Different birds eat different foods so their beaks must be suited to be able to eat the types of food that each species needs
An example of a 3rd class lever is a pair of tweezers!
The cornea is the only part of the eye that touches air.
It's the sodium ion.
When a neural impulse is fired in both neurons, it is always cause by an excited electron in one neuron moving to the other neuron to destabilize the balance of ions trying to keep them at equilibrium. This action either depolarizes or hyper-polarizes the membrane. If it does, then sodium ions--the key deficient ones--can flow into that region of low charge and maintain that state of low charge, keeping the cell membrane stable.
