Describe your professional goals you hope to achieve by pursuing a graduate degree.
Translation: “What job do you want after you finish your degree?” Or, to be even more blunt: “What do you want to be when you grow up?”
First sentence should be something like:
“I want to work to be a [ professor / technician / researcher / patent lawyer ] in a [ teaching university / research university / community college / state government / federal government / start-up company / pharmaceutical company ], because....”
The rest of your response should flow from that first sentence.
Here’s another question you might get.
Describe why you are interested in your chosen field of study.
This question uses sleight of hand. I think it’s what it’s trying to find out is not your reasons as much as whether you have a “chosen field of study.” It’s a subtle way of asking if you have an understanding of what is currently being researched. Are you engaged with an intellectual problem? Have you read any research literature?
That means your first sentence should be something like:
“I want to study cell biology / ecology / herpetology / evolutionary biology / animal behaviour / taxonomy / molecular biology, because...”
The more specific you can be about the field in the first sentence,
the better. For instance:
Good: “I want to study microbiology, because...”
Better: “I want to study extremophile archae that live in high temperatures, because...”
Still better: “I want to study enzyme stability of extremophile archae that live in high temperatures, which several faculty in your department work on, because...”