One reason people are fat is because they eat and eat and eat and don't exercise. Another reason is because some people have fast working calorie burning systems and some people have slow ones causing them to be fat.
It might be that those people that are not fat have high metabolism you eat as much as you want and not get fat.
Dissolving in water is a physical change.
Polysaccharides have more chemical bonds.
They are all assembled from a nucleic acid code
Turgor pressure is what allows a blade of grass to stand up straight. This is a type of a molecule.
Burning wood is clearly a chemical change.