Download this file for the experiment:Yr 10 PRAC Water quality Experiment2
HYGIENE Name of students in the group:____________________________________ Date:
Aim: To observe and identify the microbes found in water samples
Materials: 1 sterile nutrient agar plates (per group)
1 sterile pipettes
Marking pen, sticky tape
Water samples – tap water, untreated dam water, commercial bottled water (unopened), water bottle (drunk from), filtered water
- Collect 1 sterile agar plates (all poured with the same nutrient agar) per group. (If resources are available, you may be given 5 agar plates per group).
- Label each petri dish with the water sample to be placed in it, date, name (write information on the base of the agar plate around the edge)
- Leave one plate unopened and seal (label it – control)
- For each of the plates use sterile, aseptic techniques to draw up a 0.5ml sample of each water to be tested. Squeeze the 3 or 4 drops of water sample from the pipette onto a clean new cotton bud and ensue . Use this cotton bud to inoculate onto the plate (especially lifting the petri dish lid on angle only to minimise the risk of contamination with microbes from the air). You can draw an shape (or an alphabet) across across the surface of the agar.
- Seal petri dish with sticky tape (by winding the tape around the edge at the closure point) and place in the storage tray (with the agar base side upwards)
- Incubate the plate at 300C for 48 hours (this decreases the risk of growing human pathogens)
- Examine the plate (DO NOT OPEN)
- Record the number and types of colonies visible through the petri dish lid
- Collate class results on shared google drive (to ensure reliability of your results through repetition for a science experiment)
SAFETY RISK = potential spread of pathogenic organisms
SOLUTION = Incubate at 300C only (not body temperature to minimise chance of growing human pathogens)
= Ensure plates fully sealed and never reopen (to stop exposure to potential pathogens)
= Dispose of plates correctly at end of experiment (all plates placed in a pressure cooker and exposed to heat and pressure to destroy all microbes before disposal)
Results for Hygiene – Water samples
|Bacterial colonies (estimation)||Fungal colonies (estimation)|
|Number of different types||Total number of colonies present||Number of different types||Total number of colonies present|
|Unopened bottled water.|
|Bottled water (used)|
|Tap water from the Science lab.|
- Purpose: What do you want to learn?
2. Hypothesis: What do you predict will happen?
3. Was your hypothesis proved or disproved?
4. a) What is the dependent variables? (The variables (things) that you as a scientist focus your observation on to see how they respond to the changes made to the independent variables).
b) What is the independent variable? (The variable that is changed to allow comparisons).
c) List the controlled variables (Controlled variables are quantities that you as a scientist wants to remain constant so that the experiment can be considered as a fair test).
5. Discussion: Which water sample had the least number or range of microbial colonies?
6.Research why this may be so (hint: look at water treatment for Sydney). You may use the links below for your research.
Videos: Your drinking water (Sydney Water) 3 mins
Sydney water filtration animation (3 mins)
The science behind why you should not share the towel.