Question

Why is there a difference in taste when nose is blocked?

Answer 1

Flavor = Taste + Smell

What we call "Flavor" is a combination of taste and smell.

There are only five tastes: salty-sweet, sour, bitter, and savory/umami. Compared to taste, there are a virtually unlimited number of scents humans can detect.

So how many? It's one trillion according to The Science magazine:
"...roughly 1 trillion scents that the human nose and brain are capable of distinguishing from each other..."

Therefore, when your nose is blocked, you can only "taste" the food and are unable to "smell", missing most of your food's flavor. This is why you could not taste anything when you had a cold.