Vitamin $D$ is synthesized by one of the following with the help of sunlight.

Define/Explain the following terms:
$(1)$ Cellular respiration
$(2)$ Respiratory system

Guard cells are surrounded by

The normal temperature of the human body on the Kelvin scale is

Process of exchange of $O_{2}$ from the atmosphere with $A$ produced by the cells is called $B$, which is commonly known as $C$. Choose the appropriate options for the blanks $A$, $B$, and $C$ to complete the given $NCERT$ statement.

Plants do not need specialized respiratory organs because