NCERT Solutions for Class 11 Biology Chapter 15 : Plant Growth and Development

$\text{ Solution: }$ 

$\text{ Growth: }$ 

$\bullet$Growth is an irreversible and permanent process which can be seen by the increase in the length, size of the plant cells and tissues.
$\bullet$Few of the examples showing the growth in plants can be depicted as the lengthening of the roots and stem. 

$\bullet$The increase in the thickness of the woody plants  during their life span is also an example of growth process in plants. 

 $\text{Differentiation : }$ 

$\bullet$It is a process in which the cells derived from the apical meristem (root and shoot apex) and the cambium undergo structural changes in the cell wall and the protoplasm. 

$\bullet$These structural changes result in the achievement of the specific function.

$\bullet$One of the major example of differentiation in plants is  the formation of interfascicular and cork cambium which is derived from the fully differentiated Parenchyma cells. 

$\text{ Development: }$ 

$\bullet$Plant development is referred to as the various continuous changes occurring in the plant body. 

$\bullet$The process involves embryogenesis followed by formation of the primary plant body (embryonic root and embryonic shoot) and continuous production of new plant parts such as roots, leaves, branches, and flowers.

$\bullet$The end stage of plant development is senescence. 

$\text{ De-differentiation: }$ 

$\bullet$It is the process in which permanent plant cells regain the power to divide under certain conditions.

$\bullet$Few of the example of dedifferentiation in plants are as follows: 

$\bullet$Parenchymatous medullary rays get dedifferentiated into interfascicular cambium in dicotyledonous stem. 

$\bullet$Differentiated parenchymatous cells  get dedifferentiated into cork cambium. 

$\text{ Re-differentiation: }$ 

$\bullet$It is the process in which de-differentiated cells become mature again and lose their capacity to divide.

$\bullet$The example of the process of re-differentiation in plants is the formation of secondary phloem, secondary xylem, secondary cortex, cork, etc. 

$\bullet$This is redifferentiated from interfascicular cambium and cork cambium.

$\text{ Determinate growth}$ 

$\bullet$The type of plant growth which gets inhibited or limited at a certain stage. 

$\bullet$Examples of determinate growth is as follows:

$\bullet$The limitation of growth of the stem in an inflorescence or other reproductive structure. 

$\bullet$The branches of the stem stop growing continuously while it is deriving from the main branch. 

$\text{ Meristem: }$ 

$\bullet$Meristem is the specialised regions in the plant which is specialized in the divisions of the active cells. 

$\bullet$There are three types of meristems that are apical meristem, lateral meristem, and intercalary meristem.

$\bullet$Apical meristem is the tip of the plat root or stem which is capable of division and growth. 

$\bullet$The type of meristem located in the lateral region of the plants and responsible for increasing the lateral growth of the plants , is defined as the lateral meristem. 

$\bullet$The type of meristem located in the middle position of the plants and is associated with the growth in length in the middle position, is defined as the intercalary meristem.  

$\text{ Growth rate: }$ 

$\bullet$It can be defined as the increased growth in plants per unit time.