Science Solve Question & Answer

Science Solve Question & Answer

Group – A

(1)          In which stage of life cycle of a silkworm, silk fibre is produced?

Ans:   Silk fibre is produced in Pupa stage of life cycle of a silk worm.

(2)          Which body part of a silk worm is modified into silk gland?

Ans:   Salivary gland of a silk worm is modified into silk-gland.

(3)          What are silk moths?

Ans:   Flying insects are called moths. The moths, which produce silk, are called silk moths.

(4)          What are silk worms?

Ans:   The phases of lifecycle of silk moths, from which silk fibres are produced, are called silk worms. The first three stages (phases) of the life cycle of silk moths (Egg, Larva and Pupa) are called silk worms.

(5)          In how many days, life cycle of a silk moth completed?

Ans:   Generally, life cycle of a silk moth is completed in 50 days.

(6)          Write the kinds of silk moths, which are reared in Nepal.

Ans:   Two kinds of silk moths are reared in Nepal. They are ERI and SERI.

(7)          From which stage of the life cycle of silk moths, silk fibre is obtained?

Ans:   Silk fibre is obtained from cocoon, which is the last stage of pupa.

(8)          Why do drone bees die after mating with a queen bee?

Ans:   After mating with a queen bee, drone bees are turned out of the hive. They are not fed by worker bees. They are unable to collect and eat nectar and pollen grains themselves. So, they die after mating.

(9)          What is Apiculture?

Ans:   Farming (Keeping) bees for honey and wax is called Apiculture.

(10)      What is Apicology?

Ans:   The study of bees along with honey bees, is called Apicology or Melittology.

(11)      What is the life span of a queen bee?

Ans:   Life span of a queen bee is 2 to 3 years.

(12)      What is Nebula?

Ans:   The inter-planetary dust particles (perhaps part of dead stars), and gases; which are seen at night time between the stars and planets; are collectively called Nebula.

(13)      What is the age of our earth?

Ans:   It is believed that our earth is formed nearly 46000000000 years (4.6 Arab years) ago.

(14)      What is Geological Time Scale?

Ans:   Geological Time Scale is the scale of time which explains the history of the earth from the time of origin of the earth to the present time.

(15)      What do you mean by 1 AU?

Ans:   The distance between the earth and the sun is nearly 1.5 × 10⁸ km. This distance is known as 1 AU.

(16)      In which Era are the mammals evolved?

Ans:   Mammals are evolved on the earth nearly 195 millions years ago, which lies under Phanerozoic Eon, Mesozoic Era and Jurassic period.

(17)      Which ‘Era’ is also called the time of amphibians?

Ans:   In Devonian period of ‘Palaeozoic Era’ first amphibian was evolved and they are dominant on land in Penusylvanian Period of Palaeozoic Era. So, Palaeozoic Era is also called ‘Time of Amphibians’.

(18)      What is atmosphere?

Ans:   Our earth is surrounded by different layers of air, which is called atmosphere.

(19)      What is ozone layer?

Ans:   Ozone is the molecule of Oxygen containing three atoms of oxygen. Upper layer of stratosphere of the atmosphere contains Ozone, which is called Ozone layer.

(20)      Which layer of the atmosphere blocks UV-rays from the sun?

Ans:   Ozone layer of the stratosphere blocks UV-rays from the sun.

(21)      In which layer of our atmosphere, streaks of hot gases released from meteors are seen?

Ans:   The streaks of hot gases released from the meteors are seen in mesosphere.

(22)      What is the thickness of mesosphere?

Ans:   Mesosphere is expended between 50 km to 80 km from our earth’s surface, whose thickness is 30 km.

(23)      What do you mean by industrial gases?

Ans:   The gases, which are released from industries, are called industrial gases. For example – CO₂ , NO₂ , SO₂ , CO etc. are the industrial gases.

(24)      What is the main cause of depletion of Ozone layer in our atmosphere?

Ans:   Presence of Chlorofluorocarbons in our atmosphere is the main cause of depletion of Ozone layer in our atmosphere.

(25)      What is the universe?

Ans:   The space around us, up to which all the heavenly bodies are scattered, is called the universe.

(26)      What is the name of the planet which is also called green planet?

Ans:   There are green plants on our earth only. So, our earth is called green planet.

(27)      How many constellations are there in the sky?

Ans:   There are 88 constellations in the sky.

(28)      What is the shape of the ‘Milky Way’?

Ans:   The “Milky Way” is spiral in shape.

(29)      What is Cosmic Year?

Ans:   The time period, in which our solar system moves around the nucleus of the milky-way, is called Cosmic Year.

(30)      What is a Galaxy?

Ans:   Heavenly bodies in the sky form groups. The group of enormous stars with their planets, satellites, asteroids, comets, meteors, inter planetary dust particles, gases etc. is collectively called a galaxy.

(31)      Write the name of the galaxy whose shape is like the shape of our milky way.

Ans:   The name of the galaxy whose shape is spiral like the shape of our milky way is Andromeda.

(32)      How many “spiral arms” are there in the Milky-Way?

Ans:   There are three spiral arms in the Milky-Way. Our solar system is located in one of he three arms of the Milky-Way.

(33)      What is air pollution?

Ans:   The substances, which harm us if present in air, are called pollutants of air; and the with those substances is called polluted air. The condition being harmful substances in the air is called Air-Pollution. Air is polluted due to presence of industrial gases like NO₂ , N₂O , CO₂ , CO , SO₂ , CH₄ etc.

(34)      Is H₂S an acid?

Ans:   Yes, H₂S is taken as an acid, insoluble in water. It is a very weak acid. As it does not dissolve in water, it does not ionize giving H⁺ ion. It’s name is hydrogen sulphide or hydro sulphuric acid.

 

Group – B

(1)          Temperature increase with increase in height in the stratosphere, why?

Ans:               Upper layer of the stratosphere contains ozone layer which absorbs UV-rays from of the sun. The absorbed UV-rays heats the ozone layer of the stratosphere. Therefore, temperature of the stratosphere increases with increase in height.

(2)          What is the role of Ozone layer in our atmosphere?

Ans:               Ozone layer absorbs about 99% of the UV-rays coming from the sun towards the earth. UV-rays are harmful to living beings. Thus, ozone layer protects living beings of the earth from harmful UV-rays coming from the sun.

(3)          What is the bad effect of presence of excess amount of CO₂ in our atmosphere?

Ans:               CO₂ is needed by green plants for photosynthesis, so, CO₂ is useful to plants and so useful to animals also. But excess amount of CO₂ in our atmosphere increases green-house effect which causes global warming. This is the bad effect of CO₂.

(4)          Write the main effects of Ozone layer depletion.

Ans:   The main effects of ozone layer depletion are –

(i)      effects on human health.

(ii)    effects on animal health.

(iii)   effects on plant growth.

(iv)   effects  on environment (global warming).

(5)          What do you mean by solar system.

Ans:               All the planets revolving around the sun, all the satellites revolving around the planets, all the asteroids revolving around the sun, all the comets and meteors, constitute a family with the sun. This family is called solar system.

(6)          What is a planet? How many planets are there in the solar system?

Ans:               The heavenly body; which has sufficient mass and sufficient force of gravity, which is nearly round in shape and revolve around a star in non-intersecting egg-shaped orbit, is called a planet. There are eight planets in our solar system.

(7)          Why is the ‘Pluto’ excluded from the list of planets?

Ans:   The Pluto is excluded from the list of planets due to following reasons:-

(i)      It is very small.

(ii)    It is far away from the sun.

(iii)   It’s orbit intersects the orbit of Neptune.

(8)          Write the differences between Stars and Planets.

Ans:   Differences between the stars and the planets are:

Stars		Planets
1	Stars move around the galactic centre.	1	Planets move around a star.
2	They have their own light.	2	They do not have their own light.
3	They twinkle.	3	They do not twinkle.
4	There are innumerable stars.	4	There are only a few planets.
5	They make groups called constellation of finite shape.	5	They do not make groups.
6	Energy is produced by nuclear fusion in the stars.	6	Energy is not produced by nuclear fusion.
7	They are very hot-like balls of burning gases.	7	They are not so hot like balls of burning gases.

Write any two only.

(9)          What is a comet?

Ans:               An object, like a heavenly body in the sky; made up of dust particles, rocks, ice and frozen gases, which moves around the sun and produces a long tail like structure when reaches near the sun, is called a comet. When the comet reaches near the sun, ice and frozen gas evaporate and produce a tail like structure in opposite to the sun.

(10)      What is asteroid belt?

Ans:               The small planets, which are also called ‘minor planets’ or ‘planetoids’ or ‘baby planets’ are also known as ‘Asteroids’. There are hundreds of asteroids in the solar system, moving around the sun. Most of the asteroids lie between the Mars and the Jupiter and moves around the sun in their orbits. Hence, the belt between the Mars and the Jupiter is called Asteroid Belt.

(11)      What are the proposes of launching artificial satellites?

Ans:   Artificial satellites are launched for the following purposes:-

(i)      For forecasting weather.

(ii)    To improve the quality and speed of mass communication.

(iii)   For navigation.

(iv)   For scientific information’s.

(v)    For military intelligence.

(12)      The main cause of climate change is ‘air pollution’. Justify this statement.

Ans:               Air pollution is the condition of being harmful substances in air. Industrial gases like NO₂ , N₂O , CO₂ , SO₂ etc. pollute air. They may cause Acid-Rain also. They can cause ozone depletion. Due to ozone depletion, UV-rays of the sun reaches the surface of the earth, which may harm health of the organisms. Global warming is caused by ozone depletion. Global warming is also caused by Green House Effect which is caused by air pollution. Thus, main cause of climate change is Air Pollution.

(13)      Why does the tail of comet form for a certain period only?

Ans:               When a comet comes closer to the sun, frozen gases and ice evaporate forming a tail opposite to the sun due to the heat energy of the sun. When the comet moves farther, the returns back to it’s head shortening the tail and disappears when comet reaches very far away from the sun. Thus the tail of a comet is formed only for a certain period.

(14)      How many times the larvae of silk moths moult?

Ans:   Larvae of the silk moths moult four times at the ages of 6^th, 12^th, 18^th and 26^th days respectively.

(15)      For how many days, larvae from eggs of honey bees are fed Royal Jelly?

Ans:   All the larva from eggs of honey bees are fed Royal Jelly for 3 days; but the larva from the fertilized egg, which is to be developed as a new queen, is fed Royal Jelly for 6 days (total larva period).

(16)      What is propolis?

Ans:   Propolis is a Bee Glue, which is a resinous mixture that honey bees produce by mixing saliva and bee-wax exudate gathered from tree bud, sap flows or other botanical sources.

(17)      What is ‘Tidal Hypothesis’ of origin of solar system?

Ans:               In 1017 AD, English astronomers Sir James Jeans and Sir Harold Jeffrey proposed a hypothesis called ‘Tidal Hypothesis’ about the origin of solar system.

                        According to this hypothesis, a large comet passed near a huge gaseous mass. The comet attracted some gases from the huge gaseous mass producing a tide. The mass near the gaseous huge mass of the tide returned to it’s original huge mass, and outer part of the tide was escaped away in the space. The middle part of the tide formed a series of round structures of different sized, which are called planets, asteroids, satellites etc. The remaining original huge gaseous mass is the called sun yet. Thus, solar system is originated.

(18)      When were the dinosaurs evolved on the earth and when were they got extinct?

Ans:               Mesozoic Era is the time period between 250 millions of years ago to 65 millions of years ago. This period is also called ‘Time of reptiles’ because very very large reptile called ‘Dinosaurs’ evolved in this period of time and also got extinct in the same era.

(19)      Write any four importance of fossil fuels.

Ans:   Four importance of fossil fuels are –

(i)      Our most of the old machines are based on fossil fuels. Fossil fuels are needed to run them.

(ii)    Fossil fuels are easily available nearly all over the world.

(iii)   Fossil fuels are easy to use.

(iv)   Fossil fuels are cheap.

(20)      How many Eons are there, according to International Union of Geological Sciences (IUGS)? Write their names.

Ans:   Geological Time Scale is divided into four Eons, according to IUGS. They are –

(i)      Hadean Eon (4600 MY ago to 38 MY ago)

(ii)    Archean Eon (3800 MY ago to 2500 MY ago)

(iii)   Proterozoic Eon (2500 MY ago to 570 MY ago)

(iv)   Phanerozoic Eon (570 MY ago to present time)

                    [Here MY = Millions Years]

(21)      Fossils are found in sedimentary rocks only. Why?

Ans:       Igneous rocks are formed of very hot melted materials. Fossil, of present there, may be burnt. Metamorphic rocks are formed of old rocks which are changed several times, and so, the fossils if present there, may be destroyed. Sedimentary rocks are formed by depositions of muds and sands due to erosion on lands. Dead bodies of organisms may be covered with the muds and sands safely. Hence fossils are found in sedimentary rocks only (generally).

Group – C

(1)          How many times the larvae of silk moths moult?

Ans:   Larvae of the silk moths moult four times at the ages of 6^th, 12^th, 18^th and 26^th days respectively.

 

(2)          Write any three importances of SERICULTURE.

Ans:   Importances of Sericulture are as follows :-

(i)      Economic condition is improved.

(ii)    Light and warner clothes are produced.

(iii)   Silk is also used with other natural fibres and also with synthetic fibres to make them durable and elastic.

(3)          Write any three properties of silk fibres.

Ans:   The properties of silk fibres are as follows :-

(i)      Silk is shiny and durable.

(ii)    Silk is the longest and strongest natural fibre.

(iii)   Silk is highly elastic and easily returns to it’s original shape.

(iv)   Silk absorbs water easily.

(v)    Silk does not decay in short period of time. So, it is used in surgical stitching.

(vi)   Silk can easily be coloured.

                    (write any three)

(4)          What are the importances of honey?

Ans:   Honey is very useful to us. It supplies vitamins and minerals to our health; some importances are as follows :-

(i)      It contains vitamin A , B₁ , B₂ , B₆ , and E.

(ii)    It contains minerals like Mg, Zn, Fe, Ca, Cu etc.

(iii)   It prevents from heart disease.

(iv)   It minimize hair loss.

(v)    It helps in maintaining blood sugar.

(vi)   It is good for healthy skin.

(vii) It strengthen immune system.

                                    Etc.

(5)          Is carbonic acid (H₂CO₃) an organic acid?

Ans:               No, carbonic acid is not an organic acid, though it contains carbon atom having molecular formula H₂CO₃ and structural formula

                                                                                                        

In its structure, no H-atom is directly connected with C-atom that’s why it is not an organic compound. As we know, carbonates, bicarbonates, carbides, cyanides, carbon dioxide and carbon monoxide are taken as inorganic compounds. H₂CO₃ is a carbonate of hydrogen. Hence, it’s taken as a very weak acid among the inorganic acids.

 

Group – D

(1)          What are Honey Bees? Write their importances.

Ans:               The bees, which prepare Honey, are called Honey Bees. Bees collect nectar from flowers and prepare Honey. Honey Bees are very useful to us. The importances of Honey Bees are as follows:

(i)      They give us Honey, which is nutritious. Honey supplies vitamins and minerals.

(ii)    They give us Wax, which is used as raw materials for cosmetics and also has medicinal value.

(iii)   They give us Propolis, which is a resinous mixture and has medicinal value.

(iv)   They pollinate flowers, due to which seeds are produced in plants.

(2)          Explain the evolution process that occurred in the Mesozoic and Cenozoic Era. Also mention their differences.

Ans:               Mesozoic Era, which is also called “Age of Reptiles”, is “The time of middle life”. Gymnosperms and Dinosaurs evolved in this period of time. Dinosaurs also got extinct in this era and first bird evolved.

                        ‘Cenozoic Era’ is also called ‘The Age of mammals. Mammals became the dominant land animals. This is the Era of ‘Ice Age’.

                        Differences between Mesozoic and Cenozoic Era are as follows:

Mesozoic Era		Cenozoic Era
1	Dinosaurs evolved and Extinct.	1	No dinosaurs are present in this era.
2	Gymnosperms evolved.	2	Gymnosperms are present in this era.
3	No man was evolved.	3	Man evolved in this era.
4	Mammals appeared.	4	Mammals become dominant on lands.

(3)          What is ozone? Where is it’s layer in the atmosphere? How is it depleted? What are the effects of depletion of ozone layer?

Ans:               Oxygen molecule of three atoms of oxygen is called Ozone. A layer of ozone is present in upper part of the stratosphere of our atmosphere.

                        Ozone layer is depleted by chlorofluorocarbons. Chlorofluorocarbons are the compound gases which contain carbon, chlorine, fluorine and others. Other gases like carbon monoxide, oxides of nitrogen etc. are also responsible for depletion of ozone layer.

                        Effects of ozone layer depletion are as follows:

(i)      Bad effects on the skin, eyes etc. of human bodies.

(ii)    Larvae and eggs of aquatic and amphibian animals life.

(iii)   Decreases plant growth and so decreases crop-yieldings.

(iv)   Increase atmospheric temperature (global warming).

(4)          What are industrial gases? What are the effects of industrial gases present in our atmosphere?

Ans:               The gases, which are produced from different industries as a bi-product, are called industrial gases. For example –

(i)      CO₂ , CO and SO₂ are produced by burning petroleums in industries and vehicles.

(ii)    SO₂ , NO₂ , CO and dust particles are produced from cement industries.

(iii)   SO₂ , NO₂ , Carbon, Hydrogen and dust particles are produced from brick industries.

                                                                                                                                                                                                Etc.

            Effects of industrial gases are as follows:

(i)      SO₂ and SO₃ form sulphuric acid with water and causes Acid-Rain.

(ii)    CO₂ forms carbonic acid with water and causes Acid-Rain.

(iii)   CO₂ , CO and other cause global warming.

(iv)   CO₂ , CO , NO₂ cause ozone layer depletion.

(v)    SO₂ and dust particles cause diseases of respiration.

(vi)   NO₂ causes lung diseases.

                       

(5)          Study the figure and answer the following questions:

a.       Introduce such objects revolving around the sun.

b.      Why does the size of the tail of this mass increases when it comes closer to the sun?

Ans:  

(i)      A piece of rocks, dust particles, pieces of ice and frozen gases form a massive object in the sky and revolve around the sun in an elliptical orbit, just like a planet. They also non-luminous and have no their own light. They revolve around the sun in a very large elliptical orbit. They come closer to the sun after a long period of time. They are very cold. Such heavenly bodies are called Comets.

(ii)    When the comet reaches closer to the sun, ice and frozen gases evaporate and make a tail like structure in opposite to the sun. as the comet goes closer and closer to the sun, heat energy of the sun evaporate more and more ice and frozen gases forming greater and greater tail. The tail is longest when the comet is closest to the sun. when the comet moves away from the sun, the tail becomes shorter and shorter and lastly the tail returns back to the main mass, i.e. tail disappears.