Plant growth question - Courtsey Gervaise

QUESTION - Discuss growth processes in plants with special consideration of primary and secondary growth.

ANSWER-

INTRODUCTION TO PLANT GROWTH

Plants typically continue to grow through out their lives. Growth can be defined as permanent and irreversible change in the size and number of a cell , organ, or complete organism. Growth is the process by which a plant increases in the number and size of leaves and stems. There are different phases of cell growth – cell division , cell enlargement , cell maturation. As the cells keep multiplying, the plant grows upward and outward. New leaves will appear on it, even as flowers also appear on some plants. Plants that receive proper nutrients grow to their full height and maturity. However, the height and maturity of the plant will also depend on the variety to which it belongs.

The growth of plants depends on various factors. Some of the most important factors are age of the plant, climatic conditions, growth habits of plants, and the season. The two important activities photosynthesis and respiration play a major role in the process of growth.

Growth Requirement Of Plants

• Sunlight is one of the most important nutrients required by plants. The stems of the plant may become thin, if there is a lack of sunlight.

• All plants require sufficient water. However, the amount of water required for a given plant may differ from one variety to the other. Dryness of soil is an indicator that more water is required.

• Fertile soil is another major requirement for plant growth. The soil should be rich in minerals, such as nitrogen, phosphorous and potassium , to support plant growth.

• Adequate air and right temperature are equally essential for plant growth. The plant should get sufficient air for growth and a temperature that suits their deve

TWO TYPES OF PLANT GROWTH

1. PRIMARY GROWTH -

 The primary growth refers to increase in length of plant, number of leaves, and production of branches.

It refers to the growth taking place in apical surface where higher amount of cell division takes place in apical meristem. The high pace of cell division results in cell elongation and takes place in undifferentiated regions referred as meristems.

The primary growth in roots is concentrated at root tip and is covered by the presence of root cap. The root cap produces polysaccharide and help in rapid rate of growth. The growth at the apical meristem in roots takes place at rapid phase and results in replacement of cells at root cap.

2.SECONDARY GROWTH- Secondary growth refers to increase in girth and growth associated with girth.

Secondary growth in plants takes place in vascular cambium and at a later stage it produces secondary xylem cells in the inside of the meristem and formation of secondary phloem cells on the outside of the meristem.

It is found that the secondary growth disturbs the epidermis in terms of rupture it results in formation of cork cambium which is in general dark and gives rise to thickened cork cells. The thickened cork cells are known for their role to protect.

In some cases the secondary growth can be anomalous where in regular pattern of vascular cambium producing xylem to the inside and phloem to the outside is not followed.

DIAGRAM