Plant Growth and Development Test - 4

Auxins promote stem elongation, inhibit growth of lateral buds (maintains apical dominance). They are produced in the stem, buds, and root tips.

Example: Indole Acetic Acid (IA).

Auxin is a plant hormone produced in the stem tip that promotes cell elongation

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

Irreversible increase in mass or volume of plant part is called apparent growth. Apparent growth is permanent and cannot be reversed back as it occurs due to increase in cell number.

Absolute growth rate refers to the measurement and comparison of total growth per unit time.

Thus, Absolute growth = Growth in given time period.

Relative growth rate refers to the growth of a particular system per unit time, expressed on a common basis

An inflection point is a point on a curve at which the sign of the curvature (i.e., the concavity) changes. Inflection points may be stationary points, but are not local maxima or local minima.

For example, for the curve plotted given, the red point is an inflection point

The living differentiated cells that have lost the capacity to divide can regain the capacity of division under certain conditions. This phenomenon is termed as dedifferentiation.

The process of de-specialisation of differentiated cells so that they become undifferen­tiated and able to divide is known as dedifferentiation. It involves activation of certain genes which not only reverse differentiation but also stimulate cell division.

Cork cambium, wound cambium and inter-fascicular vascular cambium are always produced through dedifferentia­tion.

Growth is measured by a variety of parameters some of which are: increase in fresh weight, dry weight,length, area, volume and cell number.

one single maize root apical mersitem can give rise to more than17,500 new cells per hour, whereas cells in a watermelon may increase in size by upto 3,50,000 times.

In the former, growth is expressed as increase in cell number; the latter expresses growth as increase in size of the cell.

The initial growth is slow (lag phase), and it increases rapidly thereafter – at an exponential rate (log or exponential phase). Here, both the progeny cells following mitotic cell division retain the ability to divide and continue to do so. However, with limited nutrient supply, the growth slows down leading to a stationary phase.

Growth, differentiation and development are very closely related events in the life of a plant. Broadly, development is considered as the sum of growth and differentiation.

In growth curve, maximum growth occurs in exponential phase of sigmoid curve. During this periods cells divide mitotically to increase length and girth of the plant.

Plants follow different pathways in response to environment or phases of life to form different kinds of structures. This ability is called plasticity. This phenomenon of heterophylly is an example of plasticity.

An auxanometer (Gr. auxain, "to grow" + metron, "measure") is an apparatus for measuring increase or rate of growth in plants.

In case of an arc-auxanometer (see picture), there is a wire fixed with the plant apex on one end and a dead-weight on the other

Plant callus is a growing mass of unorganized plant parenchyma cells. In living plants, callus cells are those cells that cover a plant wound.

S- Shaped growth curve (Sigmoid growth curve) A pattern of growth in which, in a new environment, the population density of an organism increases slowly initially, in a positive acceleration phase; then increases rapidly approaching an exponential growth rate; but then declines in a negative acceleration phase until at zero growth rate the population stabilizes.

This slowing of the rate of growth reflects increasing environmental resistance which becomes proportionately more important at higher population densities.

This type of population growth is termed ‘density dependent