Pearson Edexcel Advanced Level Biology Unit 3 notes.
Describe the stages of mitosis and how to prepare and stain a root tip squash in order to observe them practically.
Monai Elnaasani
Describe how totipotency can be demonstrated practically using plant tissue
culture techniques.
Past paper - January 2013, October 2016
1. Use part of the seedling; explant
2. Use sterile agar with nutrient medium
3. Agar contains growth substances hormones such as auxins
4. Cover the top of the container with clean plastic film to prevent contamination and loss of
water
5. Supply with light
6. Keep the flask at optimum temperature go 25ºC in a growth chamber at constant light
intensity and humidity
7. Allow a suitable length of time for growth 1-6 weeks using suitable controlled variables
8. Look for roots and shoots, leaves forming
9. Use aseptic techniques
10. Explant divides by mitosis into callus
11. Transfer the callus to another nutrient agar with growth regulators
12. The cluster of cells that formed on the agar began to specialize and eventually develop in
to a complete plant
Totipotent - all genes are potentially active can give rise to all specialized cells, and can give rise
to other totipotent cells, can give rise to an entire human being
Pluripotent - they’re unspecialised, the cells can differentiate and become specialized and can
form any cell type in the future except extra embryonic tissues like placenta
Covering the beaker with a clear plastic film;
• Prevents microbes from contaminating
• Prevents entry of harmful pathogenic microorganisms
• Allow light in photosynthesis
• Reduces water loss
Reliability;
• Repeat with large number of seedlings at each age
• More ages of seedlings used
• Repeat any anomalous results
Dependent variable;
• Percentage of explants showing growth
Independent variable;
• Concentration of growth regulator
Control variables;
• Concentration or mass of auxin
• Temperature of incubation using a water bath
• Light using same light source
• pH using a buffer
• Humidity using a closed container
Measuring dry mass of callus;
• Heat in an oven
• Repeat until theres no change in mass
• Read balance in milligrams
Pearson Edexcel Advanced Level Biology Unit 3 - notes for success
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