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Basic Unit of Life

Studying stem cells? Studying stem cells? Stem cells are the precursor cells from which all the body's specialized cell types develop. It may be possible to implant human stem cells into people to repair or replace diseased tissues or organs. Super resolution single−molecule fluorescence microscopy is used to view stem cells. Super − resolution techniques capture the images with a higher resolution than standard techniques. To understand the concepts of stem cells and stem cell technology, it is important to find out the basics of cell biology, as life begins with cells.

Learning Objectives

After completing the topic, the student will be able to:

  • Appreciate the importance of cells to living organisms.
  • Describe why cells are considered as the basic unit of life.
  • Apply the principles of microscope to study cells which are microscopic in origin.
  • Define and distinguish light microscope and electron microscope.
  • List the principles of cell theory and different shapes of cells.
  • Define and distinguish prokaryotes and eukaryotes with their molecular organization.
  • Examine the evolutionary relatedness of Prokaryotes, Eukaryotes, and Archaeans.
  • Summarize the fundamental components of a prokaryotic (bacterial) cell.
shapes of cellular organisms Different shapes of cellular organisms Amoeba − Irregular shaped, Paramecium − Unicellular ciliate protozoan and slipper shaped, Chlamydomonas − Unicellular photosynthetic flagellate and oval shaped
Cell - The basic unit of life

Cell is the fundamental structural and functional unit of all living beings. The cell is as fundamental to biology as the atom is to physical sciences. All living things are made up of one or more cells. Cells are the smallest structures capable of independent existence and of performing basic life processes, such as taking in nutrients, expelling waste, and reproducing. Hence cell specialization is also considered as cell differentiation.

All living beings, plants and animals, start their life with a single cell. Indeed, there are diverse forms of life existing as single−celled organisms or unicellular organisms to multicellular organisms; their bodies are composed of different kinds of specialized cells where they are organized as into higher levels of organization, such as tissue systems and organ systems. Cells are singled out as the organism's basic unit of life.

Many small plants and animals are made up of just one single cell. All the cells are related as they originate from the earlier cells. The cells have the capacity of responding to the environment fluctuations. In other words cells are considered as the smallest unit of living matter that enables to carry out the processes of life.
Eg: Yeast, Bacteria, Chlamydomonas, Amoeba and Paramecium.

Multi−cellular Onion peel cells − Uninucleated cells with cell wall Some organisms are anucleated (without nucleus, example− viruses), some are uninucleated (example− amoeba) and some are multicellular like humans. Multicellular organisms − like plants, animals and brown algae − arise from a single cell and generate a multi−celled organism.
Cell Diversity

Some cells divide and give rise to organisms with more than one cell. Some very small organisms are made up of relatively few cells − just a few hundred or a few thousand cells.
Eg: Spirogyra, Volvox.

Most plants and animals including ourselves are made up of millions and billions of cells. These organisms are termed as multi−cellular.
Eg: Human beings, Mango trees, Onions, etc.

Multicellularity exists in both prokaryotes and eukaryotes, but first appeared in Cyanobacteria. Reproduction/regeneration of whole organism in multicellular organisms takes place from germ cells.

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