Cell-walls sentence example
There is no need for cuticularization here, as the external dangerous influences do not reach the interior, and the processes of absorption which Boussingault attributed to the external cuticularized cells can take place freely through the, delicate cell-walls of the interior, saturated as these are with water.
The cell-walls of plants render the entry of solid material into the organism impossible.
These include cell walls and the various stored products found in growing cells.
Again, the degree of differentiation is very slight anatomically, but delicate protoplasmic threads have been shown to extend through all cell-walls, connecting together all the protoplasts of a plant.
The cut cells die, and oxidized products are concerned in the change of color, the brown juices exuding and soaking into the cell-walls.Advertisement
If the attack of a parasite is met by the formation of some substance in the protoplasm which is chemo- tactically repulsive to the invader, it may be totally incapable of penetrating the cell, even though equipped with a whole armoury of cytases, diastatic and other enzymes, and poisons which would easily overcome the more passive resistances offered by mere cell-walls and cell-contents of other plants, the protoplasm of which forms bodies chemotactically attractive to the Fungus.
In order that a Fungus may enter a plant, it must be able to overcome not merely the resistance of cell-walls, but that of the living protoplasm; if it cannot do this, it must remain outside as a mere epiphyte, e.g.
Fumago, Herpotrichia, &c., or, at most, vegetate in the intercellular spaces and anchor itself to the cell-walls, e.g.
Besides the internal or centripetal growth, some cell-walls are thickened on the outside, such as pollen grains, oospores of Fungi, cells of Peridineae, &c. This centrifugal growth must apparently take place by the activity of protoplasm external to the cell.
Cell-walls may become modified by the impregnation of various substances.Advertisement
Woody or lignified cell-walls appear to contain substances called conifer-in and vanillin, in addition to various other compounds which are imperfectly known.
Staining reagents can also be used to differentiate lignified cell-walls.
Cuticularized or suberized cell-walls occur especially in those cells which perform a protective function.
The suberized and cuticularized cell-walls appear to contain a fatty body called suberin, and such cell-walls can be stained red by a solution of alcanin, the lignified and cellulose membranes remaining unstained.
It is interesting to note that in many species the formation of new cell-walls is initiated before any indication of nuclear division is to he seen.Advertisement
The formation of the conducting tubes or secretory sacs which occur in all parts of the higher plants is due either to the elongation of single cells or to the fusion of cells together in rows by the absorption of the cell-walls separating them.
The absorption of the cell-walls takes place very early in the germina-, ting seedling.
The animal body, if it be composed of many cells, follows a different architectural plan; the compact nature of its food, and the yielding nature of its cell-walls, result in a form of structure consisting essentially of tubular or spherical masses of cells arranged concentrically round the food-cavity.
In other cases the strands undergo differentiation into an outer layer with blackened, hardened cell-walls and a core of ordinary hyphae, and are then termed rhizomorphs (Armillaria mellea), capable not only of extending the fungus in the soil, like roots, but also of lying dormant, protected by the outer casing.
In many cases the swollen cell-walls serve as reserves, and sometimes the substance is so thickly deposited in strata as to obliterate the lumen, and the hyphae become nodular (Polyporus sacer, P. rhinoceros, Lentinus Woermanni).Advertisement
As in other cell-walls, so here the older membranes may be altered by deposits of various substances, such as resin, calcium oxalate, colouring matters; or more profoundly altered throughout, or in definite layers, by lignification, suberization (Trametes, Daedalea), or swelling to a gelatinous mucilage (Tremella, Gymnosporangium), while cutinization of the outer layers is common.
One of the most striking alterations of cell-walls is that termed carbonization, in which the substance gradually turns black, hard and brittle, as if charred - e.g.
At the other extreme the cell-walls of many lichen-fungi are soft and colourless, but turn blue in iodine, as does starch.
Many of the coloured pigments of fungi are fixed in the cell-walls or excreted to the outside (Peziza aeruginosa).
Gelatinous or mucilaginous degenerations of cell-walls are frequently employed in the interests of spore dispersal.Advertisement
Pythium is a semiaquatic form attacking seedlings which are too plentifully supplied with water; its hyphae penetrate the cell-walls and rapidly destroy the watery tissues of the living plant; then the fungus lives in the dead remains.
Marshall Ward showed that the hyphae of Botrytis pierce the cell-walls of a lily by secreting a cytase and dissolving a hole through the membrane.
In Batrachospermum the whole system of branches are retained within a diffluent gelatinous substance derived from the outer layers of the cell-walls.
The cell-walls in some forms swell up into a gelatinous mass so that the cell appears to be surrounded in the unstained condition by a clear, transparent space.
A striking feature in the roots of several genera, excluding the Abietineae, is the occurrence of thick and somewhat irregular bands ofthickening on the cell-walls of the cortical layer next to the endodermis.
A pine needle grown iji continuous light differs from one grown under ordinary conditions in the absence of hypodermal fibres, in the absence of the characteristic infoldings of the mesophyll cell-walls, in the smaller size of the resin-canals, &c. The endodermis in Pinus, Picea and many other genera is usually a well-defined layer of cells enclosing the vascular bundles, and separated from them by a tissue consisting in part of ordinary parenchyma and to some extent of isodiametric tracheids; but this tissue, usually spoken of as the pericycle, is in direct continuity with other stem-tissues as well as the pericycle.
The mesophyll of Pinus and Cedrus is characterized by its homogeneous character and by the presence of infoldings of the cell-walls.
The megaspore becomes filled with the female prothallus, the formation of cell-walls commencing at the pointed end of the spore, where from the first the nuclei are more numerous, and later extending to the base.
These sheets were readily accepted by the bees, and afterwards plates cast from metal were employed, with so good a result as to give to the bees as perfect a midrib as that of natural comb with the deep cell walls cut away.
Mr Wagner first conceived the idea of adding slightly raised side walls to the hexagonal outlines of the cells, by means of which the bees are supplied with the material for building out one-half or more of the complete cell walls or sides.
It has been found useful in some cases to examine microscopically the thin film of coal that often covers the pinnae of fossil fronds, in order to determine the form of the epidermal cells which may be preserved in the carbonized cuticle; rectilinear epidermal cell-walls are usually considered characteristic of Cycads, while cells with undulating walls are more likely to belong to Ferns.
Charlie Harrington graduated in Microbiology from Glasgow University where he developed an interest in chemical microbiology and the study of microbial cell walls.
They identified a mouse whose immune system did not react to a substance called endotoxin, a component of bacterial cell walls.
For examining root tips we often counterstain cell walls for a few minutes with 10 ug/ml propidium iodide solution.
The thin line between adjacent cell walls is the middle lamella.
Coccolithophores are small phytoplankton with calcium plates surrounding their cell walls.
Leaves can be treated with enzymes to strip away the cell walls and produce protoplasts, which are effectively ' naked ' plant cells.
It is the cell-walls which connect the different cells of a tissue (see below), and it is upon their characters (thickness, sculpture and constitution) that the qualities of the tissue largely depend.
This large evaporation, which constitutes the so-called transpiration of plants, takes place not into the external air but into this same intercellular space system, being possible only through the delicate cell-walls upon which it abuts, as the external coating, whether bark, cork or cuticle, is impermeable by watery vapour.
The older is that the water travels in the woody cell-walls of the vascular bundles, mainly under the action of the forces of root pressure and transpiration, and that the cavities of the vessels contain only air.
In these we have (1) the evaporation from the damp delicate cell-walls into the intercellular spaces; (2) the imbibition by the cell-wall of water from the vacuole; (3) osmotic action, consequent upon the subsequent increased concentration of the cell sap, drawing water from the wood cells or vessels which abut upon the leaf parenchyma.
Another objection was that even if bacteria obtained access through the stomata, they could not penetrate the cell-walls bounding the intercellular spaces, but certain anaerobic forms are known to ferment cellulose, and others possess the power of penetrating the cell-walls of living cells, as the bacteria of Leguminosae first described by Marshall Ward in 1887, and confirmed by Miss Dawson in 1898.
When it reaches the intestines, cholesterol is absorbed and moves into the bloodstream where it's used to repair damage to cell walls.
Blood agar is usually made from the cell walls of red algae (also trypticase soy, heart infusion, or Todd-Hewitt agar) and sheep's blood.
Cellulose-The primary substance composing the cell walls or fibers of all plant tissues.
This chain reaction can damage cell walls and cell structure and may contribute to aging in tissues and organs.
Antioxidants prevent damage to the cell walls by reducing the number of free radicals in the body.
Next, the machine mashes or chews the produce, breaking down cell walls.
In such cases the characters of the adult tissue clearly depend solely upon the characters of the cell-walls, and it is usual in plant-anatomy to speak of the wall with its enclosed cavity as the cell, and the contained protoplasm or other substances, if present, as cell-contents.
Communication between the various protoplasts of the colony is, however, carried on by means of fine protoplasmic threads, which are continuous through the cell-walls.
Cellulose, the material of which vegetable cell-walls are almost universally composed, at any rate in their early condition, is known to occur, though only seldom, among animal organisms. Such forms as Volvox and the group of the Myxomycetes have been continually referred to both kingdoms, and their true systematic position is still a subject of controversy.