Xylem and Phloem

Topics: Xylem, Vascular plant, Phloem Pages: 2 (659 words) Published: March 23, 2014
Xylem and Phloem
Research Task

3/8/2014

Xylem and phloem are the conducting elements of vascular plants. They function in the transport of water, nutrients, sugars, proteins and RNA throughout the plant. The xylem and phloem are generally found together in vascular bundles and can lie in various positions relative to each other. (Plant Vascular System Development) The term phloem originates from the Greek word, phloios, meaning “bark”. (Merriam-Webster) In vascular plants, phloem is the living tissue that carries organic nutrients, particularly sucrose, to all parts of the plant where needed. (Lalonde S, 2004) Phloem’s main job is to move sugars from the source tissue (ex. photosynthetic leaf cells) to sink tissues (ex. non-photosynthetic root cells or developing flowers). Molecules like proteins and mRNAs also are transported to parts of the plant by the phloem. (WiseGEEK)

Phloem is composed of several cell types including sclerenchyma, parenchyma, sieve elements and companion cells. The sieve element and companion cell are found closely associated with each other in what is referred to as the sieve element/companion cell complex. (MSU) It is believed that when phloem is damaged, P-proteins quickly aggregate at the sieve plate to form a “clot” which prevents the leakage of phloem exudates. Callose is a carbohydrate which is also placed at the sieve plate in response to injury. (MSU)

Xylem is part of the vascular system that conveys water and dissolved minerals from the roots to the rest of the plant and may also furnish mechanical support. (Encyclopedia Britannica) The word is derived from the Greek word, meaning “wood”. Xylem formation begins when the actively dividing cells of growing root and shoot tips give rise to the primary xylem. (Encyclopedia Britannica) As the growing part of the plant builds past the xylem this formed, the vascular cambium produces secondary xylem tissues that cover the primary xylem. Xylem is star shaped and...


Bibliography: Britannica, A. o. (2014, March 9). Xylem. Retrieved from Encyclopaedia Britannica: http://www.britannica.com/EBchecked/topic/650951/xylem
Lalonde S, F
Merriam-Webster. (n.d.). Phloem. Retrieved March 8, 2013, from Merriam-Webster: http://www.merriam-webster.com/dictionary/phloem
MSU
MSU. (n.d.). P-proteins and Callose: The Damage Control Team. Retrieved March 8, 2014, from MSU: https://www.msu.edu/~walwort8/page2.html#damage
Phloem
Phloem vs Xylem. (2014, March 11). Retrieved from Diffen: http://www.diffen.com/difference/Phloem_vs_Xylem
Plant Vascular System Development
Studios, A. R. (2014, March 9). Plants Vascular Systems. Retrieved from Biology4Kids: http://www.biology4kids.com/files/plants_xylemphloem.html
Transport mechanisms for organic forms of carbon and nitrogen between source and sink
WiseGEEK. (n.d.). What Is Phloem? Retrieved March 8, 2014, from wiseGEEK: http://www.wisegeek.com/what-is-phloem.htm
Xylem Structure
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