Q21 of 58 Page 1

What is meant by speciation? List four factors that could lead to speciation. Which of these cannot be a major factor in the speciation of a self-pollinating plant species. Give reason to justify your answer.

A species is a population of organisms consisting of similar individuals which can breed together and produce fertile offspring. Species can be of plants or animals, the process by which the new species develop from the existing species is known as speciation.


The factors that could lead to speciation are as follows-


(i) Geographical isolation of a population caused by various types of barriers like mountain ranges, rivers, sea etc. This leads to reproductive isolation and the species get separated due to which there is no flow of genes between separated groups of population.


(ii) Genetic drift caused by drastic changes in the frequencies of a gene by chance alone.


(iii) Variations caused in individuals due to natural selection.


(iv) Drastic change in the genes or DNA called mutation is also a cause of speciation.


Geographic isolation cannot be a major factor for the speciation of a self-pollinating plant species as it does not depend on any other plant for its reproduction process.


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(a) Write the functions of the following parts in human female reproductive system:

(i) Ovary


(ii) Oviduct


(iii) Uterus


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(a) Define the following terms in the context of spherical mirrors:

(i) Pole (ii) Centre of curvature


(iii) Principal axis (iv) Principal focus


(b) Draw ray diagrams to show the principal focus of a:


(i) Concave mirror (ii) Convex mirror


(c) Consider the following diagram in which M is a mirror and P is an object and Q


Is its magnified image formed by the mirror?



State the type of the mirror M and one characteristic property of the image Q.

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(a) Draw a ray diagram to show the formation of image by a convex lens when an object is placed in front of the lens between its optical centre and principal focus.

(b) In the above ray diagram mark the object-distance (u) and the image-distance (v) with their proper signs (+ve or -ve as per the new Cartesian sign convention) and state how these distances are related to the focal length (f) of the convex lens in this case.


(c) Find the power of a convex lens which forms a real, and inverted image of magnification -1 of an object placed at a distance of 20 cm from its optical centre.