Senzu Benas are allot used in DBZ.They are maded by Corrin,a cat out of a tower in
Corrins Tower.He makes the Senzu Beans.Mostly Yajirobe brings them to Goku and his friends
just before the battle begins.Senzu Beans gives the power to heal a person in a few
seconds.The healing time isn't that long as a Medical Tank.These Beans are green.
They were used in the Saiyan Saga and espescially on Namek[Ginyu Saga].
Now i'm gonna give a list from wich eole and characters have eaten a Senzu Bean.

Cell:He has eaten 1 Senzu Bean.
This was during the Cell Saga.It was when Gohan fougth Cell,and Cell was in a bad state.
Cell was all beaten up.That's why Goku graed a Senzu Bean out of his pocket and gave it to
Cell.Actually,it was a bad idea but well,can't change it.Also Gohan was very surprised
when Goku gave the Senzu Bean to Cell.That's how Cell was healed and fougth back again.

Goku:He has eaten 5.
After the Battle Vs. Vegeta in the Saiyan Saga.
He was in the hospital and when Corrin was ready with the Senzu Beans,Yajirobe brougth it to Goku.
He regain his strength and then flies away.
He has eaten 4 Senzu Beans when he trained in his spaceship.He did some Kamehameha's and
he was all collapsed,so that's why he has eaten tons of more Senzu Beans.

Gohan:1 1/2 Senzu Bean eaten.
Goku gave him a half Senzu Bean because he was retty young and not that messed up.
He gave him one during the Saiyan Saga in the battle Vs. Nappa.
In the Ginyu Saga Goku gave one to Gohan.Gohan fougth Recoome.Actually,Recoome was stronger
but after the Senzu Bean Goku gave him Gohan was stronger than Recoome,but Gohan didn't even noticed it.

Krillin:3 1/2
Goku gave one to him during the Saiyan Saga.
He gave him a half one during the battle Vs. Vegeta.
On Namek during the ginyu Saga.He tried to hit Recoome but Recoome kicked him.
He couldn't figth anymore so Goku gave him a Senzu Bean.