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CBSE Class 10 Science Solved Question Paper 2016

Short Answer Type

31.

How do Mendel's experiment show that traits are inherited independently?

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32.

An object of height 2.5 cm is placed at a distance of 15 cm from the optical centre ‘O’ of a convex lens of focal length 10 cm. Draw a ray diagram to find the position and size of the image formed. Mark optical centre ‘O’, principal focus F and height of the image on the diagram.

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Long Answer Type

33.

What is placenta? Describe its structure. State its functions in case of a pregnant human female.

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34.
Define evolution. How does it occur? Describe how fossils provide us evidences in support of evolution.

Biological evolution is any change in the frequency of alleles in a population of organisms. Evolution is a slow change in the heritable characteristics of biological populations over successive generations. Evolutionary processes give rise to biodiversity at every level of biological organisation, including the levels of species, individual organisms, and molecules.

Evolution occurs due to the following

i. Accumulation of variations over generations - The variations arise due to crossing over, recombination, fertilisation or errors during DNA replication, mutation, recombination during sexual reproduction, etc . Geographical barrier also plays a great role in the accumulation of these variations.

ii. Natural Selection - The organisms with the favourable mutations are selected by nature and have better chances of survival than those who do not have favourable variations.

iii. Genetic Drift refers to the fact that variations in gene frequencies within populations can occur by chance rather than by natural selection. Random genetic drift may be an important mechanism in evolutionary change in small population.

All this leads to changes in the heritable characters and finally results in evolution of the organism.

Fossils − They represent plants and animals that lived millions of years ago and are now extinct. Different aged rock sediments contain fossils of different life-forms, which probably died during the formation of the particular sediment.

It is observed that although fossils appeared different from the existing species they may show certain features similar to the existing species thus providing linkages between pre-existing and existing forms Provide information about the extinct species which were different from the existing species

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35.

It is desired to obtain an erect image of an object, using concave mirror of focal length of 12 cm

(i) What should be the range of distance of an object placed in front of the mirror?

(ii) Will the image be smaller or larger than the object. Draw ray diagram to show the formation of image in this case.

(iii) Where will the image of this object be, if it is placed 24 cm in front of the mirror ? Draw ray diagram for this situation also to justify your answer.

Show the positions of pole, principal focus and the centre of curvature in the above ray diagrams.

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36.

(a) Define optical centre of a spherical lens.

(b) A divergent lens has a focal length of 20 cm. At what distance should an object of height 4 cm from the optical centre of the lens be placed so that its image is formed 10 cm away from the lens. Find the size of the image also.

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37.

What is atmospheric refraction? Use this phenomenon to explain the following natural events:

a) Twinkling of stars
b) Advanced sunrise and delayed sunset

Draw diagrams to illustrate your answer.

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