Question

Why are xylem and phloem classified as complex tissues? Describe the structure of the phloem.

Answer 1

Hint:
Plants make their food in the leaves while the roots take up the water from the soil. But the food and water are needed by the whole body of the plant, not only leaves or roots respectively. So they have various cells and systems to regulate the whole food-water to each part of the plant. Some tissues are dead while some are living.

Complete answer:
What is xylem? It is a vascular tissue which has the role of the conduction of water and minerals from the roots to the shoots in the plants. They help to make the woody stem. It also provides physical support. They have specialized cells called treachery elements. It is found in the roots. Stems and leaves of the plants.
What is phloem? It is the tissue of the plant which transports the soluble organic substances to the various parts of the plant. This substance includes the sugars made by the photosynthesis process. They are usually found outside the xylem.
Why are they called complex tissues? Xylem and phloem are called so as they have many cells carrying out the functionalities. They all work as a unit and incoordination. There are different functions to be performed by them.
Structure of phloem- Phloem has the basic function of transporting the food from the leaves to the non-photosynthetic parts of the plant. Various cells help the phloem to do this. It is made up of sclerenchyma cells, parenchyma cells, sieve elements and companion cells.
The sieve elements are like the sieve pores which allow the passage for transportation between adjacent cells in the cytoplasm.
The companion cells are near to the sieve elements, it is the life support of the sieve element.
Sclerenchyma cells are the red coloured cells, providing structural support to the plant.
Parenchyma cells are the packaging cells. They help to transfer the materials to the cytoplasm. They are also used for storage purposes.

Note:
Phloem has a unique fact that its cells are denucleated even after being matured. They lack the organelles like ribosomes, Golgi bodies and cytosol so that the space for transmission can increase. Xylem is the dead tissue as most of the cells in it are dead except for the xylem parenchyma cells.