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Biology · 2025 · 5 marks
CBSE 2025 · Region 6 · Set 1 · Q33
(a) (i) Describe the Species-Area relationship as observed by Alexander von Humboldt, for a wide variety of taxa in nature. (ii) Draw the graph…
(a)(i)
Describe the Species-Area relationship as observed by Alexander von Humboldt, for a wide variety of taxa in nature.
(ii)
Draw the graph showing Species-Area relationship for $\displaystyle \mathrm{S}=\mathrm{CA}^{\mathrm{Z}}$. What is the significance of 'Z' in Species-Area relationship?
OR
(b)(i)
Describe the logistic population growth curve with the help of a suitable graphical representation.
(ii)
Write the equation of Verhulst-Pearl logistic growth curve and explain what 'K' and 'r' suggest in the given equation.
Marking-scheme solution
He observed that within a region species richness (the number of different
species) increase with increasing area , only up to a limit
(ii)
•Z shows relationship between species richness and area/ Regression
coefficient/ slope of graph
(i)
A population growing in a habitat with limited resources show initially a lag
phase, followed by phases of acceleration, and deceleration and finally an asymptote, when the population density reaches the carrying capacity
(ii)
DN/dt = rN(K-N/K)
Where N = Population density at time t r = Intrinsic rate of natural increase
K = Carrying capacity/ maximum possible numbers in a given habitat
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CBSE Class 12 Biology past-paper question from the 2025 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.