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Life and Cells
Characteristics of Life
 Organisms
are living things
 All share similar life functions
 Life functions: the many activities carried out by
all living things
 Metabolism: all the chemical reactions that
occur within a living thing
 Homeostasis: the maintenance of a stable
internal environment
Scientists
 Robert
Hooke : looked at a thin slice of cork
(oak cork) through a compound microscope
and observed tiny, hollow, roomlike
structures and called these structures 'cells'
because they reminded him of the rooms that
monks lived in. He only saw the outer walls
(cell walls) because cork cells are not alive.
Anton van Leeuwenhoek (around the same
time as Hooke, 1676) He observed living
cells called bacteria, which are single-cell
organisms.
.
Matthias Schleiden (1838) who viewed plant parts under a microscope and
discovered that plant parts are made of cells.
Theodor Schwann (1839) viewed animal parts under a microscope and
discovered that animal parts are also made of cells. This helped propel the
idea that cells were common building blocks of normal and possibly
abnormal bodies.
Rudolph Virchow (1855), who stated that all living cells come only from
other living cells.
Robert Brown: Discovered an organelle called the nucleus, at the center of
most cells.
 Louis
Pasteur: Proved that tiny microscopic
organisms (microbes) cause disease.
 Pasteruization: sterilizing food to inhibit
microbe growth and preserve shelf life.
Life Functions
 1.
Nutrition: obtaining materials from the
environment and processing them for use
 2. Transport: absorption and movement of
materials in an organism
 3. Respiration: processes that provide the
energy needed for life
 4. Excretion: removal of waste products
 5. Synthesis: formation of large molecules from
smaller ones
 6.
Regulation: the control and coordination of
an organism’s activities
 7. Growth: an increase in size and/or cell
number
 8. Reproduction: the production of new
individuals to allow the species to survive
Chemical Composition
 Organisms
share similar chemical compositions
 Made of mostly carbon, hydrogen, nitrogen, and
oxygen
 Organic molecules contain both carbon and
hydrogen

Ex: glucose (C6H12O6)
 Inorganic
molecules do not contain both carbon
and hydrogen

Ex: carbon dioxide (CO2), water (H2O)
Organization
 Organisms
share the same basic building plan
 Most cells contain specialized structures called
organelles
 The cell is the smallest structural and functional
unit of life
 Organisms can either be single-cellular or
multicellular
 In multicellular organisms, groups of specialized
cells are organized into tissues
 Different
kinds of tissues can be combined to
make an organ that performs a life function
 Organs work together to form an organ system
that also performs a life function
Levels of organization:
Atom – Molecule – organelle –
cell – tissue – organ –
organ systems – organism
Cells
 Two
types of cells: prokaryotic and eukaryotic
 Prokaryotic = bacteria

Do not have a nucleus or other organelles
 Eukaryotic

= animal and plant cells
Have a nucleus and other organelles
Cell Theory
 1.
All organisms are made up of one or more
cells.
 2. The cell is the basic unit of structure and
function of all living things.
 3. All cells arise from previously existing cells.
Exceptions to the Cell theory
 Exception
to "every cell came from another
cell": The first cell ever.
(Controversial)
 Exception to "a cell is the smallest unit of
life"/"all life is made of cells": viral matter.
 Mitochondria and Chloroplast contain their own
DNA so they can reproduce on their own.
Theory: The cell is a unit and will reproduce as a
unit
Cytoplasm
 The
cytoplasm is the jelly-like substance inside
the cell
 Contains specialized structures
 Transports materials
 Most of the reactions of metabolism occur here
Nucleus
nucleus controls the cell’s metabolism and
stores genetic information
 Genetic information = DNA in chromosomes
 Often found in the center of the cell
 Contains a dark area called the nucleolus
 The

Makes ribosomes
 Protected
by an outer covering called the nuclear
envelope
 Nuclear envelope contains small openings called
nuclear pores
Vacuoles
 Vacuoles
are storage sacs in the cytoplasm
 Surrounded by a membrane
 Contain food, water, or wastes
 May be specialized to digest food or pump
excess water out of the cell
 Larger in plant cells than in animal cells
 Contractile Vacuole: A specialized organelle
designed to pump out excess water. Useful only
in fresh water protozoa. Salt water protozoa do
not need them. Salt dehydrates the cell.
Endoplasmic Reticulum
 The
endoplasmic reticulum (ER) is a series of
interconnecting channels that makes lipids
 Lipids = fats
 Can also transport proteins
 Rough ER = small structures called ribosomes
are attached
 Smooth ER = no ribosomes
Ribosomes
 Ribosomes
are tiny structures that make
proteins
 Can be floating free in the cytoplasm (“free
ribosome”)
 Can be attached to the rough ER
Golgi Apparatus
 The
Golgi apparatus (or Golgi complex)
processes proteins and lipids
 Processes = modifies and packages
 Acts as the cell’s post office
 Made of membrane-bound sacs that look like a
stack of curved plates
Mitochondria
 Singular,
mitochondrion; plural, mitochondria
 Uses enzymes to extract energy from nutrients
 Most of the cell’s energy comes from the
mitochondria
 Energy is called ATP (adenosinetriphosphate)
 “Powerhouse of the cell”
Chloroplasts
 Chloroplasts
are only found in plant cells
 Contain the green pigment chlorophyll
 Chlorophyll captures light, which plants use to
make their own food

Photosynthesis
Other Organelles
 Lysosomes
are sacs that contain digestive
enzymes
 Centrioles are cylindrical structures involved in
cell reproduction

Found only in animal cells
Mitochondrion
Golgi
apparatus
Nucleolus
DNA
Smooth ER
Centrioles
Lysosome
Rough ER
Cytoplasm
Nucleus
Vacuole
Ribosomes
Cell membrane
Nuclear pore
Nucleus
Cell wall
Nuclear
pore
Cell membrane
Golgi
apparatus
Ribosomes
Lysosome
Rough ER
Cytoplasm
Vacuole
Mitochondrion
Smooth ER
Chloroplast
The Cell Membrane
 The
cell membrane (a.k.a. plasma membrane)
is a thin bilayer that surrounds the outside of the
cell Bilayer = double layer
 Separates the inside of the cell from the
environment
 Allows the cell to communicate with its
surrounding and respond to chemical signals
 Regulates the movement of materials in and out
of the cell
 Both
animal and plant cells have a cell
membrane
 Plant cells also have a cell wall on the outside of
the cell membrane
 The cell wall is made of cellulose and gives the
plant cell strength and rigidity
 Cell wall is non-living
Structure of the Cell Membrane
 Made
of phospholipids
 Phospholipids have a head and a tail
 Heads are hydrophilic

“Water-loving”; like to be in contact with water
 Tails

are hydrophobic
“Water-hating”; avoid contact with water
Phosphate head
Fatty acid tails
Hydrophilic
Hydrophobic
 Heads
are on the outside and tails are on the
inside
 Heads are in contact with water
 Tails are protected from water
 Proteins are also in the membrane
 Some proteins go through the entire bilayer;
others only go through one layer
 This structure of the cell membrane with proteins
floating in a double-layer sea of phospholipids is
called the fluid mosaic model
Proteins
Bilayer
Hydrophilic heads
Hydrophobic tails
Hydrophilic heads
Transport Across the Membrane
 The
cell membrane is selectively permeable
 It only lets certain substances in or out of the cell
 Some small molecules can pass through the
bilayer
 Others use proteins to cross the membrane
Passive Transport
 Passive
transport requires no energy
 Two forms: diffusion and osmosis
 Diffusion: the movement of molecules from an
area of high concentration to an area of low
concentration (movement is with the gradient
high to low)
 A concentration gradient occurs when there
are different amounts of the same substance on
either side of a membrane
There is a
concentration
gradient here.
There are more
squares outside
the cell than
inside the cell.
In diffusion, substances
move from high
concentration to low.
Some of the
squares from
outside the cell
moved inside.
 Osmosis:
the movement of water molecules
from a high concentration to a low concentration
 Water loves to dilute substances
Plasmolysis
 When
plant cells lose water from osmosis, the
contents of the cells shrink
 The plant cell’s cell membrane will peel away
from the cell wall

This is plasmolysis
 Occurs
when you place plant cells in a
concentrated salt solution
 Water leaves the cell to dilute the outside salt
Normal plant cells
Plasmolysis
 Plasmolysis
can be reversed if you put the cells
in fresh water
 Water moves back into the cell to dilute its
contents
 If animal cells take in too much water, they can
burst

 If
This happens if they are put in a solution that contains
more water than the cell does (distilled water)
animal cells lose too much water, they shrivel
Normal blood cell
Tap water
Took in too much Lost too much
water
water
Distilled water
(pure water)
Salt solution
Active Transport
 In
active transport, substances move from
areas of low concentration to areas of high
concentration ( against the gradient)
 This requires energy
 Special proteins in the cell membrane act as
pumps
 The protein pumps use energy to move
substances against their concentration gradient
There are more
triangles in the cell
than outside the cell.
The protein pump
(blue) is going to use
energy to pump more
triangles into the cell.
Energy was used to
force the triangles
into the cell.
Energy
Differences between Plant and
Animal cells
 1.
Plant cells have a cell wall, animal cells do
not.
 2. Plant cells have large vacuoles for water
storage and chloroplasts for photosynthesis
animal cells do not.
 3. Plant cells are squared off and green in color
animal cells are not.
 4. Animal cell have centrioles, plant cells do not.
Nucleus
Cell wall
Nuclear
pore
Cell membrane
Golgi
apparatus
Ribosomes
Lysosome
Rough ER
Cytoplasm
Vacuole
Mitochondrion
Smooth ER
Chloroplast