Trying to define life

I once had a nice discussion with my friends on the definition of life or living thing. Our discussion went for more than an hour and we had to stop it because it is the closing time of mess.I would like to share that experience.
The main difference arose because some of us thought against calling plants as living things.I present a small part of the argument.I would like the readers to develop the argument.Some of you may say it is just the way you define life, after all anyone can define anything in anyway he wants to.But I just want you to think it beyond language barrier.You see,our argument went like this:
Person 1: We can call something as a living thing only if it can have feelings i.e., it should have sense of pain, at least.The bottom line is it should have brain. Now, everybody knows that a plant doesn't have brain.
Person 2: What you say is precisely correct but this need not be the basic need for life.The basic amazing thing about this phenomenon to give it a name, LIFE, is its ability to reproduce.The very thought of one identical thing coming out of another, I mean cell division, is so exciting and great that man called it Life.Infact, if you see, this is precisely why mother is given a special place and mother's love is considered to be the ultimate.
Person 1: See how you are coming back to a FEELING finally,love in this case. Why is cell division so important?Even if cell division is great it has no sense of existence unless there is thought,right?So, only a thing that has brain which is responsible for feelings should be considered as living.
Person 2: Ok, let me put it this way.What is the opposite of LIFE?
Person 1: DEATH.
Person 2: When do you say a man is dead?
Person 1: When his heart stops pumping blood i.e., it stops beating.
Person 2: Precisely! It is not when the brain stops working right?Infact, that is why we have seperate term braindead for that organ. You knew that after heart stops beating,the brain can still function for a few minutes, right? So similarly life is when a nervous system is there and reproduction is there.
Person 1: But still don't you think if you call cell division as life, we should also call any chemical reaction as life?
Person 2: Dude, here we are getting identical being.That is not the case with a chemical reaction.
Person 1: Ok, that was a wrong point but................................

It went on like this.Isn't it interesting?

How I tried to think about brain using my brain

I have always been attracted to the functioning of brain and the concept of Artificial Intelligence. Infact, my attraction to brain is what also led me into becoming a science student. I will try to put forward my own amateur views on AI/Brain. These are some ideas I developed or thought of when I had nothing to do.

I think Mankind has not understood the functioning of brain yet.It is a very interesting thing,this brain. It is made up of simple cells as any other organ in the body but have this remarkable quality of memory and thought process, particularly experience i.e., it not only has memory but analyses it and uses it in taking decisions in future, something like learning from experience.I think if we think of it in terms of known science,it has something like a feedback of memory. When we are supposed to make a decision, it has a number of options but it goes through our past experiences and tries to select one option.

The problem with AI as shown by various sci-fi movies is to have a machine think like a human.To make it possible,we should not only have virtually infinite memory for the machine but also a feedback system that will go through past memory(which I now call experience) and choose the best possible task from again virtually infinite options.Another problem here is, various brains choose various options which cant be achieved in machines(maybe given exactly the same bringing up from childhood may result in two persons making same decisions but it is never tested and subject to argument)Further, memory from brain's point of view can be a solid descreption of what happened to a very vague one like we sometimes say 'I think his name is rahul, or is it ramu?' Such a thing, I think, is not possible with a computer.It either knows what happened precisely or nothing at all.

When we see it from this point of view, we cannot stop ourselves from wondering at how marvellous the brain is!!How did some complex chemical reactions result in a thing which can not only THINK but also question the very existence of itself? We are trying to find out about brain using our own brains!I sometimes wonder if it is like trying to lift your own body which can definetely not happen.Maybe we have been mere spectators at the wonderous nature of brain and not able to find anything about how it is working because we are doing that using brain itself.Maybe we indeed are trying to lift ourselves...Maybe some other higher form of existence is required to explain the dilemma of brain..I hope that I understand it someday....