Question

Which of the following structures is usually present only in animal cells?
(A) Vacuoles
(B) Cell walls
(C) Nucleus
(D) Centriole

Answer 1

Hint: Cell organelles are specialized subunits inside the cells with a special function assigned to them. Some of them are found in almost all eukaryotic cells whereas some are found in either plant or animal cells and absent in the other.

Complete answer:
From the given structures, centriole is found only in the case of animal cells and is not seen in plant cells. Vacuoles and Nucleus are present in both plant and animal cells whereas Cell walls are only found in the case of plant cells.
Centrioles are found in most eukaryotic cells and are cylindrical organelles composed of tubulin proteins. Along with pericentriolar material which is a mass of dense material, the pair of centrioles makes up the centrosome. Although Centrioles are not present in conifers, angiosperms, and fungi, they can be seen in the case of charophytes, bryophytes, seedless vascular plants, cycads, and ginkgo.

Additional Information: Centrioles are very important in the cell division process as they carry out the organization of the mitotic spindle and the completion of cytokinesis. They are thought to be involved in the formation of a mitotic spindle in animal cells but studies say that even the cells that don't contain centrioles can still progress through the G1 stage of interphase before centrioles can be synthesized. The centrioles have the ability to self-replicate themselves during cell division.
So, the correct answer is ‘(D) Centriole’.

Note: Vacuoles are found in plant and fungal cells, as well as some protists, animals, and bacterial cells and, are membrane bound organelles filled with water containing inorganic and organic molecules and also sometimes engulfed in solid particles. They have various shapes and sizes which vary according to the requirements. The cell wall is a structural layer outside the cell membrane and is found only in the case of plants, fungi, algae, and prokaryotic organisms but absent in the case of animal cells. They provide structural support, protection, and filtering mechanisms. The nucleus is another membrane-bound organelle that is found in all eukaryotic organisms regardless of plant or animal. They contain the genetic material of the organism and therefore are the center of all activities inside the cell.