Question

The cell theory states that _________
A. All cells have nuclei.
B. All cells are living.
C. Cells divide by both mitosis and meiosis.
D. The cell is the functional and structural unit of plants and animals.

Answer 1

Hint: The cell theory clearly suggests the fundamentals of biology and therefore it applies to each living organism and is considered to be universally true. The principles of the cell theory help in determining many solutions to questions such as how living beings take their form, how cancer cells proliferate, etc.

Complete answer: Cell theory was put forward by a famous German botanist- Matthias Schleiden and an English zoologist- Theodor Schwann in the year 1839.
It has the following propositions:
1. Cells are the basic unit of life and they are therefore considered to be the building blocks of living organisms.
2. All living organisms are made up of cells; a cell is the basic structural and functional unit of each living organism.
3. All cells are produced by cells that already pre-exist.

Additional information: All cells, whether prokaryotic or eukaryotic, have a membrane that surrounds the cell, regulates what moves in and out (selectively permeable), and maintains the constant electric potential of the cell.
Inside the membrane, the cytoplasm takes up most of the cell's space.
All cells (except red blood cells) have DNA, the hereditary material of genes, and RNA, containing the information required to build various proteins such as enzymes, the cell's primary machinery.

So, the correct answer is option D. Cell is the functional and structural unit of plants and animals.

Note: The cell theory is universal and it helped in shaping modern biology. Rudolf Virchow, later on, suggested some modifications (that cells are only produced by the division of pre-existing cells) in the cell theory that laid the foundation of modern pathology.