Read the given paragraph and answer the given question.
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 other alternatives for survival.
Identify the animals for which thermoregulation is comparatively an energetically expensive process:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Humming birds and shrews
Option (1) Humming birds and fishes — Incorrect. Humming birds are small regulators, but fishes are conformers: their body temperature changes with the water around them. So fishes spend no energy keeping body temperature constant.
Option (2) Shrews and frogs — Incorrect. Shrews are small mammals that regulate, but frogs are conformers whose body temperature follows the surroundings. Frogs therefore do not pay the energy cost of thermoregulation.
Option (3) Frogs and fishes — Incorrect. Frogs and fishes are both conformers, so neither keeps a constant body temperature. Thermoregulation is costly only for small regulators such as shrews and humming birds, which lose body heat fast through their large surface area.
Option (4) Humming birds and shrews — Correct. Small birds and mammals such as hummingbirds and shrews spend much energy to stay warm.
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.”