Question

Why can xylem transport water and minerals using dead cells, whereas phloem requires living cells?

Short answer

The major water-conducting components of the xylem are tracheids and vessels.

Xylem is dead tissue because it lacks protoplasm. It has a lignified wall and is an elongated tube-like construction. The transpiration pull and the negative pressure created by water evaporation via leaves transports water and minerals through the xylem.

On the other hand, phloem requires living cells because food transfer occurs through an active transport mechanism in the sieve tube elements.

Step-by-step solution

Introduction of transportation 

The process of moving water and minerals to all regions of the plant body is known as transportation. Plants have a specific mechanism for distributing water and nutrients throughout their bodies.

Plants utilize a variety of water-related mechanisms, including translocation, absorption, storage, and utilization. In large plants, it is conducted by xylem and phloem tissues.

Anatomy of xylem and phloem

Xylem consists of tracheid cells. They have a dense lignified membrane and no protoplasm. Their primary role is to convey water and minerals.

Phloem is a living tissue in vascular plants that transports the soluble organic molecules produced during photosynthesis downward from the leaves. It consists of extended living cells called sieve-tube that transport carbohydrates, primarily sucrose, from the leaves to the roots and fruits.

Water and minerals are transported by xylem utilizing dead cells, whereas phloem uses living cells.

Most long-distance transport in the xylem is bulk flow mediated by negative pressure potential, generated subsequently by leaf evaporation, and does not require active cells.

Phloem requires living cells because sucrose is more abundant in sieve-tube elements and companion cells than mesophyll. Sugar transfer into the phloem needs active transport. Sucrose can migrate from mesophyll cells to sieve-tube elements or partner cells because of proton pumping and H+/sucrose co-transport.