practicals

• light microscope pag description

  1. thin slice of specimen
  2. take a clean slide and use a pipette to put one drop of water in the middle - this secures the specimen in place
  3. use tweezers to place specimen on the slide
  4. drop of stain if your specimen is transparent/colourless
  5. cover slip at one end holding it an angle
  6. lower it and press gently with the needle so that no air bubbles are trapped under it
  7. clip slide onto the stage of the microscope
  8. select lowest power objective lens / coarse adjustment knob to move stage up so that the slide is just underneath / adjust focus with fine adjustment knob
• Petri dish

  1)place paper discs soaked in different types of antibiotics on an agar plate that has an even covering of bacteria. leave space between some discs

  2) antibiotic should soak into the agar jelly. antibiotic-resistant will continue to grow but non resistant strains will die. a clear zone will be left.

  3)soak paper in sterile water so you can be sure that any difference between growth of bacteria around is cause of the effect antibiotic alone

  4) leave place for 48 hours 25 degrees

  5) more effective the antibiotic is , the larger it is
• Test for glucose/starch


  IF STARCH IS PRESENT IODINE TURNS FROM ORANGE TO BLACK

  IF STARCH ISNT PRESENT IODINE REMAINS ORANGE
• starch test (photosynthesis)

  1. destarch plants (i.e. leave them in the dark for 48 hours to use up starch stores
  2. to show light is required for photosynthesis, keep one plant in the dark and move the other in the light.
  3. perform starch test on leaf from each plant.
  4. leaf from the plant kept in the dark should wont turn blue-black whilst the leaf from the plant kept in the light will.
  5. this therefore shows light is needed for photosynthesis
• • Factors affecting photosynthesis (Light intensity)
  • Independent variable : distance between plant and light source
  • Dependent variable : Rate of photosynthesis (oxygen bubbles produced)
  • Put pond pond weed in test tube , add sodium hydrogen carbonate (which gives off co2)
  • Invert and put into a beaker ensuring no air at the top
  • Position lamp at a set distance measured with a metre rule , start stop clock and count how many bubbles are produced / if a gas syringe is used measure the volume of oxygen produced
  • Change the distance and repeat
• Potometer- investigating rate of transpiration

  Independent variable

  Method :Cut a plant shoot underwater - to prevent air entering the xylem

  Place the shoot in a test tube

  Making sure its airtight using vaseline to seal gaps

  Dry the leaves of the shoot

  Remove the capillary tube to allow an oxygen bubble to form

  Record starting location leave for a set period of time

  Record the end location of the air bubble

  Change the light intensity or wind speed or level of humidity or temperature

  Reset the bubble by opening the tap below the reservoir
• Quadratic sampling

  Aim: to estimate the population of an organism

  Place a 1m^2 quadrat on random grid positions in an area using a random number generator count organisms in each quadrat

  Repeat steps 1 and 2 Work out the mean per quadrat in the first sample then multiply by the total area to give an estimate

  Repeat in a second sample area
• systematic sampling

  Aim: to investigate whether distance affects a species population Method :Use a transect from the specimen outward

  Using a tape measure place quadrats at REGULAR INTERVALS

  Count the no of different species per quadrate

  Calculate the mean after repeating the transect

  Remove all anomalies
• Osmosis Practical:

  Aim: determine the sugar conc in potato cells

  Independent variable - conc of sugar solution

  Dependent variable - Measure the change in mass

  Method :

  Cut equal size cylinders from potato and remove skin

  Remove any excess water

  Remove any excess water Place each in a test tube with different conc of sugar solution

  Leave for a set time , water will move in or out due to osmosis

  Remove cylinders and reweigh to calc change in mass
• Test for sugars (Benedicts reagent)


  Add Benedicts reagent ( blue ) to a sample and heat it

  The higher the conc of the reducing sugar the further the color change goes (to red)
• Test for fats (ethanol)

  Emulsion test for Lipids

  Shake test substance with ethanol then pour it into water

  If lipids are present they will show up as a milky emulsion
• Test for proteins ( Biuret reagent)

  Add a few drops of sodium hydroxide to make the solution alkaline

  Add copper sulfate (blue)

  If there is no protein it will stay blue

  If protein is present the solution will turn purple
• Reaction times 


  Aim and observe the effect of different factors on reaction time

  Method

  Hold a ruler between a persons thumb and index finger

  LINED UP WITH THE 0CM ARK

  Drop without warning and record distance dropped before caught

  Carry out repeats and calculate a mean / average reaction time using Newtons equation of motion
• enzyme practical #1

  1. enzyme catalase catalyses breakdown of hydrogen peroxide into water and oxygen.
  2. you can calc the oxygen and measure how much's produced
  3. use a pipette to add hydrogen peroxide to boiling tube. put the tube in a water bath at 10 degrees and wait about 5m.
  4. add a source of catalase to the hydrogen peroxide
  5. record how much oxygen produced in the 1st minute
  6. repeat steps and calculate mean. repeat whole experiment with water bath at 20 degrees, 30 degrees and 40
  7. control any variables to make a fair test
• enzyme #2 amylase

  1. catalyses breakdown of starch to maltose
  2. easy to detect starch using iodine solution if starchs present, the iodine solution will change from orange to blue-black
  3. put drops of iodine into each well on the spotting tile. see how long it takes to break down all of the starch
  4. put a drop into the new well and if it does not turn blue-black it means all the starch has been converted to maltose
  5. Repeat with water bath at different temperatures to see how it affects time taken for the starch to be broken down