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This is the last of the practical based SACs.
Be clear that although this SAC is using bacteria as the experimental organisms this SAC is NOT directly about pathogens and disease. I will not be assessing you on this at all. This SAC is to do with reponding to a stimulus. So, course notes 3, 4 and 5 are the relevant sections.
The other thing about this SAC is that you as a class will have to design the experiment and make decisions about whether it will be a class approach or small group approach etc.

biol 3 page 1 bacteria sac 2009.doc (in case you need another copy)
Link to experiment results and other info. biol 3 bacteria response results
There are four stages to this SAC.
  1. Friday (Preparatory stage)-planning of experiment and demonstration of techniques
  2. Monday (Experimental stage)-carry out inoculation of plates with bacteria under various conditions
  3. Wednesday (Results stage)-after incubation record observations and take measurements
  4. Friday (Conclusion)-Write up of summary report

Bacteria response advice
There are two main areas to this SAC. You need to be able to show an understanding of the
  1. experiment by being able to analyse/interpret your results and the methods you used
  2. theory relating to homeostasis and the stimulus-response model and apply this knowledge

Key concepts for you to focus on in relation to dot point 2 above include
  • principle of homeostasis
  • stimulus-response model
  • role of endocrine system and nervous system
  • types of signalling molecules and their role in both humans and plants
  • be familiar with an example of your own so that you can use it to explain any of the above points


Any questions related to the SAC can be posted below.

Q. sorry if i missed when we arranged this, but are we going to be in groups of 3 or 4 or work as a class, and how many different conditions will we be experimenting (e.g. test an agar dish without bacteria too?)
A. It will be up to you decide the size of the groups, whether each group works on its own and what sort of agar dishes you will set up. This is your experiment and I am not going to tell you how to go about it. Just remember that there are a total of 60 agar plates available and that you should meet the requirements that I set out in the introductory praragraph. You can ask for my advice on what you are planning to do but otherwise go for it. VM

Q. Do we need to be familiar with the specific regulatory methods of homeostasis? (i.e. specific temp. regulation pathways)
A. OK, good point. I would like you to treat this SAC as if it was the exam in this sense. So, I will not be asking you to remember specific details about any particular one. But you should be familiar with at least one specific example and more importantly understand the main principlies of how organisms detect stimuli and respond to them. VM

Q. Firstly, whoever asked the question, we are in groups of 3 or 4. Secondly, what do we actually have to do to be ready for tomorrow? How do we set up the prac? From what i understand we have two antibiotics, one natural one manufactured, we also have 2 bacteria. Do we need to test each bacteria under the two diferent antibiotics and see how they respond? that would mean there is 4 petri dishes there + 2 for the bacteria without antibiotics. Therefore 6 agar plates per group. Would it be wiser to have each group do one thing? i guess that wouldn't get us very good results if we only had one test for each condition. So if we have 6 plates per group with the different conditions i said before, does that equal the right experiment? i need a bit of guidence. Bono
A. Typically Sunday B-----dy Sunday before you ask a question. Always at the last minute :-). Anyway, your thoughts are relevant and insightful. You have raised valid points about how you should tackle the experiment. I am not going to tell you all what to do but here are three distinct possibilities and a related question that you need to think about. 1) Each group does their own experiment, how many agar plates will that leave for everyone? 2) Or as you have mentioned two groups could team up and one group does one type of bacteria and the other group does the other and you could combine your results-but what must you ensure?. 3) Or each group could do exactly the same thing as every other group and you combine your results-why would you do that? As mentioned above where the comment has no name, you can ask me for an opinion otherwise all I want is you to decide. If you still haven't found what you are looking for here, then I will comment further in tomorrow's lesson or you'll just have to rely on an angel of Harlem to give you some guidance. V(an)M(orrison)

Q. Answer taken on board but doesn't really help me. i guess im just looking for conformation that i have the right idea in mind about what we are actually doing. Also, i have absolutely no idea at this stage how the experiment shows us about detecting and responding. The fact that they might grow around the antibiotic doesn't mean anything because they could still be growing in the region of the antibiotic but dying. Are they supposed to detect the antibiotic, then respond by creating an antibody to it or some sort of immunity? I'm confused. L.Trotsky
A. Ok, it may seem a little vague but you don't have any results to anaylse yet, so it is difficult to make any conclusions at this stage. But the key here is that you have potentially three different environments that you are exposing a living organism to. You do not need to worry about understanding (at the molecular level) because the prac is not testing that. You might suggest possible molecular mechanisms but how can you possibly know? All you can do is interpret, analyse and make conclusions based on the results you obtain. You might want to read the blitzing bacteria prac in the student workbook as well as the handout on microbial drugs that I gave you in the last lesson. VM


Q. What is the role of the nervous system in homeostasis? Is it the fact that the hypothalamus is part of the brain which is a part of the CNS yet the hypothalamus is a link to the pituitary which is involved in homeostasis? Or is it a sensory receptor thing? Do neurotransmitters play a role? - because i thought they were just involved in message transmission, not homeostasis.
A. You are missing the bigger picture here. Off course the nervous system is part of homeostasis just like the endocrine system. Both of these systems are involved in sending information around the body to an effector that produces an appropriate response. Isn't shivering part of the homeostatic mechanism for temperature control? How will the skeletal muscle contract if the nerves do not send a message to them to do so? And therefore how can messages get from the hypothalamus to skeletal muscle if neurons do not communicate with each other? And what do neurotranmsitters do? Allow neurons to communicate with each other! Therefore they are crucial to homeostasis, just like any other signalling molecule we have covered (except probably pheromones which work outside of the organism). VM

Q. is it valid to say that the aim of the experiment is to investigate the response/effects of bacteria being places in different environments?
A. Absolutely. Is this not what the experimental method was trying to show. VM

Q. will there be any questions in the PRAC section relating to HOMEOSTASIS?
A. Hmmm... What can i say. I am glad someone has raised this question as I feel I need to elaborate on this. I at no stage have said that this prac directly relates to homeostasis and that you need to be able to make this link. Therefore I will not be asking you any questions on this for the prac bit. Obviously expect homeostasis questions in the not prac bit of the SAC report. However, it is important that you are thinking about how the prac relates to theory. As I have mentioned above, I will be asessing you on you ability to analyse the results and methods for the prac bit. I do expect you to be able to understand that you have put bacteria in different enviroments and that as a result of this stimulus they have responded in some way. Beseder.VM

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