Xylem and Phloem in Plants
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Questions and Answers

What is the primary function of xylem tissue in plants?

  • Facilitating photosynthesis
  • Conducting water and dissolved compounds from roots to leaves (correct)
  • Storing starch and fats
  • Transporting nutrients from leaves to roots

Which of the following correctly identifies the types of cells found in xylem tissue?

  • Phloem parenchyma and companion cells
  • Xylem parenchyma, xylem fibres, tracheids, and vessels (correct)
  • Only vessels and tracheids
  • Root hairs and stomata

What function does xylem parenchyma serve in plants?

  • Conducting photosynthesis
  • Transporting food to non-photosynthesizing parts
  • Storing starch, fats, and other substances (correct)
  • Providing mechanical strength to roots

How does xylem parenchyma differ from other parenchyma types in tissue structure?

<p>It can contain chlorophyll and other substances (D)</p> Signup and view all the answers

What happens to the cell walls of xylem parenchyma over time?

<p>They thicken due to the deposition of lignin later in life (B)</p> Signup and view all the answers

Which misconception about xylem is incorrect?

<p>Xylem is solely responsible for the transport of nutrients (A)</p> Signup and view all the answers

What type of xylem also serves as wood parenchyma?

<p>Secondary xylem (D)</p> Signup and view all the answers

What provides mechanical strength to the plant?

<p>Thick-walled parenchyma (C)</p> Signup and view all the answers

Which structure is primarily responsible for conducting water in xylem?

<p>Tracheids (D)</p> Signup and view all the answers

Which characteristic is NOT true for xylem fibres?

<p>Their cell walls are usually thin. (D)</p> Signup and view all the answers

What is another name for xylem fibres?

<p>Wood fibres (B)</p> Signup and view all the answers

Which type of xylary fibre is characterized by a very narrow lumen?

<p>Libriform fibre (B)</p> Signup and view all the answers

Which type of xylary fibre is intermediate between tracheids and libriform fibres?

<p>Fibre-tracheid (C)</p> Signup and view all the answers

In primary xylem, where do xylem fibres originate?

<p>From procambium (C)</p> Signup and view all the answers

How do the inner apertures of pit pairs in fibre-tracheids typically appear?

<p>Slit-like (A)</p> Signup and view all the answers

Which type of xylary fibre lacks lignin or contains it in very small amounts?

<p>Gelatinous or mucilaginous fibre (B)</p> Signup and view all the answers

What is the primary function of tracheids in vascular plants?

<p>Conduction of water and minerals (C)</p> Signup and view all the answers

In which type of plants are tracheids exclusively found?

<p>Pteridophytes and gymnosperms (D)</p> Signup and view all the answers

What type of pitting is characteristic of bordered pits in tracheids?

<p>Scalariform pitting (C)</p> Signup and view all the answers

Which of the following is NOT a type of pit associated with tracheid walls?

<p>Circular pits (A)</p> Signup and view all the answers

Which layer is described as highly hygroscopic in the secondary wall?

<p>G-layer (A)</p> Signup and view all the answers

In what form do tracheids primarily occur?

<p>Long and single-celled (B)</p> Signup and view all the answers

What type of thickening is observed in protoxylem tracheids?

<p>Annular and helical thickening (A)</p> Signup and view all the answers

How do tracheids communicate with neighboring cells?

<p>Via pits (A)</p> Signup and view all the answers

What is the primary function of vessels in plants?

<p>Water conduction (C)</p> Signup and view all the answers

In which type of plants are vessels exclusively found?

<p>Angiosperms (C)</p> Signup and view all the answers

Which of the following describes the shape of vessel units?

<p>Long and cylindrical (D)</p> Signup and view all the answers

What type of pitting is NOT mentioned as a characteristic of vessel walls?

<p>Random pitting (B)</p> Signup and view all the answers

Where do vessels originate in angiosperms?

<p>Procambium and cambium (D)</p> Signup and view all the answers

What is the role of lignin in vessel cell walls?

<p>Providing structural support (C)</p> Signup and view all the answers

What are the terminal ends of vessel members characterized by?

<p>Being solid and non-perforated (B)</p> Signup and view all the answers

Which of the following best describes a perforation plate?

<p>The part of a vessel member with perforations (C)</p> Signup and view all the answers

Flashcards

Xylem

A complex plant tissue responsible for transporting water and dissolved nutrients from roots to stems and leaves. It provides structural support.

Phloem

A plant tissue responsible for transporting sugars produced during photosynthesis from leaves to other parts of the plant, including roots and stems.

Tracheids

Long, narrow, dead cells with thick, lignified cell walls and pits. They transport water and provide structural support.

Vessels

Short, wide, dead cells joined end-to-end to form continuous tubes. They efficiently transport water.

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Xylem Parenchyma

Living cells within xylem tissue that store food reserves like starch and provide support.

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Xylem Fibres

Long, narrow, dead cells with thick, lignified cell walls. They provide structural support to the xylem.

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Primary Xylem

Xylem that develops from the procambium, a primary meristematic tissue in the plant.

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Secondary Xylem

Xylem that develops from the vascular cambium, a lateral meristematic tissue in the plant. It forms wood.

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Thick-walled parenchyma

A type of plant tissue with thick cell walls that provides mechanical support and strength to the plant.

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Xylary fiber

Another name for xylem fiber, emphasizing its association with xylem tissue.

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Libriform fiber

A type of xylem fiber with thick walls and small, simple pits, resembling phloem fibers.

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Fiber-tracheid

A type of xylem fiber having characteristics intermediate to tracheids (water-conducting cells) and libriform fibers.

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Gelatinous fiber

A type of xylem fiber similar to libriform or fiber-tracheid, but with a secondary wall lacking lignin or containing very little.

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Simple pits

Small openings in the cell wall of xylem fibers, allowing for communication between adjacent cells.

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Bordered pits

Pits in the cell wall of xylem fibers that have a distinct rim or border.

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Where are vessels found?

Vessels are primarily found in angiosperms (flowering plants), but also occur in some gymnosperms (e.g., Ephedra, Welwitschia, and Gnetum) and pteridophytes (e.g., Selaginella, Equisetum, and certain ferns).

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Vessel Unit

A single cell within a vessel, typically cylindrical and lacking living protoplast, with thick walls due to lignin deposition.

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Lignin in Vessel Units

Lignin, a strengthening material, deposits unevenly on vessel walls, creating different types of pitting (scalariform, opposite, alternate), which affect water flow.

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Perforation Plate

The area where a vessel unit's end wall has a hole or holes (perforations) connecting it to the next unit, facilitating continuous water flow.

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Vessel Member

A vessel unit that terminates the tube-like system, which has a tracheid-like end (no perforation) and may have perforations along its sides.

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Types of Perforation Plates

Perforation plates can have one or multiple perforations, leading to different types: single-perforate, multiple-perforate, scalariform, etc.

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How does the vessel structure contribute to water transport?

The continuous tube formed by stacked vessel units with perforated ends allows efficient and uninterrupted water flow from roots to leaves, facilitated by the strong, lignin-reinforced walls.

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What is the G-layer?

The innermost layer of the secondary wall in plant cells, composed of a-cellulose. This layer makes the wall highly hygroscopic, meaning it absorbs moisture easily.

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What are gelatinous fibers?

Specialized fibers found primarily in tension wood of angiosperms. They have a high content of a-cellulose and very little lignin, making them gelatinous and flexible.

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Tracheid structure

Long, single-celled, non-living cells in xylem. Their thick, lignified walls have pits for water transport, and the ends are tapered or chisel-like.

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Where are tracheids found?

Tracheids are found in all vascular plants, including ferns, gymnosperms, and some angiosperms. They are the primary water-conducting cells in pteridophytes and gymnosperms.

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How do tracheids connect?

Tracheids are arranged in rows, overlapping slightly. They connect to neighboring cells through pits, which are openings in their cell walls.

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Types of pits in tracheids

Tracheids have simple, bordered, or half-bordered pits. Bordered pits are present in pairs between tracheids. In ferns, bordered pits are elongated, forming scalariform pitting.

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Tracheid wall structure

Tracheid walls are thickened by lignin deposition, which can create different patterns like annular, helical, or bordered pits. This provides strength and allows for water transport.

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Tracheid function

Tracheids are responsible for water and mineral transport in plants, as well as providing structural support. There is evidence that they can also store water.

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Study Notes

Xylem and Phloem

  • Xylem is primarily for transporting water and dissolved compounds from roots to stems and leaves.
  • Phloem transports food produced by photosynthesis from leaves to non-photosynthesizing parts like roots and stems.

Xylem Structure and Types

  • Xylem is a complex tissue composed of tracheids, trachea, xylem fibers, and xylem parenchyma, with functions of water and solute conduction and structural support.
  • Xylem and phloem form the conducting tissues in plants, both primary and secondary.
  • Primary xylem and phloem develop from procambium, secondary from cambium.

Xylem Parenchyma

  • Xylem parenchyma is a type of parenchyma that forms part of the xylem.
  • It's found in both primary and secondary xylem, originating from procambium and cambium, respectively.
  • Wood parenchyma is a term for xylem parenchyma in secondary xylem, with axial and radial arrangement, running parallel and perpendicular to the plant organ's axis.

Xylem Parenchyma Cells

  • Xylem parenchyma cells are typically irregular in shape, but can be rectangular, round, or oval.
  • Their cell walls are thin and mostly comprised of cellulose.
  • Over time, lignin can deposit on cell walls, causing them to thicken.
  • Pits frequently occur on the cell walls.

Xylem Parenchyma Functions

  • Xylem parenchyma stores starch, fats, and ergastic substances like crystals and tannins.
  • They sometimes contain chlorophyll.
  • The cells transport minerals, water, and other solutes.
  • Thick walled cells provide mechanical support when turgid.

Xylem Fibres

  • Xylem fibers, also called xylary or wood fibers, are long, elongated cells.
  • Their length usually exceeds their width greatly.
  • Xylem fibers have tapering ends that form a wedge shape.
  • Cell walls are typically thick, resulting from lignin deposition, and lumens are constricted.
  • Pits may be simple or bordered, occurring on the walls.
  • Xylem fibers may retain living contents for extended periods.

Tracheids

  • Tracheids are long, single-celled and non-living water-conducting elements of xylem, with strong, thick walls containing lignin,.
  • Tracheids are characterized by oblique or tapering ends, imperforate and mostly obtuse,
  • They are present exclusively in the xylem of pteridophytes and gymnosperms.
  • In primary xylem, tracheids originate from the procambium, while in secondary xylem, their development occurs from cambium.
  • Tracheids are angular in cross-section.
  • Lignin deposits unevenly; resulting in various forms of pitting: annular and helical in protoxylem; bordered and scalariform in metaxylem.
  • Tracheids are involved in water and mineral transport, giving strength and support.
  • They potentially store water as well.

Vessels

  • Vessels are long, cylindrical, and non-living water-conducting elements found mainly in angiosperms, with vertical rows of perforated cells.
  • Perforated end walls allow the formation of continuous tubes.
  • Vessel units have thick walls due to lignin deposition.
  • Vessels are found in both primary and secondary xylem and originate from procambium and cambium, respectively.
  • Perforation types include scalariform, opposite, and alternate, often present on the lateral walls.
  • Vessel units are also known as vessel members, vessel elements, or vessel units. Their end walls may be partially or completely unperforated.

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Xylem and Phloem PDF

Description

Explore the essential roles of xylem and phloem in plant physiology. This quiz covers the structure, types, and functions of these vital vascular tissues, including details about xylem parenchyma. Test your knowledge on how these tissues contribute to water and nutrient transport in plants.

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