CBSE Class 10 science Board paper solution 2015 of set -02
2. DNA is found inside a special area of the cell called the nucleus
3. This is because the green plant is the primary producer by trapping energy from sunlight.
4. Absolute refractive index of glass = 4/3 = c/vg
=> 4/3 x vg = c
=> 4/3 x 2 x 108 = c
The speed of light in vacuum = c = 2.67 x108 m/s
Absolute refractive index of water = 3/2 = c/vw
=> The speed of light in water vw = 2c/3 = 1.78 x108 m/s
5. Improper disposal of domestic waster harmful:
a. It allow mosquito to breed and spread diseases
b. it will release harmful green house gases that pollute air we breadth
c. It will degrade the soil fertility
d. it will pollute water and not only effect marine life but also reduce percolation rate of soil
6. The advantages of water stored in the ground are many. It does not evaporate, but spreads out to recharge wells and provides moisture for vegetation over a wide area. In addition, it does not provide breeding grounds for mosquitoes like stagnant water collected in ponds or artificial lakes. The ground-water is also relatively protected from contamination by human and animal waste.
7. A series of carbon compounds in which the same functional group substitutes for hydrogen in a carbon chain is called a homologous series.
C3H6,C4H8,C5H10 – Alkene
8. Test first: Take two test tubes A and B and place about 1 g of sodium carbonate in them. Pour alcohol in test tube A and carboxylic acid in test tube B. Shake the contents of the test tubes.
The test tube in which a brisk effervescence takes place, with the liberation of a colourless gas (CO2) is carboxylic acid. The test tube in which no reaction takes place is alcohol.
2nd test: , if you add a small piece of Na metal into a test tube containing alcohol, you get to see the formation ofbubbles. This is due to the release of a gas which we call as hydrogen. Carboxylic acid remains unsuccessful to show this test.
9. a. Group 2. b. Be c. Ca
10. Atomic no. 16
Electronic configuration = 2,8,6
Period = no of shell = 3 = 3rd period
Group = valance electrone = 6 + 10 = 16th group as 10 element short in 3rd period
Valency = 8 – 6 = 2
1. It involves no formation and fusion of gametes. 2. It is uniparental 3. Reproductive units are somatic cells of parent
1. It involves formation and fusion of gametes. 2. It is generally biparental. 3. Reproductive units are germ cells of parent.
12. Four point of significance of reproductive health in society
(i) Birth control methods and family planning measures
(ii) Sexually transmitted diseases and their methods of prevention.
(iii) . Importance of breast feeding and post natal care for the mother and baby.
(iv) Equality among sexes and given fair opportunities for male and female children
The reproductive health has tremendously improved in India in the last 50 years. The areas of improvement are as follows
(i) Massive child immunization programme, which has lead to a decrease in the infant mortality rate
(ii) Maternal and infant mortality rate, which has been decreased drastically due to better post natal care
(iii) Family planning, which has motivated people to have smaller families
(iv) Use of contraceptive, which has resulted in a decrease in the rate of sexually transmitted diseases and unwanted pregnancies
13. Chromosomes are thread like structure made up of DNA and proteins. They are present inside the nucleus.
Gamete formation is the first step in sexual reproduction. Number of chromosomes is halved during gamete formation. As a result, the number of chromosomes in gamete is half the number of chromosomes in somatic cells. When male and female gametes fuse during fertilization, the number of chromosomes becomes equal to that in somatic cells. In this way number of chromosomes is maintained in the progeny.
a) The colour of the flower in the F1 generation would be blue as gene for blue colour is dominant over white.
b) The percentage of white flowers in the F2 generation would be 25%.
c) The ratio of BB: Bb would be 1:2 i.e 1 BB and 2 Bb
15. a. Speciation is the process in which one or more species arise from previously existing species. A single species may give rise to a new species or two different species may give rise to a new species.
b. Natural selection: It is a basic mechanism of evolution in which nature selects the characteristics of an organism. If the behavior of a certain organism is approved by nature, the organism will survive or else will die, hence not selected by nature.
16. When a beam of light strikes fine particles get reflected in different direction by these particles is called the scattering of light .
When sunlight passes through the atmosphere, the fine particles in air scatter the blue colour (shorter wavelengths) more strongly than red. The scattered blue light enters our eyes. thus clear sky appear blue.
During sunrise and sunset, the rays have to travel a larger part of the atmosphere because they are very close to the horizon. Therefore, light other than red is mostly scattered away. Most of the red light, which is the least scattered, enters our eyes. Hence, the sun and the sky appear red.
17. Convex mirror
Convex mirrors are commonly used as rear-view (wing) mirrors in vehicles. Convex mirrors are preferred because they always give an erect, though diminished, image. Also, they have a wider field of view as they are curved outwards. Thus, convex mirrors enable the driver to view much larger area than would be possible with a plane mirror.
18. All the interacting organisms in an area together with the non-living constituents of the environment form an ecosystem.
Biotic and Non biotic Component.
An aquarium needs to clean regularly due to lack of decomposers that can clean naturally by decomposing organic substance.
19. Fossils may be defined as the remains of the organisms which have been preserved in the form of molds or cast in rocks etc. since prehistoric ages. When a plant or an animals dies, their remains falls on the ground.
Over a period of time their body gets covered by sediments brought by rivers, winds etc. These sediments keeps on getting accumulated for over hundred of years and when that land gets eroded, the fossils can be seen Thus, the process of accumulation of dead remains of plants and animals for over hundreds of years results in the formation of fossils.
The age of the fossils can be determined by the following way:
1) Radiometric dating:
In this method, the age of the fossil can be determined by tracing the radioactive elements present in the rocks and examining it chemically.
2) Relative dating:
The fossils are found in the sedimentary rocks in the form of layers accumulated over large span of time. So, using this fact, the geologist find the age of fossils in the way that the fossil found at the bottom of those layers are found to be older than that found above those.
Analysis of the organ structure in fossils allows us to make estimates of how far back evolutionary relationships go.
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