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Cell Division
In cell division, the nucleus divides and then the cytoplasm divides to from two new identical cells.
Mitosis is the processes in which the nucleus divides to from two identical nuclei. It occurs in a series
of phases- prophase, metaphase, anaphase, telophase. After the nucleus divides, the cytoplasm and the
cell membrane divided to create two new identical cells. This process is called cytokinesis.
The Phases of Mitosis
Interphase-This is the phase where the cell spends most of its life. Normal cell activities occur here such as cell
growth, production of proteins. (This phases is not part of mitosis because the cell has not started to
divide)
Prophase-Chromatin bunches up to form double stranded chromosomes. The two strands are held together by a
centromere.
- The nuclear membrane and the nucleolus disappear.
-Centrioles appear at opposite ends of a cell.
-Spindle fibers form between the two centrioles.
Metaphase-Chromosomes line up in the middle of the cell.
-Centromeres attach to spindle fibers. Each chromosome has its own spindle fiber.
Anaphase-The centromere breaks and the two strands of a chromosome separate.
-The spindle fibers pull each strand toward the centrioles.
Telophase-Centrioles and spindle fibers disappear.
-Chromosomes stretch back out into chromatin.
-The nuclear membrane and the nucleuolus reappear around each new nuclei.
-Two new nuclei are formed.
Cytokinesis-The cytoplasm divides creating two new identical daughter cells.
Mitosis in a Plant Cell
Plant cells go through interphase, prophase, metaphase, anaphase, and telophase, but they do not go
through cytokinesis. This is because the plant cell has a rigid cell wall that is unable to pinch apart.
Instead a cell plate forms in between the two nuclei dividing the cell. A new cell wall will form along
the cell plate creating two identical plant cells.
Another difference between plant cell mitosis and animal cell mitosis is the plant cell does not have
centrioles. The cell wall supports the cell, so centrioles are not needed to hold the spindle fibers in
place.
Types of Reproduction
There are two types of reproduction- asexual reproduction and sexual reproduction.
Asexual is a type of reproduction were an offspring is produced from one parent. The
DNA of the offspring is exactly like that of the parent.
Sexual is a type of reproduction were an offspring is produced from two parents. In
sexual reproduction sex cells from each parent must join.
The male sex cell is the sperm while the female sex cell is the eggs. When these two join
together fertilization occurs and a new cell called a zygote is formed.
Each sex cell has half of the number of chromosomes an organism needs.
Meiosis
Meiosis occurs in two parts- meiosis I and meiosis II
Meiosis I
Interphases IDNA begins to copy itself.
Prophase INuclear membrane and nucleolus disappear.
Centrioles and spindle fibers form.
Like chromosomes pair up together.
Metaphase ILike chromosomes like up together is the middle of the cell.
There are two chromosomes per spindle fiber.
Anaphase ILike chromosomes separate and move toward opposite centrioles.
Telophase IThe nuclear membrane forms around the double stranded chromosomes.
Two nuclei are formed
Centrioles and spindle fiber disappear
Cytokinesis IThe cytoplasm and the cell membrane divide.
Meiosis II
Prophase IIThe nuclear membrane and nucleolus disappear.
Centrioles and spindle fibers form.
Metaphase IIChromosomes line up in the middle of the cell.
(Each chromosome is attached to its own spindle fiber)
Anaphase IIThe centromeres break and the two strands of a chromosome separate.
Telophase IIThe spindle fibers and centrioles disappear.
A nuclear membrane forms around each group of single stranded chromosome.
Cytokinesis IIThe cytoplasm and the cell membrane divide.
Four new sex cells are created each with half of the number of chromosomes as the parent cell.