"Up to" vs "up to it"

What does the phrase up to mean in the following?

That sketchy character is up to something.

That sneak is up to no good.

How does that differ from up to it in the following?

I'm sick, but if I'm up to it I may do the dishes.

Or this:

I feel like I'm up to my ears, trying to learn all these English idioms.

Are there other uses of this phrase?

Solution 1:

These are all established meanings/idioms for "up to". The first two sentences use "up to" with the meaning, "devising or scheming; occupied with". The next sentence with "up to it" has the meaning "having adequate powers or ability for; capable of; equal to". The final sentence has the meaning "as far as or approaching (a certain part, degree, point, etc.)".

I got these from this dictionary.com entry, which also has examples of many other uses.

Solution 2:

All of these are examples of "be up to" rather than "up to" alone. "Be up to" is something called a phrasal verb, and it has two meanings. See Kosmonaut's answer for definitions.