Xylem cells are elongated cells with lignified secondary thickening of the cell walls.

Xylem tracheids are pointed, elongated xylem cells, the simplest of which have continuous primary cell walls and lignified secondary wall thickenings in the form of rings, hoops, or reticulate networks.

Xylem and phloem tissues are involved in the conduction processes within plants.

Xylem also contains other cell types, for example parenchyma.

Xylem sap will exude from the cut stem for hours or days due to root pressure.

Xylem sap consists mainly of water and inorganic ions, although it can contain a number of organic chemicals as well.

Xylem vessels allow the movement of water and nutrients upwards towards the shoots and leaves through the roots and fine root hairs from the soil.

Xylem vessels and tracheids transport water up the plant but lack cell membranes.

Xylem moves water and inorganic molecules within the plant and phloem counts organic molecule transportation.

Xylem sap consists primarily of water, with hormones, mineral elements and other nutrients dissolved in it.

Xylem appeared early in the history of terrestrial plant life.

Xylem is one of the two types of transport tissue in vascular plants ( phloem is the other ).

Xylem is a chief, conducting tissue of vascular plants.

( Xylem comprises the bulk of the hard tissue of the interior of trunks and branches of woody plants and is nearly synonymous with " wood ".

Xylem transport is driven by a combination of transpirational pull from above and root pressure from below, which makes the interpretation of measurements more complicated.

Many cells, bacteria, and other microorganisms are transparent to visible light and must be stained for microscopic investigation.

Many of the cells and microorganisms which are transparent to visible light, absorb or reflect the much shorter wavelengths of the ultraviolet spectrum.

But they are still enclosed in their larval cells and remain there throughout the summer, fall, and winter.

At the present time we do not know by what biochemical mechanism TSH acts on the thyroid, but for bio-assay of the hormone there are a number of properties by which its activity may be estimated, including release of iodine from the thyroid, increase in thyroid weight, increase in mean height of the follicular cells and increase in the thyroidal uptake of Af.

For this step the computer memory is separated into three regions: cells in the W-region are used for storage of the forms in the text-form list ; ;

cells in the X-region and Y region are reserved as information cells for text forms.

The address Af and the number of cells required to store the form are written in Af ; ;

similarly, as many cells are added as are required.

The list of text forms in the W-region of memory and the contents of the information cells in the X and Y-regions are no longer required.

They are often involved in teaching anatomy, and research into certain systems, organs, tissues or cells.

In successive microsporogenesis, walls are laid down separating the daughter cells after each division.

* Other apomorphic characters of the order according to Stevens are: the presence of chelidonic acid, anthers longer than wide, tapetal cells bi-to tetra-nuclear, tegmen not persistent, endosperm helobial, and loss of mitochondrial gene sdh3.

The motor neuron diseases ( MND ) are a group of neurological disorders that selectively affect motor neurons, the cells that control voluntary muscle activity including speaking, walking, breathing, swallowing and general movement of the body.

They are distinguished by the nerve cells affected ( upper and lower motor neuron ), and the symptoms that result from this damage:

In vertebrates, the axons of many neurons are sheathed in myelin, which is formed by either of two types of glial cells: Schwann cells ensheathing peripheral neurons and oligodendrocytes insulating those of the central nervous system.

Nodes of Ranvier are short fragments of unmyelinated segments of the axon, which are found periodically in between the cells of the myelin sheath.

For example the standard glutamic acid ( glutamate ) and the non-standard gamma-amino acid gamma-amino-butyric acid ( GABA ) are respectively the brain's main excitatory and inhibitory neurotransmitters, hydroxyproline-a major component of the connective tissue collagen-is synthesised from proline, the standard amino acid glycine is used to synthesise porphyrins used in red blood cells, and the non-standard carnitine is used in lipid transport.

In general, external alpha radiation is not harmful since alpha particles are effectively shielded by a few centimeters of air, a piece of paper, or the thin layer of dead skin cells.

By endocytosis or phagocytosis, exogenous antigens are taken into the antigen-presenting cells ( APCs ) and processed into fragments.

Some T cells are specific for the peptide: MHC complex.

Cytokines are substances that can activate cytotoxic T lymphocytes ( CTL ), antibody-secreting B cells, macrophages, and other particles.

In some tissues proliferating cells are restricted to specialised areas, such as the growth plates of bones.

Each tentacle, or cnida ( plural: cnidae ), is clothed with highly specialised stinging cells called cnidocytes.

Plant epidermal cells are specialised parenchyma cells covering the external surfaces of leaves, stems and roots.

A multicellular organism may contain a number of widely differing and specialised cell types, such as muscle cells and skin cells in humans, that differ both in appearance and function yet are genetically identical.

All higher multicellular organisms contain cells specialised for different functions.

Class II MHC proteins are generally only found on the surface of specialised antigen-presenting cells ( APCs ).

The minor spliceosome is located in the nucleus like its major counterpart, though there are exceptions in some specialised cells including anucleate platelets and the dendroplasm of neuronal cells.

Where predators develop resistance to this chemical, other related chemicals such as hydroquinone develop, and in many beetles, specialised cells secrete hydroquinone from glands connected by ducts to a reservoir sac, which can be closed off by muscles to stop leakage.

In most platyhelminths, the ovaries are divided into two regions, one producing the ova, and the other producing specialised yolk cells to nourish the developing embryo.

Coleoptiles consist of very similar cells that are all specialised to fast stretch growth.

Trophoblasts are specialised cells of the placenta that play an important role in embryo implantation and interaction with the decidualised maternal uterus.

The GnRH is released by the hypothalamus by specialised nerve cells or neurones.

The electroreceptors of monotremes consist of free nerve endings unlike the specialised receptor cells of fish and amphibians.

These specialised cells convert light into electrochemical signals through the ganglion cell layer and travel along the optic nerve fibers to the brain.