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Cells and Their Functions


... classifications of cells, one of which we are really concerned with in zoology. The first two lack nuclei and other organelles. ... – PowerPoint PPT presentation

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Title: Cells and Their Functions

Cells and Their Functions
  • Think back to biology, what is a cell?
  • Cell - the functional unit of life in all living
  • This is the area where all chemical reactions and
    reproduction takes place.
  • They are the smallest independent unit of life.

  • There are three classifications of cells, one of
    which we are really concerned with in zoology.
  • The first two lack nuclei and other organelles.
  • These two types of cells are usually referred to
    as prokaryotes.
  • They are in the domains Archaea and Eubacteria.

  • The type of cell we are most concerned with is
    the Eukaryotic cell.
  • These cells have a membrane bound nucleus that
    contains the DNA.
  • They also contain organelles that are responsible
    for specific tasks in the cell.

Eukaryotic Cells
  • Eukaryotic cells have specialized structures
    called microfilaments and microtubules.
  • These structures are arranged in the
    cytoskeleton, a structure which give shape to the
    cell and allows for intracellular movement.
  • All eukaryotic cells have three basic parts
  • Plasma membrane
  • Cytoplasm
  • Nucleus

Eukaryotic Cells
  • The plasma membrane is the outer boundary of the
  • Its purpose is to allow for the passage of
    substances in and out of the cell.
  • It is semi-permeable and is composed of protein
    molecules dispersed throughout a phospolipid
  • There are also special receptors for larger

Eukaryotic Cell
  • The cytoplasm is the semi-fluid (think jello)
    portion of the cell.
  • It encases, protects, and cushions the internal
  • It is essentially the space that is not an

Eukaryotic Cell
  • The final structure is the nucleus.
  • The nucleus is where everything is controlled.
  • The nucleus has its own boundary from the rest of
    the cell.
  • It contains the chromosomes which are essential
    to reproduction of the cell.

Cell Size
  • The majority of cells are to small to see without
    the aid of a microscope.
  • There are a few reasons for this small size.
  • First, the nucleus must be able to maintain
    control of the cytoplasm.
  • Second, the surface area of the cell membrane
    cannot keep up with increases in volume.
  • Finally, the amount of DNA is huge. To package
    it into the cell requires a significant decrease
    in size.

Cell Membranes
  • The membrane is a double layer of lipids and
  • It is also fluid rather than solid.
  • The lipid layer contains a phosporus unit which
    gives it the name of a phospholipid.
  • This phospholipid layer acts like a sea where the
    proteins float like icebergs.

Cell Membranes
  • The model of the cell membrane is referred to as
    the fluid-mosaic model.
  • The fluid refers to the fluid make-up of the
    membrane, while the mosaic refers to the many
    different proteins in the bilayer.
  • The fact that the membrane is fluid means that it
    is constantly in a state of flux and therefore
    always changing while retaining its uniform

Cell Membranes
  • The fluid-mosaic model has a few important
  • The phospholipids have one polar end and one
    non-polar end.
  • Cholesterol is present in the plasma and
    organelle membranes to make them less permeable
    to water soluble substances.
  • The proteins may be located on the inner or outer
    surface of the membrane or embedded within it.
  • Carbohydrates (glycoproteins) and lipids
    (glycolipids) can unite with proteins on the cell

Cell Membranes
  • Cell membranes serve six functions
  • Regulate material movement.
  • Separate the inside from the outside.
  • Separate various organelles.
  • Provide surface area for certain reactions.
  • Separate cells from one another.
  • Serve as a site for receptors.

Cell Membranes
  • The cell membrane has a particular quality called
    selective permeability.
  • This means that the membrane can allow certain
    substances in and keep some substance out.
  • This allows the cell to maintain what is known as
  • The maintenance of a relatively stable constant
    environment despite changes in the cells external

Cell Membranes
  • There are a number of ways in which cells move
    materials across the membrane.
  • Some may involve the use of the cells energy
    while others are require no energy consumption by
    the cell.

Simple Diffusion
  • Cells are in constant, random motion as long as
    the temperature is above absolute zero.
  • This movement occurs from areas where there are a
    lot of cells to areas where there are few cells.
  • This will continue until they reach equal
  • This process is what we call simple diffusion.
  • This accounts for the majority of short distance
    transport of movement in and out of the cell.

Facilitated Diffusion
  • Polar molecules are not soluble in liquids.
  • Therefore, they must have a means of moving
    across the cell membrane.
  • The molecules may diffuse through protein
    channels in the cell membrane.
  • These channels offer direct passage through the
    membrane without coming into contact with the
    hydrophobic layer of the membrane.
  • Some materials may need assistance passing across
    the membrane.
  • This help in movement is referred to as
    facilitated diffusion.

  • When water moves across the membrane, is carries
    a special name - osmosis.
  • Osmosis, like the previous means of movement is
    from high to low.

  • With osmosis, there are certain terms we are
    concerned with.
  • Tonicity refers to the amount of solutes in water
    in and out of the cell.
  • With tonicity, there are varying levels of
    concentration to describe the tonicity.
  • Isotonic the concentration is the same in and
  • Hypertonic the concentration is higher outside
    than in.
  • Hypotonic the concentratin is lower outside the
    cell than inside.

  • Small molecules can be forced through the
    membrane by hydrostatic pressure.
  • Larger molecules (proteins) will remain in place
    when filtration occurs.
  • Filtration is common in humans and some animals
    in the kidney.
  • This is the first step in the formation of urine
    or other waste products.
  • Increased blood pressure forces the water out of
    the nephron in the kidney causing increased urine

Active Transport
  • When a cell needs to move things against its
    concentration gradient, energy in the form of ATP
    is required.
  • This type of movement of substances is referred
    to as active transport.
  • Similar to facilitated diffusion except the
    carrier protein must use energy from the cell to
    move the molecules from lower concentrations to

Active Transport
  • There are a number of different active transport
    mechanisms cells use.
  • One of the most common is the sodium-potassium
  • The type of active transport helps to maintain
    the balance of sodium and potassium ions in the
    cells environment.

Endocytosis and Exocytosis
  • Endocytosis and Exocytosis involve the bulk
    movement of materials across the membrane.
  • There are three types of endocytosis
  • Pinocytosis nonspecific uptake of small
    droplets of external fluid.
  • Phagocytosis cell takes in solid material
    rather than liquid.
  • Receptor mediated endocytosis receptor protein
    recognizes an extracellular molecule and binds
    with it.
  • Many times these reactions cause the membrane to
    form a dent and surround the material with a

Endocytosis and Exocytosis
  • One of the organelles you studied in biology is
    the Golgi apparatus.
  • Its functions is to package proteins and other
    molecules .
  • These materials are then excreted by the cell
    through exocytosis.

Endocytosis and Exocytosis
Cell Components
  • We have already discussed the function of the
  • However, cytoplasm has two parts
  • The cytomembrane system
  • The cytosol

Cell Components
  • The cytomembrane system consists of the well
    defined structures we will talk about shortly.
  • The cytosol suspends these structures and also
    contains some dissolved materials.

Cell Components
  • The next structure we are going to discuss is the
  • The site where protein synthesis occurs.
  • They are composed mostly of proteins and a
    special kind of RNA (rRNA).
  • Some are attached to another structure and some
    float freely in the cytoplasm.

Cell Components
  • Cells need to transport materials throughout the
  • They also need a place to store enzymes and
  • This structure is the endoplasmic reticulum.

Cell Components
  • The endoplasmic reticulum (ER) is a series of
    tubules and sacs that reach throughout the
  • The ER originates at the nuclear envelope and
    travels to the plasma membrane.
  • ER also serve as an attachment point for the
    ribosomes - rough ER.
  • ER without ribosomes is called smooth ER.
  • Smooth ER functions to produce lipids, detoxify
    the cell, and also ion storage for muscles.

Cell Components
  • We have already touched upon the packaging unit
    for the cell, the Golgi apparatus.
  • A series of membranes associated with the ER.
  • Materials are passed from the ER to Golgi.
  • These substances are usually proteins
  • The Golgi before packaging and sorting marks the
    proteins for identification.

Cell Components
  • Lysosomes contain enzymes that are used in
    digesting materials for the cell.
  • The enzymes are made by the ER.
  • They are then transported to the Golgi and then
    made into lysosomes or vessicles that fuse with

Cell Components
  • Cells need a means by which to produce energy.
  • The mitochondrion are where this energy
    production takes place.
  • Interestingly, this structure contains its own

Cell Components
  • Cells need a means by which to connect organelles
    to one another.
  • This connecting occurs via the cells
  • The cytoskeleton contains three major components
  • Microtubules
  • Intermediate filaments
  • Microfilaments

Cell Components
  • Cells must move and also move materials to them.
  • Cilia and Flagella account for these movements.
  • Flagella are 5-20 times longer than cilia and
    move in a different fashion than cilia.

The Nucleus
  • The big daddy of the cell, the one thing it cant
    live without, the control center, this is the
  • The nucleus has two functions
  • Direct chemical reactions
  • Storage of genetic material

The Nucleus
  • Each nucleus has three main components
  • The nuclear envelope which seperates the nucleus
    from the rest of the cell.
  • Chromosomes which contain the information in the
    form of DNA needed for heredity.
  • The Nucleolus is present in non-dividing cells
    and serves as the pre-assembly point for

Levels of Organization
  • Animals have five levels of organization
  • Cells
  • Tissues
  • Organs
  • Organ systems
  • Animal
  • As we move up each level, it becomes more complex.

Tissue Types
  • Four main types of tissues
  • Epithelial covers or lines a structure
  • Connective support and bind
  • Muscle movement of body and appendages
  • Nervous communication within the body
  • All of these tissues have a distinct appearance
  • Differences in color, texture, and location.

Tissue Types
  • Epithelial Tissue
  • Specialized for covering the internal and
    external body structures
  • Comprised of tightly packed cells
  • Classified into two groups
  • Simple epithelial
  • Stratified epithelial

Tissue Types
  • Connective Tissue
  • Two main types
  • Loose connective tissue
  • Adipose tissue (fat)
  • Fascia
  • Fibrous connective tissue
  • Tendons
  • Ligaments
  • Can be liquid or solid
  • Bone
  • Fat
  • Blood
  • Used in support and compartmentalization

Tissue Types
  • Muscle Tissue
  • Used in movement of the body and appendages
  • Three types
  • Skeletal
  • Attached to bones
  • Smooth
  • Stomach, intestines
  • Cardiac
  • Heart

Tissue Types
  • Nervous Tissue
  • Composed of several different types of cells
  • Neurons
  • Impulse conduction
  • Neuroglia
  • Protection, support, and nourishment
  • Peripheral glial cells
  • Help support the periphereal nervous system
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