Organisms and Populations — NEET UG practice

1. Recall the logistic growth model: This model describes population growth that slows down as the population approaches the carrying capacity $K$, unlike exponential growth which has no such limit.

2. State the correct equation: The Verhulst-Pearl logistic growth equation is defined as:

$$\frac{dN}{dt} = rN\left(\frac{K-N}{K}\right)$$

Here, $N$ is the population size at time $t$, $r$ is the intrinsic rate of natural increase, and $K$ is the carrying capacity.

3. Why this form makes sense: When $N$ is small compared to $K$, the term $\frac{K-N}{K}$ is close to 1, so growth is nearly exponential.

As $N$ approaches $K$, the term $\frac{K-N}{K}$ approaches 0, so growth slows down and eventually stops.

4. Eliminate incorrect options: Options A, C, and D use incorrect combinations (such as $K+N$ instead of $K-N$, or dividing by $N$ instead of $K$), which do not represent this braking effect correctly.

Hence, the answer is Option B.

1. Understand "sexual deceit": This is a special pollination strategy where a flower mimics the appearance or scent of a female insect to trick a male insect into attempting to mate with it, thereby achieving pollination.

2. Identify the correct example: The Mediterranean orchid genus Ophrys produces flowers resembling female bumblebees.

Male bumblebees attempt pseudocopulation with the flower, and in doing so, pick up and transfer pollen — this is a classic example of sexual deceit.

3. Why the other options are wrong:

• Female wasp and fig is an example of mutualism, where the wasp pollinates the fig in exchange for a place to lay eggs.

• Sea anemone and clown fish is an example of commensalism/protective mutualism, not sexual deceit.

• Cuckoo and crow is an example of brood parasitism, where the cuckoo lays eggs in the crow's nest.

Hence, the answer is Option B.

1. Recall definitions of each interaction type: Population interactions are classified by whether each participant gains, loses, or is unaffected.

2. Check statement A: This claims both parasitism and commensalism harm one species — but in commensalism, one species benefits while the other is unaffected (not harmed).

So statement A is incorrect.

3. Check statement B: In mutualism, both interacting species gain benefits from each other.

So statement B is correct.

4. Check statement C: This claims both species benefit in commensalism — but only one species benefits while the other remains unaffected.

So statement C is incorrect.

5. Check statement D: In parasitism, the parasite benefits while the host is harmed.

So statement D is correct.

6. Check statement E: In amensalism, one species is harmed while the other is unaffected.

So statement E is correct.

7. Combine correct statements: The statements that hold true are B, D, and E.

Hence, the answer is Option C.