Antibiotics (inc. RP) - Paper 1

Question 1

Describe in detail how antibiotic resistance arises

Answer 1

Mutation occurs randomly in bacteria.
Some mutations make bacteria resistant to antibiotics.
When antibiotics are used:
* Non-resistant bacteria are killed.
* Resistant bacteria survive and reproduce.

Resistance genes are passed on to offspring.
Not finishing antibiotics or overusing them increases resistant strains.

‘Strains’ is a good word to use in relation to different variations of bacteria

Question 2

Should you take the whole course of antibiotics, or stop taking them once you feel better?

Answer 2

Take the full course so all bacteria are killed

Stopping early allows survival of some bacteria, perhaps including ones with resistance which, if not killed, could reproduce to and spread antibiotic resistant strains

Question 3

When are bacteria labelled as resistant?

Answer 3

When they are no longer killed by antibiotics which were previously used as cures against them

Question 4

Can antibiotics treat HIV?

Answer 4

No
Antibiotics inhibit processes in bacterial cells and HIV is a virus

Question 5

What is Penicillin?

Answer 5

An antibiotic, produced by a mould, which killed bacteria

An antibiotic is a type of drug that inhibits bacterial processes - slows down or stops the growth of bacteria

Question 6

What is an antibiotic?

Answer 6

A type of drug that inhibits bacterial processes - slows down or stops the growth of bacteria

Question 7

Do antibiotics inhibit processes in the host organism?

Answer 7

No
Only in bacterial cells

They may break down the cell walls of bacteria but this can’t affect a human host as their body cells don’t have cell walls

Question 8

Why is it harder to destroy just a virus than it is to destroy just a bacteria?

Answer 8

Viruses reproduce using the host’s cells (lytic and lysogenic lifecycles) so it would be very difficult to develop drugs that can destroy just the virus without killing the host’s cells

Antibiotics can however kill bacteria without killing the host’s cells by only inhibiting bacterial process, e.g. cell wall production so the cell can’t divide

Question 9

Name 4 communicable diesease caused by bacteria meaning they could potentially be treated with antibiotics

Answer 9

Cholera - spread by water - spread prevented by clean water supplies
Tuberculosis - spread airborne - spread prevented by isolation, good hygiene and good ventilation
Stomach Ulcers - spread by swallowing contaminated food or water (oral transmission) - prevented by clean water and hygienic living conditions
Chlamydia - spread by sexual contact - prevented abstenence or condoms

Cholera outbreaks are a common secondary effect of natural disasters as water infrastructure gets damaged

Question 10

What is the zone of inhibition?

Answer 10

The clear area around an antibiotic in a growth medium (on an agar plate) where it has inhibited bacterial processes and therefore stopped the bacteria growing there

Question 11

The larger the zone of inhibition…

Answer 11

The more effective the antibiotic against that bacteria

Question 12

What are aseptic techniques?

Answer 12

Methods of preventing contamination of pure cultures of microorganisms, ensureing reliable and accurate results e.g. by killing unwanted airbourne pathogens with heat from a bunsen burner for example

Question 13

In the antibiotic’s practical, how do you reduce contamination?

Answer 13

• Wash hands with antibacterial soap before touching anything
• Sterilise the agar (growth medium) in an autoclave with high pressure and high temperature steam
• Only open petri dish when necessary and then only for the minimum time possible and only next to a bunsen burner with a blue flame (heat will kill potential airbourne contiminants)
• Ensure the pipette and glass spreader are sterilised in an autoclave - only touch this at one end and don’t place the end touched in the agar
• Open the bottle of bacteria with little finger and turn the bottle, not the lid
• Flame the top of the bacteria bottle before and after inserting the sterilised pipette
• Turn the petri dish upside down to prevent condensation falling onto the agar

Question 14

Give an example of a bacteria used in the antibiotics practical

Answer 14

E coli

Question 15

Which piece of equipment is used to spread bacteria all over the agar jelly in a petri dish?

Answer 15

Sterilised glass spreader

This is done after the sterilised pipette has been used to place a drop of the bacteria on the agar plate

Question 16

To enable the bacteria to grow, where must it be placed?

Answer 16

In an incubator for 48 hours

In a schoo,l this will be at about 25 degrees

Question 17

What is the independant variable in the antibiotics practical?

Answer 17

Type of antibiotic used

Question 18

What is the dependant variable in the antibiotics practical?

Answer 18

Diameter of the zone of inhibition

Question 19

Give 3 control variables for the antibiotics practical?

Answer 19

Temperature of incubation
Concentration of antibiotics
Duration of incubation

Question 20

What is the difference between an antibiotic and an antiseptic?

Answer 20

Antibiotics kill bacteria inside the body whereas antiseptics kill bacteria outside the body (e.g. on the skin)

Question 21

Describe how you would ensure that the antibiotic discs are placed fairly on the agar plate. (2 marks)

Answer 21

On the bottom of the petri dish, divide the agar plate into 3 equal sections and mark a point in the centre of each, to indicate where each disc should be placed, ensuring equal spacing and allowing fair diffusion of the antibiotic into the surrounding agar

Question 22

A student noticed that one antibiotic produced a larger clear zone than the others. What does this indicate about the antibiotic (2 marks)

Answer 22

The antibiotic is more effective at inhibiting the processes and thus growth of that bacteria, ultimately killing it. This is shown by the larger zone of inhibition

Don’t say that an antibiotic is specific to a bacteria
The question didn’t mention the key term “zone of inhibition” so try to include it

Question 23

Explain why the petri dish should be incubated upside down. (2 marks)

Answer 23

To prevent any condensation from falling onto the agar and altering the diffusio of the antibiotic

Question 24

Suggest one reason why the bacterial lawn might not grow evenly across the agar plate. (1 mark)

Answer 24

Because the bacteria wasn’t spread evnly across the surface of the agar place with the sterilised glass spreader

Question 25

Describe how to carry out the core practical to investigate the effect of different antibiotics on bacterial growth. (6 marks) In your answer, include details about: * Equipment and materials needed * Method * Safety precautions

Answer 25

1) **Sterilise all reusable equipment** like the **glass spreader** in an **autoclave** 2) **Wash hands** thoroughly with antibacterial soap 3) Open a bottle of bacteria with your little finger and flame the top of the bottle in a blue bunsen burner flame afterwards 4) **Use a sterilised pipette** to **transfer a small volume of bacteria (ecoli)** from the bottle to a **pre-sterilised agar plate**, only opening the plate for the **minimum time possible** and **near to the blue bunsen flame** (to create a sterile environment where any unwanted airbourne pathogens then can't enter the plate) 5) Again, near the flame, quickly open the dish lid to use the **sterilised glass spreader** to **evenly distribute the bacteria** so the bacteria **lawn grows evenly** 6) **Lightly push** down **three paper discs** (**two soaked in different antibiotics**) and then **one** with **no antibiotic** (the **control**) **equally spaced** on the plate 7) **Lightly tape on the lid** to maintain **aerobic conditions** and **incubate** the dish in an **oven** for **3 days** at **25 degrees celcius** 8) Thoroughly sterilise all equipment and work surface, as well as your hands, afterwards to prevent any ecoli from growing outside the dish and potentially causing harm ## Footnote Maintaining aerobic conditions by lightly taping is a safety precaution as it reduces the growth of more harmful bacterias which thrive in anaerobic conditions Additionally, as a safety precaution you could say about disposing of used plates and materials safely (e.g. biohazard bin)

Question 26

Why must the lid of the Petri dish be lightly taped rather than sealed completely?

Answer 26

**Maintain aerobic conditions** (to limit growth of more harmful bacterias which thrive in anaerobic conditions)

Question 27

Why is it important to use a control disc in the antibiotics practical?

Answer 27

To compare the effect of antibiotics with no treatment