Test: Plant Growth & Development - 3 - ACT MCQ

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 de differentiation.

Exponential growth is dependent on initial size, rate of growth and time interval. L_t= L₀+ rt.

GA3 is used to speed up the malting process in brewingindustry.

Cytokinin is added to culture medium to induce cell division and cell differentiation. If cytokine is not added to culture medium, there will be very little growth in culture.

The measurement and the comparison of total growth per unit time is called the absolute growth rate.

Growth phase consists of leg phase, exponential phase and stable phase. It do not consist of linear phase.

2, 4 D are widely used as herbicides. It is widely used to kill dicotyledonous weeds, does not affect mature monocotyledonous plants.

The callus consists of undifferentiated tumor like cells. If the concentration of auxin with respect to that of cytokinin ratio is changed, the cells of the callus undergo transformation to produce organs like roots or shoots. If the level of cytokinin is high as compared to the auxin level, the callus cells undergo transformation and produces shoots.

High concentrations of cytokinin generally inhibit or delay root formation and also prevent root growth. High levels of cytokinin usually causes many small shoots to be produced.

Hence, shoot would develop first from the callus.

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

Growth curve is the graphical representation of the total growth against time. It is also known as sigmoid curve.

Auxins (IAA,IBA)also induce parthenocarpy,(Seed less fruits) e.g., in tomatoes.

The geometric growth curve has three phases, namely:
i. Lag phase
ii. Exponential or log phase
iii. Stationary phase.

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

Exponential growth is represented by initial size and growth rate and time. If W₁ is the final size,W₀ is the initial size, r is growth rate and t is the time of growth than exponential growth is W₁ = W₀.ert.

Cytokinin is of different types. The cytokinin shown above is of kinetin which promotes cell division. It was isolated by Miller and Skoog from autoclaved herring sperm DNA.

The major precursor of Auxin is most likely the amino acid Tryptophan.

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

Cytokinins help overcome the apical dominance. They promotenutrient mobilisation which helps in the delay of leaf senescence.

A sigmoid curve is a characteristic of a living organism growing in a natural environment. It is typical for all cells, tissues and organs of a plant.

Auxanometer is a devise used to measure growth in length of plant parts.

Auxins promote flowering e.g. in pineapples.They help to prevent fruit and leaf drop at early stages but promote theabscission of older mature leaves and fruits.

Skoog and Milleridentified and crystallised the cytokinesis promoting active substance that they termed kinetin.

• The measurement and comparison of total growth per unit time are called an absolute growth rate.
• The growth of the given system per unit time expressed on a common basis is called a relative growth rate.

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

Answer : D

Solution :About 18 types of cytokinins have been discovered till now. Some of them are constituents of RNAS. Roots are considered as the major source of cytokinin synthesis, from roots, the cytokinins pass upwardly through xylem. Cytokinin synthesis also occurs in the areas where cell divisions takes place e.g., growing embryos and developing seeds, endosperm of seeds, young fruits, develpoing shoot buds, etc.