Practical activity: Growing a bacterial culture 1HVTTO 2.2

• Biologie
• Middelbare school
• havo, vwo
• Leerjaar 1

Growing a bacterial culture

• Jacket in your locker
  
• Put your things on your desk
  

       No Laptop!

       Workbook
       Notebook, pencil case

• Bag on the floor
  
• Read page 36 workbook 

Lesson goals

• You have practised with the steps of a scientific experiment
• You are able to report on your results in a logical and clear manner
• You can draw conclusions based on results

Exercise 5 - Lab: Growing a bacterial culture (page 36)

Bacteria are microorganisms that grow everywhere. We can collect and grow them in specially prepared Petri dishes. 

A single bacterium is too small to see without a microscope. 

However, as bacteria divide, they form small colonies that you can see with the naked eye.

You will transfer bacteria to the prepared Petri dish via direct contact. You will test the effectiveness of soap by treating different Petri dishes with ‘dirty’ hands before washing and ‘clean’ hands after washing. You will also press a variety of common objects like coins, combs, etc. onto different plates and compare the bacterial growth that results.

Exercise 5 - Lab: Growing a bacterial culture (page 36)

Materials:

• Prepared Petri dishes with agar medium and nutrients
  
• Bacteria on hands and other small objects (coins, combs etc.)
  
• Marker pen (waterproof)
  
• Masking tape
  
• Soap or other detergent
  
• Small objects: coins, eraser, etc.

Exercise 5 - Lab: Growing a bacterial culture (page 36)

Method:

1. Turn the Petri dish upside-down and divide the bottom into quarters, by drawing a cross with a marker pen.
   
2. Number the corners of each section 1 to 4. Also write the first letter of your first and last name
3. When opening the petridish, be quick, if it stays open for too long you can ruin the experiment!
4. Without damaging the agar surface, gently press your finger onto section number 1 of the agar.
   
5. After washing your finger and drying it, gently press the same finger onto section number 2 of the agar.
   
6. On page 37 of the workbook, indicate for each number what object you used!
7. Gently press a small object onto section number 3 and remove it. Use cotton swabs if needed.
   
8. Gently press a second small object onto section number 4 and remove it.
   
9. Replace the cover of the Petri dish, tape it closed and let your teacher put them in an incubator for several days. 

Next week > Results

Exercise 5 - Lab: Growing a bacterial culture (page 36)

Research question:

Complete the research question by filling in a 3rd and 4th object you want to test for the presence of bacteria.

Which surface contains the largest number of bacteria, a finger tip, a washed figer tip, a

_______________or a _______________ ?

Hypothesis:

Predict what the answer to the research question will be.

Exercise 5 - Growing a bacterial culture (page 37-38)

Results

1. Don't open the dishes!!! The bacteria inside can make you very sick!
2. Compare the 4 objects by counting the number of colonies (amount of dots!) in the different sections.
   
3. For each number write a short description of the amount of colonies. If you see different colours or different sizes of colonies be sure to add that to your description
4. Make a drawing in the boxes for each of the 4 number.

 if you don't have enough space in your workbook, use your notebook or laptop!

Conclusion

Reread your research question and try to answer it using your results

Discussion

Describe if something might have influenced your results, and what this might mean for

your conclusion

For example: the petridish was damaged, open very long, etc.

How to write a conclusion

Our question was ….(repeat question)…?

The answer to this is …………… 

We know this because …(add important results, that support your conclusion)…. 

Our hypothesis was wrong/correct

How to write a discussion

Describe things that happened during the experiment that might have positively/negatively impacted your results:

• We weren't/were very careful with the petri dishes
• We damaged the agar in the dishes
• We kept the dishes open for too long/made sure to keep them closed
• We didn't keep track of the results in an orderly manner/ lost some results / didn't write everything down
• We used tables or other tools to structure our results 

End your discussion with a short description of how all of this impacts your conclusion: do you think your conclusion is accurate? 

Write a report

Use everything you've written on the pages 36-38 to make a report based on this experiment.

In some time you'll hand it in and earn a mark!