The mouth is like a knife because it chops up food like a knife would cut food. The mouth also uses chemical Digestion. It uses salivary amylase to break down carbs just like a knife breaks down food into smaller pieces.

The throat/esophagus is like a tunnel because food goes through it just like something like a car would go through a tunnel.

The stomach is like a mortar and pestle because it grinds up the food like a mortar and pestle grinds spices. The stomach also uses stomach acid to break up proteins like a mortar and pestle breaks up spices into small pieces.

The small intestine is like a strainer because it lets things through and keeps something in. A strainer lets liquid through and keeps food in. The small intestines job is to let nutrients into the bloodstream and keep bad thing out. The small intestine also uses bile to break down fat.

The large intestine is like a sponge because it sucks out the water and lets the rest of the waste go away. The large intestine leads to the anus where waste goes out.

The digestive system is connected to the circulatory system because the digestive system gets nutrients out of food and put it in blood. The circulatory system circulates blood and brings it to things that needs nutrients and oxygen.