Physical and Chemical Barriers (to microbes) Code Breaker

A code breaker is a crossword like grid but with numbers substituting for the letters rather than clues.
The students slot the correct letters into the grid to reveal the key words. This is on a word document so you can delete as many of the letters given as clues as you like and make it harder to complete.
This is a good settler for the beginning of lessons and helps get challenging groups into a routine and focused.
For further differentiation you can ask the students to then define the key terms.