Required Practicals (Paper 1) Flashcards
Describe an investigation for drawing plant cells?
- Place a tissue sample on a microscope slide.
- Add a few drops of a dilute iodine solution stain to make certain structures visible
- Lower coverslip onto the tissue to remove bubbles that would obstruct image
- Place the slide on the microscope stage and focus on the cells using the low power.
- Change to higher powered lens and refocus
- Observe plant cell
- Draw any types of cells that can be seen in the field of view (scientific drawing)
- Add a magnification scale to the diagram.
The epidermis can be peeled from a leaf. The stomata can be seen using a light microscope. How may have the student collected data for the number of stomata open on the upper and lower surface of the leaf for 5 different leaf areas?
- mount epidermis on a slide
- count stomata in one area
- repeat in four more areas
- repeat method on other surface of leaf
- calculate mean
Describe a method to investigate the effect of a range of concentrations of salt solutions on the mass of plant tissue.
- Cut some same size cylinders of potato tissue and measure their mass using measuring balance
- Place the cylinders in different concentrations of salt
- After 30-60 min, remove the cylinders, dab them dry, and reweigh them
- Calculate the change in mass or length
May need to mention control variables - drying is a important one, length if time
How would you use a graph to calculate the concentration of solution inside the potato cell?
- Calculate percentage change.
- Plot percentage change on graph
- draw line of bets fit
- Determine concentration where line crosses zero percentage change (x-axis)
How would you test for sugars?
Add blue benedict’s solution to food solution and heat it (using water bath at high temo, if it turns green, yellow, orange or brick red, it indicates a positive result, thus sugars are present (colour based on concentration with red indicating high concentration)
How would you test for starch?
Add orange-brown iodine solution to food sample, if it turn blue-black, it indicates a positive result, thus starch is present
How would you test for protein?
Add blue biuret reagent to food solution, if it turns purple, it indicates a positive result and thus protein is present
2 needed
What mistakes may have been made during the chemistry food test?
- contamination
- results are subjective
Why might someone calculate the percentage change as well as the change in mass in RP2?
To allow results to be compared as [the potato tissues] had different starting masses
exhaustive
What may have caused an anomalous result in the osmosis experiment?
- not drying (though this may lead to variable amounts fo water being removed from the potato tissue)
- potato cylinders left in salt/sugar solution for different length of time
- accuracy of balance
- concentration of solutions incorrect
What improvement could you make to the osmosis experiment?
Smaller concentration intervals
other suggestions, e.g. stated CVs
How could someone see if an experiment is repeatable?
Repeat and see if results are similar
What is the purpose of a control?
for comparison
4 marks - 6 points
Describe how you would test a sample of food to show if it contains protein?
Give a safety precaution and the reason for this
- Grinding up the food (by pestle and mortar)
- Add biuret reagant to food
- Protein turns solution from blue to purple
- Wear goggles to protect eyes
- clean up spills immediately
- Biuret is an irritant
change as appropriate for sugar and starch
