Read the passage carefully. Attempt the questions.
An overwhelming majority (99 per cent) of animals and nearly all plants cannot maintain a constant internal environment. Their body temperature changes with the ambient temperature. In aquatic animals, the osmotic concentration of the body fluids change with that of the ambient water osmotic concentration. These animals and plants are simply conformers. Considering the benefits of a constant internal environment to the organism, we must ask why these conformers had not evolved to become regulators. Recall the human analogy we used above; much as they like, how many people can really afford an air conditioner? Many simply 'sweat it out' and resign themselves to suboptimal performance in hot summer months. Very small animals are rarely found in polar regions. During the course of evolution, the costs and benefits of maintaining a constant internal environment are taken into consideration. Some species have evolved the ability to regulate, but only over a limited range of environmental conditions, beyond which they simply conform.
If the stressful external conditions are localised or remain only for a short duration, the organism has two other alternatives for survival.
Conformers have not evolved to become regulators because:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Cost of becoming a regulator is very high.
Option (1) Conformers are generally small sized organisms. — Incorrect. Many conformers are small, but size alone is not the reason. The book’s reason is the energy cost: for many animals, thermoregulation is too expensive.
Option (2) Cost of becoming a regulator is very low. — Incorrect. Regulation is expensive, not cheap. If the cost were very low, conformers would be expected to have evolved into regulators.
Option (3) Their anatomical structure is simple. — Incorrect. A simple body structure is not the reason given. Conformers have not become regulators because regulation costs a lot of energy, especially for small animals.
Option (4) Cost of becoming a regulator is very high. — Correct. Keeping the internal conditions constant (thermoregulation, osmoregulation) needs a lot of energy. For many animals, especially small ones, the cost of becoming a regulator is very high, so they stay conformers.
Note 1: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
Note 2: This question is from the topic “Responses to Abiotic Factors” in Chapter 13, Organisms and Populations, of the pre-rationalised NCERT book. This portion is not in the present NCERT book, where the chapter is now Chapter 11, Organisms and Populations. The extract below is from the pre-rationalised edition.
NCERT Extract (Pre-rationalised edition, Chapter 13, Organisms and Populations):
Responses to Abiotic Factors – “… Thermoregulation is energetically expensive for many organisms. This is particularly true for small animals like shrews and humming birds. Heat loss or heat gain is a function of surface area. Since small animals have a larger surface area relative to their volume, they tend to lose body heat very fast when it is cold outside; then they have to expend much energy to generate body heat through metabolism.”