The reaction which require energy in the form of heat, light or electricity to break reactants are called endothermic reactions.

Cutin is protective, hydrophobic, waxy covering produced by epidermal cells of leaves, young shoots and other aerial parts. It minimises the water lost through transpiration (with the help of stomata) and also reduces pathogen entry. Lignin hardens the cell wall ...

The flexibility in plants is due to Collenchyma. It also provides mechanical support to plants.