Organisms and Populations

36 solved questions from Class 12 Biology, each with the full working. Tap any question to see the step-by-step solution.

• 1 What is the primary topic or theoretical principle explored in 'Organisms and Populations' (Class 12 BIOLOGY)? medium MCQ Chapter Core Principle
• 2 Which key mechanism or analytical rule is highlighted in 'Organisms and Populations'? medium MCQ Key Analytical Mechanism
• 3 What is the primary topic or principle explained in 'Organisms and Populations' (Class 12 Biology)? medium MCQ Chapter Core Concept
• 4 Which key observation or fact is central to understanding 'Organisms and Populations'? medium MCQ Key Fact & Mechanism
• 5 Why is the study of 'Organisms and Populations' important for students of Class 12? medium MCQ Learning Significance
• 6 What is a common application or real-world example related to 'Organisms and Populations'? medium MCQ Real World Application
• 7 What key takeaway should students retain after completing 'Organisms and Populations'? medium MCQ Chapter Summary & Takeaway
• 8 In a population of 200 individuals, 72 are homozygous dominant (AA), 96 are heterozygous (Aa) and the rest are homozygous recessive (aa). What is the frequency of the recessive allele (a)? medium 2 marks Allele frequency calculation
• 9 Discuss how a limiting factor leads to logistic growth of a population. Derive the logistic growth equation and explain the ecological meaning of the carrying capacity (K). hard 5 marks Logistic growth & carrying capacity
• 10 Which of the following is NOT a condition required for a population to be in Hardy–Weinberg equilibrium? easy MCQ 1 mark Hardy–Weinberg conditions
• 11 A bacterial culture doubles every 3 hours. If the initial cell count is 5×10^6, how many cells will be present after 12 hours? medium 2 marks Exponential bacterial growth
• 12 In a diploid population, allele A has frequency p=0.4 and allele a has frequency q=0.6. Suppose the fitnesses are w_AA=1, w_Aa=1, and w_aa=1-s with s=0.3 (selection against aa). What is the allele frequency of a after one generation of selection? hard 4 marks Allele frequency change due to selection
• 13 Explain how genetic drift can affect allele frequencies in a small isolated population. Consider a population of 10 diploid individuals where allele A has an initial frequency of 0.5. What is the probability that allele A will eventually become fixed? hard 5 marks Genetic drift and fixation probability
• 14 In a population of organisms, the logistic growth equation is dN/dt=rN(1-N/K). If r=0.2 day^-1, K=500, and the initial population size N_0=50, what is the population size after one day? medium MCQ 3 marks Logistic growth equation
• 15 A culture of yeast cells grows exponentially with a rate constant of 0.5 hr^-1. If the initial cell count is 2×10^4, how many cells will be present after 6 hours? easy 2 marks Exponential population growth
• 16 Which of the following is NOT an assumption of the Hardy–Weinberg principle for a large diploid population? easy MCQ 1 mark Hardy–Weinberg assumptions
• 17 A population of 1,000 individuals suffers a severe bottleneck that reduces its size to 50 individuals for two successive generations (no migration, no mutation, random mating). The initial heterozygosity is H_0=0.60. Using the drift formula H_t=H_0(1-1/2N_e)^t, calculate the expected heterozygosity after the bottleneck and comment on the loss of genetic variation. hard 4 marks Genetic drift and bottleneck effect
• 18 In a diploid population the initial allele frequencies are p=0.7 (allele A) and q=0.3 (allele a). Fitness values are w_AA=1, w_Aa=0.9, w_aa=0.5. Find the frequency of allele A after one generation of selection. medium 2 marks Allele frequency change by selection
• 19 In a population of 150 individuals the observed genotype numbers are: 36 AA, 72 Aa, and 42 aa. (i) Calculate the allele frequencies of A and a. (ii) Using a chi‑square test, determine whether the population is in Hardy–Weinberg equilibrium (use χ^2_(0.05,1)=3.841). medium 3 marks Hardy–Weinberg equilibrium test
• 20 Gene flow introduces new alleles into a population. Which of the following situations best illustrates gene flow? easy MCQ 1 mark Gene flow definition
• 21 In a diploid population, allele A has initial frequency p=0.6 and allele a has q=0.4. Each generation the population receives migrants equal to m=0.10 of its size from a large neighboring population where p_m=0.2. After migration, selection acts against the homozygous recessive genotype aa with fitness w_aa=0.7, while w_AA=w_Aa=1. Calculate the frequency of allele A after one generation (migration followed by selection). hard 4 marks Combined migration and selection on allele frequency
• 22 Discuss the three pre‑zygotic reproductive isolation mechanisms that operate in plants. For each mechanism, give a specific example relevant to Indian flora. medium 3 marks Pre‑zygotic isolation in plants
• 23 In a diploid population, the initial heterozygosity is H_0=0.48. The effective population size is N_e=200. Using the genetic drift formula H_t=H_0(1-1/2N_e)^t, calculate the expected heterozygosity after t=5 generations. medium 2 marks Genetic drift – change in heterozygosity
• 24 A population of 50 diploid individuals undergoes a severe bottleneck for 3 consecutive generations with no mutation, migration, or selection. The initial heterozygosity is H_0=0.55. Calculate the expected heterozygosity after the bottleneck and the probability that allele A (initial frequency p=0.4) becomes fixed. hard 5 marks Genetic drift and bottleneck effects
• 25 In a population of 500 diploid individuals, 200 are homozygous dominant (AA), 200 are heterozygous (Aa), and 100 are homozygous recessive (aa). Find the frequency of allele a. easy 1 mark Allele frequency calculation
• 26 In a diploid population with initial allele frequencies p=0.6 (allele A) and q=0.4 (allele a), a selection coefficient s=0.2 acts against the homozygous recessive genotype aa (fitness w_aa=0.8). There is no migration or mutation and random mating occurs. Find the allele frequency of A after one generation of selection. medium 3 marks Selection in population genetics
• 27 From a diploid population of 120 individuals, genotype counts are: 30 AA, 70 Aa, and 20 aa. (i) Calculate the allele frequencies of A and a. (ii) Using a chi–square test with chi^2_(0.05,1)=3.841, determine whether the population is in Hardy–Weinberg equilibrium. Provide the chi-square value and the conclusion. hard 5 marks Hardy–Weinberg equilibrium test
• 28 From a population of 200 diploid individuals, genotype counts are: 80 AA, 96 Aa, and 24 aa. What is the frequency of allele a? easy MCQ 2 marks Allele frequency calculation
• 29 In a diploid population, initial allele frequencies are p=0.6 (allele A) and q=0.4 (allele a). Fitness values are w_AA=1.0, w_Aa=0.9, w_aa=0.7. Find the allele frequency of A after one generation of selection. medium 3 marks Allele frequency after selection
• 30 Consider a diploid population with initial allele frequencies p=0.3 (A) and q=0.7 (a). Each generation the population receives migrants equal to m=0.20 of its size from a large neighboring population where p_m=0.80. After migration, selection acts against the homozygous recessive genotype aa with fitness w_aa=0.60, while w_AA=w_Aa=1. Calculate the frequency of allele A after one generation (migration followed by selection). hard 4 marks Migration and selection effects
• 31 In a diploid population of 100 individuals, the genotype counts are 40,AA, 50,Aa and 10,aa. What is the frequency of allele “a” in this population? easy 1 mark Allele frequency calculation
• 32 In a diploid population, the initial allele frequencies are p=0.40 for allele A and q=0.60 for allele a. The fitness values are w_AA=1.0, w_Aa=1.0 and w_aa=0.90. What is the frequency of allele A after one generation of selection? medium 2 marks Selection effect on allele frequencies
• 33 In a diploid population, the initial allele frequencies are p=0.35 for allele A and q=0.65 for allele a. Each generation the population receives migrants equal to m=0.15 of its size from a large neighboring population where allele A frequency is p_m=0.50. After migration, selection acts against the homozygous recessive genotype aa with fitness w_aa=0.70 while w_AA=w_Aa=1. What is the frequency of allele A after one generation (migration followed by selection)? hard 4 marks Migration and selection on allele frequencies
• 34 In a diploid population of 60 individuals, the genotype counts are 18 AA, 30 Aa and 12 aa. Calculate the frequencies of alleles A and a. easy 2 marks Allele frequency calculation
• 35 In a diploid population, the initial allele frequencies are p=0.70 for allele A and q=0.30 for allele a. The population receives migrants equal to m=0.10 of its size from a neighboring population where p_m=0.40. After migration, selection acts against the homozygous recessive genotype aa with fitness w_aa=0.60 while w_AA=w_Aa=1. What is the frequency of allele A after one generation (migration followed by selection)? hard 4 marks Migration and selection combined
• 36 A small isolated population consists of 8 diploid individuals. The allele A has an initial frequency of 0.3. Assuming neutral evolution (no selection, mutation, or migration), what is the probability that allele A will eventually become fixed in the population? hard 5 marks Probability of fixation under genetic drift