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Chapter 4
Cells: The Basic Units of Life
Chapter 4: Cells
Are All Cells Alike?
All living things are made up of cells. Some
organisms are composed of only one cell.
Other organisms are made up of many
cells.
Amoeba
Axolliti
Chapter 4: Cells
Are All Cells Alike?
1. What are the advantages of a one-celled
organism? Disadvantages?
 Advantage : Very small and high
SA:V ratio, nutrients enter easily and
reproduce very quickly
 Disadvantage: If cell is injured, death
of organism may result.
Chapter 4: Cells
Are All Cells Alike?
1.What are the advantages of an organism
that is made up of many cells?
 Advantages: specialized cells
increase capability of organism, more
complex.
Disadvantages: require more energy
A. The Discovery of the Cell
Cells are the basic unit of structure and
function and in living things.
Cell Theory states that:
– All living things are composed of cells.
– Cells are the basic units of structure and
function in living things.
– All cells come from preexisting cells.
A. Discovery of the Cell
How did early scientists come to these
conclusions?
1665 Hooke – observed
cork “cells” using an
early microscope
A. Discovery of the Cell
How did early scientists come to these
conclusions?
1674 Van Leeuwenhoek
Observed first living cells
A. Discovery of the Cell
How did early scientists come to these
conclusions?
1838 Schleiden – All plants have cells.
1839 Schwann – All animals have cells.
A. Discovery of the Cell
How did early scientists come to these
conclusions?
1855 Virchow – All cells come from existing
cells.
B. Exploring the Cell
Light microscope
Electron microscopes
B. Exploring the Cell
1. What are the advantages of using a light
microscope? Disadvantages?
 Advantage: Ability to observe living organisms
 Disadvantage: lower resolution of details
B. Exploring the Cell
2. What are the advantages of using an electron
microscope?
 Advantage: higher resolution
 Disadvantage: non-living organism
C. Cell Structure and Function
All Cells Share Certain Common Features:
• Cell membrane
• DNA
• Cytoplasm - portion of the cell outside the
nucleus
• Ribosomes
C. Cell Structure and Function
All Cells Share Certain Common Features:
MUST obtain energy and nutrients
MUST convert DNA into proteins
MUST keep certain biochemical reactions
separate
C. Cell Structure and Function
ALL cells are classified as either:
• Prokaryotic Cells
• Eukaryotic Cells
Prokaryotic and Eukaryotic Cells
Prokaryotes
•NO nucleus
•NO membrane-enclosed
organelles
•Small (MOST 1-10 μm)
•Unicellular
•Bacteria
Eukaryotes
Prokaryotes
•NO nucleus
•NO membrane-enclosed
organelles
•Small (MOST 1-10 μm)
•Unicellular
•Bacteria
Cell membrane
Contain DNA
Ribosomes
Cytoplasm
Eukaryotes
Prokaryotes
•NO nucleus
•NO membrane-enclosed
organelles
•Small (MOST 1-10 μm)
•Unicellular
•Bacteria
Cell membrane
Contain DNA
Ribosomes
Cytoplasm
Eukaryotes
•Nucleus
•Membrane-enclosed
organelles
•Larger than prokaryotes
(MOST 5-50 μm)
•Some unicellular
•Multicellular
•Protists, Fungi, Animals, and
Plants
•Cytoskeleton
Figure 7-5 Animal Cell
Ribosome
(attached)
Nucleolus
Nucleus
Ribosome
(free)
Cell
Membrane
Nuclear
envelope
Mitochondrion
Golgi apparatus
Rough
endoplasmic
reticulum
Centrioles
Smooth
endoplasmic
reticulum
Animal Cell
Figure 7-5 Plant Cell
Smooth endoplasmic
reticulum
Vacuole
Ribosome
(free)
Chloroplast
Ribosome
(attached)
Cell
Membrane
Cell wall
Nuclear
envelope
Nucleolus
Golgi apparatus
Nucleus
Mitochondrion
Rough endoplasmic reticulum
Plant Cell
Nucleus
Structure
– Surrounded by a nuclear envelope composed of two
membranes with thousands of nuclear pores
Function
– Contains cell’s DNA and with it the coded instructions
for making proteins and other important molecules
– Nuclear pores  allow material to move in and out of
the nucleus
BOTH plant and animals cells
Nucleolus
Structure
– Small, dense region inside the nucleus
Function
– Assembly of ribosomes
BOTH plant and animal cells
nuclear
envelope
nucleolus
chromatin
nuclear
pores
nucleus
nuclear
pores
Chromatin and Chromosomes
Ribosomes
Structure
– Small particles of RNA and protein
– Found in cytoplasm or attached to Rough ER
Function
– Assembly of proteins
BOTH plant and animal cells
mRNA
ribosomes
0.05 micrometers
Rough Endoplasmic Reticulum
Structure
– Internal membrane system that is continuous
with the nuclear envelope with attached
ribosomes  appears “rough”
Function
– Site where lipid components of cell membrane
are assembled, along with proteins and other
materials that are exported from the cell
BOTH plant and animal cells
Smooth Endoplasmic Reticulum
Structure
– Internal membrane system
– NO ribosomes on its surface  appears
“smooth”
Function
– Contains enzymes that synthesize membrane
lipids and detoxify drugs
BOTH plant and animal cells
Endoplasmic Reticulum
Golgi Apparatus
Structure
– Stack of closely apposed membranes
Function
– Modifies, sorts, and packages proteins and
other materials from the ER for storage in the
cell or secretion outside the cell
BOTH plant and animal cells
Golgi Apparatus
The Endomembrane System
Protein Modification
Lysosomes
Structure
– Small organelles filled with digestive enzymes
Function
– Digestion, or breakdown, of lipids,
carbohydrates, and proteins into small
molecules that can be used by the rest of the
cell
– Breaking down organelles that have outlived
their usefulness
BOTH plant and animal cells
Lysosomes
Lysosome
Food vacuole
Vacuoles
Structure
– Saclike structures
Function
– Store materials such as water, salts, proteins,
and carbohydrates
BOTH plant and animal cells
contractile
vacuole
collecting
ducts
central
reservoir
pore
Paramecium – Contractile
Vacuole
Contractile Vacuole
cytoplasm
central
vacuole
cell wall
plasma membrane
Mitochondria
Structure
– Enclosed by 2 membranes – outer and a
highly folded inner membrane
– Contain DNA
Function
– Convert the chemical energy stored in food
(glucose) into compounds that are more
convenient for cell use (ATP)  Cellular
Respiration
BOTH plant and animal cells
outer
membrane
inner
membrane
intermembrane
compartment
matrix
cristae
0.2 micrometer
Chloroplast
Structure
– Surrounded by 2 membranes – outer and inner
membrane
– Inside - large stacks of thylakoid membranes that
contain chlorophyll
– Contain DNA
Function
– Capture the energy from sunlight and convert it into
chemical energy (glucose)  Photosynthesis
ONLY found in plant cells
outer membrane
inner membrane
stroma
thylakoid
channel
interconnecting
thylakoids
granum
(stack of thylakoids)
1 micrometer
Organelle DNA
Why do mitochondria and chloroplasts
contain DNA but other organelles do
NOT?
Lynn Margulis - Professor in the
Department of Geosciences
University of Massachusetts
Cytoskeleton
Structure
– Network of protein filaments
Microfilaments – threadlike structures made of actin
Microtubules – hollow structures made of tubulin
Function
– Helps supports the cell
– Helps the cell to maintain its shape
– Involved in movement
BOTH plant and animal cells
Cell membrane
Endoplasmic
reticulum
Microtubule
Microfilament
Ribosomes
Mitochondrion
microtubules (red)
nucleus
microfilaments (blue)
Centrioles
Structure
– Composed of tubulin
– Found in a pair located near the nucleus
Function
– Help to organize cell division
ONLY found in animal cells
Centrioles
Cell Membrane
Structure
– Thin, flexible barrier that surrounds the cell
– Double-layered sheet composed of a lipid
bilayer, proteins, and carbohydrates – fluid
“mosaic” model
Function
– Regulates what enters and leaves the cell
– Provides protection and support
BOTH plant and animal cells
Cell Membrane
Outside
of cell
Proteins
Carbohydrate
chains
Cell
membrane
Inside
of cell
(cytoplasm)
Protein
channel
Lipid bilayer
Cell Wall
Structure
– Strong supporting layer that lies outside the cell
membrane
– Porous
– Made from fibers of carbohydrate (mostly cellulose) and
protein
Function
– Provides support and protection for the cell
ONLY found in plant cells
Eukaryotic Cells – Typical Plant Cell
Closing
Construct a Venn diagram comparing and
contrasting the structures found in a
typical plant cell and a typical animal cell.
Animal Cells
Plant Cells
EUKARYOTIC CELLS
Animal Cells
Plant Cells
Centrioles
Cell membrane
Ribosomes
Nucleus
Endoplasmic reticulum
Golgi apparatus
Lysosomes
Vacuoles
Mitochondria
Cytoskeleton
Cell Wall
Chloroplasts
In or Out?
How is a window screen similar to a cell
membrane? Read on to find out.
1. What are some things that can pass through a
window screen?
2. What are some things that cannot pass through
a window screen? Why is it important to keep
these things from moving through the screen?
3. The cell is surrounded by a cell membrane,
which regulates what enters and leaves the cell.
Why is it important to regulate what moves into
and out of a cell?
Section 7–3
Cell Boundaries
A.Cell Membrane
B.Cell Walls
C. Diffusion Through Cell Boundaries
1. Measuring Concentration
2. Diffusion
D. Osmosis
1.How Osmosis Works
2.Osmotic Pressure
E.Facilitated Diffusion
F.Active Transport
1. Molecular Transport
2. Endocytosis and Exocytosis
A. Cell Membrane
Structure
– Thin, flexible barrier that surrounds the cell
– Double-layered sheet composed of a lipid
bilayer, proteins, and carbohydrates – fluid
“mosaic” model
Function
– Regulates what enters and leaves the cell
– Provides protection and support
A. Cell Membrane
Phospholipid bilayer is shaped by the water
inside and outside the cell
– Polar phosphate “head” - hydrophilic
– 2 nonpolar fatty acid “tails” – hydrophobic
A. Cell Membrane
Proteins – channels/pumps that move
molecules in and out of the cell
Carbohydrates – act as “ID tags” or
cell markers
A. Cell Membrane
Outside
of cell
Proteins
Carbohydrate
chains
Cell
membrane
Inside
of cell
(cytoplasm)
Protein
channel
Lipid bilayer
B. Cell Wall
Structure
– Strong supporting layer that lies outside the cell
membrane in many plants, algae, fungi, and
prokaryotes
– Porous
– Made from fibers of carbohydrate (mostly cellulose)
and protein
Function
– Provides support and protection for the cell
Figure 7-5 Plant Cell
Smooth endoplasmic
reticulum
Vacuole
Ribosome
(free)
Chloroplast
Ribosome
(attached)
Cell
Membrane
Cell wall
Nuclear
envelope
Nucleolus
Golgi apparatus
Nucleus
Mitochondrion
Rough endoplasmic reticulum
Plant Cell
What substances are entering
and leaving the cell?
What substances are entering
and leaving the cell?
Water molecules
Food particles
Ions
Wastes
How do these substances enter
and exit the cell?
How do these substances enter
and exit the cell?
Cell membranes are selectively permeable
- some substances can pass through the
membrane while others cannot
Substances MUST enter and exit the cell
by:
How do these substances enter
and exit the cell?
Cell membranes are selectively permeable
- some substances can pass through the
membrane while others cannot
Substances MUST enter and exit the cell
by:
– Diffusion
– Osmosis
– Facilitated Diffusion
– Active Transport
C. Diffusion Through Cell Boundaries
When molecules of a substance move from an
area of high concentration to an area of low
concentration until equilibrium is reached
– Concentration – mass of solute in a given volume of
solution
12 grams of salt in 3 Liters of water  12g/3 L or 4 g/L salt
solution
70% salt solution  70% salt / 30% water
– Equilibrium – same concentration on both sides of the
membrane
C. Diffusion Through Cell Boundaries
Depends on random particle movements
Substances diffuse across membranes without
the use of energy
Simple diffusion
lipid-soluble molecules
(O2, CO2, H2O)
(extracellular fluid)
(cytoplasm)
drop of dye
water molecule
D. Osmosis
Diffusion of water molecules through a
selectively permeable membrane from an
area of high water concentration to an
area of low water concentration
Vital to the survival of the cell
Figure 7-15 Osmosis
D. Osmosis
When comparing solutions, the
Hypertonic solution
Hypotonic solution
Isotonic solutions
D. Osmosis
When comparing solutions, the
Hypertonic solution has more solute
Hypotonic solution
Isotonic solutions
D. Osmosis
When comparing solutions, the
Hypertonic solution has more solute
Hypotonic solution has less solute
Isotonic solutions
D. Osmosis
When comparing solutions, the
Hypertonic solution has more solute
Hypotonic solution has less solute
Isotonic solutions have equal concentrations of
solute
Figure 5.8 Osmosis Modifies the Shapes of Cells
D. Osmosis
Osmotic pressure – increase in pressure inside
a cell due to osmosis
High osmotic pressure can cause a cell to
burst
–Plant cell walls prevent the cell from
bursting
–Contractile vacuoles in protists pump out
excess water
cytoplasm
central
vacuole
cell wall
plasma membrane
contractile
vacuole
collecting
ducts
central
reservoir
pore
Paramecium – Contractile
Vacuole
Contractile Vacuole
E. Facilitated Diffusion
Process in which molecules of a
substance are transported across a
membrane by a protein
Movement of molecules from an area of
high concentration to an area of low
concentration through the protein
Facilitated Diffusion
Glucose
molecules
High
Concentration
Cell
Membrane
Low
Concentration
Protein
channel
Diffusion, osmosis, and facilitated diffusion
are forms of passive transport
PASSIVE TRANSPORT – cell transport that
does not require the cell to use energy
F. Active Transport
Movement of substances across the cell
membrane against the concentration
difference  from an area of low
concentration to an area of high
concentration
Requires the use of energy (ATP)
Figure 7-19 Active Transport
Molecule to
be carried
Energy
Molecule
being carried
F. Active Transport
Sodium-Potassium Pump – moves sodium
ions out of cells and potassium ions into
cells against the concentration difference
Proton Pumps – move protons across cell
membranes causing a large number of
protons to accumulate on one side of the
membrane
F. Active Transport
Movements of the cell membrane require
energy
– Endocytosis – process of bringing particles
into a cell using extensions of the cell
membrane
Pinocytosis “cell drinking”
Phagocytosis “cell eating”
– Exocytosis – material within sacs inside the
cell is discharged from the cell
Endocytosis Exocytosis Video
From Simple to More Complex
Many multicellular organisms have structures called
organs that have a specific function and work with other
organs. Working together, these organs carry out the
life processes of the entire organism.
1. Some activities cannot be performed by only one
person, but need a team of people. What type of
activity requires a team of people to work together in
order to complete a task?
2. What do you think are some characteristics of a
successful team?
3. How is a multicellular organism similar to a
successful team?
Section 7–4
The Diversity of Cellular Life
A.Unicellular Organisms
B.Multicellular Organisms
1.
Specialized Animal Cells
2.
Specialized Plant Cells
C. Levels of Organization
1.
Tissues
2.
Organs
3.
Organ Systems
Section 7-4:
Diversity of Cellular Life
Remember that ALL living things:
–
–
–
–
–
–
–
–
Are composed of cells
Reproduce
Contain DNA
Grow and develop
Obtain and use materials and energy
Respond to their environment
Maintain a stable internal environment
Change over time
However, ALL living things are NOT the same.
WHY???
A. Unicellular Organisms
Organism composed of only one cell
B. Multicellular Organisms
Organism composed of many cells
How are the cells in a unicellular
organism different from the cells in a
multicellular organism?
How are the cells in a unicellular
organism different from the cells in a
multicellular organism?
In unicellular organisms, the organism is a single
cell that MUST carry out ALL the functions
necessary for life.
How are the cells in a unicellular
organism different from the cells in a
multicellular organism?
In unicellular organisms, the organism is a single
cell that MUST carry out ALL the functions
necessary for life.
In multicellular organisms, each cell carries out
only one of a few particular functions in the
organism. The cells are specialists!!!
How are the cells in a unicellular
organism different from the cells in a
multicellular organism?
In unicellular organisms, the organism is a single
cell that MUST carry out ALL the functions
necessary for life.
In multicellular organisms, each cell carries out
only one of a few particular functions in the
organism. The cells are specialists!!!
Cell specialization - cells throughout a
multicellular organism can develop in different
ways to perform different tasks
Specialized
Animal Cells
Red blood cells carry O2 throughout
the body
Pancreatic cells produce insulin and
digestive enzymes
Muscle cells contract and relax to
move parts of the
body
Specialized Plant Cells
Guard cells - control the exchange of CO2,
O2, H2O vapor, and other gases by
opening and closing the stomata on the
undersides of leaves
Leaf cross section
Vein
Mesophyll
Stomata
Figure 10.3
CO2
O2
C. Levels of Organization
Cells  Tissues  Organs  Organ
Systems
Tissue – group of similar cells that group
together to perform a similar function
Organ - groups of tissues that work
together
Organ System - group of organs that work
together to perform a specific function
Levels of Organization
Muscle cell
Smooth muscle tissue
Stomach
Digestive system
C. Levels of Organization
WHY ???
C. Levels of Organization
WHY ???
Creates a division of labor that makes
multicellular life possible