What substances enter into the food vacuole in $Amoeba$ to break down the food?

List the factors on which diffusion in plants depends.

What is primarily digested in the human stomach?

Explain the role of the mouth in the digestion of food.

Name three different glands associated with the digestive system in humans. Also name their secretions.

When a person puts food in his mouth, teeth cut it into small pieces, chew, and grind it. Glands $A$ in the mouth secrete a substance $B$ which is mixed with the food by the tongue. Substance $B$ contains an enzyme $C$ which starts the digestion of food in the mouth. The slightly digested food from the mouth goes down a tube $D$. The special type of movements $E$ in the walls of tube $D$ push the food into the stomach for further digestion. The stomach wall secretes gastric juice containing three substances $F$, $G$, and $H$. One of the functions of $F$ is to kill bacteria which may enter the stomach with food. Substance $G$ protects the inner lining of the stomach from the damaging effect of substance $F$, whereas substance $H$ is an enzyme for digestion. The partially digested food then enters the small intestine for further digestion.
$(a)$ What are Gland $A$, Substance $B$, and Enzyme $C$?
$(b)$ Name the tube $D$.
$(c)$ What is the movement $E$ known as?
$(d)$ What are $F$, $G$, and $H$?