cellular division

• A zygote is the fertilized egg that develops into a new organism. This cell divides countless times to become an organism.
• As a cell grows, it places an increasing demand on its DNA for replication.
• Cells need food, water, and oxygen to enter through its cell membrane and waste products to leave in order to survive. The rate of this exchange taking place is affected by the surface area of the cell (cell membrane).
• When a cell increases to a certain size, it faces an "information crisis." To solve this issue, the cell may choose to create a duplicate copy of the same DNA and divide it into two new cells.
• Asexual reproduction is quick and easy, but produces genetically identical offspring, meaning that the population lacks genetic diversity. Sexual reproduction may take more time, but it produces genetically different offspring, meaning that the population has more genetic diversity, and can adapt easier.
• DNA are packed in chromosomes. Cells need to make a copy of the chromosomes before cell division can begin.
• Prokaryotic chromosomes have a singular, circular DNA chromosome that includes nearly all the cell's genetic information.
• Eukaryotic cells contain more than one chromosome. For example, humans have 46 chromosomes. These chromosomes have DNA tightly bound to proteins known as histones. This entire complex is called a chromatin. The DNA and histone molecules form beadlike structures called nucleosomes.
• When a cell divides, the two sister chromatids separate and become their own chromosomes.
• Prokaryotic cells start to replicate their DNA chromosomes once they have grown to a certain size. Cells start dividing once DNA replication is mostly complete.
• The stages of the eukaryotic cell cycle are: interphase, G1, S, G2, and mitosis.
• Chromosomes separate in mitosis. Mitosis has four phases: prophase, metaphase, anaphase, and telophase.
• In prophase, genetic material inside the nucleus is condensed and the nuclear membrane breaks down, allowing the duplicated chromosomes to become visible. They will appear as two thick strands attached to the centromere. The cell starts to build a spindle, or a system of microtubules that separate the duplicated chromosome. The spindle fiber extends from the centrosome, where the centrioles are located (the centrioles move towards the poles of the cell)
• In metaphase, centromeres line up across the center of the cell. Spindle fibers connect the centromere of each chromosome to the poles of the spindle.
• Chromosomes separate and begin to move apart during anaphase. Once this phase begins, the two chromatids are now each their own chromosome.
• During telophase, the final stage of mitosis, chromosomes begin to spread out into a tangle of chromatin. A nuclear envelope reforms around the clusters, creating two daughter nucleus.
• After mitosis creates two nuclei, cytokinesis divides organelles and divides one cell into two. This phase begins during anaphase or telophase.
• In cytokinesis in animal cells, the cell membrane is drawn inward until the cytoplasm is pinched into two nearly equal parts. Each half gets is own nucleus and organelles
• In plant cells, a cell plate forms during cytokinesis, eventually turning into a cell wall.