science-biology: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/science-biology - from package: science-biology

You may install the required package with command apt-get install {package}

Error in other languages:
science-biology: bevel nie gevind nie
science-biology: comandă negăsită
science-biology: comando não encontrado
science-biology: commande introuvable
science-biology: command not found
science-biology: käsku ei ole
science-biology: không tìm thấy lệnh
science-biology: komanda nerasta
science-biology: Kommando nicht gefunden.
science-biology: kommandot finns inte
science-biology: komut yok
science-biology: nie znaleziono polecenia
science-biology: níor aimsíodh an t-ordú
science-biology: no se encontró la orden
science-biology: no s'ha trobat l'ordre
science-biology: opdracht niet gevonden
science-biology: parancs nem található
science-biology: perintah tidak ditemukan
science-biology: príkaz nenájdený
science-biology: příkaz nenalezen
science-biology: команда не найдена
science-biology: командата не е открита
science-biology: 命令找不到
science-biology: コマンドが見つかりません