Parents are concerned that children who have trouble in school will 'fall through the cracks' in the school system. [=will not be given the help they need; will graduate without anyone noticing that they are unable to do the work]
The program is meant to help workers who may have 'slipped through the cracks' [=who may have not been included in other programs] because of their age.
You ought to 'get cracking' [='get going; get moving'] on that assignment. [=you should start working on that assignment right away]
(..) I'm afraid you won't survive. Some cells inside me will fight and defend their integrity to the very end. In order to attain the last few percent, I've to force it. To crack the cells open to their nucleus. All these knowledge, Lucy... I'm not even sure that mankind is ready for it. (..)2014 Lucy