Help with Spanish idioms?? :)

I am working on an essay for my advanced spanish class, and right now I don't feel so advanced because I'm not confident with the following phrases... Do these translations sound right? If they are awkward or incorrect, could you help me fix em? :) Thanks!!

(Don't know how to use accents in this forum yet..)

I'm the only one who looks like my dad.
Soy la unica persona que parece como mi papa.

Essay about myself
Ensayo sobre mi mismo

Skating is a fun sport because you can defy gravity.
El patinar es un deporte divertido porque pueda desafiar la gravidad.

Thanks to him, I began research on the brain.
Gracias a el, empece la investigacion sobre el cerebro.

Muchas gracias!! I will hopefully repay the favor on this site!

Soy el(la) único(a) que se parece a mi papá.

Ensayo autobiográfico.

El patinar es un deporte divertido porque se desafía la gravedad, o
El patinar es un deporte divertido porque desafías la gravedad.

Gracias a el, empecé a hacer investigaciones acerca del cerebro.

I suppose you meant idiomatic usage as those sentences are not idioms. One main recommendation: Don't forget the accents!

Ensayo could be a bit too much for school work, at least in Spain we use it for professional work so I'd just say "Redacción sobre mí" and you avoid mismo/a depending on whether you're a boy or a girl.

You can say "Patinar es muy divertido..." (el is not necessary here, not wrong if you include it though, just a matter of personal preference and local usages) or "El patinaje es un deporte muy divertido..." (el IS mandatory here). As for the second part it sounds more idiomatic to say "porque desafías" or also "porque se desafía", as Cucosteles suggested. Personally I prefer the impersonal form.

Hope this helps!

My 5 cents:

I'm the only one who looks like my dad.
Soy el único que se parece a mi papá.

Essay about myself
Una redacción (o un escrito o una composisión) sobre mí. (I agree with Goodnightmoon)

Skating is a fun sport because you can defy gravity.
Patinar es un deporte divertido porque puedes desafiar la gravedad.

Thanks to him, I began research on the brain.
Gracias a él, comencé (o empecé) a investigar el cerebro.

Hope it helps!