1. Cell Cycle
1.1. Interphase
1.1.1. 90% of the cell cycle and is known as the resting phase as no division takes place
1.1.2. Has Three Sub-Stages
1.1.2.1. Gap Phase 1
1.1.2.1.1. Proteins required for different organelles are synthesised
1.1.2.2. Synthesis Phase
1.1.2.2.1. DNA replication occurs which results in the doubling of the mass of DNA from 2n --> 4n
1.1.2.3. Gap Phase 2
1.1.2.3.1. Organelles grow and divide
1.1.2.3.2. ATP levels increase
1.2. Nuclear Division
1.2.1. Nucleus divides into two or four
1.2.2. Division into two
1.2.2.1. Mitosis takes places
1.2.2.2. Only one division takes place
1.2.2.3. Product will have the same no. of chromosomes as the original
1.2.3. Division into four
1.2.3.1. Meiosis takes place
1.2.3.2. Each cell has half the no. of chromosomes as the original
1.3. Cell Division
1.3.1. Division of the cytoplasm
1.3.2. Cell divides into two or four
1.4. The cell cycle takes 24 hours to complete in a mammalian cell
2. Investigation of Observing the Stages of Mitosis
2.1. Background Information
2.1.1. Growth in plants occurs in specific regions called meristems
2.1.2. The root tip meristem can be used to study mitosis
2.1.3. The root tip meristem can be found just behind the protective root cap
2.1.4. In the root tip meristem, there is a zone of cell division that contains cells undergoing mitosis.
2.1.5. Pre-prepared slides of root tips can be studied or temporary slides can be prepared using the squash technique
2.1.5.1. Root tips are stained
2.1.5.2. Then gently squashed
2.1.5.2.1. Spreading the cells out into a thin sheet
2.1.5.2.2. Allowing individual cells undergoing mitosis to be clearly seen
2.2. Apparatus
2.2.1. Roots of Onion
2.2.2. Microscope Slide
2.2.3. Cover Skip
2.2.4. 1 M Hydrochloric Acid (HCl)
2.2.5. Stain (Acetic Orcein or Toluidine Blue)
2.2.6. Paper Towel
2.2.7. Scalpel Blade
2.2.8. Cutting Tile
2.2.9. Boiling Tube
2.2.10. Waterbath at 60C
2.2.11. Optical Microscope
2.3. Method
2.3.1. Prepare a boiling tube of 1M HCl
2.3.2. Place in a water bath at 60C for 10 minutes
2.3.3. Remove about 1cm of the tips of the roots
2.3.3.1. Place in the warmed HCl for 5 minutes
2.3.4. Rinse the tips well in cold water using a pipette
2.3.4.1. Blot dry with a paper towel
2.3.5. Cut approximately 2mm off the tip and place onto a microscope slide
2.3.6. Add a drop of a suitable stain
2.3.7. The stained root tip is gently squashed on a glass slide using a blunt instrument
2.3.7.1. This is done with a cover slip with the help of your finger to gently apply pressure in a rolling motion
2.3.8. View the slide under the microscope
2.3.9. Cells undergoing mitosis can be seen and drawn
2.3.9.1. Drawn only if required
2.3.10. Annotations can then be added to these drawings to show the different stages of mitosis
2.3.10.1. These are to allow us to accurately see which cells are undergoing mitosis then allow us to calculate the mitotic index using this information.
3. Meiosis
3.1. Uses in the Body
3.1.1. Sexual Reproduction
3.1.2. Production of Gametes
3.2. Stages of Meiosis
3.2.1. Prophase I
3.2.1.1. Chromosomes condense
3.2.1.1.1. Become more visible
3.2.1.2. Nuclear Envelope disintigrates
3.2.2. Interphase I
3.2.2.1. Replication of chromosomes
3.2.2.2. Resulting sister chromatids are held together at the centromere
3.2.2.3. Centrosomes are also replicated
3.2.3. Metaphase I
3.2.3.1. Chromosomes align at the centre of the cell
3.2.3.2. Spindle fibres attach to centromeres
3.2.4. Anaphase I
3.2.4.1. Spindle fibres pull chromatids to oppositve poles of the cell
3.2.5. Telophase and Cytokinesis I
3.2.5.1. Cell Starts to Divide
3.2.5.1.1. Nuclear envelope re-froms
3.2.5.1.2. Contractile ring formed
3.2.5.2. Cell Has Divided
3.2.5.2.1. Two genetically identical daughter cells formed
3.2.6. Prophase II
3.2.6.1. Sister chromatids condense
3.2.6.2. A new spindle begins to form
3.2.6.3. The nuclear envelope starts to fragment.
3.2.7. Metaphase II
3.2.7.1. Sister chromatids line up at the metaphase plate
3.2.8. Anaphase II
3.2.8.1. The shortening of the kinetochore microtubules pulls sister chromatids apart
3.2.8.2. Nonkinetochore microtubules lengthen the cell
3.2.9. Telophase and Cytokinesis II
3.2.9.1. Chromosomes arrive at the poles of the cell and decondense
3.2.9.2. Nuclear envelopes surround the four nuclei
3.2.9.3. Cleavage furrows divide the two cells into four haploid cells
4. Mitosis
4.1. Uses in the Body
4.1.1. Asexual Reproduction
4.1.2. Growth and Repair
4.2. Occupies about 5-10% of the cell cycle
4.3. Stages of Mitosis
4.3.1. Interphase
4.3.1.1. Replication of DNA
4.3.1.2. Replacation of all organelles
4.3.2. Prophase
4.3.2.1. Chromosomes condense
4.3.2.1.1. Become more visible
4.3.2.2. Nuclear envelope disintegrates
4.3.3. Metaphase
4.3.3.1. Chromosomes align at the centre of the cell
4.3.3.2. Spindle fibres attach to centromeres of the chromosomes
4.3.4. Anaphase
4.3.4.1. Spindle fibres pull chromatids to opposite poles of the cell
4.3.5. Telophase
4.3.5.1. Cell starts to divide
4.3.5.2. Nuclear envelope starts to re-form
4.3.5.3. Contractile ring formed
4.3.5.3.1. Present between nuclear envelopes of cells
4.3.6. Cytokinesis
4.3.6.1. Cell has divided
4.3.6.1.1. Two genetically identical daughter cells formed
5. Binary Fission
5.1. Type of division that occurs in prakaryotic cells
5.2. Stages of Binary Fission
5.2.1. Replication of the circular DNA and plasmids in the cytoplasm
5.2.2. Division of the cytoplasm to produce two daughter cells
5.2.2.1. Each with a single copy of the circular DNA and a variable number of copies of any plasmids
5.3. As viruses are non-living, they do not undergo cell division
5.3.1. Following the injection of their nucleic acids into another cell
5.3.1.1. The infected host cell replicates the virus particles