Organisms and Populations — NEET Botany MCQs with answers

Organisms and Populations is a Class 12 Botany chapter in the NEET (UG) syllabus. NEET720 has 620 reviewed practice questions on it, each with a quick answer and a step-by-step explanation. The 8 questions below are free and fixed, so you can bookmark this page; the full chapter, plus mistake tracking and spaced revision, is in the app.

Topics covered

Organism and its Environment · Population Attributes · Population Growth Models · Population Interactions · Populations · Species interactions · Ecological niche · Ecological adaptations · Species distribution · Ecology · Ecology · Population Growth · Adaptations · Population Attributes and Growth · Population Interactions and Growth · Population Interactions and Adaptations · Adaptations and Population Attributes · Population Growth and Interactions · Population Growth and Attributes · Adaptations and Interactions · Adaptations and Population Growth · Organism and environment

8 free Organisms and Populations practice questions with answers

Choose an answer in your head before opening it. Each explanation says why the correct option is right and, where relevant, why the tempting wrong option is wrong.

1. Question 1 · easy · Organism and its Environment

   Which term describes an organism's ability to maintain a constant internal environment (homeostasis) by physiological or behavioural means, irrespective of fluctuations in the external environment?

   • A.Suspend
   • B.Regulate
   • C.Conform
   • D.Migrate
   Show answer and explanation

   Answer: B. Regulate

   Regulators actively maintain a constant internal milieu despite external change, e.g. mammals keep body temperature constant; this is 'regulate'.

   Organisms respond to environmental variation in four broad ways: regulate (homeostatic maintenance of a constant internal environment, e.g. thermoregulation in mammals/birds), conform (internal state changes with the external one, true of most animals and nearly all plants), migrate (temporary movement to a hospitable habitat), and suspend (reduced metabolic activity/dormancy). The question asks for the homeostasis-based strategy, which is regulation (option B).

   Common mistake: Calling any physiological adaptation 'regulation' without checking whether the internal state is actually kept constant.

   Key point: Regulate = active homeostasis; conform = passive tracking of external conditions.

2. Question 2 · medium · Organism and its Environment

   With respect to body temperature, why are nearly all plants and about 99% of animals described as 'conformers' rather than 'regulators'?

   • A.They actively lower their internal temperature below ambient temperature at all times
   • B.They can migrate to avoid unfavourable temperatures, so regulation is unnecessary
   • C.They lack the sophisticated homeostatic (thermoregulatory) mechanisms found in mammals and birds
   • D.They convert all absorbed heat into chemical energy via photosynthesis
   Show answer and explanation

   Answer: C. They lack the sophisticated homeostatic (thermoregulatory) mechanisms found in mammals and birds

   Conformers let their internal temperature change with the external environment because they lack the elaborate physiological homeostatic machinery (e.g., sweating, shivering, insulation) that regulators like mammals possess.

   Regulation of body temperature independent of ambient temperature requires energetically expensive, sophisticated physiological control systems seen only in mammals and birds. Plants and most other animals do not have this machinery, so their internal temperature simply rises and falls with the surroundings — they 'conform'. This is not a deliberate strategy but a consequence of limited physiological capacity.

   Common mistake: Assuming conformers actively adjust temperature rather than simply lacking regulatory capacity.

   Key point: Conformity is the default state for organisms lacking advanced homeostatic mechanisms — it includes almost all plants.

3. Question 3 · medium · Organism and its Environment

   Statement I: Plants generally cannot migrate away from environmental stress the way many animals can. Statement II: Seed dormancy allows plants to survive extremely unfavourable conditions in a highly reduced metabolic state. In light of the above statements, choose the correct answer.

   • A.Both Statement I and Statement II are true, and Statement II is the correct explanation of Statement I
   • B.Both Statement I and Statement II are true, but Statement II is NOT the correct explanation of Statement I
   • C.Statement I is true but Statement II is false
   • D.Statement I is false but Statement II is true
   Show answer and explanation

   Answer: B. Both Statement I and Statement II are true, but Statement II is NOT the correct explanation of Statement I

   Both statements are independently true — plants are generally sessile (Statement I), and seed dormancy is their way of enduring stress (Statement II) — but dormancy is a distinct, alternative adaptation, not a direct 'explanation' of immobility.

   Statement I is true: unlike animals, plants generally cannot move away from a stressful habitat, so migration is rarely an option for them. Statement II is also true: dormancy in seeds is a key adaptation that lets plants survive harsh periods by drastically lowering metabolic activity until favourable conditions return. However, Statement II does not 'explain' Statement I — sessility is a structural/biological fact about plants, while dormancy is a separate strategy plants use precisely because they cannot migrate. Hence both are true but II is not the correct explanation of I.

   Common mistake: Assuming any two true statements about the same topic must be causally linked.

   Key point: Plants substitute the 'suspend' strategy (dormancy) for the 'migrate' strategy they largely cannot use.

4. Question 4 · medium · Organism and its Environment

   A botanist finds a plant growing in the Thar Desert with a thick waxy cuticle, stomata sunken in pits, spine-like reduced leaves, and CAM-type photosynthesis. Which environmental stress do these features primarily help the plant cope with?

   • A.Excess soil salinity
   • B.Low atmospheric oxygen
   • C.High irradiance alone, unrelated to water
   • D.Excessive water loss through transpiration in a hot, dry habitat
   Show answer and explanation

   Answer: D. Excessive water loss through transpiration in a hot, dry habitat

   Thick cuticle, sunken stomata, reduced leaf area, and CAM photosynthesis (stomata open at night) are classic xerophytic adaptations that minimize water loss by transpiration in arid desert conditions.

   Desert plants face severe water scarcity and high evaporative demand. A thick waxy cuticle reduces cuticular water loss; stomata sunken in pits create a humid microenvironment that reduces the diffusion gradient for water vapour; reduced leaf area (often modified into spines) minimizes the transpiring surface; and CAM (Crassulacean Acid Metabolism) photosynthesis allows stomata to remain closed during the hot day and open only at night, drastically cutting transpirational water loss while still fixing CO2. All these traits converge on one goal: conserving water under chronic water stress.

   Common mistake: Treating each desert adaptation as addressing a different, unrelated stress instead of recognising the common theme of water conservation.

   Key point: Desert plant traits (thick cuticle, sunken stomata, reduced leaves, CAM) are unified by one function — minimizing water loss.

5. Question 5 · medium · Organism and its Environment

   A student states: "Hibernation and aestivation are the same phenomenon, just occurring in different seasons." Which statement correctly evaluates this claim in the context of the 'suspend' strategy?

   • A.They are entirely unrelated phenomena; only hibernation counts as 'suspend', aestivation is a form of migration
   • B.Hibernation and aestivation are identical in every respect and the seasonal distinction is irrelevant to biology
   • C.Both are examples of the 'suspend' strategy where metabolic activity is reduced to escape unfavourable conditions, but hibernation avoids winter cold while aestivation avoids summer heat/desiccation
   • D.Both terms refer exclusively to plant seed dormancy and have no application to animals
   Show answer and explanation

   Answer: C. Both are examples of the 'suspend' strategy where metabolic activity is reduced to escape unfavourable conditions, but hibernation avoids winter cold while aestivation avoids summer heat/desiccation

   Hibernation (winter dormancy, e.g. in bears) and aestivation (summer dormancy, e.g. in snails/fish) are both instances of the 'suspend' response, differing in the season and the specific stress (cold vs heat/desiccation) they help avoid.

   The 'suspend' strategy covers organisms that reduce metabolic activity to avoid stressful periods rather than actively regulating against them or moving away. Hibernation is winter dormancy triggered by cold and food scarcity (e.g., bears). Aestivation is dormancy during hot, dry summer conditions to avoid desiccation (e.g., snails, certain fish). Diapause in zooplankton is a related suspended-development state triggered by adverse conditions. All three are variations on the same underlying theme — 'suspend' — but distinguished by the stressor and timing, not by being identical phenomena.

   Common mistake: Treating hibernation and aestivation as interchangeable synonyms rather than season/stressor-specific variants of dormancy.

   Key point: Suspend = reduced metabolism to avoid stress; hibernation (cold), aestivation (heat/desiccation), diapause (adverse conditions, e.g. zooplankton) are its specific manifestations.

6. Question 6 · medium · Organism and its Environment

   The kangaroo rat of the American deserts meets almost all of its water requirement without drinking free water. Which physiological mechanisms allow this?

   • A.It produces highly dilute urine and sweats profusely to cool down
   • B.It meets water needs through internal (metabolic) fat oxidation and produces highly concentrated urine to minimize water loss
   • C.It migrates seasonally to water-rich oases and stores water in specialized bladders
   • D.It enters aestivation throughout the dry season, eliminating any water requirement
   Show answer and explanation

   Answer: B. It meets water needs through internal (metabolic) fat oxidation and produces highly concentrated urine to minimize water loss

   The kangaroo rat obtains water metabolically by oxidizing fat and conserves it through extremely concentrated urine and efficient kidneys, a classic physiological desert adaptation.

   The kangaroo rat is a textbook NCERT example of physiological adaptation to extreme desert aridity. Rather than drinking free water, it derives water internally from the oxidation of fat (metabolic water). To minimize water loss, its kidneys produce extremely concentrated urine, far more concentrated than most mammals can achieve. This combination allows it to survive without ever needing to drink, distinguishing it from behavioural (migration) or dormancy-based (suspend) strategies used by other desert organisms.

   Common mistake: Assuming desert animals always conserve water via dilute urine, when concentrated urine is actually the water-conserving strategy.

   Key point: Kangaroo rat: water from internal fat oxidation + highly concentrated urine = no need to drink free water.

7. Question 7 · easy · Organism and its Environment

   Organisms that can tolerate and thrive across only a narrow range of temperature are termed:

   • A.Eurythermal
   • B.Euryhaline
   • C.Stenohaline
   • D.Stenothermal
   Show answer and explanation

   Answer: D. Stenothermal

   'Steno-' means narrow, so stenothermal organisms tolerate only a narrow temperature range.

   The prefix 'eury-' means wide/broad, and 'steno-' means narrow. Applied to temperature: eurythermal organisms tolerate a wide range of temperatures, while stenothermal organisms tolerate only a narrow range. The same prefixes apply to salinity: euryhaline (wide salinity tolerance) and stenohaline (narrow salinity tolerance). The question asks specifically about temperature tolerance, so the correct term is 'Stenothermal' (option D).

   Common mistake: Mixing up eury/steno prefixes or confusing thermal (temperature) terms with haline (salinity) terms.

   Key point: eury- = wide range tolerated; steno- = narrow range tolerated; applies to both -thermal (temperature) and -haline (salinity).

8. Question 8 · medium · Organism and its Environment

   Statement I: A person moving from sea level to a high-altitude region shows increased red blood cell production and increased breathing rate to compensate for low oxygen availability. Statement II: This high-altitude acclimatization represents a permanent genetic change that is passed on to offspring. Choose the correct option regarding these statements.

   • A.Both statements are true
   • B.Statement I is true, Statement II is false
   • C.Statement I is false, Statement II is true
   • D.Both statements are false
   Show answer and explanation

   Answer: B. Statement I is true, Statement II is false

   Statement I is a true physiological fact (increased RBCs and breathing rate at altitude), but Statement II is false — acclimatization is a reversible physiological response within an individual's lifetime, not a permanent genetic/heritable change.

   At high altitude, low atmospheric oxygen (pO2) triggers physiological acclimatization: increased red blood cell production, increased breathing rate, and decreased binding affinity of haemoglobin for oxygen (facilitating oxygen release to tissues) — all compensating for reduced oxygen availability. Crucially, acclimatization is a reversible, individual-level physiological adjustment; it is not a permanent genetic change and is not inherited by offspring, unlike a true evolutionary adaptation. This distinguishes acclimatization from genetic adaptation.

   Common mistake: Confusing acclimatization (physiological, reversible) with genetic adaptation (heritable, evolutionary).

   Key point: Acclimatization is reversible physiological adjustment during an organism's lifetime, NOT a permanent genetic change.

Questions about Organisms and Populations for NEET

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Questions are original NEET720 compositions reviewed for correctness, syllabus fit and option quality. Counts update as the bank grows (620 active practice questions in this chapter today).