chapter 3 the cellular level of...
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Chapter 3The Cellular Level of Organization
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A Generalized Cell
1. Plasma membrane- forms the cell’s outer boundary- separates the cell’s internal environment
from the outside environment- is a selective barrier- plays a role in cellular communication
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A Generalized Cell
2. Cytoplasm- all the cellular contents between the plasma membrane and the nucleus- cytosol - the fluid portion, mostly water- organelles - subcellular structures having characteristic shapes and specific functions
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A Generalized Cell
3. Nucleus- large organelle that contains DNA- contains chromosomes, each of which consists of a single molecule of DNA and associated proteins
- a chromosome contains thousands of hereditary units called genes
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Fig. 3.1 Generalized Body Cell
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Plasma Membrane
Flexible yet sturdy barrier The fluid mosaic model - the arrangement of
molecules within the membrane resembles a sea of lipids containing many types of proteins
The lipids act as a barrier to certain substances
The proteins act as “gatekeepers” to certain molecules and ions
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Structure of a Membrane
Consists of a lipid bilayer - made up of phospholipids, cholesterol and glycolipids
Integral proteins - extend into or through the lipid bilayer
Transmembrane proteins - most integral proteins, span the entire lipid bilayer
Peripheral proteins - attached to the inner or outer surface of the membrane, do not extend through it
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Structure of the Plasma Membrane
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Structure of a Membrane
Glycoproteins - membrane proteins with a carbohydrate group attached that protrudes into the extracellular fluid
Glycocalyx - the “sugary coating” surrounding the membrane made up of the carbohydrate portions of the glycolipids and glycoproteins
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Functions of Membrane Proteins
Some integral proteins are ion channels Transporters - selectively move substances
through the membrane Receptors - for cellular recognition; a ligand
is a molecule that binds with a receptor Enzymes - catalyze chemical reactions Others act as cell-identity markers
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Figure 3.3
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Membrane Permeability
The cell is either permeable or impermeable to certain substances
The lipid bilayer is permeable to oxygen, carbon dioxide, water and steroids, but impermeable to glucose
Transmembrane proteins act as channels and transporters to assist the entrance of certain substances, for example, glucose and ions
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Passive vs. Active Processes
Passive processes - substances move across cell membranes without the input of any energy; use the kinetic energy of individual molecules or ions
Active processes - a cell uses energy, primarily from the breakdown of ATP, to move a substance across the membrane, i.e.,against a concentration gradient
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Diffusion
Steepness of concentration
gradient Temperature Mass of diffusing
substance Surface area Diffusion
distance
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Simple Diffusion, Channel-mediated Facilitated Diffusion, and Carrier-mediated Facilitated Diffusion
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Channel-mediated Facilitated Diffusion of Potassium ions through a Gated K + Channel
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Carrier-mediated Facilitated Diffusion of Glucose across a Plasma Membrane
Glucosetransporter
Glucosegradient
Glucose
Extracellular fluid Plasma membrane Cytosol
1
Glucosetransporter
Glucosegradient
Glucose
Extracellular fluid Plasma membrane Cytosol
1
2
Glucosetransporter
Glucosegradient
Glucose
Glucose
Extracellular fluid Plasma membrane Cytosol
1
2
3
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Osmosis
Net movement of water through a selectively permeable membrane from an area of high concentration of water (lower concentration of solutes) to one of lower concentration of water
Water can pass through plasma membrane in 2 ways:
1. through lipid bilayer by simple diffusion2. through aquaporins, integral membrane
proteins
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Tonicity and its effect on RBCS
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Active TransportSolutes are transported across plasma membranes with the use of energy, from an area
of lower concentration to an area of higher Concentration Sodium-potassium pump
1
3 Na+
K+
gradient
Na+
gradientNa+/K+ ATPase
Extracellular fluid
Cytosol
1
3 Na+ expelled
3 Na+
ADP
P
K+
gradient
Na+
gradientNa+/K+ ATPase
Extracellular fluid
CytosolATP
21
3 Na+ expelled
3 Na+
ADP P
P
K+
gradient
Na+
gradientNa+/K+ ATPase
Extracellular fluid
Cytosol
2K+
ATP2 31
3 Na+ expelled
3 Na+
ADP P
P
2 K+
importedK+
gradient
Na+
gradientNa+/K+ ATPase
Extracellular fluid
Cytosol
2K+
ATP2 3 4
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Transport in Vesicles
Vesicle - a small spherical sac formed by budding off from a membrane
Endocytosis - materials move into a cell in a vesicleformed from the plasma membrane
three types: receptor-mediated endocytosis phagocytosisbulk-phase endocytosis (pinocytosis)
Exocytosis - vesicles fuse with the plasma membrane, releasing their contents into the extracellular fluid
Transcytosis - a combination of endocytosis and exocytosis
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Receptor-Mediated Endocytosis
1
Clathrin-coatedpit
Binding
Receptor
Receptor-LDLcomplex LDL particle Plasma
membrane
Invaginated plasmamembrane
1
Clathrin-coatedvesicle
Clathrin-coatedpit
Binding
Vesicle formation
Receptor
Receptor-LDLcomplex LDL particle Plasma
membrane
Invaginated plasmamembrane
2
1
Clathrin-coatedvesicle
Clathrin-coatedpit
Binding
Vesicle formation
Receptor
Receptor-LDLcomplex
Uncoated vesicle
Uncoating
LDL particle Plasmamembrane
Invaginated plasmamembrane
2
3
1
Clathrin-coatedvesicle
Clathrin-coatedpit
Binding
Vesicle formation
Receptor
Receptor-LDLcomplex
Uncoated vesicle
Fusion withendosome
Uncoating
LDL particle Plasmamembrane
Invaginated plasmamembrane
Endosome
2
3
4
Transportvesicle
1
Clathrin-coatedvesicle
Clathrin-coatedpit
Binding
Vesicle formation
Receptor
Receptor-LDLcomplex
Uncoated vesicleTransportvesicle
Fusion withendosome
Recyclingof receptorsto plasmamembrane
Uncoating
LDL particle Plasmamembrane
Invaginated plasmamembrane
Endosome
2
3
4
5
Transportvesicle
1
Clathrin-coatedvesicle
Clathrin-coatedpit
Binding
Vesicle formation
Receptor
Receptor-LDLcomplex
Uncoated vesicle
Degradationin lysosome
Lysosome
Transportvesicle
Transportvesicle
Fusion withendosome
Recyclingof receptorsto plasmamembrane
Uncoating
LDL particle Plasmamembrane
Invaginated plasmamembrane
Endosome
Digestiveenzymes
2
3
4
5
6
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Phagocytosis
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Bulk-phase Endocytosis
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Cytoplasm - 2 components
1. Cytosol - intracellular fluid, surrounds the organelles- the site of many chemical reactions- energy is usually released by these reactions- reactions provide the building blocks for cell maintenance, structure, function and growth
2. OrganellesSpecialized structures within the cellThe cytoskeleton - network of protein filaments throughout the cytosol-provides structural support for the cell-three types according to increasing size: microfilaments, intermediate filaments, and microtubules
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The Cytoskeleton
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Organelles
Centrosome - located near the nucleus, consists of two centrioles and pericentriolar material (Fig. 2.7)
Cilia - short, hair-like projections from the cell surface, move fluids along a cell surface
Flagella - longer than cilia, move an entire cell; only example is the sperm cell’s tail (Fig. 2.8)
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The Centrosome
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Cilia and Flagella
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Organelles
Ribosomes - sites of protein synthesis Endoplasmic reticulum - network of membranes in
the shape of flattened sacs or tubules- Rough ER - connected to the nuclear envelope, a series of flattened sacs, surface is studded with ribosomes, produces various proteins-Smooth ER - a network of membrane tubules, does not have ribosomes, synthesizes fatty acids and steroids, detoxifies certain drugs
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Ribosomes
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Endoplasmic Reticulum
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Organelles
Golgi complex - consists of 3-20 flattened, membranous sacs called cisternae
- modify, sort, and package proteins for transport to different destinations- proteins are transported by various vesicles
Lysosomes - vesicles that form from the Golgi complex, contain powerful digestive enzymes
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Golgi Complex
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Processing and Packaging
Transport vesicleRibosomeSynthesizedprotein 1
Rough ER
Transport vesicleRibosomeSynthesizedprotein
Rough ER
21 Transport vesicleRibosome
Entry face cisterna
Exit face cisterna
Medial cisterna
Synthesizedprotein
Rough ER
3
21 Transport vesicleRibosome
Entry face cisterna
Exit face cisterna
Medial cisterna
Synthesizedprotein
Transfer vesicle
Rough ER
Transfer vesicle
4
3
21
4
Transport vesicleRibosomeEntry face cisterna
Exit face cisterna
Medial cisterna
Synthesizedprotein
Transfer vesicle
Rough ER
Transfer vesicle
54
3
21
4
Transport vesicleRibosomeEntry face cisterna
Exit face cisterna
Medial cisterna
Synthesizedprotein
Transfer vesicle
Rough ER
Transfer vesicle
6
54
3
21
4
Transport vesicleRibosomeEntry face cisterna
Exit face cisterna
Medial cisterna
Synthesizedprotein
Transfer vesicle
Rough ER
Transfer vesicleSecretoryvesicle
7
6
54
3
21
4
Proteins exportedfrom cell by exocytosis
Plasmamembrane
Proteins in vesiclemembrane mergewith plasmamembrane
Proteins exportedfrom cell by exocytosis
Plasmamembrane
Transport vesicleRibosomeEntry face cisterna
Exit face cisterna
Medial cisterna
Synthesizedprotein
Transfer vesicle
Rough ER
Transfer vesicle
Membranevesicle
Secretoryvesicle
8
7
6
54
3
21
4
Proteins in vesiclemembrane mergewith plasmamembrane
Proteins exportedfrom cell by exocytosis
Plasmamembrane
Transport vesicleRibosomeEntry face cisterna
Exit face cisterna
Medial cisterna
Synthesizedprotein
Transport vesicle(to lysosome)
Transfer vesicle
Rough ER
Transfer vesicle
Membranevesicle
Secretoryvesicle
9
8
7
6
54
3
21
4
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Lysosomes
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Organelles
Peroxisomes - smaller than lysosomes, detoxify several toxic substances such as alcohol, abundant in the liver
Proteasomes - continuously destroy unneeded, damaged, or faulty proteins, found in the cytosol and the nucleus
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Organelles
Mitochondria - the “powerhouses” of the cell Generate ATP More prevalent in physiologically active cells: muscles, liver
and kidneys Inner and outer mitochondrial membranes Cristae - the series of folds of the inner membrane Matrix - the large central fluid-filled cavity Self-replicate during times of increased cellular demand or
before cell division
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Mitochondria
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Organelles - Nucleus Spherical or oval shaped structure Usually most prominent feature of a cell Nuclear envelope - a double membrane that
separates the nucleus from the cytoplasm Nuclear pores - numerous openings in the nuclear
envelope, control movement of substances between nucleus and cytoplasm
Nucleolus - spherical body that produces ribosomes Genes - are the cell’s hereditary units, control
activities and structure of the cell Chromosomes - long molecules of DNA combined
with protein molecules
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Packing of DNA into a Chromosome of a Dividing Cell
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Overview of Gene Expression
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Transcription
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Translation
1
Key:
Initiator tRNA attaches to astart codon.
Amino acid(methionine)
AnticodonmRNA
mRNAbindingsite
Initiator tRNA
Start codon
Smallsubunit
= Adenine
= Guanine
= Cytosine
= Uracil
U GGG AU A C
1
Key:
Initiator tRNA attaches to astart codon.
Large and small ribosomalsubunits join to form a functionalribosome and initiator tRNAfits into P site.Amino acid
(methionine)
AnticodonmRNA
mRNAbindingsite
Initiator tRNA
Start codon
Smallsubunit
Initiator tRNA
Smallsubunit
LargesubunitP site
A site
= Adenine
= Guanine
= Cytosine
= Uracil
U GGG AU A C
UGG AU A C
G
2
1
Key:
Initiator tRNA attaches to astart codon.
Large and small ribosomalsubunits join to form a functionalribosome and initiator tRNAfits into P site.Amino acid
(methionine)
Amino acid
Anticodon
Anticodon
Codons
mRNA
mRNA
mRNAbindingsite
Initiator tRNA
tRNA
Start codon
Smallsubunit
Initiator tRNA
Smallsubunit
LargesubunitP site
A site
Anticodon of incoming tRNA pairswith next mRNA codon at A site.
P site
A site
= Adenine
= Guanine
= Cytosine
= Uracil
U GGG AU A C
UGG AU A C
G C
U GGG AU A C
2
3
1
Key:
Initiator tRNA attaches to astart codon.
Large and small ribosomalsubunits join to form a functionalribosome and initiator tRNAfits into P site.Amino acid
(methionine)
Amino acid
Anticodon
Anticodon
Codons
mRNA
mRNA
mRNAbindingsite
Initiator tRNA
tRNA
Start codon
Smallsubunit
Initiator tRNA
Smallsubunit
LargesubunitP site
A site
Anticodon of incoming tRNA pairswith next mRNA codon at A site.
Amino acid on tRNA at P siteforms a peptide bond withamino acid at A site.
P site
A site
= Adenine
= Guanine
= Cytosine
= Uracil
U GGG AU A C
UGG AU A C
G C
U GGG AU A C
GAUU GGG AU A C U
2
3
4
1
Key:
Initiator tRNA attaches to astart codon.
Large and small ribosomalsubunits join to form a functionalribosome and initiator tRNAfits into P site.Amino acid
(methionine)
Amino acid
Anticodon
Anticodon
Codons
mRNA
mRNA
mRNAmovement
mRNAbindingsite
Initiator tRNA
tRNA
Start codon
Smallsubunit
Initiator tRNA
Smallsubunit
LargesubunitP site
A site
Anticodon of incoming tRNA pairswith next mRNA codon at A site.
tRNA at P site leaves ribosome,ribosome shifts by one codon;tRNA previously at A site is nowat the P site.
Newpeptidebond Amino acid on tRNA at P site
forms a peptide bond withamino acid at A site.
P site
A site
= Adenine
= Guanine
= Cytosine
= Uracil
U GGG AU A C
UGG AU A C
G C
U GGG AU A C
GAUU GGG AU A C U
GUU GGG A CU
2
3
4
5
1
Key:
Initiator tRNA attaches to astart codon.
Large and small ribosomalsubunits join to form a functionalribosome and initiator tRNAfits into P site.Amino acid
(methionine)
Amino acid
Anticodon
Anticodon
Codons
Stop codon
mRNA
mRNA
mRNAmovement
mRNAbindingsite
Initiator tRNA
tRNA
Start codon
Smallsubunit
Initiator tRNA
Smallsubunit
LargesubunitP site
A site
Anticodon of incoming tRNA pairswith next mRNA codon at A site.
Protein synthesis stops whenthe ribosome reaches stopcodon on mRNA.
tRNA at P site leaves ribosome,ribosome shifts by one codon;tRNA previously at A site is nowat the P site.
Newpeptidebond Amino acid on tRNA at P site
forms a peptide bond withamino acid at A site.
P site
A site
Summary of movement of ribosome along mRNA
mRNAtRNA
Complete proteinGrowingprotein= Adenine
= Guanine
= Cytosine
= Uracil
U GGG AU A C
UGG AU A C
G C
U GGG AU A C
GAUU GGG AU A C U
GUU GGG A CU
C
2
3
4
56
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Somatic Cell Division - Mitosis
The cell cycle is a sequence of events in which a body cell duplicates its contents and divides in two
Human somatic cells contain 23 pairs of chromosomes (total = 46)
The two chromosomes that make up each pair are called homologous chromosomes (homologs)
Somatic cells contain two sets of chromosomes and are called diploid cells
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Cell Division
Interphase - the cell is not dividing- the cell replicates its DNA - consists of three phases, G1, S, and G2,
replication of DNA occurs in the S phase Mitotic phase - consists of a nuclear division (mitosis) and a cytoplasmic division (cytokinesis) to form two identical cells
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The Cell Cycle
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DNA Replication
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Nuclear Division: Mitosis
Prophase - the chromatin fibers change into chromosomes
Metaphase - microtubules align the centromeres of the chromatid pairs at the metaphase plate
Anaphase - the chromatid pairs split at the centromere and move to opposite poles of the cell;the chromatids are now called chromosomes
Telophase - two identical nuclei are formed around the identical sets of chromosomes now in their chromatin form
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Cytoplasmic Division: Cytokinesis
Division of a cell’s cytoplasm to form two identical cells
Usually begins in late anaphase The plasma membrane constricts at its
middle forming a cleavage furrow The cell eventually splits into two daughter
cells Interphase begins when cytokinesis is
complete
1
Pericentriolar materialNucleolusNuclear envelopeChromatinPlasma membraneCytosol
(a) INTERPHASE
CentriolesCentrosome:
all at 700xLM
1
LateEarly
Pericentriolar materialNucleolusNuclear envelopeChromatinPlasma membraneCytosol
Chromosome(two chromatidsjoined atcentromere
(a) INTERPHASE
(b) PROPHASE
CentriolesCentrosome:
Fragments ofnuclear envelope
Mitotic spindle(microtubules)
Kinetochore
2
all at 700xLM
Centromere
1
Pericentriolar materialNucleolusNuclear envelopeChromatinPlasma membraneCytosol
Metaphase plate
(a) INTERPHASE
CentriolesCentrosome:
(c) METAPHASE
2
3
LateEarly (b) PROPHASE
Fragments ofnuclear envelope
Mitotic spindle(microtubules)
Kinetochore
all at 700xLM
Chromosome(two chromatidsjoined atcentromere
Centromere
1
EarlyLate(d) ANAPHASE
Pericentriolar materialNucleolusNuclear envelopeChromatinPlasma membraneCytosol
Chromosome
(a) INTERPHASE
CentriolesCentrosome:
(c) METAPHASE
2
3
4
Cleavage furrow
LateEarly (b) PROPHASE
Fragments ofnuclear envelope
Mitotic spindle(microtubules)
Kinetochore
Metaphase plate
all at 700xLM
Chromosome(two chromatidsjoined atcentromere
Centromere
1
EarlyLate(d) ANAPHASE
Pericentriolar materialNucleolusNuclear envelopeChromatinPlasma membraneCytosol
(a) INTERPHASE
CentriolesCentrosome:
Cleavage furrow
(e) TELOPHASE
(c) METAPHASE
2
3
4
5
Cleavage furrow
LateEarly (b) PROPHASE
Fragments ofnuclear envelope
Mitotic spindle(microtubules)
Kinetochore
Metaphase plate
Chromosome
all at 700xLM
Chromosome(two chromatidsjoined atcentromere
Centromere
1
EarlyLate(d) ANAPHASE
Pericentriolar materialNucleolusNuclear envelopeChromatinPlasma membraneCytosol
(a) INTERPHASE
CentriolesCentrosome:
(f) IDENTICAL CELLS IN INTERPHASE
Cleavage furrow
(e) TELOPHASE
(c) METAPHASE
Cleavage furrow
2
3
4
5
6
LateEarly (b) PROPHASE
Fragments ofnuclear envelope
Mitotic spindle(microtubules)
Kinetochore
Metaphase plate
Chromosome
all at 700xLM
Centromere
Chromosome(two chromatidsjoined atcentromere
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Reproductive Cell Division
During sexual reproduction each new organism is the result of the union of two gametes (fertilization), one from each parent
Meiosis - reproductive cell division that occurs in the gonads (ovaries and testes) that produces gametes with half the number of chromosomes
Haploid cells - gametes contain a single set of 23 chromosomes
Fertilization restores the diploid number of chromosomes (46)
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Reproductive Cell Division Meiosis occurs in two successive stages:
meiosis I and meiosis II Each of these two stages has 4 phases:
prophase, metaphase, anaphase, and telophase
Summary - Meiosis I begins with a diploid cell and ends with two cells having the haploid number of chromosomes; in Meiosis II, each of the two haploid cells divides, the net result is four haploid gametes that are genetically different from the original diploid starting cell
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Cellular Diversity
The average adult has nearly 100 trillion cells
There are about 200 different types of cells
Cells come in a variety of shapes and sizes
Cellular diversity permits organization of cells into more complex tissues and organs
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End of Chapter 3
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