3.2.10 Cells Divide by Binary Fission and Mitosis Flashcards
Cells that keep their ability to divide follow the ____ ____
cell cycle
What is interphase?
Period of cell growth and DNA replication
Name the 2 phases that the cell cycle consists of
- Interphase
- Mitosis
Name the 3 growth stages that interphase is subdivided into
- Gap phase 1
- Synthesis
- Gap phase 2
Where does the cell cycle start and end?
At mitosis
Draw the cell cycle
What happens in gap phase 1?
Cells grows and new organelles and proteins are made
What happens in synthesis?
Cell replicates its DNA, ready to divide by mitosis
What happens in gap phase 2?
Cell keeps growing and proteins needed for cell division are made
What is mitosis?
When a parent cell divides to produce 2 genetically identical daughter cells
(Contain exact copy of DNA of parent cell)
Why is mitosis needed?
For growth of multicellular organisms and repairing damaged tissues
Describe what occurs before mitosis, during interphase
- Caries out its normal functions but prepares to divide
- DNA unravels and replicates, organelles are replicated
- ATP content increased
Name the 4 main stages in mitosis
- Prophase
- Metaphase
- Anaphase
- Telophase
As mitosis begins why are chromosomes made of 2 strands (chromatids) joined by a centromere?
∵ each chromosome has already made an identical copy of itself during interphase
When mitosis is over, what do the chromatids end up as?
One-strand chromosomes in the daughter cells
Describe Prophase
- Chromosomes condense and super coil & become visible
- Centrioles (tiny bundles of protein) move towards opposite end of cell, forming the spindle (network of protein fibres)
- Nuclear envelope breaks down allows chromosomes to move
Describe Metaphase
- Chromosomes line up along centre of cell
- Become attached to the spindle by their centromere
Describe Anaphase
- Centromeres divide, separating each pair of sister chromatids
- Spindles contract, pull chromatids to opposite poles of the spindle, centromere first (are separated)
- Makes chromatids appear v-shaped
Describe Telophase
- Chromatids reach opposite poles on spindle
- They uncoil & become long and thin again = chromosomes
- Nuclear envelope reforms preventing chromosomes moving away
- Cytoplasm divides (cytokinesis) so they’re now two daughter cells that are genetically identical to original cell
- (Each daughter cells starts interphase)
Describe how you use root tips to observe mitosis
- Cut 1 cm from tip of growing root (e.g. onion)
- Hydrochloric acid in boiling tube, put in water bath at 60°C
- Transfer root tip into boiling tube & leave for 5 mins
- Use pipette to rinse root tip with cold water
- Leave tip to dry on paper towel
- Place root tip on microscopic slide & cut 2 mm from very tip of it
- Discard the rest
- Use mounted needle to break tip open and spread cells thinly
- Add few drops of stain and leave it for few minutes
- Place cover slip over cells and push down firmly to squash tissue
- Look at all stages of mitosis under optical microscope
Investigating Mitosis
Why do you have cut the from the tip of a growing root?
Has to be tip ∵ it’s where growth occurs (i.e. mitosis)
Investigating Mitosis
Why do you have add stain to the sample?
Stain makes it easier for chromosomes to be seen
Investigating Mitosis
Why do you squash the tissue (by pushing down the cover slip firmly over the cells)?
This makes tissue thinner = allows light to pass through it
Investigating Mitosis
Why shouldn’t you smear the cover slip sideways?
∵ you’ll damage the chromosomes
