Practicals Flashcards
Why was a root tip and stain used, and why was the root firmly squashed (RQ2 - mitosis)?
Root tip: Where mitosis occurs
Stain: To distinguish chromosomes
Squashed: Thin layer to allow light through
What is the equation for calculating how long cells spent in one stage of mitosis (RQ2)?
number of cells in that stage/total number of cells) x time taken for 1 cell cycle
What is the equation for calculating mitotic index (RQ2)?
number of cells in mitosis/total number of cells
How is the length of a cell estimated using an optical microscope (RQ2)?
Measure length with eyepiece graticule and calibrate against stage micrometer of known length
How can a results table be used to find the water potential of plant tissue (RQ3)?
- Plot graph with conc. on x-axis and % change in mass on y-axis
- Find conc. where curve crosses x-axis
- Use another resource to find water potential where curve crosses x-axis
Why is the tissue cut into discs and blotted dry before weighing (RQ3 - water potential)?
Discs: Increases surface area for osmosis
Blotted dry: Solution would add to mass of discs which would vary results, giving inaccurate change in mass
What are the reasons for differing results with the same procedure (RQ4 - membrane permeability)?
Variation in beetroot or judgement of colour
Why does the amount of colour in the solution increase as concentration of alcohol increases (RQ4 - membrane permeability)?
Phospholipids in membranes dissolve in alcohol so membranes break down faster which allows faster rate of diffusion of pigments so more pigments move out of cells
What precautions should be taken when carrying out a dissection (RQ5)?
Take care with scalpel when cutting tissue by not cutting towards hand, use gloves, disinfect bench, safely dispose of sample
Why is working in close proximity to a Bunsen burner important (RQ6 - effect of aseptic technique on microbial growth)
Creates convection current that causes bacteria to rise up away from plate so bacteria doesn’t contaminate plate
Why is flaming the neck of the bottle containing E.coli culture important (RQ6 - effect of aseptic technique on microbial growth)?
Kills any other bacteria which may be on bottle so sterile pipette used to collect bacteria isn’t contaminated
Why is only slightly raising the lid of the Petri dish important (RQ6 - effect of aseptic technique on microbial growth)?
Avoids any bacteria in the air contaminating Petri dish
Why is dipping the glass spreader in alcohol and flaming it before and after use important (RQ6 - effect of aseptic technique on microbial growth)?
Sterilises the spreader
Why is leaving the spreader to cool before spreading the liquid over the surface of the agar important (RQ6 - effect of aseptic technique on microbial growth)?
Doesn’t kill bacteria on the plate that you want to grow and investigate
Why is securing the lid of the Petri dish with 2 pieces of tape important (RQ6 - effect of aseptic technique on microbial growth)?
Allows O2 to get in so bacteria can respire to produce ATP needed in growth/replication
