Question

What are the components of the transport system in highly organized plants?

Answer 1

Transport system:

Xylem and phloem make up the transport system of organized plants.

i) Xylem:

1. Xylem is a complex tissue.
2. Water and minerals are carried from the roots to the stem and leaves via the xylem.
3. It also gives the plant parts mechanical strength.

Tracheids, vessels, xylem fibers, and xylem parenchyma are the four types of elements that make up the xylem.

Tracheids:

1. Tracheids are long, tube-like cells with lignified walls and a tapering end.
2. These are non-protoplasmic and dead.

Vessels:

1. A vessel is a long cylindrical tube-like structure composed of multiple vessel parts with lignified walls and a big central cavity.
2. The vascular cells are also protoplasm-free.
3. The vessel's parts are joined by perforations in their common walls.

Xylem fibers:

1. The walls of xylem fibers are thicker, and the central lumens are removed.
2. These can be septate or aseptate.

Xylem parenchyma:

1. Xylem parenchyma cells are live, thin-walled cells with cellulose-based cell walls.
2. They store food items such as starch or fat and other compounds such as tannins.

ii) Phloem:

1. Food supplies are transported via phloem from leaves to other plant sections.

Phloem is comprised of companion cells, sieve tube elements, phloem fibers, and phloem parenchyma.

Sieve tube elements:

1. They are long, tube-like structures that are aligned longitudinally.
2. The sieve plates are formed by perforating their end walls in a sieve-like pattern.
3. A developed sieve element has a big vacuole and peripheral cytoplasm but no nucleus.

Companion cells:

1. Companion cells are parenchymatous cells with specialized functions.
2. Pit fields connect the sieve tube elements and companion cells between their common longitudinal walls.
3. They aid in maintaining the sieve tubes' pressure gradient.

Phloem parenchyma:

1. Elongated, tapered cylindrical cells with rich cytoplasm and nucleus make up phloem parenchyma.
2. The cellulose cell wall has pores through which plasmodesmata connections exist between the cells.
3. Food and other compounds like resins, latex, and mucilage are stored in the phloem parenchyma.

Phloem fibers:

1. Sclerenchymatous cells make up phloem fibers.
2. These are long and unbranched, with sharp, needle-like apices.
3. Phloem fibers have a very thick cell wall.