sieve tubes used for food transport
their companion cells.
Each vascular bundle contains:
four xylem vessels
a group of xylem tracheids.
both carry water and dissolved minerals up the stem.
sieve tubes. See phloem.
skeletonize. To remove leaf tissue between the veins, leaving the network of veins intact.
soil profile. A vertical section of the soil through all its horizontal layers, extending into the parent material.
sieve tubes
A series of long cells lying end to end and forming a tube, found in the phloem of Angiosperms.
simple eye (ocellus)
a single eye with a single lens found in insects and some other invertebrates.
[edit] Sieve Tubes
The sieve-tube cells lack a nucleus, have very few vacuoles, but contain other organelles such as ribosomes. The endoplasmic reticulum is concentrated at the lateral walls.
transfer of soluble materials through the sieve tubes of the phloem of vascular plants; the exchange of parts of chromosomes
Source: Noland, George B. 1983. General Biology, 11th Edition. St. Louis, MO. C. V. Mosby ...
Companion cells load sugar into the sieve element (sieve elements are connected into sieve tubes). Fluids can move up or down within the phloem, and are translocated from one place to another. Sources are places where sugars are being produced.
Because of this multi-directional flow, coupled with the fact that sap cannot with ease move between adjacent sieve tubes, it is not unusual for sap in adjacent sieve tubes to be flowing in opposite directions.
A hypothesis accounting for sap flow through the phloem system. According to this hypothesis, the solution containing nutrient sugars moves through the sieve tubes by bulk flow, moving into and out of the sieve tubes by active transport and diffusion.
phloem - living conducting tissue of a plant, a system basically composed of sieve tubes, companion cells, fibers and sclereids to convey the products of photosynthesis, particularly sucrose, from the leaves to growing tissues.
sieve tube members Phloem cells that form long sieve tubes. See sieve elements.
silica Silicon dioxide.
 See also: Trans, Cells, Phloem, Organ, Tissue
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