Required Practicals Flashcards
Required practical 1 : investigation into the effect of a named variable on the rate of an enzyme controlled reaction . What is the method for ph
- Cut 2cm cube of fresh potato and place in a conical flask with 2cm^3 ph buffer
2.put the bung securely in the flask - twist and push cafefully
3.half fill a bowl with water and a measuring cylinder and invert it over the bowl of water and the end of the rubber tubing in the measuring cylinder
4.measure 2cm^3 hydrogen peroxide into the 2cm^3 syringe . Push the plunger on the syringe and immediately start the stop clock
5.repeat with different PH buffers - Plot a graph with oxygen produced against ph
required practical 2 : mitosis in an alium root tip
procedure
1) cut off about 1cm from several root tips of some growing garlic roots. choose root tips which are white and have a firm rounded end , tips that are turning brown will give poor results
2) put the root tips into a hollow glass block containing 2cm3 1M hydrochloric acid for exactly 5 min
3) put the root tips in cold water for 5 min then dry with filter paper
4)transfer one of the root tips to a clean microscope slide . cut about 2-3 mm from the rounded growing tip
5) press down hard onto the slide with coverslip and add one small drop of toluidine blue and leave to stain for a few minutes
6)cover with coverslip and can blot if excess dye.
7) view under microscope
For beetroot practical , the student put the same volume of water in each tube , explain why it was important that he controlled this experimental value
If there’s too much water the concentration of pigment will be lower so solution will appear lighter (harder to compare solutions colour ) and therefore we use the same volume so results are comparable
How could the student monitor the temp
Take readings using a thermometer
Suggest how the increase in temperature of the water caused the release of the red pigment
As the temperature increases , this causes damage to the cell surface membrane and therefore the membrane proteins denature and increased fluidity as there’s damage to the the phospholipid bilayer
Explain the purpose of boiling the agar before pouring it onto the agar plate ( colony of bacteria has not yet been added)
Kills all unwanted bacteria so no contamination
Explain the purpose of transferring the same volume of liquid culture onto each agar plate
So same number of bacteria is transferred to allow comparison
what is students t test suitable for
when looking for differences between 2 means
describe how you would obtain a reliable mitotic index
- repeat many times
- select fields of view at random
why would bacteria in the culture after 24 hours be lower if the student did not use a sterilised pippette
new bacteria are introduced and these take up food , space and produce toxins
how do you calculate a dilution factor
origional volume / total volume now
how does a colorimeter work
- the more absorbance , the lower the transmission of light and therefore the more pigment present
what are some issues with the photosynthesis dehydrogenase practical
end point is subjective
unequal distribution of light
foil not blocking out light in all directions
why do we need to stop the photosynthesis chromatography before the solvent reaches the top of the paper
solvent front wont be able to be calculated as pigments would keep moving
Describe and explain three ways in which the scientist would ensure he used aseptic techniques to move each cube of Agar onto a new Agar plate
- Bunsen close to create upward current of air preventing contamination
- lift lid slightly to prevent entry of microbes
- flame equipment to kill microbes and prevent contamination
