How to avoid huge json documents in mongoDB - mongodb

Question

I am new to mongoDB modelling, I have been working in a small app that just used to have one collection with all my data like this:
{
"name": "Thanos",
"age": 999,
"lastName": "whatever",
"subjects": [
{
"name": "algebra",
"mark": 999
},
{
"name": "quemistry",
"mark": 999
},
{
"name": "whatever",
"mark": 999
}
]
}
I know this is standard in mongoDB since we don't have to map relotionships to other collections like in a relational database. My problem is that my app is growing and my json, even tho it works perfectly fine, it is starting to be huge since it has a few more (and quite big) nested fields:
{
"name": "Thanos",
"age": 999,
"lastName": "whatever",
"subjects": [
{
"name": "algebra",
"mark": 999
},
{
"name": "quemistry",
"mark": 999
},
{
"name": "whatever",
"mark": 999
}
],
"tutors": [
{
"name": "John",
"phone": 2000,
"status": "father"
},
{
"name": "Anne",
"phone": 200000,
"status": "mother"
}
],
"exams": [
{
"id": "exam1",
"file": "file"
},
{
"id": "exam2",
"file": "file"
},
{
"id": "exam3",
"file": "file"
}
]
}
notice that I have simplified the json a lot, the nested fields have way more fields. I have two questions:
Is this a proper way to model Mongodb one to many relationships and how do I avoid such long json documents without splitting into more documents?
Isn't it a performance issue that I have to go through all the students just to get subjects for example?