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Biology · 2025 · 5 marks
CBSE 2025 · Region 4 · Set 1 · Q33
(a) (i) Describe the population growth curve applicable in a population of any species in nature that has limited resources at its disposal. (ii)…
(i)
Describe the population growth curve applicable in a population of any species in nature that has limited resources at its disposal.
(ii)
Give the equation of this growth curve.
(iii)
Name the growth curve and depict a graphical plot for this type of population growth.
(i)
Explain the Species-Area relationship within a natural forest and also predict the nature of graph when species richness is plotted against the area for a wide variety of taxa.
(ii)
Depict the graphical relationship between species richness and area.
(iii)
Give the equation of the Species-Area relationship for a wide variety of taxa on a logarithmic scale.
Marking-scheme solution
(i)
A population growing in a habitat with limited resources initially shows a lag phase, followed by phases of acceleration and deceleration and, finally a asymptote when the population density reaches the carrying capacity.
(ii)
Equation: dN/dt = rN(K-N/K)
(N = population density at time t, r = intrinsic rate of natural increase, k
= carrying capacity)
(iii)
Logistic growth curve / Verhulst – Pearl Logistic Growth curve/sigmoid growth curve/S-Shaped curve.
(i)
• Within a region species richness increases with increasing
explored area but only upto a limit
• Nature of the graph - rectangular hyperbola.
(ii)
(iii)
Correct equation –
S = CA^Z / log S = log C + Z log A
(S = Species richness, A = Area, Z = Slope of the line (regression coefficient), C = Y-intercept)
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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.