Edexcel Biology B is very scarce when it comes to finding information on it online. I've taken it upon my self to publish my own notes to help fellow students that have a hard time understanding the subject. The information in the text book is very large and can be hard to narrow down to a particu...
i Understand the basic aseptic techniques used in culturing organisms
Aseptic techniques:
● All equipment should be sterilised
● Flaming equipment in a bunsen flame ensures sterility
● Inoculation should be done with a flamed instrument
● Lids should be replaced as quickly as possible
ii Understand the principles and techniques involved in culturing microorganisms.
Problems with culturing microorganisms:
-Pathogens may enter the culture and grow, risking the spread of disease
-Safe organisms may mutate to dangerous forms
-contamination with unwanted organisms can spoil an investigation
Precautions to take
-adequate O2 supply as anaerobic conditions encourage the growth of pathogens
-culture temperature 20℃ or below as human body temperature encourages growth of
human pathogens
iii Understand the use of different media (broth cultures, agar and selective media
Microorganisms can be grown in a laboratory culture using a variety of media which provide
them with the nutrients they need.
Agar plate- Contains nutrient agar, a solid medium in which bacteria can grow. Molten agar
is usually mixed with nutrient broth and is poured into a petri and allowed to set. It acts as a
sponge to hold the nutrients in a solid block.
Selective Media-Can be used to grow specific types of organisms by using a recipe which
discourages the growth of unwanted organisms. It could rely on the addition or omission of a
certain nutrient or include an antibiotic if the desired bacteria is resistant
iv Understand the different methods of measuring the growth of a bacterial culture as
illustrated by cell counts, dilution plating, mass and optical methods (turbidity)
, Bacteria growth can be measured in various ways:
Cell counts:
● Cells can be counted using a haemocytometer. This is a microscopic grid engraved
(with a grid) with a known depth of sample which allows counts in a known volume
using a microscope.
● It is useful as it only counts viable cells so it is accurate, however the process is slow
and the equipment involved is expensive
Dilution plating:
● A culture is diluted until the number of cultures can be coined when spread on a plate
● It is useful as equipment is not expensive,only counts viable cells and obtains a direct
cell count. However it is slow as incubations periods and serial dilutions are required
Dry mass:
● A known volume of culture can be dried and weighed to find the dry mass of bacterial
cells.
Optical methods:
● Turbidimetry is a specialised form of calorimetry.As turbidimetry increases
transmission decreases and absorption increases.
● It is useful as it is quick and can be conducted in the field. However equipment is
expensive and a collaboration curve is required
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller adam24. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $32.85. You're not tied to anything after your purchase.