I go up and I go down towards the sky and the ground

Question: I go up and I go down,
towards the sky and the ground.
I'm present and past tense too,
Let's go for a ride, me and you.

What am I?

Question: What is square and green?

Question: What tastes better than it smells?

Question: What goes in the water black and comes out red?

Question: What loses its head in the morning and gets it back at night?

Question: What two things can you never eat for breakfast?