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Cells Come From Where?
Cells have to come from somewhere they don’t Endoplasmic Reticulum appear out of nowhere. This very topic
has been of much debate ever since scientists the first scientist saw cells under the microscope.
Schleiden and Schwann are well known for their role in discovering that all living things are made of cells, but
they were mistaken in their beliefs of where the cells came from. They knew that Spontaneous Generation for
whole animals was completely incorrect, however, they still held on to the idea that cells might come from
nowhere kind of like crystals that grow on non-living objects. Even though they did not have all of their theory
correct, their thoughts were the basis for the first two parts of the cell theory. The cell is the basic unit of life
and all living things have one or more cells.
Louis Pasteur spent most of his career trying to become famous for
his scientific thoughts. It was not until 1860 that his ideas really
came to light. The French Royal Society set up a competition for
scientists to disprove Spontaneous Generation once and for all.
Pasteur won the competition and the 2,500
francs. ($2,700)
His Swan neck flask experiment proved that
cells have to come from living things. The
microbes would be trapped in the dip of the
neck and the broth remains cell free.
It was not until the work of Virchow and Remack did scientists actually prove that cells come from the division
of cells. They used chicken eggs to study cell growth under the microscope. Because chicken eggs are growing
a new baby chick the cells are constantly growing and dividing. They were the first to see that cell division
happened in stages. Virchow’s famous statement, “Omnis cellula a cellula,” cells from other cells, along with
Remack’s experiments are the whole reasons that we know where cells arose. Virchow is accredited with the
last part of the cell theory. All cells come from pre-existing cells.
1. How has the theory of where cells came from changed over time?
Why is cell division important?
Every second millions of cells in your body are growing, dividing, and dieing off. Some cells constantly need
replacing because of their environment. Take the cells that line your stomach. Those cells are replaced every
few days because the acid in your stomach damages and eats away at them. Other cells have a longer life
because they are not in such harsh environments. Skin cells are replaced about once a month, but muscles that
cover your ribs can live up to 15 years. Bone cells live about 25 to 30 years. Brain cells are never replaced, even
if they are damaged or dead.
The cells in your body grow and make new cells to replace old, damaged, and warn
out cells. Most cells in your body follow what is known as the cell cycle. Simply put
the cell cycle represents the stages of the cell’s life from growth to death. Your body
is constantly growing from the second the sperm and the egg are joined. Your favorite
topic…I know! ☺ From that moment on one cell simply divides into two and that is
how most cells are replaced. The human body is made up of trillions of cells and it
takes a while to make that many cells.
2. Which type of animal cell lives the longest?
The Beginning
The first stage of the cell cycle is the same for all cells.
It is called Interphase. The cell will spend most if its
time in this stage and very little time in the second phase
known as Mitosis. (actual division of cells).
At the beginning of this phase the cell grows slightly
bigger and begins to make more organelles. The most
important organelle that it makes is exact copies of the
chromosomes in the nucleus. Remember chromosomes
are the genetic material that determines what a cell is
going to be and do in the organism.
Now do not think that because we are humans and we
are smart creatures therefore we have a special number
of chromosomes. Humans have 46 chromosomes. A
potato has 48 chromosomes and a fruit fly has 8
chromosomes. A dog has 78 chromosomes. The most
shocking was that a Fern (type of tree) has 1,440
chromosomes. Wow!!
3. Do more complex organisms always have more chromosomes?
4. What is the first phase of the cell cycle? What happens in this phase?
5. Interphase used to be called the resting stage for a cell, but why is that an incorrect idea?
Mitosis
Once a cell has completed Interphase the cell will begin to divide.
Because everything in the cell has been copied, it is easy to slit into
to new cells. The process of mitosis is when the nucleus of a cell
divides followed by the cytoplasm. Once the cytoplasm spits into
two the cell cycle is complete and each cell goes back into
Interphase.
The original cell, known as the parent cell will split into two exact
copies known as daughter cells. The daughter cells have exact
copies of the chromosomes and other organelles.
If something goes wrong in the cell cycle, like Interphase is not long
enough, it can cause things like cancer cell to form. Each new cell
from that original split will have the same problems and the cancer
will form what is known as a tumor.
Mitosis Four Phases
1. Prophase: This is the beginning phase. The membrane that surrounds the nucleus disappears so
everything inside the nucleus is just floating in the cytoplasm. The chromosomes that usually look like
loose strings tighten up and pull together.
2. Metaphase: The chromosomes line up in the center of the cell. The chromosomes line up in a row, one
on top of the next. It almost looks like a dance is getting ready to happen in the center of the cell.
3. Anaphase: The copies of each chromosome separate moving to opposite sides of the cell resulting in
two sets of identical chromosomes. The separate like opposite ends of a magnet pushing as far apart as
possible.
4. Telophase: A nuclear membrane forms around the chromosomes in both cells. Each new nucleus
contains the exact same number and type of chromosomes as the original cell.
5. In what phase of mitosis are chromosomes moving toward opposite sides of the cell?
At the end of mitosis is a stage known as Cytokinesis. Simply
put cytokinesis is when the cytoplasm splits into two. This
happens after mitosis and is the actual splitting of the cell. See
the animal cells to the left, the cells in the center are going
through cytokinesis, the splitting of the cytoplasm.