The Cell
|
The one-celled organism
amoeba proteus
|
|
A single-celled bacteria
of the type: E. coli
|
|
|
A human red blood cell
|
|
A plant cell from the leaf
of a poplar tree
|
The cell is one of the
most basic units of life. There are millions of different types of
cells. There are cells that are organisms onto themselves, such as
microscopic amoeba and bacteria cells. And there are cells that only
function when part of a larger organism, such as the cells that make up
your body. The cell is the smallest unit of life in our bodies.
In the body, there are brain cells, skin cells, liver cells, stomach cells,
and the list goes on. All of these cells have unique functions and
features. And all have some recognizable similarities. All
cells have a 'skin', called the plasma membrane, protecting it from
the outside environment. The cell membrane regulates the movement
of water, nutrients and wastes into and out of the cell. Inside of
the cell membrane are the working parts of the cell. At the center
of the cell is the cell nucleus. The cell nucleus contains
the cell's DNA, the genetic code that coordinates
protein synthesis. In addition to the nucleus, there are many organelles
inside of the cell - small structures that help carry out the day-to-day
operations of the cell. One important cellular organelle is the ribosome.
Ribosomes participate in protein synthesis. The transcription
phase of protein synthesis takes places in the cell nucleus. After
this step is complete, the mRNA leaves the nucleus and travels to the cell's
ribosomes, where translation occurs.
Another important cellular organelle is the mitochondrion.
Mitochondria (many mitochondrion) are often referred to as the power plants
of the cell because many of the reactions that produce energy take place
in mitochondria. Also important in the life of a cell are the lysosomes.
Lysosomes are organelles that contain enzymes that aid in the digestion
of nutrient molecules and other materials. Below is a labelled diagram
of a cell to help you identify some of these structures.
There are many different types of cells. One major difference in
cells occurs between plant cells and animal cells. While both plant
and animal cells contain the structures discussed above, plant cells have
some additional specialized structures. Many animals have skeletons
to give their body structure and support. Plants do not have a skeleton
for support and yet plants don't just flop over in a big spongy mess.
This is because of a unique cellular structure called the cell wall.
The cell wall is a rigid structure outside of the cell membrane composed
mainly of the polysaccharide cellulose.
As pictured at left, the cell wall gives the plant cell a defined shape
which helps support individual parts of plants. In addition to the
cell wall, plant cells contain an organelle called the chloroplast.
The chloroplast allow plants to harvest energy from sunlight. Specialized
pigments in the chloroplast (including the common green pigment chlorophyll)
absorb sunlight and use this energy to complete the chemical reaction:
6 CO2 + 6 H2O + energy (from sunlight) 
C6H12O6 + 6 O2
In this way, plant cells manufacture glucose and other carbohydrates
that they can store for later use.
Organisms contain many different
types of cells that perform many different functions. In the next
lesson, we will examine how individual cells come together to form larger
structures in the human body.
For more information about cells, check out:
Copyright © 1998-1999, All
Rights Reserved, Anthony
Carpi
Cell photographs courtesy of The
Cell web site
Cell diagram courtesy of Dr.
G. Weaver, Colorado University at Denver
