SBI3U Page 6

Bacterial Growth and Inhibition Lab V3

Name: ______Partner: ______Due Date: ______

Complete a self-assessment before submitting the lab report. Be sure all work is attached.

Section

/ Mark

Pre-Lab Question

- materials list ......
-storyboard ......
- purpose ......
- hypothesis ......
- 6 variables affecting bacterial growth ......
- independent variable ......
- dependent variable ......
- controlled variables ......
- reason for observing a not inoculated plate ...... /
0 1 2
0 1 2
0 1
0 1
0 1 2 3
0 1
0 1
0 1 2
0 1

Observations – must hand in original data

- Logical design of table for 2 days and 4 quadrants
- Observations include the colour, amount of growth(% of surface area), surface texture of colonies, edges of colonies, height of colonies
- The sketch follows all of the rules for a scientific drawing: uses pencil, blank paper, title, labels, drawn to scale, stippling, neat / 0 1 2
0 1 2 3 4
0 1 2 3 4

Conclusion

States whether or not the hypothesis was supported / 0 1 2

Discussion and Analysis Questions

- conditions required for bacterial growth
- incubation directions and reasons for incubation
- alcohols effectiveness / 0 1 2
0 1
0 1 2
Errors and Improvements
- two sources of error
- improvement to lab design
- future research directions / 0 1 2
0 1
0 1 2

Overall Communication

a)  The lab report is complete and in the correct order, is neat and easy to read and on time. Label each section.
b)  Grammar, spelling and sentence structure are correct
c)  Uses formal laboratory language, written in the third person past passive verb tense, “my bacteria growth was excellent” vs. “The bacteria growth was noticeable.” / 0 1 2
0 1 2
0 1 2

TOTAL

/ /42


Bacterial Growth and Inhibition Lab - 2011 (V3)

Name: ______Partner: ______

Introduction

You can find bacteria everywhere, even on your desk and on your skin. Although they are much too small to be seen individually without the help of a powerful microscope, you can see evidence of their presence by growing colonies in this lab. In the first part of this investigation, you will collect bacterial samples from our school and investigate the effect of a disinfectant on bacterial growth. After a few days of incubation, you will examine and describe the bacterial colonies and possibly fungi growth.

There are many variables that can affect the growth of bacteria. In this lab bacteria from surfaces in the school will be cultured and the use of alcohol to inhibit bacterial growth will be examined. The lab answers will be written in a formal style with the use of the third person past passive verb tense.

Safety:

You must use caution and good judgment when working with bacterial cultures. Always wear gloves and wash your hands after handling any culture. Petri dish lids should remain closed unless you are transferring samples. Once you have collected your samples, your Petri dishes must be closed and never opened. You must follow your teacher’s instructions for disposing of all swabs, cultures and Petri dishes.

Note: For safety reasons, you are not permitted to sample inside washrooms, or take samples from individuals. Samples from here will receive a mark of zero.

Pre-Lab

1. Carefully read the entire lab and the rubric before answering the following questions.

2. Complete a two column list of the materials.

3. Sketch a storyboard with 6 scenes showing the procedure.

4. Make an observation table.

The following answers must be neatly written on a separate paper. Double space. Use your text for support.

5. What is the purpose of the lab?

6. State a hypothesis.

7.a) List six variables that will affect bacterial growth.

b) What is the independent variable in the lab?

c) What is the dependent variable in the lab?

d) What are three controlled variables in the lab?

e) Why is a not inoculated plate required for observation?

Materials:


Procedure:

1.  Wipe your desk thoroughly with cleanser. Dry the desk with paper towels.

2.  Turn the Petri dish upside down and using a grease pencil or permanent marker, label the bottom as shown below. Add the date and your initials to the edge of the plate.

Note: Prior to collecting Samples B and D, the area will be sterilized with alcohol.

3.  Collect bacteria from 2 different locations in the school. Record the locations on your observation table.

a) Sample Transfer technique

Transfer the sample immediately after collection. To transfer samples, slide off the lid of your Petri dish, using a “Z” pattern, gently streak the surface of the agar with a swab of each sample. Ensure that you place your sample in the center of the quadrant.

b) Location 1

Sample A and B represent samples that will be taken from the first location. Sample A will be collected by dipping the swab in the source agar bottle, and then gently wiping the surface of the selected object. Next the swab will be gently swiped across the agar plate quadrant A. Do not break the surface of the agar.

Prior to taking Sample B, the area will be disinfected with rubbing alcohol. Repeat the same process as above and swiped on quadrant B.

c) Location 2:

Quadrants C and D represent samples that will be taken from the second location Sample C will be collected by using the procedure outlined for Sample A. Sample D will collected in the same manner as described for Sample B.

4.  Bring all materials back to class. Put all materials in their designated spots. Dispose of the swabs in the biohazard disposal bag provided by your teacher.

5.  Tape the Petri dishes closed, turn it upside down and place it in the incubator.

6.  Spray Enviroclean on desk and wipe. Wash your hands with soap and warm water.

Observations

In two subsequent classes the Petrie dishes will be examined. The following page provides information about features of bacterial colonies that can be observed. Record qualitative observations about the appearance of the bacterial colonies.

Using the grid provided, determine the % of each quadrant’s surface that the total bacteria colonies occupy. This is a quantitative observation.

On the second day of observations complete a sketch of the Petrie dish as well as the day 1 observations. Use the circle on the last page of the handout for the diagram.

Be sure to record observations of the Petri dish that was not inoculated with bacteria.

Observation Tables

The following answers must be neatly written on a separate paper. Double space. Use your text for support.

Conclusion

Write a statement about whether or not the hypothesis was supported.

Discussion and Analysis

1. What general statements can be made about the conditions required for bacterial growth?

2. What temperature are the bacteria incubated at? Why is that temperature used? Why are Petrie dishes incubated upside down?

3. What general statements can be made about the effectiveness of alcohol as a disinfectant based on the results of this lab?

Errors and Improvements

1. Describe two possible sources of human error in this lab.

2. What is one suggestion for improving the lab design? This is not asking about how to correct the human errors.

3. What are two future research questions that could be asked based on the results of this lab?

Criteria Used to Describe Bacterial Colonies

·  Form - What is the basic shape of the colony? For example, circular, filamentous, etc.

·  Elevation - What is the cross sectional shape of the colony? Turn the Petri dish on end.

·  Margin - What is the magnified shape of the edge of the colony?

·  Surface - How does the surface of the colony appear? For example, smooth, glistening, rough, dull (opposite of glistening), rugose (wrinkled), etc.

·  Opacity - For example, transparent (clear), opaque, translucent (almost clear, but distorted vision, like looking through frosted glass), iridescent (changing colors in reflected light), etc.

·  Pigmentation - For example, white, buff, red, purple, etc.

From: http://www.sciencebuddies.org/science-fair-projects/project_ideas/MicroBio_Interpreting_Plates.shtml


Sketch of Petrie Dish – Observation Day 2

Follow all the rules for a good scientific diagram listed on the rubric.