.


Protozoans (3 of 7)

• Other flagellates live symbiotically in a relationship

that benefits both partners.

– Termites are notoriously destructive to wooden

structures, but they lack enzymes to digest the tough,

complex cellulose molecules that makes up wood.

– Flagellates that reside in the termite’s digestive tract

break down the cellulose into simpler molecules,

sharing the bounty with their hosts.


Protozoans (4 of 7)

• Amoebas are characterized by

– great flexibility in their body shape and

– the absence of permanent organelles for locomotion.

• Most species move and feed by means of

pseudopodia (singular, pseudopodium), temporary

extensions of the cell.

• Other protozoans with pseudopodia include the

forams, which have shells.


Video: Amoeba


Video: Amoeba Pseudopodia


Protozoans (5 of 7)

• Apicomplexans are

– named for a structure at their apex (tip) that is

specialized for penetrating host cells and tissues,

– all parasitic, and

– able to cause serious human diseases, such as

malaria caused by Plasmodium.


Protozoans (6 of 7)

• Another apicomplexan is Toxoplasma, which requires

a feline host to complete its complex life cycle.

• A woman who is newly infected with Toxoplasma

during pregnancy can pass the parasite to her unborn

child, who may suffer damage to the nervous system

as a result.


Protozoans (7 of 7)

• Ciliates are protozoans that

– are named for their hairlike structures called cilia,

which provide movement of the protist and sweep

food into the protist’s “mouth,”

– are mostly free-living (nonparasitic), such as the

freshwater ciliate Paramecium, and

– include heterotrophs and mixotrophs.


Video: Paramecium Cilia


Video: Paramecium Vacuole


Video: Vorticella Cilia


Video: Vorticella Detail


Video: Vorticella Habitat


Slime Molds (1 of 3)

• Slime molds are multicellular protists related to

amoebas and feed on dead plant material.

– Although slime molds were once classified as fungi,

DNA analysis showed that they arose from different

evolutionary lineages.

– Two distinct types of slime molds have been identified:

1. plasmodial slime molds and

2. cellular slime molds.



• Plasmodial slime molds have a feeding body that is an

amoeboid mass called a plasmodium that extends

pseudopodia among the leaf litter and other decaying

material on a forest floor.


Video: Plasmodial Slime Mold

Streaming


Video: Plasmodial Slime Mold


Figure 15.24 A Plasmodial Slime Mold



• In cellular slime molds, the feeding stage consists of

solitary amoeboid cells that function independently of

each other rather than a plasmodium.

– But when food is in short supply, the amoeboid

cells swarm together to form a slug-like colony

that moves and functions as a single unit.


Figure 15.25 Life Stages of a Cellular

Slime Mold (1 of 4)



Slime Mold (2 of 4)



Slime Mold (3 of 4)



Slime Mold (4 of 4)


Unicellular and Colonial Algae (1 of 5)

• Algae are protists and cyanobacteria whose

photosynthesis supports food chains in freshwater

and marine ecosystems.

– Researchers are currently trying to harness their ability

to convert light energy to chemical energy for another

purpose—to produce biofuels.



• Many unicellular algae are components of phytoplankton,

the mostly microscopic photosynthetic organisms that drift

near the surfaces of ponds, lakes, and oceans.



• Dinoflagellates are abundant in the vast aquatic

pastures of phytoplankton.

– Each dinoflagellate species has a characteristic

shape reinforced by external plates made of cellulose.

– The beating of two flagella in perpendicular grooves

produces a spinning movement.


Figure 15.26 Unicellular and Colonial

Algae (1 of 4)



• Diatoms have glassy cell walls containing silica, the

mineral used to make glass.

– The cell walls consist of two halves that fit together like

the bottom and lid of a shoe box.

– Diatoms store their food reserves in the form of an oil

that provides buoyancy, keeping diatoms floating as

plankton near the sunlit surface.

– The organic remains of diatoms that lived hundreds of

millions of years ago are thought to be the main

component of oil deposits.



Algae (2 of 4)



• Green algae are named for their grass-green

chloroplasts.

– Unicellular green algae flourish in most freshwater

lakes and ponds.

– The green algal group also includes colonial forms,

such as Volvox, which is a hollow ball of

flagellated cells that are very similar to certain

unicellular green algae.



Algae (3 of 4)


Video: Dinoflagellate


Video: Water Mold Oogonium


Video: Water Mold Zoospores


Video: Diatoms Moving


Video: Various Diatoms


Video: Chlamydomonas


Video: Volvox Colony


Video: Volvox Daughter


Video: Volvox Flagella


Seaweeds (1 of 2)

• Seaweeds

– are large, multicellular marine algae,

– grow on rocky shores and just offshore beyond the

zone of the pounding surf,

– are only similar to plants because of convergent

evolution,

– are most closely related to unicellular algae, and

– are often edible.


Seaweeds (2 of 2)

• Seaweeds are classified into three different groups,

based partly on the types of pigments present in their

chloroplasts:

1. green algae,

2. red algae, and

3. brown algae (some of which are known as kelp).


Figure 15.27 The Three Major Groups

of Seaweeds (1 of 4)


Evolution Connection: The Sweet Life

of Streptococcus mutans (1 of 3)

• A biofilm-forming species of bacteria called

Streptococcus mutans thrives in the anaerobic

environment found in the tiny crevices in tooth

enamel.

– The bacteria use sucrose (table sugar) to make a

sticky polysaccharide, glue themselves in place,

and build up thick deposits of plaque.


Figure 15.28 Checking the Effects

of Streptococcus Mutans




• Studies of prehistoric human remains have correlated

dental disease with changes in diet.

– Recent research links S. mutans directly to these rises

in tooth decay.

– Diversity of the oral microbiota dropped dramatically

about 400 years ago, around the time sugar was

introduced into the diet and S. mutans became the

overwhelmingly dominant species.




• What adaptations gave S. mutans an advantage over

other species? Researchers discovered

– more than a dozen genes that improved the ability

of S. mutans to metabolize sugars and survive

increased acidity and

– chemical weapons produced by S. mutans that

kill harmless bacteria, their competitors for space

in the limited terrain of the human oral cavity.



Nutrition (4 of 4)



Algae (4 of 4)


Figure 15.UN01

Major Episode Millions of Years Ago

Plants and fungi colonize land 500

Fossils of large, diverse

multicellular organisms

600

Oldest fossils of multicellular

organisms

1,200

Oldest eukaryotic fossils 1,800

Beginning of atmospheric

accumulation of O2

2,700

Oldest prokaryotic fossils 3,500

Origin of Earth 4,600


Figure 15.UN02


Figure 15.UN03


Figure 15.UN04


Figure 15.UN05


Figure 15.UN06

Time (Hours) Number of

Generations

Number of

Bacteria

0 0 10

1 2 40

2 4 blank

3 6 blank

4 8 blank

5 10 blank

6 12 blank

8 16 blank

10 20 blank

12 24 blank

Essential Biology with Physiology, 5e

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