eli5, what is a knot in a plank of wood (or tree) and why are they so much harder to cut through?

Question

eli5, what is a knot in a plank of wood (or tree) and why are they so much harder to cut through?

In: Earth Science

Answer 1

You know how trees grow branches? Well the knot is where the tree connects to a branch. Branches get fed from the stem and over time become hard and form dark rings, known as knots!