These sample papers have been taken from CBSE
(a) Name the part of human brain which controls: (i) voluntary actions (ii) involuntary actions
Answer: (i) Cerebrum (ii) Medulla
(b) State the significance of peripheral nervous system. Name the components of this nervous system and distinguish between their origins.
Answer: Peripheral nervous system works as the conduit between the central nervous system and various organs of the body. Peripheral nervous system is composed of two types of nerves, viz. cranial nerves and spinal nerves. Cranial nerves come out of the brain, while spinal nerves come out of the nerve cord.
Question 11: What are fossils? How are these formed? List two methods of determining the age of fossils.
Answer: Preserved remains of animals and plants from distant past are called fossils. Fossils are formed when a living being gets buried under sediment and remain there for hundreds of years. Two main processes of formation of fossil are called permineralisation and mould or cast formation. Two methods of determining the age of fossil are stratigraphy and carbon dating.
What is speciation? List four factors responsible for speciation.
Answer: The evolutionary process by which populations evolve to become distinct species is called speciation. Four factors responsible for speciation are as follows:
Question 12: Explain giving reason why the sky appears blue to the observers from the surface of the Earth. What will be the colour of the sky for an Astronaut staying in an International Space Station orbiting the Earth? Explain your answer with reason.
Answer: We know that the wavelength of red colour is more than that of blue colour. The size of particles in air is smaller than the wavelength of visible light. Hence, these particles scatter the light of shorter wavelength more effectively than light of longer wavelength. The blue end of the visible spectrum has shorter wavelength than the red end. Due to this, blue colour is scattered more strongly in the atmosphere; compared to the red colour. This is the reason sky appears blue. No color is scattered in space. Hence, the sky appears black to the astronaut staying in International Space Station.
Question 13: We know that an electric current through a metallic conductor produces a magnetic field around it. Explain giving reason whether a similar magnetic field will be produced around a thin beam of moving (i) alpha particles, (ii) neutrons. Name the rule applied to determine the direction of magnetic field produced around a current carrying straight conductor.
Answer: Since alpha particles are charged particles so a magnetic field will be produced around the beam of moving alpha particles. But as neutrons are electrically neutral to this will not happen in case of a beam of neutrons. Right Hand Thumb Rule explains the direction of magnetic field produced around a current-carrying straight conductor.
Question 14: Explain the role of an electric fuse joined in series with an electrical appliance. Why should a fuse with a defined rating not be replaced by one with a larger rating?
Answer: Electric fuse is a safety device which breaks the circuit in case of overload or short-circuit. Thus, the electric fuse helps in preventing any damage to the electrical appliance. If an electric fuse with larger rating is used for an appliance the fuse will not melt in case of overload. Thus, it will not do the work for which it has been installed.
Question 15: We are all familiar with the “Chipko Movement” which originated in the early 1970s in a remote village of Garhwal high up in Himalayas. This was a result of dispute between the local villagers and a greedy contractor who had been allowed to fell the trees in a forest close to the village. When contractor’s workers appeared in the forest to cut the trees, the men folk were not present, so the women folk took the lead in the movement of preventing the contractor from felling the tree.
They hugged the trees and forced the contractor to withdraw:
(i) Why were the villagers against felling of trees?
Answer: The villagers wanted to protect their environment. So, they were against the felling of trees.
(ii) How do forests maintain ecological balance in nature?
Answer: Trees help in maintaining the balance between carbon dioxide and oxygen in air. Trees help in precipitation by way of transpiration. Trees also provide habitat to a large variety of creatures. Thus, forests maintain ecological balance in nature.
(iii) List two values exhibited by the “Chipko Movement”.
Answer: Two values exhibited by this movement are:
(a) What is a balanced chemical equation? Why should chemical equations be balanced?
Answer: A balanced chemical equation has number atoms of each element equal on both sides. According to Law of Conservation of Mass, mass can neither be created nor destroyed in a chemical reaction. To obey this law, the total mass of elements present in reactants must be equal to the total mass of elements present in products.
(b) Write the chemical equation of the reaction in which the following changes have taken place:
(i) Change in colour.
Answer: CuSO4 + Fe → FeSO4 + Cu
(ii) Change in temperature.
Answer: NaOH + HCl → NaCl + H2O
(iii) Formation of precipitate.
Answer: BaCl2 + Na2SO4 → BaSO4 (ppt)+ 2NaCl
(a) Explain why the method of extraction of metals high up in the reactivity series is different from the method of extraction of metals in the middle of the series. Why cannot the same process be applied for them?
Answer: Carbon is used for reduction of metals ores from middle of the series. But carbon is less reactive than metals of high reactivity. So, metals of high reactivity cannot be extracted by the same process as used for metals of middle reactivity.
(b) With the help of equation explain the process of extraction of sodium.
Answer: When electric current is passed through molten state or solution of sodium chloride, sodium metal deposited over cathode.
Na+ + e− → Na
2Cl− − e− → Cl22NaCl → 2Na + Cl2
(a) What are amphoteric oxides? Give examples of two amphoteric oxides.
Answer: Metal oxides are generally basic in nature. But oxides of some metals show dual nature, i.e. acidic and basic nature. Examples: Al2O3 and ZnO
(b) What is Cinnabar? How is metal extracted from Cinnabar? Explain in brief.
Answer: Cinnabar (HgS) is the ore of mercury. Cinnabar (HgS) is first heated in air. This turns HgS [mercury sulphide or cinnabar] into HgO (mercury oxide); by liberation of sulphur dioxide.
Mercury oxide so obtained is again heated strongly. This reduces mercury oxide to mercury metal.
2HgS + 3O2 → 2HgO + 2SO2
2HgO → 2Hg + O2
(a) Write the name of different components of transport system in human beings and state their functions in brief.
Answer: Different Components of Transport System in Human Beings are as follows:
|Heart||Pumping the blood|
|Blood||Carrying food, oxygen and other materials|
|Blood Vessels||Serving as channel for blood flow|
(b) How is blood clot form, if a leak develops in the system of blood vessels?
Answer: In case of leak in the system of blood vessel, platelets and fibrin create a mesh-like structure at the site of injury. The mesh-like structure forms the clot.
Question 19: What is Pollination? How does it occur in plants? Explain how pollination leads to fertilisation.
Answer: Transfer of pollen grains from anthers to stigma is called pollination. Plants carry out pollination in two ways, viz. sel-pollination and cross-pollination.
Self Pollination: When pollen grains land on the stigma of the same flower, it is called self-pollination.
Cross Pollination: When pollen grains land on the stigma of a different flower, it is called cross-pollination. Plant takes help of various agents to facilitate cross-pollination.
After pollination, pollen grains germinate and produce pollen tubes. The pollen tube pierces through the style to reach the egg apparatus. Pollen nuclei are finally transferred to the egg apparatus and fertilization takes place.
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