paper 1 practicals Flashcards
parts of a microscope
stage
slide held by clips
lamp
objective lenses, 4x 10x 40x
eyepiece
eyepiece lens, 10x
coarse adjustment knob
fine adjustment knob
how to use a microscope
- use clips to hold prepared slide in place on stage
- turn to lowest objective magnification
- at eye level, adjust coarse adjustment knob until stage is directly below lens
- look down eyepiece and readjust coarse adjustment until image comes into focus
- adjust fine adjustment knob until image is clear
- change objective lens and repeat steps 3-5 for larger magnifications
how to avoid contamination when culturing microorganisms and why
- petri dish, nutrient broth and agar must be sterilised
- pass inoculating loop through flame to sterilise it
- petri dish lid should be taped on to
- store petri dish upside down
kill or prevent unwanted microorganisms and prevent contamination
what temperature are culture mediums kept in
in school - 25 degrees, to prevent harmful pathogens that grow at temperatures above
how to culture microorganisms for antibiotics
- sterilise petri dish and culture medium
- pass inoculating loop over flame to sterilise it
- use loop to evenly cover plate with bacteria
- place paper discs soaking in different antibiotics onto plate
- place one control disc, that has been soaked in sterile water to make sure the antibiotic is the only factor affecting bacteria
- incubate upside down for 48 hours at 25 degrees
- observe inhibition zones - larger = more effective antibiotic
how does culturing microorganisms work
antibiotic soaks into jelly.
antibiotic resistant bacteria can continue to grow around the discs, whereas non resistants will die. clear area left where bacteria dies: inhibition zone
how to investigate concentration on osmosis
- peel a potato and use a cork borer to get 3 cylinders on equal diameter
- use scalpel and ruler to cut each cylinder to 3cm
- record mass of each cylinder
- place each into test tubes of different concentrations, one being pure distilled water
- leave overnight
- remove cylinders and pat dry to remove excess water
- remeasure masses, calculate percentage change, plot graph
how to prepare food for food test
- grind sample with distilled water in mortar and pestle to make paste
- transfer to beaker and stir with more distilled water to dissolve the chemicals
- filter the solution to remove solid food
what carbohydrates can be tested for
starch and sugars
how to test for starch
- put 2cm cubed food solution in test tube
- add a few drops of iodine solution
if present: iodine turns browny-orange to bluey-black
how to test for sugar
- put 2cm cubed food solution in test tube
- add 10 drops benedicts solution
- place test tube into water bath of hot water from kettle
- leave for 5 mins
if present: B’s solution turns blue to green to yellow to brick red depending on how much reducing sugar
how to test for protein
- put 2cm cubed food solution in test tube
- add 2cm cubed biuret solution
if present: B solution turns blue to purple
how to test for lipids
- put 2cm cubed UNFILTERED food solution in test tube
- add a 3 drops Sudan III stain solution and gently shake
if present: two layers form, top one bright red
how to investigate effect of pH on amylase
- place 1 drop of iodine solution into each well of spotting tile. amylase enzyme catalyses the breakdown of starch, iodine turns blue black if starch is present
- fill three test tubes with 2cm cubed of: starch solution, amylase solution, and pH 5 buffer solution (controls pH)
- place test tubes in 30 degree water bath for 10 mins to allow them to reach correct temp
- combine three solutions into one solution and mix with stirring rod
- start stopwatch
- after 30 secs, transfer one drop of solution to a well on tile. iodine should turn blue black
- add solution to each tile at every 30 secs until iodine remains orange, when starch is no longer present, and record time of this
- repeat with different pH buffers
limitations of investigation of pH on amylase
- only taking samples every 30 secs, result is approximate
- stopping when iodine stays orange is not always obvious, subjective
how to investigate effect of light on photosynthesis
- place boiling tube 10cm away from led light source (keeps temp stable)
- fill tube with sodium hydrogen carbonate solution (gives CO2)
- put pondweed in tube
- attach capillary tube with gas syringe attached
- start timer
- after 1 min, use syringe to draw gas bubble alongside a ruler. this is proportional to volume of O2 produced
- repeat 2 more times at 10cm
- repeat whole experiment at 20cm, 30, 40, 50
