How many sides does a circle have?

If I remove one from eleven it becomes Ten and if I remove one from nine also becomes Ten. How?

What jumps when it walks and sits when it stands?

Lifeless eyes on my smiling face and watch your child's sleeping place. In their dreams they hold me tight. What am I?

Can you find the missing piece of the Porsche?

I look flat, but I am deep. Hidden realms I shelter. Lives I take, but the food I offer. At times I am beautiful. I can be calm, angry, and turbulent. I have no heart but offer pleasure as well as death. No man can own me, yet I encompass what all men must have. What am I?

I am a type of vehicle that has two wheels and is powered by humans. What am I?
Hint 1: You can ride me for exercise.
Hint 2: I am environment-friendly.

I live in a bowl. I can swim. I have a tail. I also have fins and big eyes. What am I?

I have an eye but still cannot see.

Who am I?

What can run but never walk, have a mouth that never speaks, have a head that never weeps, and have a bed but never sleeps?