How are gridcoin transactions validated? Bitcoin uses it's calculations to validate transactions but apperently gridcoin doesn't take any transaction data into the calculation of BOINC projects. 
On the wikipedia page of Gridcoin the following is stated:


  Gridcoin (sign: Ǥ, symbol: GRC) is an open source network protocol using blockchain


It says blockchain is used but how? How are transactions validated?
Gridcoin is a proof-of-stake coin. Transactions are bundled and signed like any other blockchain, but with proof-of-stake the chance to sign is determined by coin balance and the time since your last block staked rather than by a simple hash race like Bitcoin. The freed-up electricity is encouraged to be directed toward BOINC; if you stake a block and you are also running whitelisted BOINC projects, you will receive bonus amounts of GRC on top of the basic stake reward (which is itself a simple 1.5% annual percentage of your current balance).

So no, BOINC is a software development kit used by distributed computing projects to distribute work and track results. Gridcoin doesn't use BOINC for anything other than bonus reward calculations; the two are symbiotic, not interdependent. If every BOINC project was shut down tomorrow, Gridcoin would work just fine forever as a basic proof-of-stake coin like Blackcoin (which it was forked from) or Peercoin.