Microscopy + Bacterial division

Question 1

State the two types of microscopes

Answer 1

Light microscope
Electron microscope

Question 2

Microscopes allow us to ____

Answer 2

Microscopes allow us to magnify

Question 3

State the limitations of using light microscopes

Answer 3

Light microscopes have a limited resolution

Question 4

State the advantages of using electron microscopes over light microscopes

Answer 4

Electron microscopes have a much greater magnification and resolution than light microscopes

Question 5

What is the equation needed to calculate the magnification of the microscope

Answer 5

magnification = size of image / size of real object

Question 6

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

Answer 6

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

Question 7

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

Answer 7

Magnification = x2000
Size of image = 100mm
Size of real object = size of image / magnification

= 100/2000 = 0.05 mm

Question 8

Define magnification

Answer 8

Magnification is the degree to which an image is made to appear bigger

Question 9

Define resolution

Answer 9

Resolution is the smallest interval measurable between two points on an image

Question 10

Define binary fission

Answer 10

Binary fission is reproduction by simple cell division, for example in bacteria

Question 11

describeHow do bacteria multiply/reproduce

Answer 11

Bacteria multiply by simple cell division (binary fission)
One bacteria cell splits into two bacterial cells (binary fission)

Bacteria reproduce by binary fission

Question 12

Give two things that help maximise the rate of binary fission

Answer 12

Bacteria multiply by simple cell division (binary fission) as often as once every 20 minutes if they have (enough nutrients and a suitable
temperature).

Question 13

If conditions are suitable how often can a type of bacterium divide by binary fission

Answer 13

Bacteria can reproduce as often as once every 20 minutes

Question 14

Under ideal conditions, a type of bacterium divides every twenty minutes. Calculate the number of bacteria present after three hours

Answer 14

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

Question 15

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.

Answer 15

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)

Question 16

State some ways to culture bacteria

Answer 16

The culture medium used can be a nutrient broth solution or agar gel plates (contains agar gel and petri dish)

Question 17

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

Answer 17

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

Question 18

What is a culture medium

Answer 18

A culture medium is a liquid or gel used to support the growth of microorganisms or other cultures, often containing specific nutrients

Question 19

What does the culture medium contain

Answer 19

The culture medium contains the carbohydrates, minerals, proteins and vitamins the bacteria need to grow

Question 20

Describe how to prepare an uncontaminated
culture using aseptic technique

Answer 20

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.

Question 21

Explain why in school laboratories we normally incubate bacteria at 25 degrees celcius

Answer 21

In school laboratories, we normally incubate bacteria at 25 degrees celcius
This reduces the chances that harmful bacteria will grow.

Question 22

Describe how to investigate the effect of antibiotics on bacterial growth

Answer 22

1. Clean the bench with disinfectant solution. This kills microorganisms that could contaminate the culture.
2. Sterilise an inoculating loop by passing it through a Bunsen Burner flame
3. Open a sterile agar gel plate near a Bunsen burner flame. The flame kills bacteria in the air.
4. Use the inoculating loop to spread the chosen bacteria evenly over the plate.
5. 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

6. 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.

Question 23

Describe what can be seen when the experiment on investigating the effect of antibiotics on bacterial growth has been completed.

Answer 23

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

Question 24

How to measure the effect of the antibiotic

Answer 24

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

Question 25

If the radius is 12mm work out the zone of inhibition

Answer 25

area = πr^2
area = 3.142 x 12^2
araa = 452.45 mm^2 (to 2d.p.)

Question 26

Why is it important to use a control (paper disc) when investigating the effect of antibiotics on Bacterial growth

Answer 26

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

Question 27

Suggest what a student could use as a control when investigating the effect of antibiotics on Bacterial growth

Answer 27

A paper disc soaked in sterile water

Question 28

No zone of inhibition was formed around the disc soaked in antibiotic Z. Suggest a reason why

Answer 28

The strain of bacteria used in the experiment was resistant to antibiotic Z