Cells Have Cycles Too!
(3) So we all know that organisms grow – they increase in the amount of cells that they
have. But where do all those cells come from? They don’t really reproduce the same
way that humans or animals do – cells use a process called mitosis to divide into 2 new
cells. They then keep dividing over and over again and now you have a multicellular
organism! But there are a lot of things that need to happen before mitosis.
(5) Each cell has a ‘life cycle’ that it moves through – in cells, this is called the Cell Cycle.
There are several stages that cells go through before they
can divide. Most of the life of a cell is spent in a stage called
interphase. During this stage, 3 important things need to
happen in order for the cell to divide. The cell needs to grow
– it uses up energy and gets bigger in size (this is called the
G1 stage – growth 1). Then, the chromosomes made of DNA
inside the cell’s nucleus make copies of themselves –
meaning, there are now 2 copies of the DNA inside the
nucleus! After the chromosomes duplicate, the cell spends
the rest of interphase growing (this is called the G2 phase)
and getting ready to divide into 2 new cells.
(4) Once a cell is ready to divide, it enters a phase called
prophase, which is the first stage of mitosis. In prophase, the
membrane around the nucleus fades away and the DNA
scrunches into short pairs called chromatids, which you can see
clearly under a microscope. These chromatids are linked
together by a centromere, which acts sort of like a rubber band
holding them together.
(3) In metaphase, the second phase of mitosis, the
chromatids line up along the middle of the cell, which
is called the equator (just like the Earth!). They line up
in the middle, which is a good way to remember what
happens in metaphase. Metaphase = middle.
(3) In anaphase, the third phase of mitosis, the
chromatids are pulled apart by threads called the
spindle fiber. A side of each chromatid is pulled to
either end of the cell so that each new cell gets a
full set of DNA. The cell also starts to look longer as
well, as if it is being pulled apart. This is a good way
to remember anaphase – the DNA is pulled apart
and the cell starts to pull apart. Anaphase = apart.
(4) In telophase, the fourth phase of mitosis, the DNA
starts to shrink back into a small ball, which is going to
become the new nucleus of each cell. The spindle fiber
starts to disappear and now you should be able to see a
small dent forming down the middle of the long cell.
Mitosis is almost over!
(3) The last phase is called Cytokinesis. Cytokinesis starts with
the same 4 letters as cytoplasm….and that’s what cytokinesis is
– the division of the cytoplasm. The cell pinches off into 2 new,
smaller cells that each get an equal amount of cytoplasm. Bam!
2 new cells – small ones - but they have all of their interphase
stage to grow and get ready to divide again.
Total Questions: 25
Total Pictures: 7
Total Points: 32