There may be many forms of a single gene. Each such form is called an allele
The nervous system is responsible for voluntary/involuntary movement. The glands of the endocrine system produce hormones that are responsible for growth, metabolism, sexual function, etc.
Organ system is the most complex in organization
A carpel on a typical flower is located on the bud tips, what I mean is that where the stamen is nearly right beside it is the carpel. A carpel is like the reproductive organism of a flower.