Lab 8 Biology

You will serially dilute a known mass of soil, make agar plates ofthe dilutions and estimate the number of microorganisms in theoriginal mass of soil by counting thenumber of colonies on selected agar plates and multiplying by thedilution. Easy. Kind of fun but makesyou use the old bean. Plus you cantake the incubated agar plates homeif you like.

These are the dilution bottles

The first one (10-1) has glass beadsto help disperse the soil you add.

Add soil to first dilution bottle and shake to disperseSince you used 10 g of soil andthere are 90 mL of (sterilized) waterin it to begin with, every 1 mL of thesuspension contains 0.1 g of soil,hence, it is the 10-1 dilution.

Take 10 mL of it and transfer to thenext dilution bottle to give the 10-2

dilution and so forth on to 10-7

Pipette 1 mL of specified dilutions to petri dish, add agar, swirl and incubate 1 week