Structure of transport tissues

Structure of Transportation Tissues

Xylem

Composed of xylem vessels and tracheids that are designed to transport water and minerals.
Xylem vessels have lignified cell walls and form a continuous pipeline running the length of the plant.
Tracheids are more flexible and can serve a supportive role in addition to transporting water.
Lack of cytoplasm in mature xylem cells makes for an unrestricted flow of water and nutrients.
Parenchyma cells store food and water, aiding the functioning of xylem tissue.
Fibre cells provide additional structural support with their thick, lignified walls.

Phloem

Composed of sieve tube elements and companion cells.
Sieve tube elements are living cells (unlike xylem vessels) and are arranged end-to-end forming a continuous tube.
The distinct walls between sieve tubes, known as sieve plates, allow for the passage of substances.
Companion cells maintain the functionality of sieve tubes. They are metabolically active cells and help in the loading/unloading of sugars into the sieve elements.
Phloem parenchyma stores food and fibres provide support.
Responsible for the transport of dissolved sugars, particularly sucrose, from leaves to other parts of the plant.

Functions of Xylem and Phloem

Xylem primarily transports water and mineral nutrients from the roots to the rest of the plant, this process is known as transpiration.
Phloem is responsible for translocation, the bidirectional transport of organic compounds, especially sugar, from the leaves (source) to the growing and storage parts (sink) of the plant.
Together, the phloem and xylem provide the plant with a vascular system.

Casparian Strip

It is part of the endodermal cells in the root.
Acts as a barrier to passive flow of materials into the xylem in the plant’s roots.
Made up of suberin, a waxy substance, which prevents water and dissolved nutrients from passing between cell walls.
It ensures materials must cross a cell membrane, allowing the root to regulate which substances it absorbs.

Root Hair Cells

Individual cells on the root surface that increase the surface area for water absorption.
Have a thin cell membrane and a large vacuole, enhancing water uptake by osmosis.
Accumulates mineral ions from the soil, creating a water potential gradient causing water to move into the cell.

Remember to make sure you understand the different structure of the transport tissues to help explain how they carry out their functions in the plant.