Ch 5Plant Growth and Development — Class 12 Botany, concept-first.

Chapter 5 has already introduced how a flowering plant is organised — its roots, stems, leaves, flowers, fruits and seeds.

Growth ranks among the most fundamental and easily observed characteristics of any living organism. It can be defined as an irreversible, permanent increase in the size of an organ, of any of its part…

Plant growth is unique because plants retain the capacity for unlimited growth throughout their life. This remarkable ability is due to the presence of meristems at certain locations in the plant body…

At the cellular level, growth is principally a consequence of an increase in the amount of protoplasm.

The period of growth is generally divided into three phases: the meristematic, the elongation and the maturation phase.

The increased growth per unit time is termed the growth rate. The rate of growth can be expressed mathematically, because an organism, or a part of an organism, can produce more cells in a variety of…

Several conditions are necessary for growth, and the most essential are water, oxygen and nutrients.

The cells derived from the root apical meristem, the shoot apical meristem and the cambium differentiate and mature to perform specific functions.

Development is a term that includes all the changes an organism goes through during its life cycle, from the germination of the seed right up to senescence.

Plant growth regulators (PGRs) are the intercellular chemical messengers among the intrinsic factors that control development.

The plant growth regulators (PGRs) are small, simple molecules of diverse chemical composition. Chemically they may be:

Interestingly, the discovery of each of the five major groups of PGRs has been accidental — in every case an observation made for some other reason led to the identification of a growth regulator.

Having seen how the five major groups of plant growth regulators were discovered, we can now look at some of the physiological effects that each of these categories produces in plants.

Auxins (from the Greek word 'auxein', meaning 'to grow') were first isolated from human urine. The term auxin is applied to indole-3-acetic acid (IAA) and to other natural and synthetic compounds that…

Gibberellins are another kind of promotory PGR. There are more than 100 gibberellins reported from a wide range of organisms, including fungi and higher plants.

Cytokinins have specific effects on cytokinesis (cell division). They were discovered as kinetin, a modified form of adenine (a purine), obtained from autoclaved herring sperm DNA.

Ethylene is a simple gaseous PGR. It is synthesised in large amounts by tissues undergoing senescence and by ripening fruits.

As mentioned earlier, abscisic acid (ABA) was discovered for its role in regulating abscission and dormancy.

Not every plant flowers at the same time of year, and one of the main environmental cues a plant uses to decide when to flower is the relative length of day and night it experiences.

Day length is not the only environmental cue that can control the timing of flowering. In a number of plants, particularly those from temperate regions, flowering is instead promoted or hastened by a…

Growth stands out as one of the most visible features of any living thing. It shows up as an irreversible rise in measurable quantities — size, area, length, height, volume or cell number — and at its…

Higher-order thinking / exemplar-style practice problems.