Tag: number and shape of cells

Schleiden and Schwann presented a cell theory which proposed that each cell is itself is an organism which has all attributes of life. Each cell is living its individual life as well as the as a group of tissue which has become an integral part of plant. So Schleiden while observing plant cells discovered this double life of each cell. So option A is correct.

The average size of a human cell is about 100 μm in diameter. The smallest of which is the red blood cell, and it also has not nucleus.

An organism which performs and exhibits all functions of life via a single cell, it is an unicellular organism. Such as prokaryotes like bacteria, eukaryotes like yeast are unicellular organisms. They lack conglomerate of cells (tissue) or organ systems to perform specific functions. All the cellular functions for it to be living are performed by the individual cell.  So, the correct answer is 'Unicellular'.

Reproduction is the characteristic for living organisms i.e., both unicellular and multi cellular organisms can reproduce irrespective of their cellular level. But, only multi cellular organisms have specialized organs for digestion and respiration/breathing that is GIT (Gastro Intestinal Tract) and Respiratory tract respectively, unlike unicellular organisms who respire and engulf food by general body surface. Thus, digestive tract and respiratory tract are defining feature of multicellular organism (ruminant). 
So, the correct answer is 'Both A and C'.

Some living organisms are made up of once cell only, these are called unicellular. These organisms have a large surface area to volume ratio and rely on simple diffusion to meet their needs. An example of a unicellular animal is Amoeba. Amoeba feed on smaller organisms such as bacteria.