Download Chapter 5: Cell Structure and Function

Chapter 5:
Cell Structure and Function
5-1 The Cell Theory
The Cell Theory
All living things are made of cells
 Cells are the basic units of structure and
function in living things
 Anton van Leeuwenhoek, a Dutch
biologist, was the inventor of the
microscope

– Enabled him to see things that no one had
ever seen before
The Cell Theory
Van Leeuwenhoek’s work interested other people
– Robert Hooke examined slices of cork
– Saw that it was composed of thousands of tiny chambers
– Called these chambers cells
 Over the next 200 years, other scientists began to discover
that cells were not only found in plants but in other living
things too
– Robert Brown—1833—discovered the nucleus
– Matthias Schleiden—1838—stated that all plants are
made of cells
– Theodore Schwann—1839—all animals are made of cells
– Rudolf Virchow—1855—all cells arise from preexisting
cells

The Cell Theory

The observations of these scientists are
summarized into the cell theory
– 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.
Chapter 5:
Cell Structure and Function
5-2: Cell Structure
Cell Structure

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Enormous variety in the size and shape of
cells
Despite differences in size and shape, there
are certain structures that are common to
most cells
The cells of animals, plants, and related
organisms have three basic structures:
the cell membrane, or boundary of the
cell; the nucleus, or control center; and
the cytoplasm, or material between the
cell membrane and the nucleus
Cell Membrane

All cells are separated from their
surroundings by a cell membrane
– Regulates what enters and leaves the cell
– Aids in protection and support of the cell

It must communicate with other cells, take in
food and water, and eliminate wastes
 Composed of several kinds of molecules
– Lipids (bilayer)
– Proteins
– Carbohydrates
Cell Wall

In organisms such as plants, algae, and
some bacteria, the cell membrane is
surrounded by a cell wall
– Helps protect and support the cell
– Very porous—allows water, oxygen, carbon
dioxide, and other substances to pass
through
– Made of cellulose
Nucleus

In many cells we can see a large, dark
structure, called the nucleus
– Contains DNA

Prokaryotes are organisms whose cells lack
nuclei
– Bacteria
– Small and unicellular

Eukaryotes are organisms whose cells
contain nuclei
– Mostly multicellular
Nuclear Envelope

Surrounding the nucleus are two membranes
that form the nuclear envelope
– Form the boundary around the nucleus
• Contains dozens of nuclear pores
allowing substances to flow in and out of
the nucleus
Nucleolus

Most nuclei contain a small region called
the nucleolus that is made up of RNA and
proteins
– The structure in which ribosomes are
made
• Aid in the production of proteins within
the cell
Chromosomes

The DNA in the nucleus of eukaryotic
cells is attached to special proteins and
forms large structures called
chromosomes
– Contain the genetic information that must
be passed to each new generation of cells
Cytoplasm
The cytoplasm is the area between the
nucleus and the cell membrane
 Contains many important structures

Chapter 5:
Cell Structure and Function
5-3: Cytoplasmic Organelles
Cytoplasmic Organelles
The structures inside the cytoplasm are
generally called organelles
 An organelle is a tiny structure that
performs a specialized function in
the cell.

– Each organelle has a special job
Mitochondria and Chloroplasts:
Power Stations
All living things require energy
 The mitochondrion and the
chloroplast are key organelles that
change energy from one form to
another

– Mitochondria change chemical energy in
food into compounds that the cell can use
– Chloroplasts trap solar energy and convert
it into chemical energy
Mitochondria and Chloroplasts:
Power Stations
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Mitochondrion
– Contains two special membranes
• Outer membrane surrounds the organelle
• Inner membrane has many folds that increase the
surface area of the mitochondrion
Chloroplast
– Found only in plant cells and algae
– Three membranes
• Two envelope-like membranes
• Third membrane where the sun’s energy is
changed into chemical energy
Ribosomes: Protein Factories

Ribosomes are the structures in which
proteins are made
– Made of RNA and protein
– Some are attached to membranes; some
are found free in the cytoplasm
– Among the smallest organelles
Endoplasmic Reticulum and Golgi
Apparatus: Manufacturers and Shippers

Many cells are filled with a complex network of
sacs known as the endoplasmic reticulum, or
ER
– Transports materials through the inside of the
cell
– Two types:
• Smooth—no ribosomes attached
• Rough—ribosomes attached—involved in
the synthesis of proteins
Endoplasmic Reticulum and Golgi
Apparatus: Manufacturers and Shippers
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Proteins are often modified by special enzymes
that attach carbs and lipids to them
In most cases, the proteins are first moved into
special compartments known as the Golgi
apparatus
– Flattened stack of membranes
– After modification, the proteins may then be
released from the cell
**The Golgi apparatus modifies, collects,
packages, and distributes molecules made at
one location of the cell and used at another**
Lysosomes: Cleanup Crews
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When a cell encircles a particle, the cell
membrane forms a pocket around the foreign
material
The foreign material must now be digested,or
broken down
– Lysosome
• Contain chemicals and enzymes necessary
for digestion
• Formed by the Golgi apparatus
• Plants cells do not have lysosomes
Vacuoles and Plastids: Storage
Tanks

Vacuoles store materials such as water,
salts, proteins, and carbohydrates
 Plastids are plant organelles that may take
many forms, one of which is the chloroplast
– Involved in the storage of food and
pigments
– Examples:
• Leukoplasts—store starch
• Chromoplasts—store pigments
Cytoskeleton: Framework

Most cells are capable of some type of
movement
 Cytoskeleton – framework of filaments
and fibers that support cell structure and
drive cell movement
– Microfilaments-long, thin fibers that function in
the movement and support of the cell
– Microtubules-hollow tubes made out of
proteins
• Cilia and flagella
Chapter 5:
Cell Structure and Function
5–4
Movement of Materials
Through the Cell
Membrane
Diffusion
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The driving force behind the movement of many
substances across the cell membrane is called
diffusion
Diffusion is the process by which molecules of a
substance move from areas of higher
concentration of that substance to areas of lower
concentration
Several factors determine whether diffusion occurs
across a membrane
– Equilibrium point is reached
– Permeability
• Most membranes are known as selectively permeable
Osmosis

Water molecules pass through most cell
membranes very rapidly
 The diffusion of water molecules through a
selectively permeable membrane is called
osmosis
 The force exerted by osmosis, or osmotic pressure,
tends to move water across membranes from a
more dilute solution into a more concentrated
solution
 If water moves in too freely, the volume of a cell will
increase until the cell becomes swollen and bursts
like an over inflated balloon
Osmosis

Cells deal with the problem of osmotic
pressure in a variety of ways
– Cells of many organisms do not come into
contact with fresh water
– Plant cells and bacteria have cell walls that
prevent the cells from expanding
– Some cells pump out the water with a
contractile vacuole
Facilitated Diffusion

Osmosis and diffusion are forms of passive transport
across the cell membrane because energy is not needed
 But, many molecules are transported across a membrane
in the direction of lowest concentration by a carrier protein
– Facilitated diffusion
• Is fast, specific, and does not require energy…it is
still driven by diffusion
• Can only occur if a concentration distance exists
cross that membrane
Active Transport

Active transport is an energy-requiring process that enables material
to move across a cell membrane against a concentration difference
 Two types
– Individual molecules are carried through membrane-associated
pumps
– Large amounts of materials are transported through movements of
the cell membrane
• Endocytosis
– Process of taking material into the cell by means of
infoldings, or pockets, of the cell membrane
• Phagocytosis
– Process that occurs when large particles are taken in by
endocytosis
• Pinocytosis
– Process in which cells take in liquid and pinch off to form
vacuoles within the cell
• Exocytosis
– Process that occurs when large materials are removed
from the cell
Chapter 5:
Cell Structure and Function
5–5
Cell Specialization
Cell Specialization

Cell specialization is one of the key
characteristics of cells in a multicellular
organisms
 By cell specialization, we mean that cells
are often uniquely suited to perform a
particular function within the organism
– Movement
– Make products
Chapter 5:
Cell Structure and Function
5–6
Levels of Organization
Levels of Organization

The levels of organization in a
multicellular organism include cells,
tissues, organs, and organ systems
that make up the organism
Tissues

In multicellular organisms, cells – the first level of
organization – are organized in specialized
groups called tissues
– A group of similar cells that perform similar
functions
– Most animals, which are multicellular
organisms, have four main types of tissues
• Muscle, epithelial, nerve, and connective
tissue
Organs
 An
organ is a group of tissues that
work together to perform a specific
function
 Many types of tissue may be used to
form a particular organ
 Each tissue performs an essential
task to help the organ function
successfully
Organ Systems
 An
organ system, or a group of
organs, works together to perform a
certain function
 There are 10 organ systems in the
body including the muscular system,
circulatory system, and digestive
system