Cells Cells and the Cell Theory Robert Hooke was the

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					Cells and the Cell Theory

Robert Hooke was the first
person to describe cells. In         February 23,
1665, he built a microscope
to look at tiny objects. One
day, he looked at a thin slice
of cork. Cork is found in the
bark of cork trees. The cork
looked like it was made of
little boxes. Hooke named
these boxes cells, which
means “little rooms” in Latin.
                                 Cell Theory
Hooke’s cells were really the    Objectives
outer layers of dead cork        Explain the Cell Theory.
cells. Hooke’s microscope
and his drawing of the cork
cells.                           1
                                    2                    February 23, 2012

   The Cell Theory
   Almost 200 years passed before scientists concluded
    that cells are present in all living things. Scientist Matthias
    Schleiden (mah THEE uhs SHLIE duhn) studied plants. In
    1838, he concluded that all plant parts were made of
    cells. Theodor Schwann (TAY oh dohr SHVAHN) studied
    animals. In 1839, Schwann concluded that all animal
    tissues were made of cells. Soon after that, Schwann
    wrote the first two parts of what is now known as the cell
                                     3                    February 23, 2012

  Allorganisms are made up of 1 or more
  The Cell is the basic unit of all living things.

Later, in 1858, Rudolf Virchow (ROO dawlf FIR koh), a doctor, stated
that all cells could form only from other cells. Virchow then added
the third part of the cell theory.

  Cells    come from existing Cells
                        4             February 23, 2012

Many Small Cells

 Thereis a physical reason why most cells
 are so small. Cells take in food and get rid
 of wastes through their outer surface. As a
 cell gets larger, it needs more food and
 produces more waste. Therefore, more
 materials pass through its outer surface.
                                  5                   February 23, 2012

Cell Size Continues….
As the cell’s volume increases, its surface area grows
too. But the cell’s volume grows faster than its surface
area. If a cell gets too large, the cell’s surface area will
not be large enough to take in enough nutrients or
pump out enough wastes. So, the area of a cell’s
surface—compared with the cell’s volume—limits the
cell’s size. The ratio of the cell’s outer surface area to
the cell’s volume is called the surface area–to-volume
ratio, which can be calculated by using the following
                         6              February 23, 2012

Two Kinds of Cells

 Allcells have cell membranes, organelles,
  cytoplasm, and DNA. But there are two
  basic types of cells—cells without a
  nucleus and cells with a nucleus. Cells
  with no nucleus are prokaryotic (proh KAR
  ee AHT ik) cells. Cells that have a nucleus
  are eukaryotic (yoo KAR ee AHT ik) cells.
  Prokaryotic cells are further classified into
  two groups: bacteria (bak TIR ee uh) and
  archaea (AHR kee uh).
                              7                February 23, 2012

Identify the different parts of a eukaryotic cell.
Explain the function of each part of a eukaryotic cell.

   Even though most cells are small, cells are still
    complex. A eukaryotic cell has many parts
    that help the cell stay alive.
    Plant cells and animal cells are two types of
    eukaryotic cells. These two types of cells have
    many cell parts in common. But plant cells
    and animal cells also have cell parts that are
    different. Compare the plant cell in Figure 1
    and the animal cell in Figure 2 to see the
    differences between these two types of cells.
                  8   February 23, 2012

 Cell Wall
 Nucleus
 Cytoplasm
 Chloroplast

 Cell membrane
 Nucleus
 Cytoplasm
                         9              February 23, 2012

Plant and Animal Cells

a  cell is the smallest unit that can perform
  all life processes.

 Cellsare covered by a membrane that
  separates the inside of the cell and the
  cytoplasm from the outside.

    cells have DNA, and many store the
 All
  DNA in a nucleus.
                                            10                  February 23, 2012

1. List three advantages of being multicellular.
2. Describe the four levels of organization in living things.
3. Explain the relationship between the structure and function of a part of an organism

  The Benefits of Being Multicellular
   You are a multicellular organism. This means that
    you are made of many cells. Multicellular
    organisms grow by making more small cells, not
    by making their cells larger. For example, an
    elephant is bigger than you are, but its cells are
    about the same size as yours.
                     11           February 23, 2012

Benefits of Larger Cells
 Largersize
 Longer Life
 Specialization

 Read page 20 in the textbook and
 provide an explanation to each one.
                                12               February 23, 2012

   A tissue is a group of cells that work together to
    perform a specific job. The material around and
    between the cells is also part of the tissue. The
    cardiac muscle tissue, shown in Figure 2, is made
    of many cardiac muscle cells. Cardiac muscle
    tissue is just one type of tissue in a heart.
                       13            February 23, 2012

Tissues Working Together

A  structure that is made up of two or
 more tissues working together to perform
 a specific function is called an organ. For
 example, your heart is an organ. It is
 made mostly of cardiac muscle tissue. But
 your heart also has nerve tissue and
 tissues of the blood vessels that all work
 together to make your heart the powerful
 pump that it is.
                                14               February 23, 2012

Organs Working Together

   A group of organs working together to perform a
    particular function is called an organ system. Each
    organ system has a specific job to do in the body.

    For example, the digestive system is made up of
    several organs, including the stomach and
    intestines. The digestive system’s job is to break
    down food into small particles. Other parts of the
    body then use these small particles as fuel. In turn,
    the digestive system depends on the respiratory
    and cardiovascular systems for oxygen.
             15      February 23, 2012

Organs working together
                                       16                 February 23, 2012

Structure and Function
Structure and Function
In organisms, structure and function are related. Structure is the
arrangement of parts in an organism. It includes the shape of a part
and the material of which the part is made. Function is the job the part
does. For example, the structure of the lungs is a large, spongy sac. In
the lungs, there are millions of tiny air sacs called alveoli. Blood vessels
wrap around the alveoli, as shown in Figure 4. Oxygen from air in the
alveoli enters the blood. Blood then brings oxygen to body tissues.
Also, in the alveoli, carbon dioxide leaves the blood and is exhaled.
The structures of alveoli and blood vessels enable them to perform a
function. Together, they bring oxygen to the body and get rid of its
carbon dioxide.
                                     17                      February 23, 2012

  • Explain the process of diffusion.
  • Describe how osmosis occurs.
  • Compare passive transport with active transport.
  • Explain how large particles get into and out of cells.

What happens if you pour dye on top of a layer of gelatin? At first,
it is easy to see where the dye ends and the gelatin begins. But
over time, the line between the two layers will blur, as shown in
Figure 1. Why? Everything, including the gelatin and the dye, is
made up of tiny moving particles. Particles travel from where they
are crowded to where they are less crowded. This movement
from areas of high concentration (crowded) to areas of low
concentration (less crowded) is called diffusion (di FYOO zhuhn).
Dye particles diffuse from where they are crowded (near the top
of the glass) to where they are less crowded (in the gelatin).
Diffusion also happens within and between living cells. Cells do
not need to use energy for diffusion.
                          18                           February 23, 2012

Figure 1 The particles of the dye and the gelatin slowly mix by diffusion.
                                   19                 February 23, 2012

Diffusion of Water
 The cells of organisms are surrounded by and filled with fluids that
   are made mostly of water. The diffusion of water through cell
   membranes is so important to life processes that it has been
   given a special name—osmosis (ahs MOH sis).

    Water is made up of particles, called molecules. Pure water has
    the highest concentration of water molecules. When you mix
    something, such as food coloring, sugar, or salt, with water, you
    lower the concentration of water molecules. Figure 2 shows how
    water molecules move through a membrane that is
    semipermeable (SEM i PUHR mee uh buhl). Semipermeable
    means that only certain substances can pass through. The
    picture on the left in Figure 2 shows liquids that have different
    concentrations of water. Over time, the water molecules move
    from the liquid with the high concentration of water molecules to
    the liquid with the lower concentration of water molecules.
   Figure Page 35 in text.
                                      20                February 23, 2012

The Cell and Osmosis
   Osmosis is important to cell functions. For example, red blood cells
    are surrounded by plasma. Plasma is made up of water, salts,
    sugars, and other particles. The concentration of these particles is
    kept in balance by osmosis. If red blood cells were in pure water,
    water molecules would flood into the cells and cause them to
    burst. When red blood cells are put into a salty solution, the
    concentration of water molecules inside the cell is higher than the
    concentration of water outside. This difference makes water move
    out of the cells, and the cells shrivel up. Osmosis also occurs in
    plant cells. When a wilted plant is watered, osmosis makes the
    plant firm again.
                                  21                    February 23, 2012

Moving Small Particles

   Small particles, such as sugars, cross the cell membrane
    through passageways called channels. These channels
    are made up of proteins in the cell membrane. Particles
    travel through these channels by either passive or
    active transport. The movement of particles across a
    cell membrane without the use of energy by the cell is
    called passive transport, and is shown in Figure 3. During
    passive transport, particles move from an area of high
    concentration to an area of low concentration.
    Diffusion and osmosis are examples of passive transport.

                                            Figure on page 36 in textbook.
                                     22                  February 23, 2012

Active Transport
 A process of transporting particles that requires the cell to use
  energy is called active transport. Active transport usually involves
  the movement of particles from an area of low concentration to
  an area of high concentration.

Moving Large Particles
 Small particles cross the cell membrane by diffusion, passive
  transport, and active transport. Large particles move into and out
  of the cell by processes called endocytosis and exocytosis.

 The active-transport process by which a cell surrounds a large
  particle, such as a large protein, and encloses the particle in a
  vesicle to bring the particle into the cell is called endocytosis (EN
  doh sie TOH sis). Vesicles are sacs formed from pieces of cell
                            23                February 23, 2012


 When  large particles, such as wastes,
 leave the cell, the cell uses an active-
 transport process called exocytosis (EK
 soh sie TOH sis). During exocytosis, a
 vesicle forms around a large particle
 within the cell. The vesicle carries the
 particle to the cell membrane. The vesicle
 fuses with the cell membrane and
 releases the particle to the outside of the
 cell.                                  Figure on page 36

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