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Summary Investigating totipotency practically.
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Pearson Edexcel Advanced Level biology Unit 3 notes. Describe how totipotency can be demonstrated practically using plant tissue culture techniques.
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Monai ElnaasaniDescribe the stages of mitosis and how to prepare and stain a root tip squash
in order to observe them practically.
Past paper - June 2013, June 2017
1. Cut off 5-10mm from a root tip
2. Heat the root tip at 60ºC in 2cm3 dilute hydrochloric acid in a waterbath
3. Transfer the tip on a glass slide
4. Break the cells apart using a needle
5. Place a drop of orcein ethanoic acid stain or tuluidine blue
6. Heat the slide to intensify the stain
7. Squash the root tip gently with the slide and the coverslip to separate the cells
8. Observe the cells under the microscope
9. Count the number of cells undergoing mitosis and calculate mitotic index
Safety;
• Staining clothes from orcein ethanoic, wear lab coat
• Hydrochloric acid irritating hands, wear gloves
• Harm using the knife, cut root tip away from the body
Orcein Etanoic acid stain is used to make the chromosomes visible, its blue in color
Hydrochloric acid separates the cells by breaking down the middle lamella softening the tissue
Variables to control;
• Temperature by growing seeds in an incubator or water-bath
• pH by using a buffer
• Humidity by air conditioning
• Variety or type of seed, collect seeds from same parent plant
• Light intensity by using same light source
• Availability of water
Observe with several root tips;
• To calculate a mean and standard deviation
• To then measure the rate of reliability and repeat any anomalous results
The cell cycle;
• A source of all the new cells needed for organisms to grow and to replace worn out cells and
method by which organisms under go asexual reproduction
• Function;
• Control growth of organism and replace dead cells and repair damaged tissue
• Increase in cell numbers by producing new cells
• Production of clone by asexual reproduction
• Synthesis of new organelles
• Controlled by a number chemical signals called cyclins brought about at a number of
checkpoints where the cell cycle moves from one phase to the next
1. Interphase which is a non-division period where the cells increase in mass and size
(G1), replicate their DNA (S) and carry out normal cellular activities, sufficient new
proteins, cytoplasm and cell organelles are synthesized for the new cell (G2)
2. Prophase,
• Nucleolus and nuclear envelope break down
• Centrioles separate and move to opposite poles
• Spindle fibers form from centrioles
• Chromosomes condense DNA coils and they become visible
Pearson Edexcel Advanced Level Biology Unit 3 - notes for success
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