Give one significant contribution of each of the scientist :
Jacob and Monad

Explanation

**Step-by-Step Solution:**

1. **Identify the Scientists**: The question asks for significant contributions from two scientists: Jacob and Monod.

2. **Understand Their Contribution**: Jacob and Monod are renowned for their work on the LAC operon model in Escherichia coli (E. coli). This model explains how the bacterium regulates the metabolism of lactose.

3. **Explain the LAC Operon**: The LAC operon is a set of genes responsible for the transport and breakdown of lactose into glucose and galactose. It is typically in a "switched off" position, meaning that the genes are not expressed unless lactose is present in the environment.

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