All living things are made of the same basic building blocks, cells. A human is
made of 65 trillion cells. Cells are everywhere, on you skin, in your blood, and
even on your tongue. In fact, your blood is clear but red blood cells are what
make your blood red. Most living things are made up of many cells but some are
made of only one cell, like amebas, paramecium, fungi, protists, monerans, and
bacteria. There are two basic types of cells, animal cells and plant cells. They
have some common parts found in both and other parts that are unique to each. A
cell membrane is found in both plant and animal cells. It is the structure that
surrounds the cell and protects it. Plant cells have a cell wall, a rigid
structure surrounding the cell membrane. Animal cells do not have a cell wall.
Cytoplasm is the thick, jelly-like substance that makes up most of the cell.
Vacuoles are fluid filled sacs in the cell. The vacuoles contain stored water or
food that will be used by the cell. Cells also contain other "small
organs" called organelles that carryout various cell functions. And then
there is the control center of the cell, the nucleus, surrounded by a protective
outer covering call the nuclear membrane. The nucleus contains the DNA, or
chromosomes, that carries all the instructions on how a cell will function,
live, and reproduce. Every cell needs to energy to live and reproduce. Plant and
animal cells obtain energy in different ways. Animals can not make their own
food. They obtain energy by taking in food, water, and oxygen and converting it
to sugar. Sugar is the only food a cell can eat. Plant cells can make their own
food from water and sunlight. This process is called photosynthesis. Both plant
and animal cells use energy from the food they obtain to reproduce. All living
things produce more living things. Cell reproduction is called mitosis. Mitosis
is the process of a single cell dividing in two and then two more and so on. In
mitosis, the pairs of chromosomes in the nucleus of the parent cell divide into
two daughter cells. There are four phases of mitosis. In the first phase, the
chromosomes are in a tangle and the nuclear membrane dissolves, or breaks apart.
In the second phase, special fibers line up the chromosomal pairs. In the third
phase, the fibers pull the pairs apart to opposite ends of the nucleus. In the
final phase, the parent cell splits in two, creating two completely new daughter
cells exactly like the parent cell. The two daughter cells will grow and
eventually the process of mitosis will start again in each one. This is how all
living things grow and continue. In closing, it is important to remember that
all living things are made up of cells. Some have only one cell while others
have very complicated systems of many cells working together. Second, plant and
animal cells take in food, water, and oxygen in very different ways, but both
need these substances to make the energy needed to live, grow, and reproduce.
Finally, every cell passes on their DNA to future generations through the
process of mitosis. The DNA, in both plant and animal cells, contains all the
instructions needed for cell to grow and function.