The source of light in an electron microscope is .......

Adult human $RBCs$ are enucleate. Which of the following statement$(s)$ is/are most appropriate explanation for this feature?
$(1)$ They do not need to reproduce.
$(2)$ They are somatic cells.
$(3)$ They do not metabolise.
$(4)$ All their internal space is available for oxygen transport.

Which one of the following pairs is not correctly matched?

The contribution of cytoplasmic $DNA$ in cells to total $DNA$ is

Identify the labels $A, B, C, D$ and $E$ in the given diagram. The following components are listed:
$(i)$ $SER$
$(ii)$ Ribosome
$(iii)$ Nucleus
$(iv)$ Nuclear pore
$(v)$ $RER$

Which of the following statements is correct?