Question

The smallest structural and functional unit of life is
A. Organ
B. Cell
C. Tissue
D. Organ system

Answer 1

Hint: For any organism, a complete living system of organs that work together is capable of coordinating its specific functions and conducting all the biological processes of life in order to keep it alive.

Complete answer:
The body has several levels of organization that build on each other. Cells make up every tissue, a group of tissues make up organs, and then two or more organs constitute the organ systems in the human body to perform several specific physiological functions.
Cell: The cell is one of the basic principles of biology. It is considered as the smallest structural and functional unit of all living organisms. Therefore, it is called as the building blocks of life, which can exist on its own. Some of the examples are nerve cells and red blood cells.

Cell theory states three basic points:
-All living organisms are made up of one or more number of cells that may be either unicellular or multicellular.
-The cell is the basic and smallest unit of matter that is living in which it can perform all the functions of life.
-All cells arise from pre-existing cells and are not derived from spontaneous generation.

Tissues: A group of cells which have a common structure and function in order to work together as a unit is known as Tissue.
Organs: A group of tissues which are arranged in a specific manner to support and share a similar physiological function. Examples of organs in the human body include the heart, brain, lungs and liver.
Organ systems: Two or more organs that contribute to a specific physiological function within the body is known as organ system. There are about eleven organ systems that constitute the human body. Some of the examples include the digestive system, circulatory system, reproductive system and central nervous system.

Hence, the correct answer is option (B).

Additional information:
Cells are also classified into two different kinds. They are eukaryotic and prokaryotic cells. The cells which contain the true nucleus with DNA are known as eukaryotic cells and its examples include plant cells, animal cells and fungal cells. The cells which don't have any nucleus and the DNA is associated in a region called nucleoid is known as prokaryotic cells. Bacteria is one of the best examples for this type of prokaryotic cell.

Note:
There are four different kinds of tissues in the human body in which each is designated to perform its specific functions. They are as follows:
-connective tissue, which supports and connects with other tissues;
-epithelial tissue, which provides a covering lines and protects organs;
-muscle tissue, which includes muscles to contract the movement and support along with the skeleton;
-nerve tissue, which is used to carry messages to and from various parts of the body in order to respond and react to signals in the environment.