(a) Define ‘natural selection’.
(b) “Only variations that confer an advantage to an individual organism will survive in a population”. Do you agree with this statement ? Give reason for your answer.
(a) Natural selection is the process of evolution of a species whereby characteristics which help individual organisms to survive and reproduce are passed on to their offspring, and those characteristics which do not help are not passed on.
(b) Yes, only those variations that confer advantage to an individual organism will survive in a population. This will become clear from the following example. Suppose there is a population of red beetles in the green bushes and a colour variation arises during reproduction so that one beetle is now green in colour (instead of red). This variation offers advantage of survival because the green beetle can mix up with green bushes, it cannot be spotted and eaten up by a crow and hence its population will increase. If, however, the variation had produced a blue coloured beetle, then this colour could not offer any survival advantage because blue beetle in green bushes could be easily spotted by a crow and eaten by it.
Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually ? Give reason for your answer.
What is meant by the term speciation? List four factors which could lead to speciation. [Delhi]
Name five varieties of vegetables which have been produced from ‘wild cabbage’ by the process of artificial selection.
What are the different ways in which individuals with a particular trait may increase in a population ?
State one characteristic which shows that the birds are very closely related to dinosaurs.
Choose the one term from the following which includes the other three :
broccoli, wild cabbage, cauliflower, cabbage
Name the various tools of tracing evolutionary relationships which have been used for studying human evolution.
In human beings, the statistical probability of getting either a male or female child is 50 : 50. Give a suitable explanation.
What type of plants were used by Mendel for conducting his experiments on inheritance ?
An individual cannot pass on to its progeny the experiences of its lifetime.” Justify the statement with the help of an example and also give reason for the same. [Foreign]
The forelimbs of a frog, a bird and a man show the same basic design (or basic structure) of bones. What name is given to such organs ?
If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% Of the same population, which trait is likely to have arisen earlier ?
Explain the mechanism of sex determination in humans. [All India]
Or
With the help of a flow chart explain in brief how the sex of a newborn is genetically determined in human beings. Which of the two parents, the mother or the father, is responsible for determination of sex of a child? [Foreign]
Which of the processes, sexual reproduction or asexual reproduction, brings about maximum variations in the offsprings ?
Study the following cross and showing self-pollination in Flf fill in the blank and answer the question that follows
”The sex of the children is determined by what they inherit from their father and not their mother.” Justify.
Give an example of body characteristics used to determine how close two species are in terms of evolution and explain it. [All India]
Define the term ‘evolution’. “Evolution cannot be equated with progress”. Justify this statement. [Delhi]
Mendel said that the characteristics or traits of organisms are carried from one generation to the next by internal factors which occur in pairs. What is the modern name for these factors ?
(a) What do you understand by the term ‘variation’ ?
(b) Name two human traits which show variation.
Write the names of at least three inorganic molecules which helped in the origin of life on the earth.
Can the wing of butterfly and the wing of a bat be considered homologous organs ? Why or why not ?
During which stage can the chromosomes be seen clearly? Write the features of the eukaryotic and prokaryotic chromosomes.
Out of bacteria, spider, fish and chimpanzee, which organism has a better body design in evolutionary terms ? Give reason for your answer.
Will geographical isolation be a major factor in the speciation of a self-pollinating plant species ? Why or why not ?