Cell Structure and Function Quiz

Characteristics of Living Organisms

• The presence of cells is the basic unit of life that distinguishes living organisms from non-living things.
• All organisms, whether unicellular or multicellular, are composed of cells.

Unicellular Organisms

• Unicellular organisms are capable of independent existence and performing essential functions of life.
• Anything less than a complete cell structure does not ensure independent living.

Cell Theory

• In 1838, Matthias Schleiden observed that all plants are composed of different kinds of cells that form tissues.
• Theodore Schwann, in 1839, studied animal cells and reported that cells have a thin outer layer called the plasma membrane.
• Schwann proposed that bodies of animals and plants are composed of cells and products of cells.
• Rudolf Virchow, in 1855, explained that cells divide and new cells are formed from pre-existing cells (Omnis cellula-e cellula).
• The cell theory states that all living organisms are composed of cells and products of cells, and all cells arise from pre-existing cells.

Cell Structure

• Plant cells have a distinct cell wall as their outer boundary and a cell membrane just within it.
• Animal cells have an outer membrane as the delimiting structure of the cell.
• Cells have a dense membrane-bound structure called the nucleus, which contains chromosomes and genetic material (DNA).
• Cells have a semi-fluid matrix called cytoplasm, which is the main arena of cellular activities.
• Eukaryotic cells have membrane-bound organelles like the endoplasmic reticulum (ER), golgi complex, lysosomes, mitochondria, microbodies, and vacuoles.
• Prokaryotic cells lack membrane-bound organelles.
• Ribosomes are non-membrane bound organelles found in all cells.
• Cells differ greatly in size, shape, and activities.