Where is bile juice produced?

$(a)$ Why does a piece of bread taste sweet when chewed for some time?
$(b)$ Cellulose acts as roughage in humans but serves as a source of nutrients in cows. Justify the statement.

Name the biological catalysts which bring about chemical digestion of food.

Explain the mechanism of photosynthesis.

An organism $A$, which cannot move from one place to another, makes a simple food $B$ from the substances $C$ and $D$ available in the environment. This food is made in the presence of a green-coloured substance $E$ present in organs $F$ in the presence of light energy in a process called $G$. Some of the simple food $B$ also gets converted into a complex food $H$ for storage purposes. The food $H$ gives a blue-black colour with dilute iodine solution.
$(a)$ What are $(i)$ organism $A$, (ii) food $B$, and (iii) food $H$?
$(b)$ What are $C$ and $D$?
$(c)$ Name $(i)$ green-coloured substance $E$, and (ii) organ $F$.
$(d)$ What is the process $G$?

Why are green plants called 'producers'?