Asked by: Dina Goldsmith
science biological sciences

Are sieve tube cells living?

Last Updated: 30th March, 2020

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In plant anatomy, sieve tube elements, also called sieve tube members, are highly specialised type of elongated cell in the phloem tissue of flowering plants. Unlike the water-conducting xylem vessel elements that are dead when mature, sieve elements are living cells. They are unique in lacking a nucleus at maturity.

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Thereof, why are sieve tubes considered living cells?

The main functions of sieve tube members include maintaining cells and transporting necessary molecules with the help of companion cells. The sieve tube members are living cells (which do not contain a nucleus) that are responsible for transporting carbohydrates throughout the plant.

how are sieve tubes supported and kept alive? Each STM is a living cell. They have to be alive because phloem transport only occurs in living cells with intact, functioning plasma membranes. The cytoplasm of a sieve tube is continuous; where the STMs abut, there are many large pores connecting them.

Additionally, are sieve tube elements alive?

sieve-tube element. An elongated, food-conducting cell in phloem in angiosperms. Unlike the tracheary elements of xylem, sieve elements have living protoplasts when mature, but they lack a nucleus and are dependent upon companion cells for certain functions.

Are companion cells living?

Companion cell is a living cell found within the phloem of angiosperms (flowering plants). Each companion cell is usually closely associated with a sieve tube cell. It regulates the activities of a sieve cell. Sieve cells lack nucleus and are therefore dependent on adjacent companion cells.

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What is a sieve cell in biology?

noun, plural: sieve cells. (botany) The main conductive cell in the phloem of the gymnosperms and pteridophytes. Supplement. The vascular plants have vascular tissues from where essential materials are transported throughout the plant. Two major vascular tissues are xylem and phloem.

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Are xylem cells dead?

Xylem vessels are a long straight chain made of tough long dead cells known as vessel elements. The vessel have no cytoplasm. They are not living, but are made by living cells. The cells are arranged end to end and the cell walls have disappeared.

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What is the function of sieve plates?

The end walls of cells in phloem form sieve plates,which have small holes in them. These holes in sieve plates allow the food to pass along the phloem tubes. Answer: The sieve plates are present in phloem of the plant.

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Do sieve tubes have cytoplasm?

The sieve tubes of the phloem in angiosperms consist of sieve tube elements or members. These are cells which lose their nucleus, ribosomes, and vacuoles at maturity. They of course have cytoplasm, and it is connected by channels to companion cells (which do have these organelles).

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What do sieve tubes do?

Sieve tube, in flowering plants, elongated living cells (sieve-tube elements) of the phloem, the nuclei of which have fragmented and disappeared and the transverse end walls of which are pierced by sievelike groups of pores (sieve plates). They are the conduits of food (mostly sugar) transport.

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What is cambium cells?

Cambium, plural Cambiums, orCambia, in plants, layer of actively dividing cells between xylem (wood) and phloem (bast) tissues that is responsible for the secondary growth of stems and roots (secondary growth occurs after the first season and results in increase in thickness).

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What is the difference between sieve tubes and companion cells?

The key difference between sieve tubes and companion cells is that the sieve tubes are the phloem sieve elements that conduct food in angiosperms whereas, companion cells are the associated cells of sieve tubes. Moreover, sieve tubes have pores in the transverse walls while companion cells do not have pores.

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Are companion cells dead at maturity?

Although still alive at maturity, the nucleus and other cell components of the sieve-tube cells have disintegrated. Companion cells are found alongside the sieve-tube cells, providing them with metabolic support.

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How are sieve tubes connected?

Sieve tubes consist of sieve elements which are elongated cells, connected to each other via sieve plates to form a continous tube system that spreads out through the entire plant. Mature sieve elements contain structural phloem specific proteins (P-proteins), mitochondria, ER, and sieve elements plastids.

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Why are phloem cells alive?

Phloem cells are alive, using ATP to actively move the sugars from the leaves to the phloem. This lowers the water potential within the phloem, drawing water from the Xylem. The cells in the phloem need to be alive to provide energy for active transport when transporting sucrose around the plant.

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What happens if a plant cell lacks Plasmodesmata?

Due to the presence of plasmodesmata, plant cells can be considered to form a synctium, or multinucleate mass with cytoplasmic continuity. The desmotubule does not completely fill the plasmodesma and, consequently, a ring of shared cytoplasm is located between it and the inner surface of the membrane-lined channel.

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What transports phloem?

The xylem and the phloem make up the vascular tissue of a plant and transports water, sugars, and other important substances around a plant. Phloem is responsible for transporting food produced from photosynthesis from leaves to non-photosynthesizing parts of a plant such as roots and stems.

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What is sieve pore?

noun In botany, one of the pores or openings through the sieve-plate permitting communication between contiguous sieve-cells.

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Do companion cells have chloroplasts?

Yes, companion cells do have chloroplasts. Companion cells are specialised parenchymatous cells present within the phloem of flowering plants. They are closely associated with the sieve tube elements as they help in maintaining the pressure gradient in them.

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What is secondary plant growth?

In many vascular plants, secondary growth is the result of the activity of the two lateral meristems, the cork cambium and vascular cambium. Arising from lateral meristems, secondary growth increases the girth of the plant root or stem, rather than its length.

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Do gymnosperms have companion cells?

Explanation: Companion cells are the cells with abaundent plasma and nucleus present in angiosperms. But these cells are absent in gymnosperms. Gymnosperms do not need root pressure to get water from soil as most of them are grown in cold and dry climates.

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Are Tracheids living?

They have specialized some of the cells to help in the ascent of sap. Tracheary elements, both tracheids and vessels, are highly specialized cells. These cells are devoid of protoplast when mature. These non-living cells are elongated with lignified cell walls.

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Are xylem cells completely hollow?

Xylem consists of dead cells. The cells that make up the xylem are adapted to their function: They lose their end walls so the xylem forms a continuous, hollow tube.

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Do phloem sieve tubes have lignin?

Phloem are hollow tubes made of up many connected cells (sieve tubes elements). The cell walls between each of the cells are perforated into structures called sieve plates. The cells are dead and hollow and have very thickened cell walls that are impregnated with lignin.