Ch 15Plant Growth and Development — Class 11 Botany, concept-first.

Arithmetic growth is the slower of the two basic growth patterns a plant organ can follow. In this pattern, after a cell divides only one of the two resulting daughter cells goes on dividing again, wh…

Geometric growth is the faster, exponential alternative to arithmetic growth, and it is the pattern most higher plant organs actually use during active growth.

A whole developing plant is never purely arithmetic or purely geometric in how it grows - it typically starts out as a young embryo growing geometrically throughout its body, then, as development proc…

Plant growth responds to a combination of factors from outside the plant and factors generated within it.

Because plant growth typically proceeds too slowly to observe with the naked eye, it needs purpose-built techniques to measure it.

Development is the broad umbrella term for every change an organism undergoes across its entire life cycle, from a germinating seed all the way to senescence, and at the level of an individual cell it…

Across all five classical groups, phytohormones share a common set of traits: they are usually produced at the growing tips of roots, stems and leaves; they move from their site of production to their…

Movements of locomotion cover any case where protoplasm inside a cell moves, or where an entire unicellular or free-swimming multicellular plant structure - such as Chlamydomonas, a gamete, or a zoosp…

In higher plants, autonomic movements of curvature - triggered purely by the plant's own internal changes, without an external stimulus - include a growth-driven sub-type where unequal growth rates on…

A second, non-growth type of autonomic movement is rhythmic and quickly reversible, and its textbook example is the Indian telegraph plant, Desmodium gyrans (Figure 15.18).

Tropic movements (tropisms) are curvature responses triggered by a stimulus coming from one specific direction, and the response bends the organ either toward or away from that exact direction (contra…

Nastic movements are also triggered by an external stimulus, but unlike tropisms the stimulus is diffused rather than unidirectional, so the direction of the plant's response depends on the organ's ow…

Not every movement a plant shows requires a living, irritable cell - some movements occur purely from physical or mechanical changes taking place in tissue that is already dead, and these are called p…

An appropriate photoperiod completed within a single 24-hour cycle counts as one inductive cycle, and depending on the species a plant may need just one or many such cycles before flowering is trigger…

Phytochrome is the specific pigment responsible for a plant sensing light in these photoperiodic and other photo-physiological responses - a bluish biliprotein named by Butler and colleagues in 1959.

At the cellular level, senescence follows a defined biochemical progression rather than random decline.

Senescence in plants is not a passive breakdown - it runs under the plant's own genetic control, and when this controlled process is carried through to its conclusion at the level of the plant, an org…

Abscission is the physiological process by which a plant deliberately sheds an entire organ - a leaf, flower, fruit or seed - from the rest of the plant body, and it represents the final stage of that…

Biotic stress is stress caused on a plant by other living organisms - viruses, bacteria, fungi, parasites, insects, weeds and competing plants - and it is also linked to human activity such as cutting…

Abiotic stress arises from non-living conditions in the plant's environment, and the chapter splits it into atmospheric stress (from the air around the plant) and edaphic stress (from the soil).