Define determinate growth.
Important Points to Remember in Chapter -1 - Plant Growth and Development from NCERT BIOLOGY Textbook for Class XI Solutions
(i) Growth is one of the most conspicuous events in any living organism.
(ii) It is an irreversible increase that can be expressed in size, area, length, height, weight, etc.
(iii) It conspicuously involves increased protoplasmic material.
(iv) Root and shoot apical meristems, sometimes along with intercalary meristem, contribute to the growth of plants.
(v) Growth in plants is indeterminate as plants retain the capacity for unlimited growth throughout their life.
(vi)The sum of all events that take place from the germination of a seed to the death of the plant is called development.
(vii) Growth has three major phases: Meristematic or the phase of cell division, Elongation phase, and Maturation or differentiation phase.
(x) Growth rate is the increase in number per unit of time (growth/time). There are two major growth rates: arithmetic rate and Geometric rate.
2. Differentiation, Dedifferentiation, and Redifferentiation:
(i) When a cell loses the capacity to divide, it leads to differentiation that results in the development of structures that is commensurate with the function the cells finally have to perform.
(ii) A differentiated cell may dedifferentiate and then redifferentiate.
(iii) Plants exhibit plasticity in development, i.e., the same organ may show different structures in different phases of life or in different habitats.
(iv) Plant growth and development are under the control of both intrinsic and extrinsic factors.
3. Plant Growth Regulators:
(i) Plant growth regulators () are organic molecules of diverse chemical composition which are synthesized in one part of the plant body and transported to another part where they are active.
(ii) mainly belong to five categories of chemicals called auxins, gibberellins, cytokinins, abscisic acid and ethylene.
(iii) Plant growth and development are also affected by light, temperature, nutrition, oxygen status, gravity, and such external factors.
(iv) The growth hormones are translocated through different tissues, e.g., auxins through parenchyma, GAS, and ABA, mainly through phloem and cytokinins through the xylem.
(v) Ethylene is a gaseous hormone readily absorbed and transported within the plant body.
4. Photoperiodism and Vernalisation:
(i) Flowering in some plants is induced only when exposed to a certain duration of photoperiod. It is mainly influenced by light and temperature.
(ii) Depending on the requirement of critical photoperiod, the plants can be called Short Day Plant (SDP), Long Day Plant (LDP) and Day Neutral Plant (DNP).
(iii) There are two kinds of flowering stimuli, a hormone called florigen and another is proteinaceous pigment known as phytochrome.
(iv) Florigen and phytochrome are linked to photoperiodic induction.
(v) The low-temperature stimulation to cause early flowering is also essential mostly in case of plants of temperate regions.
(vi) Photoperiodic induction is called photoperiodism and low-temperature stimulation is vernalization.
(vii) Florigen and vernalin are two hypothetical hormones and have not been isolated. But available evidence suggest the role of these stimuli in the induction of flowering.
(viii) Dormancy is the temporary physiological inactive stage found in seeds, buds of many plants.
