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Cell Division (Cancer (Cancer occurs when cells lose the ability
to…
Cell Division
Cancer
Cancer occurs when cells lose the ability
to control the rate and the number of times
mitosis takes place.
A tumour results when one or more cells lose aibility
to control the rate of mitosis.
Benign tumors are not life-threatening.
Mailignant tumours are called cancers.
Cancers are dangerous because :
-Cells never stop dividing.
-Invade other tissues.
-May spread from one body part
to another.
Caused by carcinogens eg cigarette smoke.
Treatment = Surgery, radiation,
chemotherapy.
Mitosis
Mitosis is a form of nuclear division in which one nucleus divides to form two, each containing the same number of chromosomes with identical genes.
Stages of Mitosis
1)Interphase
-Period between cell divisions when cell is carrying out its function.
2)Propahse
-Nuclear membrane starts to break down.
-Centrioles migrate north & south, send out spindle fibres.
-Chromsomes duplicate.
-Cell organelles duplicate.
3)Metaphase
-Nuclear membrane broken down.
-Chromsomes thicken even more.
-Fibres attach to chromosomes.
-Each chromosome has 2 fibers attached, 1from each side of the cell.
4)Anophase
-Fibres contract, Chromsomes pulled apart.
-Each strand is pulled to opposite end of cell.
-Hence, identical set of genes pulled to each end of cell.
5)Telophase
-Nuclear membrane forms around each of the 2 sets of chromosomes.
-Chromosomes elongate within each nucleus.
-Cytoplasm splits (cytokinesis).
Functions of Mitosis
1)Reproduction in unicellular (single cell) organisms.
2)Growth & repair in multicellular organisms.
Haploid & Diploid cells
A haploid cell has one set of chromsomes.
Symbolised by letter n.
Only haploid cell in humans = sex cell/gamete.
-
Meiosis
Meiosis is a form of nuclear division in which the four daughter nuclei contain half the chromosome number of the parent nucleus.
Functions of Meoisis
1)Sexual reproduction.
-Meoisis halfs the chromosome number.
-Two haploid (n) cells/gametes join to form a
diploid (2n) zygote.
-Fertilisation restores chromosome number to 46.
2)New combinations of genes formed.
-Cells resulting from meoisis are not identical.
-Genetic variation.
-
Chromatin = structure of DNA when not dividing.
Chromosome = single strand of DNA & is dividing.
Homologous chromosomes = chromosome pairs that carry genes to control the same characteristics.
A gene = section of DNA that contains the instructions for the formation of a protein.
Crossing Over = the passing of genetic
material during Meoisis that leads to
continous variation in gametes.