51531986 Biology Form 4 Chapter 5 Cell Division

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Biology form 4 – Chapter 5

Mitosis
Mitosis is a division of the nucleus to produce two new daughter cells containing chromosomes identical to the parent cell.

Significance of mitosis
Growth- allows a zygote to produce more cell in order to grow Repair and replacement- allow the multicellular organism maintain its tissues, example skin cells and blood Asexual reproduction- clone

The cell cycle divided into two major phases
a. Interphase
b. Mitosis
Interphase is the period between division, divided into 3 sub phases (G1, S and G2) a. G1- cells grow rapidly and new organelle are synthesis
b. S- synthesis of DNA and chromosomes are replicated
c. G2- cells prepares for mitosis, synthesis protein and mitotic spindle begin to form M PHASE(Cell Division)
Mitosis : nucleus divides
-Prophase-Metaphase-Anaphase-Telophase
Cytokinesis : division of cytoplasm

Prophase
Early prophase
Chomatids condense and become visible in a light microscope
Nucleolus disappears
Paired centrioles move to opposite ends of the cell
Late prophase
Nuclear membrane disappears
Spindle form

Metaphase
Spindle fibres are fully form
Sister cromatids line up at the spindle equator
At the end of metaphase, the centromers divide

Anaphase
Anaphase begin with the separation of the centromers
The sister cromatids are drawn to opposite poles of the cell by contraction of spindle fibres

Telophase
Telophase begin when the two sets of daughter chromosomes have reached the two poles of the cell. The spindle fibres disintegrate, the nuclear membrane forms around each set of daughter chromosomes and the nucleoli reappear The chromosomes uncoil and become less visible under the light microscope -In plant cells, the stages of mitosis are same. Only cytokinesis in plant cells is markedly different. -A cleavage furrow does not form. Instead, membrane-enclosed vesicle gather at a plant cell’s equator between the two nuclei. -Vesicle fuse to form a cell plate

Cytokinesis
The division of cytoplasm.
Animal cell = actin filaments in the cytoplasm contracts to pull a ring of the plasma membrane inwards to form a cleavage furrow  the cell is separated into 2 daughter cells. Plant cell = starts with the formation of cell plate at the equator of the cell  cell plate enlarge  new cell wall is formed  2 daughter cells are produced.

Meiosis
In a diploid cell, chromosomes occur as pairs (homologous chromosomes). Meiosis is a process to convert a diploid cell to a haploid gamete and cause a change in the genetic information to increase diversity in the offspring Meiosis involves two successive nuclear division that produce four haploid cells. The first division (meiosis I) is the reduction division; the second division (meiosis II) separates the chromatids.

The effects of uncontrolled mitosis in living things
Mutation is the change in the DNA structure of the cell.
This change in the DNA corrupts the coded genetic instructions for mitosis control. This leads to uncontrolled mitosis, which is the non-stop division of cells, producing a mass of new daughter cells, called tumour.

Causes of cancer
Genetic- some forms of cancer like prostate, colon, breast, skin, ovary are suspected to be inherited from the parents Carcinogens- these are chemicals which affect genetic activity and cause cancer, e.g. of carcinogen a diesel exhaust, cigarette smoke, hair dyes, soot, arsenic, benzene and formaldehyde. Radiation- excess exposure to x-ray, gamma-rays and ultra violet rays lead to increase cancer risk. Age- some cancers are found primarily in young people (e.g. leukemia), while some cancers (e.g. colon cancers) are found mostly in older adults. Viruses- some viruses (such as the EB and HIV-1) cause cancer.

Cloning
1. Cloning is the process of the making Clones are genetically identical cells produced from a single parent cell by mitotic division, or through asexual reproduction. 2. genetically identical copies of an...
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