cell theory

Examples of cell theory in the following topics:

• Cell Theory

  • Cell theory states: living things are composed of one or more cells; the cell is the basic unit of life; cells arise from existing cells.
  • By the late 1830s, botanist Matthias Schleiden and zoologist Theodor Schwann were studying tissues and proposed the unified cell theory.
  • The unified cell theory states that: all living things are composed of one or more cells; the cell is the basic unit of life; and new cells arise from existing cells.
  • The generally accepted portions of the modern Cell Theory are as follows:
  • The cell is the basic unit of life and the study of the cell led to the development of the cell theory.

• Disadvantages of fuel cells

  • The price of electricity produced by fuel cells makes the technology somewhat prohibitive.
  • Fuel cells large enough to power a home can cost thousands of dollars (resulting in a payback period of up to 15 years), which means that the electricity they produce costs around $1,500–$6,000 per kW (before payback).
  • Depending on the cost of the hydrogen source (such as natural gas), electricity from a 2 kW fuel cell system could, in theory, provide power at eight to ten cents per kWh within the next decade or so.
  • Long-term performance estimates for fuel cells have not yet been determined although, to date, most fuel cells require maintenance overhauls every five years or so.
  • Fuel Cell Council website at www.usfcc.com.

• Gene Expression in Stem Cells

  • Stem cells can now be artificially grown and differentiated into specialized cell types with characteristics consistent with muscle or nerve cells through cell culture.
  • An alternative theory is that stem cells remain undifferentiated due to environmental cues in their particular niche.
  • In one, the daughter cells are initially equivalent but a difference is induced by signaling between the cells, from surrounding cells, or from the precursor cell.
  • Stem cells are indicated by (A), progenitor cells by (B), and differentiated cells by (C).
  • Pluripotent, embryonic stem cells originate as inner cell mass (ICM) cells within a blastocyst.

• Concentration of Cells

  • In the late 19th century, Josiah Willard Gibbs formulated a theory to predict whether a chemical reaction would be spontaneous based on free energy:
  • In the 20th century, German chemist Walther Nernst extended Gibbs' theory to include the contribution from electric potential on charged species.
  • The change in Gibbs free energy for an electrochemical cell can be related to the cell potential.
  • Therefore, Gibbs' theory is:
  • Under standard conditions, the output of this pair of half-cells is well known.

• Clonal Selection and B-Cell Differentiation

  • T Cell Dependent Activation- activation of B cells by type 2 helper T cells in the lymph nodes.
  • B Cell differentiation refers to the process by which B cells change into different types, such as plasma cells and plasma blasts.
  • Clonal selection is theory in which it is postulated that a B cell expresses antigen specific receptors before antibodies even encounter an antigen or before that antigen is ever found in the body.
  • This theory may explain why secondary immune responses from memory cells are so effective that repeated infections by the same pathogen are stopped before symptoms even develop.
  • T cell-dependent B cell activation, showing a TH2-cell (left), B cell (right), and several interaction molecules

• Clonal Selection and T-Cell Differentiation

  • Clonal selection is an theory that attempts to explain why lymphocytes are able to respond to so many different types of antigens.
  • This mass production of daughter cells is termed "clonal expansion," in which daughter cells proliferate into several generations of clones of the original parent cells.
  • This idea is still only considered a theory, however it explains many of the nuances of the adaptive immune system.
  • Cloned daughter cells differentiate into either effector T cells or memory T cells.
  • Cytotoxic effector T cells are finished, but helper T cells continue to differentiate into individual subsets of helper T cells.

• Centrosome

  • The centrosome is an organelle that is the main microtubule organizing center of the animal cell and a regulator of cell-cycle progression.
  • In cell biology, the centrosome is an organelle that serves as the main microtubule organizing center (MTOC) of the animal cell as well as a regulator of cell-cycle progression.
  • In the theory of evolution the centrosome is thought to have evolved only in the metazoan lineage of eukaryotic cells.
  • During the prophase in the process of cell division called mitosis, the centrosomes migrate to opposite poles of the cell.
  • Some cell types arrest in the following cell cycle when centrosomes are absent.

• Clonal Selection and Tolerance

  • Central tolerance is the mechanism by which newly developing T cells and B cells are rendered non-reactive to self.
  • The concept of central tolerance was proposed in 1959 as part of a general theory of immunity and tolerance.
  • The theory that self-tolerance is 'learned' during lymphocyte development was a major conceptual contribution to immunology.
  • Regulatory T cells can be considered both central tolerance and peripheral tolerance mechanisms, as they can be generated from self (or foreign)-reactive T cells in the thymus during T cell differentiation.
  • Hematopoietic stem cell 2.

• Endosymbiosis and the Evolution of Eukaryotes

  • Eukaryotes may have been a product of one cell engulfing another and evolving over time until the separate cells became a single organism.
  • This major theme in the origin of eukaryotes is known as endosymbiosis, where one cell engulfs another such that the engulfed cell survives and both cells benefit .
  • The endosymbiotic theory was first articulated by the Russian botanist Konstantin Mereschkowski in 1905.
  • These theories were initially dismissed or ignored.
  • The endosymbiotic theory was advanced and substantiated with microbiological evidence by Lynn Margulis in 1967 .

• Aging and the Immune System

  • The cytotoxicity of Natural Killer (NK) cells and the antigen-presenting function of dendritic cells is known to diminish with old age.
  • In addition to changes in immune responses, the beneficial effects of inflammation devoted to the neutralization of dangerous and harmful agents early in life and in adulthood become detrimental late in life in a period largely not foreseen by evolution, according to the antagonistic pleiotropy theory of aging.
  • The functional capacity of T-cells is most influenced by the effects of aging.
  • After birth, the decline of T-cell function begins with the progressive involution of the thymus, which is the organ essential for T-cell maturation following the migration of precursor cells from the bone marrow.
  • the accumulation and the clonal expansion of memory and effector T-cells