Question

Write the functional differences between xylem and phloem.

Answer 1

Both xylem and phloem are collectively known as vascular tissues. They are present in plant groups from and above Pteridophytes in the hierarchy. The main general function of vascular tissues is to transport material from one part to another.

Complete answer:
The primary functional difference between xylem and phloem is that xylem transports water across the plant whereas phloem transports food materials.
Let’s start with the definition of Xylem and Phloem and tabulate the differences between the two.
Xylem: It is the vascular tissue responsible for water transport. This is composed of four elements, namely, Tracheids, vessels, xylem parenchyma, and fibres. Xylem goes through primary and secondary growth in gymnosperms and most dicot angiosperms.
Phloem: This is the vascular tissue in charge of food transport. It also has four elements, namely, sieve elements, companion cells (parenchyma), sclereids, and fibres. Phloem also goes through primary and secondary growth in gymnosperms and most dicot angiosperms, like xylem.
The differences are as follows:

Xylem	Phloem
Carries out the transport of water and minerals.	Mainly the transport of food is carried out.
The transport is unidirectional.	The transport is multidirectional (both ways).
There are no walls between the cells present. This makes transport fast and smooth.	Perforated walls between the cells allow better control over the flow. But results in a slower transport.
They are in control of replacing the water lost in the plant by photosynthesis and transpiration.	They have to transport mRNAs and proteins throughout the plant body.
The transport is adequately explained by the adhesion tension transpiration pull model. By this, the xylem transport occurs independently of phloem.	The transport is explained by mass flow/pressure flow model. This model takes help from xylem water flow to aid the phloem transport.

Note:
The xylem cells are dead while phloem cells are alive. This is necessary for the transport through the phloem, because of the active transport of sugar occurring in the process. Whereas, it is energetically more favourable for xylem cells to be dead, as there is no active transport. The dead xylem cells give support to the structure of the plant as well.