Question

Assertion :- A sigmoid curve is characteristic of plants growing in a natural environment.
Reason:- In natural conditions the supply of nutrients and food is ever increasing.

• A. Both assertion and reason are true and reason is the correct explanation of assertion.
• B. Both assertion and reason are true but reason is not the correct explanation of assertion.
• C. The assertion is true but reason is false.
• D. Both assertion and reason are false.

Answer 1

The correct option is C The assertion is true but reason is false.

Growth curve is the graphical representation of the total growth of an organism (here plants) that is plotted against a particular time interval.

An S- shaped or sigmoid curve is obtained upon plotting the total growth of a plant against a fixed time interval. It consists of 4 phases- lag phase, log (exponential) phase, stationary phase (steady growth phase for organs or organisms of indefinite growth) and diminishing growth phase.

During the lag phase, growth is slow, rapid during the log or exponential phase, slow again during the diminishing growth phase. Growth stops completely during the stationary phase due to limited nutrient supply, deposition of toxic waste materials and limitation posed due to the availability of space for the growth of the organisms. A sigmoid curve is characteristic to an organism growing in a natural environment.