Organisms and Populations PYQs on the CBT Screen

Question 1 · NEET 2026 · Q156 · +4 / −1

Which of the following equations depicts Verhulst-Pearl logistic population growth?

Answer and explanation

Answer: (2)

The Verhulst-Pearl logistic growth equation is $\frac{dN}{dt}=rN\left(\frac{K-N}{K}\right)$ , where K is the carrying capacity, r is the intrinsic rate of natural increase and N is the population density at time t. The term (K-N)/K represents environmental resistance, so option (2) is correct.

Question 2 · NEET 2026 · Q165 · +4 / −1

Which one of the following is an appropriate example of sexual deceit?

Answer and explanation

Answer: (2)

In sexual deceit the Mediterranean orchid Ophrys mimics a female bumblebee so that the male bee attempts pseudocopulation and inadvertently pollinates the flower. Female wasp and fig is mutualism, sea anemone and clown fish is commensalism, and cuckoo and crow is brood parasitism, so only Ophrys and bumblebee is sexual deceit.

Question 3 · NEET 2026 · Q180 · +4 / −1

Choose the correct statements regarding population interactions between two species.

Statement I: In both parasitism and commensalism, only one species benefits and the other species is harmed.
Statement II: Both species benefit in mutualism.
Statement III: Both species benefit in commensalism.
Statement IV: In parasitism, only one species benefits and the other species is harmed.
Statement V: In amensalism, one species is harmed and the other is unaffected.

Choose the correct answer from the options given below:

Answer and explanation

Answer: (3)

In mutualism both interacting species benefit (II correct).
In parasitism one species benefits while the other is harmed (IV correct).
In amensalism one species is harmed while the other remains unaffected (V correct).
Commensalism benefits one species and leaves the other unaffected (not harmed), so Statement III is wrong, and Statement I is wrong because commensalism does not harm either partner.
Hence Statements II, IV and V are correct.

Question 4 · Re-NEET 2026 · Q161 · +4 / −1

Consider a population of 10 million cells. Given the per-capita birth rate of 0.002 (per unit time) and the per-capita death rate of 0.002 (per unit time), the expected number of cells after 10 generations is ______.

Answer and explanation

Answer: (3)

The intrinsic rate of natural increase is $r = b - d$ . Here the birth and death rates are identical, so $r = 0.002 - 0.002 = 0$ and the exponential growth equation $N_t = N_0 e^{rt}$ reduces to $N_t = N_0$ . The population is at ZERO population growth and stays at 10 million however many generations pass. NCERT Class 12, Organisms and Populations.

Question 5 · Re-NEET 2026 · Q163 · +4 / −1

Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R.

Assertion (A): The logistic growth model of populations is considered more realistic than the exponential growth model.

Reason (R): Resources are finite.

In the light of the above statements, choose the most appropriate answer from the options given below :

Answer and explanation

Answer: (1)

Exponential growth assumes unlimited resources and predicts a J-shaped curve rising without bound, which no real population sustains. Because resources are in fact finite, every habitat has a carrying capacity K beyond which it cannot support more individuals, and growth slows as the population approaches it - producing the S-shaped (sigmoid) logistic curve. Finite resources are therefore exactly the reason the logistic model is the realistic one. NCERT Class 12, Organisms and Populations.

Question 6 · Re-NEET 2026 · Q172 · +4 / −1

Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R.

Assertion (A): Abingdon tortoise in Galapagos islands became extinct within a decade after goats were introduced.

Reason (R): Goats were more efficient at browsing than Abingdon tortoise.

In the light of the above statements, choose the most appropriate answer from the options given below:

Answer and explanation

Answer: (1)

This is NCERT's standard illustration of competitive exclusion in the wild. Once goats were introduced to Abingdon Island they stripped the vegetation far more efficiently than the tortoises could, and the resulting shortage of food drove the tortoise to extinction within about ten years. Superior resource exploitation by the goats is therefore the direct cause of the tortoise's disappearance, so R explains A. NCERT Class 12, Organisms and Populations (interspecific interactions).

Question 7 · Re-NEET 2026 · Q174 · +4 / −1

Match List-I with List-II.

List I	List II
P) Both species are harmed	I) Predation
Q) One species is harmed and the other is benefited	II) Mutualism
R) Both species are benefited	III) Competition
S) One is benefited while the other has no effect	IV) Commensalism

Choose the correct answer from the options given below:

Answer and explanation

Answer: (4)

Interspecific interactions are classified by the sign of the effect on each partner. Competition harms both (P-III, - -). Predation benefits one at the cost of the other (Q-I, + -). Mutualism benefits both (R-II, + +). Commensalism benefits one and leaves the other unaffected (S-IV, + 0). Writing the sign pairs out is the quickest way to sort these. NCERT Class 12, Organisms and Populations.

Question 8 · NEET 2020 · Q47 · +4 / −1

Secondary metabolites such as nicotine, strychnine and caffeine are produced by plants for their

Answer and explanation

Answer: (2)

Secondary metabolites like nicotine, strychnine, and caffeine are produced by plants for defence against herbivores and pathogens. Chapter: Organisms and Populations.

Question 9 · NEET 2020 · Q50 · +4 / −1

Which of the following is not an attribute of a population?

Answer and explanation

Answer: (3)

Species interaction is a characteristic of communities, not populations. Chapter: Organisms and Populations.

Organisms and Populations, on the exam screen.