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CELL STRUCTURE AND FUNCTION 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.
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