Biology Chapter 18: Cell Division
Growth: permanent growth in size accompanied by cell particle and differentiation
Mitosis: Cell division during growth
* Growth in plants restricted to emergence points: shoot and root tips
A nuclear division such that the daughter nuclei produced contain the same number of chromosomes as the stir nucleus
* Non-dividing stage of a cell (still absorb nutrients and build protoplasm)
* Chromosomes attend as long thin threads called chromatin which cannot be distinguished individually
* Centrioles in animal cells divide and chromatin threads replicate
Interphase
nuclear envelope
centrioles
chromatin
cytoplasm
Zygote cells need to be genetically stalls for the embryo to develop normally.
Replication of Chromatin Threads
1. Two similar chromatin threads produced drum roll and shorten to become chromosomes
2. each(prenominal) chromosome consists of two identical DNA molecules called sister chromatids.
3. Chromatids joined at a point called centromere.
Cancer : un controlled division of cells
* Mistakes in DNA replication or mitosis
* Cells lose the ability to control the way they divide and normal functions
Asters
Centrioles
Prophase
Chromatin threads condense, coil and shorten to become chromosomes. Each chromosome consists of two sister chromatids affiliated at the centromere. The chromosomes be now visible under a microscope.
sister chromatids (one chromosome)
centromere
Late prophase:
* Nuclear Envelope disintegrates
* Spindle forms with arbor fibres extending from one pole of the cell to the other
In animal cells:
* Structures called asters(made up of microtubules) form around centrioles
* Centrioles move apart to opposite ends of cells
Microtubules are hollow protein structures found in cytoplasm of cells. They provide morphologic support and help to move substances within the cell.
Spindle Fibres forming...If you expect to get a full essay, order it on our website: Orderessay
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