It

It is possible that if you place some fertilizer, a tree would grow on Melvyn's head.
It is likely to rain today.
It seems to be Diana lived her life like a candle in the wind.
A cat slept on the bonnet of Dominic's car. It is white in colour.
A rare orchid grows out of the pot filled with charcoal. It is a real beauty.
The beach ball is round and it is covered in bright blue stripes.
Rowena has curls in her hair, while Robert only has curls in his moustache.
"It" is contextual and refers to a non-human subject; human subjects are referred to by their espective female / male gender, "her / his" as seen above.
It can refer to animals, plants and inanimate objects. It can be situational.
If that's the case, what is it in the first 3 situations?