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.

Statement $P$: The middle lamella is composed of cellulose plates.
Statement $Q$: During the formation of gametes,cell division occurs by mitosis.

The invention of the electron microscope led to a major breakthrough in the study of cells. What could be the reason for this?

Given below are two statements:
Statement $I$: Mitochondria and chloroplasts are both double-membrane-bound organelles.
Statement $II$: The inner membrane of mitochondria is relatively more permeable compared to the inner membrane of chloroplasts.
In the light of the above statements,choose the most appropriate answer from the options given below:

Name two cell-organelles that are double membrane-bound. What are the characteristics of these two organelles? State their functions and draw labelled diagrams of both.

Find the correct set of structures/organelles not surrounded by membrane.