BBC - GCSE Bitesize: Xylem and phloem

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Science

Transport in plants

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Plants have two different types of transport tissue. Xylem transports water
and solutes from the roots to the leaves, phloem transports food from the
leaves to the rest of the plant. Transpiration is the process by which
water evaporates from the leaves, which results in more water being drawn
up from the roots. Plants have adaptations to reduce excessive water loss.

** Xylem and phloem **

Plants have transport systems to move food, water and minerals around.
These systems use continuous tubes called xylem


Source: www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_gateway/green_world/planttransportrev1.shtml


what is a xylem


Xylem - Wikipedia

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** Xylem **

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Schematic cross section of part of a leaf, xylem shown as red circles at
figure 8

*Xylem* is one of the two types of transport tissue in vascular plants,
phloem being the other. The basic function of xylem is to transport water
from roots to shoot and leaves, but it also transports some nutrients.^[1]
The word /xylem/ is derived from the Greek word ξύλον
(/xylon/), meaning "wood"; the best-known xylem tissue is wood, though it
is found throughout the plant.

*Contents*

· 1 Structure
· 2 Primary and secondary xylem
· 3 Main function – upwards water transport

· 3.1 Cohesion-tension theory
· 3.2 Measurement of pressure

· 4 Evolution
· 5 Development

· 5.1 Protoxylem and metaxylem
· 5.2 Patterns of protoxylem and metaxylem

· 6 See also
· 7 References

· 7.1 General references

*Structure[edit]*

Cross section of some xylem cells
Cross section of some xylem cells

The most distinctive xylem cells are the long tracheary elements that
transport water. Tracheids and vessel elements are distinguished by their
shape; vessel elements are shorter, and are connected together into long
tubes that are called /vessels/.^[2]

Xylem also contains two other cell types: parenchyma and fibers.^[3]

Xylem can be found:

· in vascular bundles, present in non-woody plants and non-woody parts of
woody plants
· in secondary xylem, laid down by a meristem called the vascular cambium
in woody plants
· as part of a stelar arrangement not divided into bundles, as in many
ferns.

In transitional stages of plants with secondary growth, the first two
categories are not mutually exclusive, although usually a vascular bundle
will contain /primary xylem/ only.

The branching pattern exhibited by


Source: en.wikipedia.org/wiki/Xylem

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