Q.Define growth, differentiation, development, dedifferentiation, redifferentiation, determinate growth, meristem and growth rate.

Growth is an irreversible and permanent increase in the size of an organ, its parts, or an individual cell. Differentiation is the process by which cells derived from meristems mature to perform specific functions. Development is the sum of growth and differentiation, covering all changes an organism goes through from germination to senescence. Dedifferentiation is the ability of already differentiated cells to regain the capacity to divide. Redifferentiation is when such dedifferentiated cells again lose their capacity to divide and mature. Determinate growth is limited growth that stops after reaching a certain size (as in leaves). A meristem is a group of actively dividing cells located at growing points. Growth rate is the increased growth per unit time.

Growth is regarded as one of the most fundamental and conspicuous characteristics of a living being. It is defined as an irreversible and permanent increase in size of an organ, its parts, or even an individual cell. It is accompanied by metabolic processes (both anabolic and catabolic) that use energy, and it involves an increase in protoplasmic material seen as increase in fresh weight, dry weight, length, area, volume and cell number.

Differentiation is the process in which cells derived from the root and shoot apical meristems and cambium undergo structural changes in their cell walls and protoplasm to perform specific functions. For example, to form a tracheary element, a cell loses its protoplasm and develops a strong, lignified wall.

Development is a term that includes all the changes an organism goes through during its life cycle, from seed germination to senescence. Broadly, development = growth + differentiation, and it is under the control of both intrinsic (genetic, plant growth regulators) and extrinsic (light, temperature, water, oxygen, nutrition) factors.

Dedifferentiation is the phenomenon in which living differentiated cells, which had lost the capacity to divide, regain that capacity under certain conditions. Examples are the formation of interfascicular cambium and cork cambium from parenchyma cells.

Redifferentiation occurs when the dedifferentiated tissues again lose their capacity to divide and mature to perform specific functions, for example the secondary xylem and secondary cortex produced by the cambia.

Determinate growth is limited growth — growth that ceases once a structure attains a certain, characteristic size, as seen in leaves, flowers and fruits, in contrast to the indeterminate growth of roots and shoots.

A meristem is a localised group of actively and continuously dividing cells found at growing regions of the plant, such as the root and shoot apical meristems and the intercalary and lateral meristems (cambium).

Growth rate is the increased growth per unit time. It can be expressed mathematically, and growth may be arithmetic (only one daughter cell continues to divide) or geometric (both daughter cells continue to divide).

Method: Defining Paired Botanical Terms Without Conflating Them

This chapter pairs several closely related terms (growth/development, dedifferentiation/redifferentiation) — the trick is isolating exactly what each one changes before writing a definition.

Steps

Step 1: Ask what is changing — size, maturity, or the capacity to divide?

Growth changes size (irreversibly). Differentiation changes a cell's structure and function to suit a specialised role. Development is not a separate process at all — it is simply growth plus differentiation taken together across the whole life span, so never define it independently of those two.

Step 2: Check reversibility to separate the de-/re- pair.

Dedifferentiation is differentiated cells regaining the ability to divide (a step backward). Redifferentiation is those same dividing cells maturing again and losing that ability (a step forward again). If a term describes a cell waking up to divide, it is dedifferentiation; if it describes a cell settling down again afterward, it is redifferentiation.

Step 3: Anchor meristem, determinate growth and growth rate to a location, a limit, and a unit of time respectively.

A meristem is defined by where dividing cells sit (root/shoot tips, cambium). Determinate growth is defined by a ceiling (growth that stops at a fixed size, as in leaves). Growth rate is defined by a ratio (increase per unit time) — always name the denominator.