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Posted by bitesizebiologyteacher (U15169682) on Sunday, 10th February 2013
Mitosis and Meiosis are two important processes you need to know about in Biology.
For Standard Grade you only need to know about Mitosis (cell division), for Int 2 and Higher you need to understand Mitosis and know about Meiosis.
Try and write out the main stages in either process and I will post an answer tomorrow evening. You could try and do it with no help or if your stuck use Bitesize or your course notes to help.
Posted by bitesizebiologyteacher (U15169682) on Monday, 11th February 2013
Check out this link on Bitesize, I will post a summary of Mitosis and Meiosis over the next few days. If anyone is struggling with any of it, don't forget to post your questions.
Posted by bitesizebiologyteacher (U15169682) on Tuesday, 12th February 2013
How did you get on with Mitosis and Meiosis? Know the difference between chromosomes and chromatids? Know why it is important to keep the same number of chromosomes? Here is a summary of these two process.
MITOSIS is important as it increases the number of cells in an organisms It occurs in the following stages:
1 - Chromosomes appear in the nucleus
2 - The chromosomes shorten and appear as two CHROMATIDS joined together at one point (centromere)
3 - The nuclear membrane disappears, CHROMOSOMES line up at the centre of the cell (equator).
4 - The CHROMATIDS are pulled apart and move to opposite ends of the cell.
5 - The nuclear membrane reforms round each group of chromatids and cytoplasm divides.
6 - Two new daughter cells are produced with the same number of chromosomes as the mother cell.
It is important that the each daughter cell contains the correct number of chromosomes so that it has everything required for life. - NB this is often asked in exam questions.
MEIOSIS is the process by which gametes are produced. This occurs in the ovaries or testies in mammals an ovaries and anthers in plants. Meiosis involves the production of haploid cells (one set of chromosomes) from a diploid cells (two sets) It involves the following stages:
1 - Each chromosome replicates to form a pair of identical CHROMATIDS attached by a centromere. Homologous chromosomes pair up.
2 - Homologous pairs line up along the equator and become attached to the spindle fibres by the centromeres. Independent assortment and crossing over can occur at this stage.
3 - Spindle fibres contract separating the homologus chromosomes, cytoplasm divides. This is the first meiotic division.
4 - New spindle form at each end of the cell, at right angles to the first. Chromosomes become attached by their centromeres.
5 - Spindle fibres contract and chromatids separate. Cytoplasms divides to produce four daughter cells each with only one set of chromosomes. This is the end of the second meiotic division.
How did you get on? Any questions about anything to do with either Mitosis or Meiosis get in touch. Happy studying