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Looking Inside the Cell
Cells are the basic units of structure and
function in living things.
All plants and animals from the smallest
plankton to the largest trees, and from the
smallest amoebas to the largest whales are
made up of groups of cells or single cells.
Amoeba
Blue
Whale
Protozoa
Bacteria
Levels of Organization in Nature
Cell – smallest unit that can live and reproduce on its own
or as part of a multicelled organism. It has an outer
membrane, DNA, and other components called
organelles.
Tissue – cells form tissues. It is an organized group of
similar cells that perform the same task. For
example, muscle is a tissue that is made up
of muscle cells.
Cardiac muscle
Organ – which is composed of one or more types of
tissues. For example, the heart is composed
of muscle, nerve, fat, and other types of
tissues.
Human
Heart
System – which is composed of different organs. For
example, the circulatory system is composed of the heart
and blood vessels.
Individual Organism – which is composed of different
systems of organs.
The human is composed of the circulatory system, the
digestive system, the respiratory system, the nervous
system, the reproductive system, the endocrine system,
the skeletal system,
the muscular system,
the lymphatic system,
and the
urinary system.
Think of a cell as a factory. Most factories are set up in
essentially the same way. All factories have exterior
walls that create separate work areas.
They usually have some kind of production line
where a product is assembled and
an executive department that decides
what product is made. A finishing
department processes and prepares the
product for shipping, and a packing
department wraps the product.
In addition, a factory has a receiving department
that brings in the components it needs to
make its product, a communications
department that allows it to contact
suppliers, and a power plant that provides
the energy it needs to run.
Finally a custodial staff keeps everything clean
and in good working order.
Cells are very similar to factories. To stay
alive and function properly, cells have a
division of labor similar to that found in
factories.
All cells are composed of a cell (plasma) membrane, a nucleus, and
cytoplasm. These structures can be compared with a factory’s
departments.
Cell (Plasma) Membrane – the membrane of the cell
provides a very thin, but effective, protective surrounding
for the cell. It also gives the cell shape and strength.
The membrane keeps the material substance of the cell
from leaking out into its surroundings. Nourishment
and waste do pass through the membrane.
Cytoplasm – is the cellular material between
the nucleus and the cell membrane. It is a
clear, thick liquid containing the vacuoles, the
mitochondria, and the ribosomes.
Think of the cell membrane as the skin of the
cell, and the cytoplasm
as the body of the
cell. Many functions
for life occur in the
cytoplasm.
Nucleus – runs the cell factory and controls
all cell activity. It determines what proteins
are to made and stores all the plans for
any proteins that the cell currently
makes or has made in the past.
The nucleus is the “brain” of the cell.
A nuclear envelope surrounds the nucleus.
It protects the nucleus. Materials pass
in and out of the nucleus through pores
in the nuclear envelope.
Chromatin are the strands of genetic material
found in the nucleus. These contain the
instructions for directing the cell’s functions.
Nucleous is where
ribosomes are made.
Ribosomes are the
organelles where proteins
are produced.
Organelles in the Cytoplasm
Mitochondria – are rod-shaped structures.
These are known as the “powerhouses” of the
cell. They convert
energy in food
molecules to energy
the cell can use
to carry out its
functions.
Endoplasmic Reticulum – looks like a maze
of passageways (or halls). These passageways
carry proteins and other materials from one
part of the cell to another.
Ribosomes – attached to some surfaces of the
endoplasmic reticulum are small, grainlike
bodies called ribosomes. Ribosomes function
as factories to produce proteins.
Lysosome = organelles that contain protein
digesting enzymes that break down large food
particles into smaller ones.
Cell Wall – are found in plants cells. It is a
tough, rigid structure made of cellulose
which is the outside of the cell membrane. It
provides physical support and shape.
Vacuole -- a large organelle in cells that stores various
products. In plant cells, water is stored here. In animal
cells, water, food material, and wastes are among the
materials that can be stored here.
Chloroplasts – organelles present in plant cells
that contains chlorophyll and absorbs light
energy from sun that used in photosynthesis.