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.
Identify the set of aquatic animals whose osmotic concentration is not constant.
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Amoeba and Paramoecium
In conformers, the osmotic concentration of the body fluids changes with that of the water around them. Regulators keep it constant (osmoregulation), and all birds and mammals are regulators. Whales and dolphins are mammals, so any pair with a whale or a dolphin is ruled out.
Option (1) Whale and Fish — Incorrect. The whale is a mammal. It keeps the osmotic concentration of its body fluids constant, so this pair does not fit.
Option (2) Amoeba and Paramoecium — Correct. This is the only pair with no mammal in it. Amoeba and Paramoecium are single-celled organisms, so of the pairs given, only this one can be counted among the conformers.
Option (3) Whale and Dolphin — Incorrect. Both are mammals and both are regulators.
Option (4) Dolphin and Fish — Incorrect. The dolphin is a mammal and a regulator, so this pair does not fit.
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 – “… (i) Regulate: Some organisms are able to maintain homeostasis by physiological (sometimes behavioural also) means which ensures constant body temperature, constant osmotic concentration, etc. All birds and mammals, and a very few lower vertebrate and invertebrate species are indeed capable of such regulation (thermoregulation and osmoregulation).”