Microscopy + Bacterial division Flashcards
State the two types of microscopes
Light microscope
Electron microscope
Microscopes allow us to ____
Microscopes allow us to magnify
State the limitations of using light microscopes
Light microscopes have a limited resolution
State the advantages of using electron microscopes over light microscopes
Electron microscopes have a much greater magnification and resolution than light microscopes
What is the equation needed to calculate the magnification of the microscope
magnification = size of image / size of real object
https://bam.files.bbci.co.uk/bam/live/content/zywqy4j/large
https://bam.files.bbci.co.uk/bam/live/content/zywqy4j/large
The real size of the cell dividing is 0.05 mm. Calculate the magnification
Use a ruler to measure the image size of the dividing cell dividing in mm
https://bam.files.bbci.co.uk/bam/live/content/zywqy4j/large
magnification = size of image / size of real object
magnification = 100mm / 0.05 mm
magnification = x2000
Measure the length of the cell shown
The magnification is 2000x
Calculate the real size of this cell in mm
https://bam.files.bbci.co.uk/bam/live/content/zywqy4j/large
Magnification = x2000
Size of image = 100mm
Size of real object = size of image / magnification
= 100/2000 = 0.05 mm
Define magnification
Magnification is the degree to which an image is made to appear bigger
Define resolution
Resolution is the smallest interval measurable between two points on an image
Define binary fission
Binary fission is reproduction by simple cell division, for example in bacteria
describeHow do bacteria multiply/reproduce
Bacteria multiply by simple cell division (binary fission)
One bacteria cell splits into two bacterial cells (binary fission)
Bacteria reproduce by binary fission
Give two things that help maximise the rate of binary fission
Bacteria multiply by simple cell division (binary fission) as often as once every 20 minutes if they have (enough nutrients and a suitable
temperature).
If conditions are suitable how often can a type of bacterium divide by binary fission
Bacteria can reproduce as often as once every 20 minutes
Under ideal conditions, a type of bacterium divides every twenty minutes. Calculate the number of bacteria present after three hours
number of bacteria = bacteria at the start of growth period x 2 ^(number of divisions)
Step1) Work out how many bacteria have divided in 3 hours
3 hours = 180 minutes
Bacteria divide every 20 minutes
180/20 = 9 rounds of division
number of bacteria = 1 x 2^9 = 512 bacteria
Under ideal conditions, a type of bacterium divides every twenty minutes. Calculate the number of bacteria present after eight hours
Write your answer in standard form.
number of bacteria = bacteria at the start of growth period x 2 ^(number of divisions)
8 hours = 480 minutes
480 / 20 = 24 rounds of division
number of bacteria = 1 x 2^24 = 16, 777, 216
1.6777216 x10^7
or
1.678 x 10^7 (to 3dp)
State some ways to culture bacteria
The culture medium used can be a nutrient broth solution or agar gel plates (contains agar gel and petri dish)
what does the nutrient broth solution contain
Why is the nutrient broth solution cloudy
https://www.youtube.com/watch?v=BkbLI2mAMP8&list=PL9IouNCPbCxVU74eQtCcqbaQdYmwzAnlC&index=11
bacteria growing in a nutrient broth solution
Nutrient broth solution contains all the nutrients the bacteria need to grow and divide
contains a very large number of bacteria
What is a culture medium
A culture medium is a liquid or gel used to support the growth of microorganisms or other cultures, often containing specific nutrients
What does the culture medium contain
The culture medium contains the carbohydrates, minerals, proteins and vitamins the bacteria need to grow
Describe how to prepare an uncontaminated
culture using aseptic technique
Sterilise all Petri dishes, bacterial nutrient broth and agar. This kills any unwanted microorganisms and it prevents contamination.
Transfer the bacteria into the culture using an inoculating loop. Before using it, sterilise the inoculating loop by passing it through a Bunsen burner flame
After transferring the bacteria onto the dish, attach the lid of the Petri dish using adhesive tape. This stops the lid from falling off and unwanted microorganisms from entering.
Place the agar plate upside down into an incubator. This stops moisture from dripping down on the bacteria and disrupting the colonies
In school laboratories, cultures should generally be incubated at
25°C. This reduces the chances that harmful bacteria will grow.
Explain why in school laboratories we normally incubate bacteria at 25 degrees celcius
In school laboratories, we normally incubate bacteria at 25 degrees celcius
This reduces the chances that harmful bacteria will grow.
Describe how to investigate the effect of antibiotics on bacterial growth
- Clean the bench with disinfectant solution. This kills microorganisms that could contaminate the culture.
- Sterilise an inoculating loop by passing it through a Bunsen Burner flame
- Open a sterile agar gel plate near a Bunsen burner flame. The flame kills bacteria in the air.
- Use the inoculating loop to spread the chosen bacteria evenly over the plate.
- Place sterile filter paper discs containing different types of /different concentrations of the same antibiotic onto the plate.
make sure you use a control - this is a paper disc that has not been soaked in an antibiotic. Instead soak it in sterile water.
leavesome space between the discs
- Incubate the agar gel plate at 25 degrees celcius. The plate is incubated at this temperature to reduce the chances that harmful bacteria will grow.
Describe what can be seen when the experiment on investigating the effect of antibiotics on bacterial growth has been completed.
The bacteria formed a layer on the surface of the agar gel.
Around the antibiotic discs, we have a region where the bacteria have not grown. This is called the zone of inhibition
How to measure the effect of the antibiotic
To measure the effect of the antibiotic, calculate the area of the zone of inhibition.
Use the equation: area = πr^2
r is the radius of the zone of inhibition
If the radius is 12mm work out the zone of inhibition
area = πr^2
area = 3.142 x 12^2
araa = 452.45 mm^2 (to 2d.p.)
Why is it important to use a control (paper disc) when investigating the effect of antibiotics on Bacterial growth
By using a control paper disc, you can be sure that any difference between the growth of the bacteria around the control disc and around one of the antibiotic discs is due to the effect of the antibiotic alone
To show that any difference in growth of the bacteria is only due to the effect of the antiseptic/antibiotic alone
Suggest what a student could use as a control when investigating the effect of antibiotics on Bacterial growth
A paper disc soaked in sterile water
No zone of inhibition was formed around the disc soaked in antibiotic Z. Suggest a reason why
The strain of bacteria used in the experiment was resistant to antibiotic Z
