Life Sciences lab classes explained

I have had a request to write a post on significant figures!! So, here we go…. There is one simple rule for you to follow. Look at the information you are putting in to your calculation, and identify the value that has the  fewest significant figures  – this is the number of significant figures you will put in your answer!    It is that simple. An example: Lets look at the question in your 109 workbook (workshop 2) on the mass of the whale plus all the barnacles, micro-crustaceans and bacteria on that whale…. Lets just think about the mass of all of those micro crustaceans. You are told that a micro crustacean weighs  0.5 mg , and that there are  150  of them on one barnacle, and there are  34000  barnacles on the whale. So what is the total mass of the micro crustaceans on the whale? This is a simple enough question, you just multiply the mass of one micro crustacean with how many micro crustaceans you have on one barnacle, by how many barnacles you have on o

This post is related to the third activity in your next practical - the one dealing with mushroom compost.... Part of this activity will involve  re-suspending  your mushroom compost sample into a solution, and then  diluting  this down using  serial dilutions  before plating it onto agar plates ready to grow for next week. You may be feeling unsure about how to do these serial dilutions. Here is a quick schematic for what you will be doing: Things to note from this figure: - Obviously this week you will not see any colonies on your plates - these will appear for you to look at next week - I have drawn these on the above figure so you can see what to expect. - The serial dilutions are all 10 x dilutions. i.e. each time you do a dilution you are diluting the cells 10 x.   - For the Novobiocin treatment (see table 1 on page 88 of your lab manual) you will plate out your undiluted sample and your 10 -1  and 1 0 -2  samples....any thoughts on why you use different dilutions for

In practical 5 you will be  streaking bacteria onto agar plates . The whole point of this is to  dilute the bacteria  so you end up with one region on the plate that has  discreet bacterial colonies  that have originated from one bacterium. You can then assume that all bacteria in one colony are identical. To give you a head start, here is a video that shows you how to streak an agar plate... So it is pretty simple really. The biggest problem a lot of you will have is that you will press down too hard on the agar with the loop, and end up digging the loop into the agar. Just be gentle and remember, practice makes perfect!

In you next practical you are going to be plating out bacteria onto agar plates, and there are a couple of terms you are going to come across,   selective media   and   differential media ...so, what are these? Selective media   is exactly what it sounds like - 'media' that 'selects'! (When someone says 'media' in the context of growing bacteria, they really mean food.)   So, selective media is basically food that you can give to a mixture of bacteria on which only some of the types of bacteria in that mixture will be able to grow. For example, you might have an antibiotic in the media. In this case, only bacteria that are resistant to that antibiotic will be able to grow on that media - any other bacteria won't survive. Differential media   is more fancy. It is selective as it will only allow certain bacteria to grow, but it also makes the colonies of the strains that it does allow to grow have different morphologies so

Practicals 5 and 6 are all about working with   bacteria .  You will be learning how to separate out the bacteria from a mixture, and how to then characterise these bacteria. ! IMPORTANT ! Practical 5 is divided into two parts.  You will be doing the first part one week, and then because the bacteria you are working with need time to grow, you will be doing the second part of the practical the next week.  During the next two weeks you will be: learning how to safely handle and manipulate microorganisms (using aseptic technique) using the microscope using various techniques to characterise bacteria such as the Gram Stain plating bacteria on agar plates to obtain single colonies testing bacteria for antibiotic sensitivity testing whether bacteria are anaerobic or aerobic determining viable cell counts There is quite a lot to do for this practical -  it is really important that you read your manual before you come  so you have an id

Worried about how to calculate concentrations or volumes when you do dilutions? You might appreciate a little demo of  C1 V1   =  C2 V2  in action.... First some definitions: C1  = The concentration of your stock solution C2  = The final concentration after performing the dilution V1  = The volume of your stock solution your need to take V2  = The final volume your diluted sample will have Ok, so lets say we have a stock solution of 1M of NaCl. We want to have 500mM NaCl  AND  we want our diluted sample to be 2mls total volume. How much of our stock solution will we need? Lets look at this again, but this time I have written in where the  C1   V1   C2  and   V2  are: We have a stock solution of 1M of NaCl ( C1 )  . We want to have 500mM NaCl  ( C2 )   AND  we want our diluted sample to be 2mls total volume  ( V2 ) . How much of our stock solution will we need  ( V1 ) ? So, now you just need to slot all this in to the wonderful  C1 V

I know a lot of you find  % (w/v)  as a way to express concentrations a little tricky. Here is a % (w/v) question to help me explain.... Question: Express 4g in 2L as % (w/v) With % (w/v) you want to find out what percentage the weight you have  (in grams)  is of the volume you have  (in millilitres).  It is important to always have your units in  grams  and  ml  when dealing with  % (w/v) . In this specific question, you need to find out what percentage 4 g is of 2 L of water, which is 2000 ml... So to figure this out you could do: 4/2000 x 100 =  0.2  % (w/v) . If that doesn't make sense to you, you could do 2000/100 = 20 -> so now you know that 1 % of 2000 is 20. Then you could find out what percentage 4 is of 2000 by doing 4/20 =   0.2  % (w/v). If you were then making up this solution in the lab, you would weigh out your 4 g of solute, and then put it into a 2L volumetric flask - you would then make the volume up to 2L. You would not take 4 g of solute and add to