Which of the following is not true for a species ?
- Members of a species can interbreed
- Variations occurs among members of a species
- Each species is reproductively isolated from every other species
- Gene flow does not occur between the populations of a species
The Correct Option is D
Solution and Explanation
Gene flow can and does occur between populations of the same species. Gene flow is the exchange of genetic material (such as alleles) between different populations within a species, and it helps maintain genetic diversity and the cohesion of a species over time. The other statements are generally true for a species: members of a species can interbreed, variations occur among members of a species, and each species is reproductively isolated from every other species.
So, the correct option is (D): Gene flow does not occur between the populations of a species
Top Questions on Organisms and Populations
- Read the following passage and answer the questions that follow:
In nature, we rarely find isolated, single individuals of any species; majority of them live in groups in a well-defined geographical area, share or compete for similar resources, potentially interbreed and thus constitute a population. The population has certain attributes whereas, an individual organism does not. A population at a given time is composed of individuals of different ages. The size of the population tells us a lot about its status in the habitat. Whatever ecological processes we wish to investigate in a population, be it the outcome of competition with another species, the impact of the predator or the effect of pesticide application, we always evaluate in terms of any change in the population size. The size, in nature, could be low or go into millions. Population size, technically called population density (N) need not necessarily be measured in numbers only. The size of a population for any species is not a static parameter. It keeps on changing with time depending on various factors including food availability, predation pressure and adverse weather. (a) The Monarch butterfly is highly distasteful to its predator because of a special chemical present in its body. How does the butterfly acquire this chemical?
(b) If population density at a time t + 1 is 800, Emigration = 100, Immigration = 200, Natality = 200 and Mortality = 150, calculate the population density at time t and comment upon the type of age pyramid that will be formed in this case.
Student to attempt either sub-part (c) or (d):
(c) What is the difference in a method of measuring population density in an area if there are 200 carrot grass plants to only single huge banyan tree?
\begin{center} OR \end{center} (d) Name two methods to measure the population density of tigers.- CBSE CLASS XII - 2025
- Biology
- Organisms and Populations
- Who proposed the competitive exclusion principle?
- CBSE Compartment XII - 2025
- Biology
- Organisms and Populations
- The population interaction where one species is harmed and the other is unaffected is:
- CBSE Compartment XII - 2025
- Biology
- Organisms and Populations
- (a) Draw a graph for a population whose population density has reached the carrying capacity.
(b) Out of the two population growth curves, which one is considered a more realistic for most populations? Why?
(c) Draw a growth curve where resources are not limiting for the growth of a population and give its equation.
- CBSE CLASS XII - 2025
- Biology
- Organisms and Populations
Student to attempt either option (A) or (B):
(A) How is the interaction between Ophrys and its specific bee pollinator one of the best examples of co-evolution? Explain.
OR
(B) Arrange the given important steps of decomposition in their correct order of occurrence in the breakdown of complex organic matter and explain the fourth step in the process.- CBSE CLASS XII - 2025
- Biology
- Organisms and Populations
Concepts Used:
Evolution
Evolution is a process that occurs in changes in the genetic content of a population over time. Evolutionary change is generally classified into two: microevolution and macroevolution. The process of changes in allele frequencies in a population over time is a microevolutionary process. Three main mechanisms that cause allele frequency change are natural selection, genetic drift, and gene flow. On the other hand, macroevolution refers to change at or above the level of the species.