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.

• 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.

• Transduction of Sound

  • The outer hair cells are arranged in three or four rows.
  • Place theory, which is the model for how biologists think pitch detection works in the human ear, states that high frequency sounds selectively vibrate the basilar membrane of the inner ear near the entrance port (the oval window).
  • The place theory is the first step toward an understanding of pitch perception.
  • About 90 percent of the afferent neurons carry information from inner hair cells, with each hair cell synapsing with 10 or so neurons.
  • Outer hair cells connect to only 10 percent of the afferent neurons, and each afferent neuron innervates many hair cells.

• Movement of Water and Minerals in the Xylem

  • This is called the cohesion–tension theory of sap ascent.
  • The cohesion-tension theory explains how water moves up through the xylem.
  • Inside the leaf at the cellular level, water on the surface of mesophyll cells saturates the cellulose microfibrils of the primary cell wall.
  • The wet cell wall is exposed to the internal air space and the water on the surface of the cells evaporates into the air spaces.
  • The cohesion–tension theory of sap ascent is shown.

• 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 .

• Chromosomal Theory of Inheritance

  • The Chromosomal Theory of Inheritance identified chromosomes as the genetic material responsible for Mendelian inheritance.
  • That same year, Walter Sutton observed the separation of chromosomes into daughter cells during meiosis .
  • Together, these observations led to the development of the Chromosomal Theory of Inheritance, which identified chromosomes as the genetic material responsible for Mendelian inheritance.
  • The Chromosomal Theory of Inheritance was consistent with Mendel's laws and was supported by the following observations:
  • (a) Walter Sutton and (b) Theodor Boveri are credited with developing the Chromosomal Theory of Inheritance, which states that chromosomes carry the unit of heredity (genes).

• Mitochondria

  • Eukaryotic cells may contain anywhere from one to several thousand mitochondria, depending on the cell's level of energy consumption.
  • ATP represents the short-term stored energy of the cell.
  • Your muscle cells need a lot of energy to keep your body moving.
  • When your cells don't get enough oxygen, they do not make a lot of ATP.
  • There are two hypotheses about the origin of mitochondria: endosymbiotic and autogenous, but the most accredited theory at present is endosymbiosis.

• Endosymbiotic Theory and the Evolution of Eukaryotes

  • Genome fusion occurs during endosymbiosis, which is the mechanism proposed as responsible for the first eukaryotic cells.
  • This mechanism is an aspect of the Endosymbiont Theory, which is accepted by a majority of biologists as the mechanism whereby eukaryotic cells obtained their mitochondria and chloroplasts.
  • Within the past decade, the process of genome fusion by endosymbiosis has been proposed to be responsible for the evolution of the first eukaryotic cells .
  • One idea about how the eukaryotic nucleus evolved is that prokaryotic cells produced an additional membrane which surrounded the bacterial chromosome.
  • The theory that mitochondria and chloroplasts are endosymbiotic in origin is now widely accepted.

• Misconceptions of Evolution

  • Critics of the theory of evolution dismiss its importance by purposefully confounding the everyday usage of the word "theory" with the way scientists use the word.
  • Scientists have a theory of the atom, a theory of gravity, and the theory of relativity, each of which describes understood facts about the world.
  • It does not shed light on the beginnings of life, including the origins of the first cells, which is how life is defined.
  • Once a mechanism of inheritance was in place in the form of a molecule like DNA, either within a cell or pre-cell, these entities would be subject to the principle of natural selection.
  • The antibiotic, which kills the bacterial cells without the resistance gene, strongly selects individuals that are resistant, since these would be the only ones that survived and divided.

• Cellular Differentiation

  • Three basic categories of cells make up the mammalian body: germ cells, somatic cells, and stem cells.
  • Pluripotent stem cells undergo further specialization into multipotent progenitor cells that then give rise to functional cells.
  • Hematopoietic stem cells (adult stem cells) from the bone marrow that give rise to red blood cells, white blood cells, and platelets
  • Mesenchymal stem cells (adult stem cells) from the bone marrow that give rise to stromal cells, fat cells, and types of bone cells;
  • Epithelial stem cells (progenitor cells) that give rise to the various types of skin cells