1a. "In my defence" means you are making an excuse or giving a reason. You're giving the idea that you have been accused and are in court. You have done something wrong, but there is a valid reason behind it. "Yes I spent all you money, but in my defence...(add reason here)"
1b. I love it. ^^ You are eating so fast it's like you are breathing in your food, like air. "Already finished? Wow, you really inhale your food."
2. "Put up" means construct. And you construct things from the ground up. You could equally say "put in a new door", meaning install.