“Shika” is use to indicate that there is only a specific numbers. Example :
Q : Are there 8 apples? – Ringo ga yattsu arimasu ka?
A : No, there is only 1 apple – Iie, Ringo wa hitotsu shika arimasen

Q : Are there 20 textbooks? – Nihongo no kyoukasho ga nijuu satsu arimasu ka?
A : No, There is only 5 books – Iie, go satsu shika arimasen

“Mo” means “too” but there is other meaning depending how you form a sentence. Example :
Q : Are there 10 mandarin oranges? – Mikan ga jukko arimasu ka?
A : No, there isn’t any mandarin orange OR No, not even 1 orange is there- Iie, Mikan wa ikko mo arimasen.

John and I go to school too – Watashi mo John mo gakkou e ikimasu

Meaning : Ringo (Apple), Kyoukasho (Textbook), Mikan (Mandarin Orange)