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The biosphere (which is technically a spherical shell) is virtually a closed system with regard to matter, [1] with minimal inputs and outputs. Regarding energy, it is an open system, with photosynthesis capturing solar energy at a rate of around 100 terawatts. [2] By the most general biophysiological definition, the biosphere is the global ...
The cell is the basic structural and functional unit of all forms of life. Every cell consists of cytoplasm enclosed within a membrane; many cells contain organelles, each with a specific function. The term comes from the Latin word cellula meaning 'small room'. Most cells are only visible under a microscope.
The eukaryotic cell cycle consists of four distinct phases: G 1 phase, S phase (synthesis), G 2 phase (collectively known as interphase) and M phase (mitosis and cytokinesis). M phase is itself composed of two tightly coupled processes: mitosis, in which the cell's nucleus divides, and cytokinesis, in which the cell's cytoplasm and cell membrane divides forming two daughter cells.
1. All living organisms are composed of one or more cells. 2. The cell is the most basic unit of life. Schleiden's theory of free cell formation through crystallization was refuted in the 1850s by Robert Remak, Rudolf Virchow, and Albert Kolliker. [5] In 1855, Rudolf Virchow added the third tenet to cell theory.
The ancestry of each present day cell presumably traces back, in an unbroken lineage for over 3 billion years to the origin of life. It is not actually cells that are immortal but multi-generational cell lineages. [30] The immortality of a cell lineage depends on the maintenance of cell division potential.
The origin of the eukaryotic cell, or eukaryogenesis, is a milestone in the evolution of life, since eukaryotes include all complex cells and almost all multicellular organisms. The last eukaryotic common ancestor (LECA) is the hypothetical origin of all living eukaryotes, [ 70 ] and was most likely a biological population , not a single ...
Mitosis in the animal cell cycle (phases ordered counter-clockwise). Mitosis divides the chromosomes in a cell nucleus. Onion cells in different phases of the cell cycle enlarged 800 diameters. Mitosis (/ maɪˈtoʊsɪs /) is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei.
The timeline of the evolutionary history of life represents the current scientific theory outlining the major events during the development of life on planet Earth. Dates in this article are consensus estimates based on scientific evidence, mainly fossils. In biology, evolution is any change across successive generations in the heritable ...