Which of the following is characteristic of cilia?
A) They are used for cellular adhesion.
B) They move substances in any direction across cell surfaces.
C) They are substantially longer than flagella, and are most easily seen in human sperm cells.
D) They are whiplike, motile cellular extensions that occur in large numbers on the exposed surfaces of certain cells.
The Correct Answer and Explanation is :
The correct answer is D) They are whiplike, motile cellular extensions that occur in large numbers on the exposed surfaces of certain cells.
Explanation:
Cilia are hair-like structures that extend from the surface of many types of cells, and they play crucial roles in cellular function and movement. Each cilium is composed of microtubules arranged in a specific “9+2” configuration, where nine pairs of microtubules form a ring around two central microtubules. This structure allows cilia to exhibit a coordinated, whip-like motion, enabling them to move fluids and particles over the cell surface effectively.
Cilia are typically found in large numbers on the surfaces of certain epithelial cells, particularly in the respiratory tract and the female reproductive system. In the respiratory tract, cilia help to clear mucus and debris, which is essential for maintaining clear airways and preventing infections. They beat in a coordinated manner to propel mucus toward the throat, where it can be swallowed or expelled. In the female reproductive system, cilia in the fallopian tubes help to move the egg from the ovary toward the uterus.
The other options do not accurately describe cilia.
- A) They are used for cellular adhesion is incorrect as cilia are primarily involved in movement, not adhesion. Other structures, such as cell adhesion molecules, facilitate adhesion between cells.
- B) They move substances in any direction across cell surfaces is misleading. Cilia typically move substances in a specific direction, often unidirectionally, such as pushing mucus up in the respiratory tract.
- C) They are substantially longer than flagella is also incorrect; in fact, cilia are generally shorter than flagella, which are longer, whip-like structures found in cells such as sperm.
In summary, option D accurately encapsulates the primary characteristics and functions of cilia, distinguishing them from other cellular structures.