1) Explain the formation of complex permanent tissue in plants. Mention the two types of complex tissues and write their functions.
A complex or compound tissue can be defined as a collection of different types of cells that help in performing a common function. Xylem and phloem are complex tissues which are assemblage of living and dead cells. The cells constituting these tissues differ in shape, size, structure and their mode of origin. However, they perfom the same function by working in a coordinated fashion. Xylem and phloem are called vascular tissues as they form the vascular system.
Xylem: It is the principal water-conducting tissue in vascular plants. Its main functions are transportation of water and solutes from root to the leaves, to provide mechanical strength to the plant and food storage. It forms a continuous vascular system throughout the plant body along with the principal food-conducting tissue or the phloem. The first xylem differentiates in the embryo or young seedling. New xylem along with phloem develops continuously, as the plant grows, from the apical meristem. The vascular tissues differentiating in the primary plant body are called primary xylem and primary phloem, respectively. The meristematic tissue that leads to the development of vascular tissues and is their immediate precursor in the procambium. In some plants, secondary growth is observed in which additional growth takes place leading to the thickening of stems and roots. This growth is called secondary growth. This growth is partly due to the activity of vascular cambium (lateral meristem) that leads to the production of secondary xylem and secondary phloem.
Phloem: It is the principal food-conducting tissue of vascular plant. It transports food from the leaves to other parts of the plant body. A wide range of substances such as sugars, amino acids, micronutrients, lipids, hormones, floral stimulus are transported in the phloem. Phloem also transports water to fruits, young leaves and storage organs such as tubers. As already discussed, phloem is associated with xylem in the vascular tissue. The primary phloem differentiates in the embryo or young seedling while the secondary phloem differentiates from vascular cambium.
Xylem: It is the principal water-conducting tissue in vascular plants. Its main functions are transportation of water and solutes from root to the leaves, to provide mechanical strength to the plant and food storage. It forms a continuous vascular system throughout the plant body along with the principal food-conducting tissue or the phloem. The first xylem differentiates in the embryo or young seedling. New xylem along with phloem develops continuously, as the plant grows, from the apical meristem. The vascular tissues differentiating in the primary plant body are called primary xylem and primary phloem, respectively. The meristematic tissue that leads to the development of vascular tissues and is their immediate precursor in the procambium. In some plants, secondary growth is observed in which additional growth takes place leading to the thickening of stems and roots. This growth is called secondary growth. This growth is partly due to the activity of vascular cambium (lateral meristem) that leads to the production of secondary xylem and secondary phloem.
Phloem: It is the principal food-conducting tissue of vascular plant. It transports food from the leaves to other parts of the plant body. A wide range of substances such as sugars, amino acids, micronutrients, lipids, hormones, floral stimulus are transported in the phloem. Phloem also transports water to fruits, young leaves and storage organs such as tubers. As already discussed, phloem is associated with xylem in the vascular tissue. The primary phloem differentiates in the embryo or young seedling while the secondary phloem differentiates from vascular cambium.