Edexcel Biology Gcse - Treating, Curing and Preventing Diseases Part 4

1) A virus enters a cell.
2) Substances in the cell begin to to strip of the virus' outer protein coat.
3) The nucleic acid in the centre of the virus is released.
4) the nucleic acid gets into the cell's chemical manufacturing system.
5) The cell ignores it's own chemical needs and switches to making new viruses
6) The cell is sometimes destroyed in the process. Many of the new viruses are released to infect other cells.

Since Penicillin was discovered in 1928, the use of antibiotics for the treatment of diseases has increased exponentially. Antibiotics are being overused in many ways in our world today.

• over use of antibiotics

• failing to complete the fully prescribed course by a doctor

• use of antibiotics in farming

These can lead to the effectiveness of antibiotics being reduced, and the incidence of antibiotic resistance increasing. These bacteria are commonly known as superbugs.

People feel unwell and when going to the doctors, they expect antibiotics to be prescribed. If patients have viral infections, such as the common cold and not a bacterial one, the antibiotics are ineffective and unnecessary.

Patients should always fully complete the prescribed course of antibiotics, every time they are taken. This ensures all bacteria are killed, and so none survive which can subsequently mutate and produce resistant strains. Some patients begin to feel well after a few days of taking the medicine, and stop taking them. This is potentially very harmful, as random mutations can occur which can lead to antibiotic resistance. The resistant bacteria reproduce quickly, and the resistance spreads.

Previously, antibiotics were regularly used in farming, and these can be used to prevent disease, keep the animals well and allow them to grow quickly. The high use in agriculture may have a cost, as it could lead to spread of antibiotic resistance from animals into human hosts. Legal controls are now in place to try and reduce the use of antibiotics in this way.

• Only take when necessary.

• Treat specific bacteria with specific antibiotics.

• High hospital hygiene levels, including regular hand washing by staff and visitors.

• Patients, who are infected with antibiotic resistant strains of bacteria, should be isolated from other patients.

The development of new antibiotics has slowed down as it becomes difficult to find new versions to tackle different bacterial infections. Some limited success with new antibiotic search has occurred recently. People are concerned that in the near future, some bacteria will be resistant to all known antibiotics.

Bacteria can replicate approximately every 20 minutes by binary fission, which is a simple form of cell division. This level of replication will depend on the availability of nutrients and other suitable conditions such as temperature.

• nutrient broth solution in a culture vial

| - colonies on an agar plate

Nutrient broth solution or culture medium, allows a liquid or gel to provide all the nutrients needed for bacteria to grow successfully. These must include: carbohydrates for energy, nitrogen for protein synthesis, plus other minerals.

Agar plates are created by pouring hot molten agar into sterile Petri dishes, which are then allowed to set. Bacteria can be streaked onto the plates using a loop, and allowed to form individual colonies of the specific bacterium. Alternatively, bacteria can be spread all over the agar plate to form a lawn of bacterial growth, rather than individual colonies.

Nutrient broth solutions, culture vials, agar solution and Petri dishes are all sterilised to stop any other microorganisms growing on or in them. This is often done in an autoclave. These are strong containers, a little like ovens, which use high temperatures and pressures to kill microorganisms.

If a specific bacterium is going to be cultured or grown, other contaminating bacteria would compete for nutrients in the broth or agar. Plus some bacteria could be harmful (such as pathogens) and would complicate the results of experiments when testing the efficiency of antibiotics or other anti-microbial compounds.

• killing all microorganisms on equipment such as inoculating loops by flaming equipment in a Bunsen burner or dipping them in alcohol

• keeping all lids on equipment when not in use

• wearing gloves, eye goggles, lab coats or other protective equipment

This avoids contaminating cultures that should already be sterile. The growth medium (broth solutions and agar) will be sterile after autoclaving. The containers (Petri dishes and culture vials) will also be sterile after autoclaving.

In order to answer this, you can split the calculations into two sections.

1) Calculate how many times the bacteria divide in 6 hours.
Bacteria divide every 20 minutes, and will divide three times every hour (60 ÷ 20 = 3)
3 × 6 = 18

2) Calculate the number of bacteria in the population.

Every time the bacteria reproduce, the number doubles. You can use an equation to calculate this.

Bacteria at the end of the growth period = bacteria at the beginning × 2number of divisions of the growth period

Number of bacteria at the beginning = 1

Number of divisions = 18

Using the above equation: 1 × 218 = 1 × 262,144 = 262,144 bacteria

For a higher mark, you could express answers in standard form.

For example, the above answer of 262,144 bacteria can also be written as 2.62 × 105 bacteria.

2 divisions per hour. 2 × 8 = 16 total divisions, therefore 1 × 216 = 1 × 65,536 which is 65,536 bacteria or 6.55 × 104 bacteria (standard form).

3 divisions per hour. 3 × 2 = 6 total divisions, therefore 10 × 26 = 10 × 64 which is 640 bacteria or 6.4 × 102 bacteria (standard form).

Phagocytes

Alexander Fleming

| Penicillin

Antibodies

Skin

Mucus

Enzymes