All Cells Arise From Other Cells Flashcards
How do eukaryotic cells replicate?
- enter the cell cycle and divide by mitosis or meiosis
How do prokaryotic cells replicate?
- binary fission and viruses do not undergo cell division as they are non living
How do viruses replicate?
- replicate inside of the host cells they invade by injecting their nucleic acid in to cell to replicate the virus particles
What does the cell cycle comprise of?
- interphase (G1, S, G2)
- nuclear division (mitosis or meiosis)
- cytokinesis
What is G1?
- growth
What is S?
- synthesis
What is G2?
- growth and preparation for mitosis
What is M?
- mitosis (cell division)
What is interphase?
- longest stage in the cell cycle wheee organelles double, the cell grows and DNA replicates
What is nuclear division?
- can be mitosis, creating two identical diploid cells or meiosis, creating four genetically different haploid cells
- mitosis creates cells with identical DNA for growth and repair whereas meiosis creates gametes
What is cytokinesis?
- final stage, division of cytoplasm to create new cells
What are the four stages of mitosis?
- Prophase
- Metaphase
- Anaphase
- Telophase
What is the purpose of mitosis?
- growth and relate eg. Clonal expansion of B cells
Prophase
- Chromosomes condense and become visible
Metaphase
- Chromosomes align along the equator of the cell, spindle fibres released from the poles now attach to the centromere and chromatid
Anaphase
- Spindle fibres pull centromere and chromatids to opposite poles causing centromere to divide into two and the chromatids get pulled to opposite poles
- requires energy in the form of ATP which is provided by respiration in mitochondria
Telophase
- Chromosomes at each pole become longer and thinner, spindle fibres disintegrate and nucleus starts to reform
- cytoplasm splits into two to create two new generically identical cells
How to find the mitotic index
- mitotic index = number of cells in mitosis / total number of cells X 100
What is mitotic index?
- percentage of cells undergoing mitosis
What can uncontrolled cell division lead to?
- formation of tumours and cancers
Why is hydrochloric used for mitosis root top squash?
- softens and loosens root tissues
Why is stain used in mitosis root tip squash?
- stain chromosomes in nucleus so it is visible under microscope
Why is mounted needle used in mitosis root tip squash?
- to lower the cover slip and prevent air bubbles under the cover slip
Why is the root tip of an onion or garlic used in mitosis root tip squash?
- tip is growing region, mitosis should be occurring here
Describe the method of the root tip squash
- Grow garlic in the dark over a beaker of water for 3 days. New young roots will grow which will be used for experiment
- Using scalpel, cut off tip of root 5mm from end as it’s the growing region so cells should be undergoing mitosis
- Pace root tip into test tube of hydrochloric acid and then into water bath at 60 degrees Celsius and leave for 10 minutes so acid can soften cells
- Pour acid out of test tube and place root tip on watch glass and rinse with distilled water. Place root tip on microscope slide and using filter paper, soak up excess water
- Add two drops of stain to the root tip and using mounted needle, lower on the coverslip and leave for ten minutes
- Place filter paper on top of slide and gently press down making sure cover slip does not slip sideways
Why should you leave the coverslip on for ten minutes?
- allows time for the dye to stain the chromosomes
Why should the root tip be squashed?
- spreads out the cells to get a single layer so light can pass through when viewing through microscope
How to prevent cuts using scalpel?
- cut on top of white tile to help prevent slipping
- cut away from body
How to prevent hydrochloric acid risk?
- wear goggles
- wash hands if spilt
When counting cells to calculate the mitotic index what should you do to ensure the count is accurate?
- examine large number of fields of view/many cells
- to ensure representative sample
