Starter

1. Bacterial colonies often grow very quickly. Sketch a graph to show the population growth curve of a colony of bacteria.

2. Discuss how the reproduction of bacteria leads to rapid growth, and why such growth cannot continue indefinitely.

Starter

1. Completes the graph, as J or S-shape curve.

Time (min)

No.

Bac

teria

Time (min)

No.

Bac

teria

Starter

2. Reproduce by binary fission / describe dividing in two each generation.

Reason for shape is due to population doubling in each reproductive period

Explains that exponential growth cannot continue indefinitely due to limiting factors.

Harmful Bacteria

Harmful Bacteria

A few types of microbes cause diseases, these are referred to as pathogens.

An infectious disease is one that can be passed on from person to person.

Diseases can be passed on in a variety of ways:

Catching Diseases

Contact with body fluids (bloods,

saliva, etc)

Contact with infected materials

(towels, etc)

Through the air (coughing, sneezing)

Contaminated food or water

Skin contact – particularly broken

skin

Harmful Bacteria

Pathogenic bacteria make people feel sick by getting into the body and producing enzymes which break down body tissues or by excreting very strong poisons called toxins.

By taking a sample of blood, tissue or faeces and growing the bacteria on agar plates the type of bacteria that causes the disease can be determined.

Harmful Bacteria

Pathogenic Bacteria Cause:

DiphtheriaSyphilisTyphoidTetanusTuberculosis

Sore ThroatMeningitisSalmonellaWhooping

CoughFood Poisoning

Diphtheria

Leprosy

Syphillis

Tetanus

Necrotizing Fasciitis

Harmful Bacteria

Antibiotics are chemicals (or drugs) that are used to prevent the growth or kill bacteria.

Penicillin

Discovered, by accident, by Scottish scientist Sir Alexander Fleming (1881-1955).

Found that penicillium mould produced a compound that prevented the growth of bacteria.

Earned the Nobel Prize in 1945.

Antibiotics - Penicillin

Antibiotic Resistance

Some bacteria have become immune to antibiotics.

This problem has become worse by

Trying to treat viral infections with antibiotics.

Not taking the full course of antibiotics.

Antibiotics being used as a preventative drug in farm animals.

Antibiotic Resistance

This means that those microbes that are naturally resistant survive and reproduce.

This leads to microbe populations that have greater resistance.

Let’s Try some Practice Questions

Practice Questions

1. List 3 environmental factors that bacteria need in order to grow.

2. Why will bacteria, growing on an agar plate, not keep increasing at an exponential rate?

3. Why is it important to use the entire prescription that has been suggested by the doctor?

Practice Answers

1. Warmth, Moisture, Food Source, Space.A

2. Run out of space and nutrients and build up of toxic wastes. A

3. Need to kill all the bacteria. If you stop taking antibiotics before they have all been killed then you risk them growing back and getting sick again. M

Practice Questions

4. Describe two ways in which food can become contaminated during preparation and storage, and two ways of preventing contamination.

5. Explain how the reproduction of bacteria can cause high numbers of bacteria in food in a very short time.

Practice Answers ACan be Contaminated Can be Prevented

Not washing hands properly before preparation.

Always wash hands before preparing food.

Storing food at temperatures not cold enough to prevent growth.

Store food at correct temperature (4°C)

Not covering food. Ensure food that is left out has been covered.

Unclean work surface, appliances or utensils.

Ensure all work surfaces and utensils have been cleaned.

Uncooked food can have bacteria that have not been killed by high temperature.

Cook food thoroughly.

Practice Answers M

5. Bacteria reproduce by Binary Fission – they grow and split in two.A

In correct conditions with enough warmth, moisture, nutrients and space, each bacteria can reproduce approximately every 20 minutes. In a very short time the number of bacteria increases. M