Disable checkbox if value selected

I need a short jQuery code to do the following.

I got a dropdown like this:

<select id="pa_size">
<option value="32cm">32 cm</option>
<option value="52cm">52 cm</option>
</select>

And some other checkboxes under that dropdown.

Now my problem is: I want to disable the checkboxes IF the 52 cm option is selected. By default the checkboxes are enabled, and if returned to 32cm from 52cm it should be working again.