2 Cell Division and Reproduction

75 Pages·2015·9.03 MB·English

7: Cells and Heredity
Laura Enama
Jean Brainard, Ph.D.
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AUTHORS
LauraEnama
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JeanBrainard,Ph.D.
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EDITOR
DouglasWilkin,Ph.D.
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Printed: August3,2015
iii
Contents www.ck12.org
Contents
1 IntroductiontoCells 1
1.1 CharacteristicsofLife . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 ClassificationofLife . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.3 Life’sBuildingBlocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.4 CellStructures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
1.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2 CellDivisionandReproduction 30
2.1 CellDivision. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
2.2 Reproduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
2.3 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3 Genetics 47
3.1 Mendel’sDiscoveries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
3.2 ProbabilityandHeredity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
3.3 PatternsofInheritance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
3.4 AdvancesinGenetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
3.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
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www.ck12.org Chapter1. IntroductiontoCells
C 1
HAPTER
Introduction to Cells
Chapter Outline
1.1 CHARACTERISTICS OF LIFE
1.2 CLASSIFICATION OF LIFE
1.3 LIFE’S BUILDING BLOCKS
1.4 CELL STRUCTURES
1.5 REFERENCES
FIGURE1.1
This colorful image represents a virus that commonly causes respiratory infections in people. Living organisms
calledbacteriaarealsocommoncausesofhumaninfections. Areviruseslivingorganismsaswell?
Actually, this is one of the great unanswered questions of life science. Some scientists think viruses should be
consideredlivingorganisms. Otherscientistsdisagree. Inthischapter,you’lllearnthebasiccharacteristicsofliving
things and the characteristics of viruses. At the end of the chapter, you can decide for yourself whether you think
virusesarelivingorganisms.
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1.1. CharacteristicsofLife www.ck12.org
1.1 Characteristics of Life
i
LessonObjectives
• Identifycharacteristicsoflivingorganisms.
• Describecells.
• Explainwhylivingthingsneedenergy.
• Giveanexampleofastimulusandresponse.
• Comparesexualandasexualreproduction.
• Definehomeostasis.
LessonVocabulary
• cell
• energy
• homeostasis
• reproduction
• response
• stimulus(stimuli,plural)
Introduction
LookatthephotosinFigure1.2. Howaretheysimilar? Allofthemshowlivingorganisms. Observehowdifferent
the organisms are from each other. Clearly, living things are very diverse. Yet all of the organisms in the pictures
sharethesamebasiccharacteristicsoflife. Canyouguesswhatthesecharacteristicsare?
FIGURE1.2
These pictures represent the diversity of
living organisms. Organisms in the top
row(a–c)aremicroscopic.
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www.ck12.org Chapter1. IntroductiontoCells
DefiningLife
Fivecharacteristicsareusedtodefinelife. Alllivingthingssharethesecharacteristics. Alllivingthings:
1. aremadeofoneormorecells.
2. needenergytostayalive.
3. respondtostimuliintheirenvironment.
4. growandreproduce.
5. maintainastableinternalenvironment.
LivingThingsAreMadeofCells
Cells are the basic building blocks of life. They are like tiny factories where virtually all life processes take place.
Somelivingthings,likethebacteriainFigure1.2,consistofjustonecell. Theyarecalledsingle-celledorganisms.
You can see other single-celled organisms in Figure below. Some living things are composed of a few to many
trillionsofcells. Theyarecalledmulticellularorganisms. Yourbodyiscomposedoftrillionsofcells.
FIGURE1.3
The green scum in this canal consists
of billions of single-celled green algae.
Algae are plant-like microorganisms that
producefoodbyphotosynthesis.
Regardlessofthetypeoforganism,alllivingcellssharecertainbasicstructures. Forexample,allcellsareenclosed
by a membrane. The cell membrane separates the cell from its environment. It also controls what enters or leaves
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1.1. CharacteristicsofLife www.ck12.org
thecell.
LivingThingsNeedEnergy
Everything you do takes energy. Energy is the ability to change or move matter. Whether it’s reading these words
or running a sprint, it requires energy. In fact, it takes energy just to stay alive. Where do you get energy? You
probablyknowtheanswer. Yougetenergyfromfood. Figurebelowshowssomehealthyfoodsthatcanprovideyou
withenergy.
FIGURE1.4
Fruits, vegetables, and nuts are healthy
sourcesoffoodenergy.
Just like you, other living things need a source of energy. But they may use a different source. Organisms may be
groupedonthebasisofthesourceofenergytheyuse. Inwhichgroupdoyoubelong?
• Producers such as the tree in Figure 1.2 use sunlight for energy to produce their own “food.” The process is
calledphotosynthesis,andthe“food”issugar. Plantsandotherorganismsusethisfoodforenergy.
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www.ck12.org Chapter1. IntroductiontoCells
• Consumers such as the raccoon in Figure 1.2 eat plants—or other consumers that eat plants—as a source of
energy.
• SomeconsumerssuchasthemushroominFigure1.2gettheirenergyfromdeadorganicmatter. Forexample,
theymightconsumedeadleavesonaforestfloor.
LivingThingsRespondtotheirEnvironment
When a living thing responds to its environment, it is responding to a stimulus. A stimulus ( stimuli, plural) is
something in the environment that causes a reaction in an organism. The reaction a stimulus produces is called a
response.
Imaginehowyouwouldrespondtothefollowingstimuli:
• You’reabouttocrossastreetwhenthewalklightturnsred.
• Youhearasmokealarmgooffinthekitchen.
• Yousteponanupturnedtackwithabarefoot.
• Yousmellthearomaofyourfavoritefood.
• Youtastesomethingreallysour.
Itdoesn’ttakemuchimaginationtorealizethatrespondingappropriatelytosuchstimulimighthelpkeepyousafe.
Itmightevenhelpyousurvive.
Like you, all other living things sense and respond to stimuli in their environment. In general, their responses help
themsurviveorreproduce. Watchthisamazingtime-lapsevideotoseehowaplantrespondstothestimulioflight
and gravity as it grows. Why do you think it is important for a plant to respond appropriately to these stimuli for
propergrowth?
http://www.youtube.com/watch?v=RzD4skFeJ7Y
MEDIA
ClickimagetotheleftorusetheURLbelow.
URL:http://www.ck12.org/flx/render/embeddedobject/149611
Likeplants, alllivingthingshavethecapacityforgrowth. TheducklingsinFigure1.5havealotofgrowingtodo
to catch up in size to their mother. Multicellular organisms like ducks grow by increasing the size and number of
theircells. Single-celledorganismsjustgrowinsize.
As the ducklings grow, they will develop and mature into adults. By adulthood, they will be able to reproduce.
Reproductionistheproductionofoffspring. Theabilitytoreproduceisanothercharacteristicoflivingthings.
Many organisms reproduce sexually. In sexual reproduction, parents of different sexes mate to produce offspring.
The offspring havesome combination of the traitsof the two parents. Ducks are examples ofsexually reproducing
organisms. Other organisms reproduce asexually. In asexual reproduction, a single parent can produce offspring
alone. Forexample,abacterialcellreproducesbydividingintotwodaughtercells. Thedaughtercellsareidentical
toeachotherandtotheparentcell.
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1.1. CharacteristicsofLife www.ck12.org
FIGURE1.5
These ducklings will grow to become as
big as their mother by the time they are
aboutayearold.
LivingThingsMaintainaStableInternalEnvironment
ThetennisplayerinFigure1.6hasreallyworkedupasweat. Doyouknowwhywesweat? Sweatinghelpstokeep
us cool. When sweat evaporates from the skin, it uses up some of the body’s heat energy. Sweating is one of the
ways that the body maintains a stable internal environment. It helps keep the body’s internal temperature constant.
Whenthebody’sinternalenvironmentisstable,theconditioniscalledhomeostasis.
FIGURE1.6
Sweating is one way the body maintains
homeostasis.
Alllivingorganismshavewaysofmaintaininghomeostasis. Theyhavemechanismsforcontrollingsuchfactorsas
their internal temperature, water balance, and acidity. Homeostasis is necessary for normal life processes that take
place inside cells. If an organism can’t maintain homeostasis, normal life processes are disrupted. Disease or even
deathmayresult.
LessonSummary
• All living things are made of cells, use energy, respond to stimuli, grow and reproduce, and maintain home-
ostasis.
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