required practicals

• reaction time

  1.person 1 sits with their dominant arm resting on a table and their hand overhanging the edge of a table

  2. person 2 holds a ruler vertically with the 0cm mark between person 1's thumb and forefinger

  3. person 2 tells person 1 to prepare to catch the ruler

  4. person 2 drops the ruler at a random time

  5. when person 1 catches the ruler, person 2 records the measurement on the ruler that is level with the top of person 1's thumb

  6. repeat several times and calculate a mean

  7. use a conversion table to convert the results to a reaction time
• Effect of light on newly germinated seedlings

  1. Place a damp cotton wool in two petri dishes and place 10 seeds in each petri dish

  2. Allow the seeds to germinate for 48 hours

  3. Use a ruler to measure the starting height of each shoot

  4. Place one petri dish with light all around and place the second petri dish in a box with a hole in one side (allow light from one side only)

  5. Make sure the batch of seeds, temperature and the volume of water used to water the seedlings are the same

  6. After several hours record the appearance of the seedlings in relation to the light

  7. Re-measure the height of each shoot (if bent straighten them before measuring)

  8. Use a protractor to estimate the angle of bending
• quadrats - measure the population size of a common species in a habitat

  1.divide the area into a grid and use a random number generator to randomly select coordinates

  2. place quadrats at each coordinate

  3. use a large number of quadrats

  4. record the number of organisms within the quadrat or estimate the percentage cover if the plant is too small to count individually

  5. calculate the mean number of organisms per quadrat

  6. estimate the total population size by multiplying the mean number of organisms per meter squared by the total area in meter squared
• transects - investigating the effect of a factor on the distribution of species

  1.mark out a transect using a tape measure

  2. place quadrats at regular intervals along the transect

  3. record the abiotic factor at each point

  4. make sure the abiotic factor is measured at the same time of day

  5. repeat with more transects (repeat transects should be parallel to the first transect) to allow a mean to be calculated

  6. plot a graph of the abiotic factor against the mean number of organisms to determine if there is any relationship
• Effect of temperature on decay

  1. Add 5cm^3 of lipase solution to a test tube

  2. Add 5 drops of pH indicator solution (phenolphthalein) to a test tube, then add 5cm^3 of milk and 7cm^3 of sodium carbonate solution (solution will be alkaline)

  3. Place a thermometer into the milk test tube

  4. Place both test tubes into a water bath set to 10 degrees and leave until the solution reach the temperature and leave until the solution reach the temp of the water bath

  5. Use a pipette to transfer 1cm of lipase solution to the milk solution and stir

  6. Start a start watch at the same time

  7. Record the time taken for the solution to change colour

  8. Repeat experiment at different temperatures

  9. Repeat each temp and calculate mean

  10. Rate of decay calculated using rate=1000/time
• phenolphthalein colour change from pink to colourless
• colour changes because the lipase has broken down lipids in the milk into fatty acids (and glycerol), presence of fatty acids causes solution to become acidic