layering

Examples of layering in the following topics:

• Physical Properties of Soil

  • The soil profile has four distinct layers:
  • Topsoil, the top layer of soil, is usually two to three inches deep, but this depth can vary considerably.
  • For instance, river deltas, such as the Mississippi River delta, have deep layers of topsoil.
  • In some soils, the B horizon contains nodules or a layer of calcium carbonate.
  • Some soils may have additional layers, or lack one of these layers.

• Cleavage, the Blastula Stage, and Gastrulation

  • Here the cells in the blastula arrange themselves in two layers: the inner cell mass and an outer layer called the trophoblast .
  • The cells in the blastula rearrange themselves spatially to form three layers of cells in a process known as gastrulation.
  • During gastrulation, the blastula folds upon itself to form the three layers of cells.
  • Each of these layers is called a germ layer, which differentiate into different organ systems .
  • The three germs layers are the endoderm, the ectoderm, and the mesoderm.

• Epithelial Tissues

  • They also line the lumens of organs in a single layer or multiple layers of cells.
  • Epithelia composed of a single layer of cells is called simple epithelia; epithelial tissue composed of multiple layers is called stratified epithelia.
  • They are most-commonly found in a single-layer arrangement.
  • The nuclei are arranged at different levels in the layer of cells, making it appear as though there is more than one layer.
  • They exist in one layer, but the arrangement of nuclei at different levels makes it appear that there is more than one layer.

• Animal Characterization Based on Features of Embryological Development

  • Animals develop either two or three embryonic germs layers .
  • Radially-symmetrical animals are diploblasts, developing two germ layers: an inner layer (endoderm) and an outer layer (ectoderm).
  • Diploblasts have a non-living layer between the endoderm and ectoderm.
  • Bilaterally-symmetrical animals are called triploblasts, developing three tissue layers: an inner layer (endoderm), an outer layer (ectoderm), and a middle layer (mesoderm).
  • Triploblasts develop a third layer, the mesoderm, between the endoderm and ectoderm

• Leaf Structure, Function, and Adaptation

  • The outermost layer of the leaf is the epidermis.
  • The epidermis is usually one cell layer thick.
  • It may be present in one, two, or three layers.
  • Both layers of the mesophyll contain many chloroplasts.
  • The mesophyll has two layers: an upper palisade layer and a lower spongy layer.

• Soil Formation

  • Soil distribution is not homogenous because its formation results in the production of layers; the vertical section of the layers of soil is called the soil profile.
  • Within the soil profile, soil scientists define zones called horizons: a soil layer with distinct physical and chemical properties that differ from those of other layers.
  • The vertical section of soil layers is called the soil profile.
  • The soil profile contains defined zones called horizons whicht have distinct physical and chemical properties that differ from those of other layers.

• The Mechanics of Human Breathing

  • The layer of tissue that covers the lung and dips into spaces is called the visceral pleura.
  • A second layer of parietal pleura lines the interior of the thorax .
  • The space between these layers, the intrapleural space, contains a small amount of fluid that protects the tissue by reducing the friction generated from rubbing the tissue layers together as the lungs contract and relax.
  • If these layers of tissues become inflamed, this is categorized as pleurisy: a painful inflammation that increases the pressure within the thoracic cavity, reducing the volume of the lung.
  • A tissue layer called pleura surrounds the lung and interior of the thoracic cavity.

• Phylum Cnidaria

  • Phylum Cnidaria includes animals that show radial or biradial symmetry and are diploblastic: they develop from two embryonic layers.
  • All cnidarians show the presence of two membrane layers in the body that are derived from the endoderm and ectoderm of the embryo.
  • The outer layer (from ectoderm) is called the epidermis and lines the outside of the animal, whereas the inner layer (from endoderm) is called the gastrodermis and lines the digestive cavity.
  • Between these two membrane layers is a non-living, jelly-like mesoglea connective layer.
  • All cnidarians have two membrane layers, with a jelly-like mesoglea between them.

• Superphylum Lophotrochozoa

  • Animals belonging to superphylum Lophotrochozoa are protostomes: the blastopore (or the point of involution of the ectoderm or outer germ layer) becomes the mouth opening to the alimentary canal.
  • In protostomy, solid groups of cells split from the endoderm or inner germ layer to form a central mesodermal layer of cells.
  • This layer multiplies into a band which then splits internally to form the coelom; this protostomic coelom is termed schizocoelom.

• Carbon Dating and Estimating Fossil Age

  • Stratigraphy is the science of understanding the strata, or layers, that form the sedimentary record.
  • These rocks normally form relatively horizontal, parallel layers, with younger layers forming on top.
  • If a fossil is found between two layers of rock whose ages are known, the fossil's age is thought to be between those two known ages.
  • The layers of sedimentary rock, or strata, can be seen as horizontal bands of differently colored or differently structured materials exposed in this cliff.
  • The deeper layers are older than the layers found at the top, which aids in determining the relative age of fossils found within the strata.