Biology · Organisms and Populations · NEET
NCERT gives two because population growth depends on how much food and space is available. When resources are unlimited, a population grows at its full innate potential (exponential, J-shaped). But no habitat in nature has truly unlimited resources, so growth slows as space and food run out (logistic, S-shaped). Think of the two models as two situations: ideal (exponential) and real (logistic).
The logistic model is more realistic because resources for most populations are finite and become limiting sooner or later. This exact statement (with the reason 'resources are finite') has been asked as an Assertion-Reason question. Learn it as one line: logistic is realistic because carrying capacity (K) exists.
No. K appears only in the logistic model. Exponential growth assumes unlimited resources, so there is no upper limit and the J-curve keeps rising. The moment a question mentions K or 'limited resources' or an S-shaped/asymptote curve, the answer is logistic, not exponential. This distinction is a very common trap.
Exponential growth = J-shaped curve (keeps climbing steeply). Logistic growth = S-shaped or sigmoid curve (slow start, rapid middle, then flattens into an asymptote at K). NEET often shows the graph and asks you to name it, so link the letter to the shape: J for exponential, S for logistic.
In the NEET 2023 List-matching PYQ, logistic growth pairs with 'limited resource availability' and exponential growth pairs with 'unlimited resource availability'. The trap is that logistic is listed first but matches limited resources (II), not unlimited. Read each pair by its resource condition, not by its position.
Match List I with List II: A. Logistic growth B. Exponential growth C. Expanding age pyramid D. Stable age pyramid; with I. Unlimited resource availability condition II. Limited resource availability condition III. Pre-reproductive age group is largest, followed by reproductive and post-reproductive IV. Pre-reproductive and reproductive age groups are same.
Assertion A: The logistic growth model of populations is considered more realistic than the exponential growth model. Reason R: Resources are finite. Choose the most appropriate answer.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
The exponential (geometric) growth model for unlimited resources, giving a J-shaped curve, and the logistic (Verhulst-Pearl) growth model for limited resources, giving an S-shaped curve that plateaus at the carrying capacity K.
The logistic model, because resources for most populations are finite and become limiting sooner or later, so growth cannot continue forever.
Exponential growth gives a J-shaped curve, and logistic growth gives an S-shaped (sigmoid) curve.
Exponential growth assumes unlimited resources and has no carrying capacity, while logistic growth assumes limited resources and levels off at the carrying capacity K.
