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Lesson 4:Scientific discoveries

Worksheet:

The importance of penicillin

Part A

Read the information provided and answer the questions

We take our healthy lives for granted today, but before penicillin a simple scratch from a rose thorn could have been enough to kill you. Bacteria could get into the open sore and multiply. The infection would spread throughout your body, destroying the cells and could eventually kill you.

Alexander Fleming had been studying bacteria for some time; how they grow larger and divide in two. A single bacterium can become two in as little as twenty minutes. Then two becomes four and four becomes eight.

  1. If it takes 20 minutes for one bacterial cell to divide into two, how many bacteria will be present in 2 hours?

It was a bad cold that helped Alexander Fleming discover there was a way to stop bacteria growing. One day he was plating bacteria onto nutrient agar plates when a drop fell from his runny nose, onto the plate. No bacteria grew where the drop fell. Alexander knew there must be something in his nose mucus that killed the bacteria. He called it lysozyme.

He then went looking for more ways to prevent bacterial growth. His next most important discovery was again by accident. In 1928 he was eating sandwiches for lunch one day while he prepared some new nutrient agar plates. He usually disinfected these plates before using them, however this particular day he was in a hurry to go away for a holiday so he left them on the bench. When he came back a few days later, he noticed that they were covered in bacteria. As he sorted through them, he saw a few crumbs from his sandwich sitting on one of the plates. Mould had grown on the bread, and left a ring around it where the bacteria could not grow.

  1. Why should you never eat in a laboratory?

Alexander Fleming tried to purify the ‘penicillin’ but was unable to grow it in large enough quantities to be used. Twelve years later, World War II had started and many people were dying from infected wounds. It was Australian Howard Florey and German refugee Ernst Chain who developed a way to grow and purify large amounts of the drug. Mass production was started immediately and as a result many people survived the final battles of the war. Fleming, Flory and Chain were awarded the 1945 Nobel Prize in Physiology and Medicine for their discoveries.

Part B

Bacterial cells are different to plant and animal cells. They do not have a nucleus or other membrane-bound organelles. Instead they have their genetic material (DNA) and ribosomes moving freely in the cytoplasm.

A bacterial cell

  1. What role do ribosomes play in a cell?
  1. What is the function of the cell wall in a cell?

All bacteria have cell walls similar to plants. Penicillin prevents the bacteria from making a new cell wall. This means the bacteria grow larger but are unable to divide in two. As a result they die.

  1. Why does penicillin not affect animal cells?

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