Biology · Class 12 · Chapter 11
Organisms and Populations
13 lessons 96 min 2 simulations
This chapter looks at ecology at the level of the population. It covers what a population has that an individual lacks (birth and death rates, sex ratio, age pyramids), how density is measured, how the four processes change it, exponential and logistic growth with r and K, life history strategies, and the six kinds of interaction between species: predation, competition, parasitism, commensalism, amensalism and mutualism.
What the exam asks
NEET asks for per capita birth and death rate sums, the growth equation Nt+1 = Nt + [(B + I) − (D + E)], the exponential and logistic equations with r and K and the J and S curves, r values, the sign table of interactions, and example-to-interaction matching: Pisaster, prickly pear, Monarch butterfly, Calotropis, Abingdon tortoise, Balanus and Chthamalus, MacArthur's warblers, Cuscuta, the koel, cattle egret, clown fish, fig and wasp, and Ophrys. Marks are lost by mixing commensalism with amensalism, calling the J-shaped curve logistic, and forgetting that competition can occur between unrelated species or without limiting resources.
Lessons
13 lessons · 96 min
1Ecology and populationsNCERT §11.1, §11.1.16 min2Population attributesNCERT §11.1.17 min3Population densityNCERT §11.1.16 min4Four processes of population growthNCERT §11.1.26 min5Exponential growthNCERT §11.1.2 (i)6 min6Logistic growth and life historyNCERT §11.1.2 (ii), §11.1.310 min 1 sim7Population interactionsNCERT §11.1.49 min 1 sim8PredationNCERT §11.1.4 (i)7 min9CompetitionNCERT §11.1.4 (ii)6 min10ParasitismNCERT §11.1.4 (iii)7 min11CommensalismNCERT §11.1.4 (iv)6 min12MutualismNCERT §11.1.4 (v)7 min13Chapter reviewMust-know facts, traps and formulas13 min