Class 10
SCIENCE
SECTION A
Q 1 Write in one Word about the Following:
(i) Mirrors used by dentists to examine teeth.
Ans. Concave mirror
(ii) the smallest distance at which the eye can see the object clearly without strain.
Ans. 25 cm
Q 2 Find the period and group of the element whose atomic number is 12.
Ans. The electronic configuration of the element is 2, 8, 2.
Q 3 What is organic evolution?
Ans. Organic evolution is a process by which new species develop from earlier forms.
Q 4 which is meant by power of accommodation of the eye How is it related to the focal length of the eye lens?
Ans. The ability of the eye lens to adjust its focal length blossoming from distant as well as near objects on the retina is called the power error accommodation of the eye. When the eye is viewing a distant object, the focal length of the eye lens is more. However, when one looks at the nearby object the curvature of the eye lens increases, and its focal length decreases to form a sharp image of the object at the retina.
Q 5 Study the ray diagram given below and answer the following question:
(i) State the type of lens used in the figure.
(ii) List two properties of the image formed.
(iii) In which position of the object will the magnification be - 1?
Ans. (i) The lens used is a convex (converging) lens.
(ii) The image formed is real, inverted, and magnified.
(iii) Magnification shall be -1 when the object is situated at 2f¹.
Q 6 What the key is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
Ans. The phenomenon of a progressive increase in the concentration of certain harmful known biodegradable chemicals such as DDT at a different level of the food chain is an old biological notification for biomagnification.
The concentration of harmful chemicals will be e different at different trophic levels. It will be e lowest in the first trophic level and highest in the last trophic level of the food chain.
Q 7 Write any two differences between binary fission and multiple fission in a tabular form as observed in the cell of organisms.
Ans. Binary fission
(i) The unicellular organism splits into two equal daughter cells by cell division.
(ii) Nucleus and cytoplasm divide simultaneously.
(iii) Many different patterns of division transverse and longitudinal.
Example - Amoeba.
Multiple fission
(i) Unicellular organisms are divided into many daughter cells.
(ii) First the nucleus divides into many nuclei and then each nucleus is surrounded by cytoplasm and the daughter nuclei are related by rupture of the parent cell.
(ii) No definite pattern of division.
Example: malarial parasite.
Q 8 Explain why the planets do not twinkle but do the Twinkle.
Ans. Stars are very far away and behave as almost point sources of light. On account of atmospheric reflection, the path of a ray of light coming from a star goes on varying slightly, the apparent position of the star fluctuates and the amount of starlight entering the eye flickers. So, sometimes, the star appears brighter, and at some other time, Fainter. Thus, the stars twinkle.
Planets are much closer to the earth and are seen as extended sources. So, a planet may be considered as a collection large number of point-sized sources flickers but the total amount of light entering our eyes from all the vidual point-sized sources average out to be constant. Thereby, planets appear equally bright and there is not twinkling of planets.
Q 9 what changes would you our hhashableule of three Rs:
(i) Reduce: Use natural resources of limited quality avoiding wastage.
(ii) Recycle: Recycle plastic, paper, glass, and materials for future use so that there is no drain on natural resources.
(iii) Reuse: Envelopes can be e reversed from reuse. Bottles and cans supplied with pickles, jams and squashes can be used for storing kitchen items.
Q 10 In human beings there are only 23 pairs of chromosomes but there are unlimited characteristic features. Justify.
Ans. There are only 23 pairs of chromosomes in human beings but 30,000 to 40,000 numbers of genes. These genes are responsible for the characteristic features. That is why there is so much variation in the characteristic features.
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