You have said भवति since your very first conversations. Today you will see why it is भवति and not भूति or भोति — three sūtras transform भू + ति step by step.
शप् is the ‘vikaraṇa' — the class-marker wedged between root and ending. Its श् makes it śit (hence itself sārvadhātuka), its प् makes it pit. भ्वादि verbs take शप्; the other nine gaṇas will each replace it with their own marker in lessons 9-16.
A sārvadhātuka that is not pit behaves as if ṅit — and क्ङिति च (1.1.5) then blocks guṇa/vṛddhi before it. This is why तस्, झि, थस् never trigger guṇa, while pit तिप्, सिप्, मिप् allow it.
‘भवतः' इत्यत्र गुणः कथं न तिप्-वत् वार्यते — किं कारणं तस्-प्रत्यये गुणः अस्ति एव?In भवतः the root still shows guṇa (भो → भव). Why does ṅit-like तस् not block it?
भू + शप् + ति → भो + अ + ति इत्यत्र सूत्रम् ________।Which sūtra turns भू into भो here?
रूपं वचनेन योजयतु।Match form to person-number.
भवामि इत्यत्र दीर्घः केन? ________ इति सूत्रेण।Which sūtra lengthens the अ in भवामि?