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English: This is the official list of questions (and expected answers) that can be asked on the civics portion of the American naturalization test, revised in January of 2019. While most of these questions are supplied with answers, the ones that ask about specific members of the American government are not.
In biology, tissue is an assembly of similar cells and their extracellular matrix from the same embryonic origin that together carry out a specific function. [1] [2] Tissues occupy a biological organizational level between cells and a complete organ. Accordingly, organs are formed by the functional grouping together of multiple tissues. [3]
There are four basic types of animal tissues: muscle tissue, nervous tissue, connective tissue, and epithelial tissue. [5] [9] All animal tissues are considered to be subtypes of these four principal tissue types (for example, blood is classified as connective tissue, since the blood cells are suspended in an extracellular matrix, the plasma). [9]
In a multicellular organism, an organ is a collection of tissues joined in a structural unit to serve a common function. [1] In the hierarchy of life, an organ lies between tissue and an organ system. Tissues are formed from same type cells to act together in a function. Tissues of different types combine to form an organ which has a specific ...
Primary mesenchyme is the first embryonic mesenchymal tissue to emerge, and it is produced from EMT in epiblast cells. In the epiblast, it is induced by the primitive streak through Wnt signaling, and produces endoderm and mesoderm from a transitory tissue called mesendoderm during the process of gastrulation. [17]
On the other hand, the strict meaning of "tissue culture" refers to the culturing of tissue pieces, i.e. explant culture. Tissue culture is an important tool for the study of the biology of cells from multicellular organisms. It provides an in vitro model of the tissue in a well defined environment which can be easily manipulated and analysed ...
Haematopoietic stem cells (HSCs) reside in the medulla of the bone (bone marrow) and have the unique ability to give rise to all of the different mature blood cell types and tissues. [2] [3] HSCs are self-renewing cells: when they differentiate, at least some of their daughter cells remain as HSCs, so the pool of stem cells is not depleted.
The endothelium (pl.: endothelia) is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. [1] The endothelium forms an interface between circulating blood or lymph in the lumen and the rest of the vessel wall.