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An irreversible or permanent increase in size, mass or volume of a cell, organ or organism is called as ________.
Growth is defined as a permanent or irreversible increase in dry weight, size, mass or volume of a cell organ or organism. Plant growth is unique because plants retain the capacity for unlimited growth throughout their life. This ability of the plants is due to the presence of meristems at curtain locations in their body. The cells of such meristems have the capacity to divide and self-perpetuate. The product, however, soon loses the capacity to divide and such cells make up the plant body. This form of growth wherein new als are always being added to the plant body by the activity of the meristem is called the open form of growth.
_________ indudes all the changes that an organism undergoes during its life cycle, from seed germination to senescence.
Development is the sequence of events that occur in the life history of a plant which includes seed germination, growth, differentiation, maturation, flowering, seed formation and senescence. The process of development is considered as the sum of growth and differentiation controlled by several intrinsic factors (including genetic and hormonal) and extrinsic factors (including light, temperature, water, oxygen, nutrients, etc).
Read the following statements regarding arithmetic growth and select the correct answer.
(i) Rate of growth is constant.
(ii) One daughter cell remains meristematic while the other one differentiates and matures.
(iii) Mathematical expression is Lt =L0 +rt.
ncrease in growth per unit time is called as growth rate. The growth rate may be arithmetic or geometrical. Arithmetic Growth is a type of growth in which the rate of growth is constant and increase in growth occurs in arithmetic progression-- 2, 4, 6, 8, 10,12. Meristematic cells at the growing point divide in such a fashion that one daughter cell remains meristematic while the other grows and differentiates. the process continues. Mathematically, arithmetic growth is expressed as
Lt =L0 +rt.
where Lt = length after time t, L0 = length at the beginning, and r = growth rate. On plotting growth against time, a linear graph is obtained.
The given figure shows development of an embryo that undergoes two phases A and B. Select the correct option regarding it.
An embryo shows geometrical growth initially but later it passes into arithematic phase.
Growth at cellular level, is principally a consequence of increase in the amount of
Growth, at a cellular level, is principally a consequence of increase in the amount of protoplasm. Growth is measured by a variety of parameters such as (i) increase in length, e.g, stem,root, pollen tube (ii) increase in volume eg., fruits. (iii) Increase in area, eg.leaves (iv) increase in diameter, eg, tree trunks, fruits (v) Increase in fresh or dry weight. One single maize root apical meristem can given to more than 17,500 new cells per hour, wheres as cell in watermelon may increase in size by upto 3, 50,000 the former, growth is expressed as increase the cell number latter expresses growth as increase in the size of cell.
The given figure shows growth of two leaves over the period of one day. If, AG = absolute growth and RGR = relative growth rate, then select the correct option.
Absolute growth rate (AGR): Increase in total growth of two organs or organisms is measured and comparison of total growth per unit time is called absolute growth. Absolute growth rate is the total growth per unit time. Relative growth rate (RGR) : It is growth per unit time per unit initial growth.
RGR= Growth in given time period / Measurement at start of time period
AG for leaf A = 10cm2 = 5cm2 = 5cm2
RGR for leaf A = 5/5 × 100 = 100%
AG for leaf B = 55cm2 − 50cm2 = 5cm2
RGR for leaf B = 5/50 × 100 = 10%
Though the absolute growth is same for both the leaves (A and B), relative rate of growth is more in leaf A because of its initial small size.
Growth in plants is
The meristem which is consumed in the formation of an organ is called determinate meristem. The meristem which continues its activity throughout life of the plant is called indeterminate meristem. Root apical meristem, shoot apical meristem, intercalary meristem (e.g., grass) and lateral meristems are all Indeterminate meristems. Plant growth is generally indeterminate, i.e., plants retain the capacity for unlimited growth throughout their life, whereas it is determinate in the meristem which is consumed in the formation of an organ.
Increase in girth (diameter).of plant as a result of the activities of lateral meristems is called _______________.
The Lateral meristem e.g. vascular cambium and cork cambium(in dicotyledons and gymnosperms) are the meristems that cause increase in girth of the organs in which they are active, This is known as secondary growth of the plant.
Vascular cambium and cork cambium are
Lateral meristem occurs on the sides and takes part in increasing girth of the plant. Intra fascicular cambium is the primary lateral meristem which lies in vascular bundles of dicot and gymnosperm stems in between phloem and xylem. Examples of secondary lateral meristems are vascular cambium of the root, inter fascicular cambium of stem,cork cambium etc. that take part in the secondary growth.
Meristematic cells are characterized by
A meristematic tissue is a group of similar and immature cells that are in continuous state of division. These tissues are found in growing regions of plants. The chief characteristics of these tissues are:
(i) The cells may be round, oval, polygonal or rectangular.
(ii) They have thin cellulosic cell walls.
(iii) They do not have intercellular spaces.
(iv) They have dense cytoplasm with prominent nuclei.
(v) Vacuoles are absent or many small vacuoles may be present. The cells are in active state of metabolism.
Cells of tracheary elements (tracheids and vessels) become dead at maturity and lose their protoplasm due to the deposition of lignocellulosic cell wall thickenings. This is an example of
The cells derived from root apical and shoot apical meristems and cambium differentiate and mature to perform specific functions. This process leading to maturation of cells is termed as differentiation. During differentiation, cells undergo few to major structural changes both in their cell walls and protoplasm e.g., to form a tracheary element the cells would lose their protoplasm, they also develop strong, elastic, lignocellulosic secondary cell walls, to carry water to long distances even under extreme tension.
Living differentiated cells which have otherwise lost the capacity to divide, can regain the power of division under certain conditions. This phenomenon is termed as
The living differentiated cells, that have lost the capacity to divide can regain the power of division under certain conditions, this phenomenon is termed as de-differentiation. E.g. formation of meristems-interfascicular combium (formed form outer layer of cortex) from fully differentiated parencyma cells. while doing so, such meristems/tissues are able to divide and produce cells that once again lose the capacity to divide but mature to perform specific functions, i.e., get redifferentiated. E.g., cells of secondary xylem, secondary phloem, periderm. Thus redifferentiation can be defined as maturation or differentiation of dedifferentiated tissues.
If a part of pith from the stem of a plant is used as an explant and cultured on nutrient medium, which of the following processes is responsible for the formation of an undifferentiated mass of cells called callus?
The portion of pith taken as an explant comprises of parenchymatous cells (i.e., simple permanent tissue which have lost the capcity to divide). When such cells are cultured on solid culture media, the parenchymatous cells of pith become meristematic and start dividing resulting in a mass of undifferentiated cells called callus. this is an example of dedifferentiation. These cells may be made to divide in different manners in order to produce different organs so that the meristematic cells of callus may become permanent tissues by the process of redifferentiation. for exmaple, treatment of certain hormones may lead to the differentitation of shoot buds or roots.
Different kinds of structures develop in plants in different phases of growth or in response to environment. This ability is called _________.
Different structures develop in different phases of growth as well as in response to environment. The ability to change under the influence of internal or external stimuli is called plasticity.
Auxin synthesis occurs in
Auxin is a plant hormone. Its synthesis occurs in young meristematic tissues like root and shoot tips. It is synthesized from tryptophan amino acid. It acts as plant growth promoter. It is involved in various physiological processes of plants. It stimulates apical dominance and suppresses the growth of lateral buds. It also plays important role in phototropism.