Define a nutrient. Name four important nutrients present in our food.

Fill in the following blank with a suitable word:
All non-green plants and animals are . . . . . . .

The organisms $A$, $B$ and $C$ can obtain their food in three different ways. Organism $A$ derives its food from the body of another living organism which is called its $D$, without killing it. The organism $B$ takes in solid food by the process of ingestion, digests a part of this food and throws out undigested food in the process called $E$. The organism $C$ obtains its food from dead and decaying plants.
$(a)$ What is the mode of nutrition of $(i)$ organism $A$ (ii) organism $B$, and (iii) organism $C$?
$(b)$ What is the organism like $D$ called?
$(c)$ Name the process $E$.
$(d)$ Give one example each of organisms like $A$, $B$ and $C$.
$(e)$ What is the general name of the three modes of nutrition exhibited by organisms $A$, $B$ and $C$?

Name a gas produced in photosynthesis.

What is photosynthesis?

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 $H$?