SSC science

Ch. No. 1. SCHOOL OF ELEMENTS

Q1. A. Fill in the blanks.

1.     The formula of chloride of metal M is MCl₂. The metal M belongs to group 2.

2.     18^th group in the periodic table contains elements that are all gases at room temperature.

3.     The arrangement of elements in a group of three is known as ­traids.

4.     The law used by Newlands to arrange elements is known as Newlands’ Octaves.

5.     The element eka – aluminum in Mendeleev’s periodic table is known as Gallium in modern periodic table.

6.     Elements showing properties of both metals and non – metals are known as metalloids.

Q1. B. Match the columns.

Column I	Column II
1.     Sodium 2.     Cerium 3.     Sulphur 4.     Manganese	a.     Lanthanide b.     Metalloid c.      Transition metal d.     Noble metal e.     Metal f.       Non – metal.

Ans.

Column I	Column II
1.     Sodium 2.     Cerium 3.     Sulphur 4.     Manganese	e. Metal a. Lanthanide f. Non – metal c. Transition metal b. Metalloid

Q2. Give scientific reasons.

1.     Atomic size increases down the group.

Ans.

i.                 The atomic numbers of the elements increase as we go down the group. Thus, the elements placed lower have more electrons.

ii.               To accommodate these electrons new shells are added to the atom.

iii.              These new shells take the outermost electrons farther from the nucleus causing atomic size (radius) to increase as we go down the group.

2.     Metallic character decreases from left to right in a period.

Ans.

i.                 Atoms of metals tend to lose electrons, whereas those of non – metals tend to gain them.

ii.               In a period, as we go from left to right, atomic number increases, increasing the number of electrons and protons.

iii.              These additional electrons are placed in the same outer shell and are strongly attracted towards the positively – charged nucleus.

iv.              This strong attraction does not allow loss of electrons, causing metallic character to decrease from left to right in a period.

3.     Elements in the same group show the same valency.

Ans.

i.                 Valency is the number of electrons given, taken or shared by an atom to complete its outermost shell.

ii.               All the elements in the same group have the same number of electrons in their outermost shells.

iii.              Thus, all these elements take, give or share the same number of electrons.

iv.              Hence, elements in the same group show the same valencys.

Q3. Answer the following

1.     How could the modern periodic table remove various anomalies of Mendeleev’s periodic table?

Ans.

i.       A periodic table is a tabular arrangement of elements such that the elements can be classified on the basis of their common properties.

ii.     Properties of elements are related to their electronic configuration which in turn depends on their atomic numbers.

iii.    In the modern periodic table, the elements are arranged in the ascending order of their atomic numbers such that the elements having similar properties fall in the same group.

iv.    This arrangement removed various anomalies of Mendeleev’s periodic table which depended on atomic masses of the elements.

2.     In modern periodic table, which are the metals, non metals and metalloids among the first 20 elements?

Ans.  In the modern periodic table, among the first 20 elements, following are the metals, non – metals and metalloids.

Metals	Non  metals	Metalloids
Lithium (Li) Beryllium (Be) Sodium (Na) Magnesium (Mg) Aluminium (Al) Potassium (K) Calcium (Ca)	Hydrogen (H) Helium (He) Carbon (C) Nitrogen (N) Oxygen (O) Fluorine (F) Neon (Ne) Phosphorus (P) Sulphur (S) Chlorine (Cl) Argon (Ar)	Boron (B) Silicon (Si)

3.     What are the demerits of Mendeleev’s periodic table?

Ans.

i.                 Mendeleev could not assign a correct position to hydrogen in the periodic table as hydrogen resembles alkali metals as well as halogens.

ii.               Isotopes had to be given the same position in the periodic table though isotopes of the same elements have different atomic masses.

iii.              It was observed that at certain places, an element of higher atomic mass Cobalt (Co=58.93) has been placed before an element of lower atomic mass Nickel (Ni = 58.71).

iv.              Some elements placed in the same sub - group varies in their properties. Manganese is placed with halogens which totally differ in the properties.

4.     Define atomic size. How does it vary in a period and in a group?

Ans.

i.                 Atomic size is determined by the atomic radius.

ii.               For an isolated atom, its atomic radius is the distance between the centre of the atom (i.e. centre of its nucleus) and its outermost shell.

iii.              Generally, in the period, the atomic radius decreases from left to right.

iv.              In a group, the atomic radius increases from top to bottom.

Q. 4. Name

1.     Three elements having a single electrons in their outermost shell.

Ans.  Hydrogen, Lithium, Sodium, Potassium.

2.     Three elements with filled outermost shell.

Ans. Helium, Neon, Argon, Krypton, Xenon.

3.     Three elements having 7 electrons in their outermost shell.

Ans. Fluorine, Chlorine, Bromine, Iodine.

Ch. No. 2. THE MAGIC OF CHEMICAL REACTIONS

Q1. Fill in the blanks:

1.     The chemical formula of POP is 2CaSO­₄.H₂O.

2.     The chemical reaction during which H_2(g) is lost is termed as oxidation.

3.     Corrosion can be prevented by using anti-rust solution.

4.     When acids and alkalis react together, salt and water are formed.

5.     The chemical reactions is which heat is liberated are called exothermic reactions.

Q2. Match the following

Reactants	Products	Types of reactions.
Fe + S CuSO­4 + Zn 2Cu+O2 HCl + NaOH	NaCl + H2O 2CuO ZnSO4 + Cu FeS	Oxidation Neutralization Displacement Combination

Ans

Reactants	Products	Types of reactions.
Fe + S CuSO­4 + Zn 2Cu+O2 HCl + NaOH	FeS ZnSO4 + Cu 2CuO NaCl + H2O	Combination Displacement Oxidation Neutralization

Q3. Answer the following.

1.     What is the importance of a chemical equation?

Ans.  A chemical equation can convey the following information.

i.                 Reactants and products involved in the reaction.

ii.               Symbols and formulae of all substances involved in the reaction.

iii.              Relative number of reactants and product participating in the reaction.

iv.              Relative masses of reactants and products.

v.                Physical states of reactants and products.  

2.     What do you observe when H₂S gas is passed through Cadmium Chloride solution? Name the type of reaction.

Ans.

i.                 When H₂S is passed through cadmium chloride solution, yellow precipitate of cadmium sulphate and hydrochloric acid solution are obtained.

ii.               The reaction is a double displacement reaction.

        

3.     What do you understand by the term “Redox Reactions”? Explain with one example.

Ans.

i.                 When oxidation and reduction take place simultaneously in a given chemical reaction, it is called redox reaction or oxidation-reduction.

ii.               No oxidation can take place without reduction and there is no reduction without oxidation at the same time.

iii.              When carbon monoxide is passed over heated ferric oxide, carbon monoxide gains oxygen (i.e. gets oxidized) to form carbon dioxide. At the same time, iron oxide gets reduced to metallic iron by the loss of oxygen.

iv.              Fe₂O₃ + CO → 2Fe +2CO₂ ↑

4.     What is corrosion? Do gold ornaments corrode? Justify.

Ans.

i.                 The slow process of decay or distinction ions of a metal due to the effect of air, moisture, acids, alkalies, or other chemicals on it is called corrosion.

ii.               Ordinarily, gold ornaments do not get corroded.

iii.              Gold is one of the least reactive metals. It does not react with air, moisture, sweat, or ordinary pollutants in air or water. Hence, it does not get corroded.

Q4. Give scientific reasons.

1.     Grills of doors and windows are always painted before they are used.

Ans.

i.                 Usually grills of doors and windows are made of iron.

ii.               Iron objects get rusted on exposure to moist air.

iii.              Since air always contains moisture, iron grills get rusted.

iv.              Painting iron objects prevents rusting, hence iron grills of doors and windows are painted before they are used.

2.     Physical states of reactants and products are mentioned while writing a chemical equation.

Ans.

i.                 To make a chemical equation more informative, the physical states of the reactants and products are mentioned along with their chemical formulae.

ii.               The gaseous, liquid, aqueous and solid states of reactants and products are represented by the notations (g), (l), (aq) and (s) respectively.

iii.              The word aqueous (aq) is written if the reactant or product is present as a solution in water.  

3.     Potassium Ferrocyanide is stored in dark coloured bottles and kept away from sunlight.

Ans.

i.                 Potassium Ferrocyanide gets decomposed when exposed to bright light.

ii.               The dark colours of the bottles absorb a lot of energy from the light passing through it.

iii.              If stored in dark – coloured bottles, it does not get enough light energy to decompose.

iv.              Hence, potassium Ferrocyanide is stored in dark – coloured bottles and kept away from sunlight to prevent its decomposition.

4.     Iron articles rust readily whereas steel which is also mainly made of iron will not undergo corrosion.

Ans.

i.                 One of the properties of iron is that it reacts with oxygen in the presence of moisture and gets corroded by forming rust.

ii.               Air contains oxygen and moisture. Hence, iron readily rust when exposed to air.

iii.              Steel (stainless steel, not mild steel) is an alloy of iron having the property to resist corrosion including rusting.

iv.              Hence, stainless steel, though it contains iron, does not undergo corrosion.

5.     Edible oil is not allowed to stand for a long time in an iron or tin container.

Ans.

i.                 If edible oil is allowed to stand for a long time in an iron or tin container the fatty acids in the oil react with rust flakes or powder to form salts.

ii.               These salts contaminate the oil and hence the oil becomes rancid.

iii.              Rancid oils have a foul odour and unpleasant taste.

iv.              Thus, rancid oil is of no use. Hence, Edible oil is not allowed to stand for a long time in an iron or tin container to avoid rancidity.

6.     Edible oil is not allowed to stand for a long time in air.  

Ans.

i.                 When edible oils are left exposed to air for long period of time, they become rancid (i.e. the oils get oxidized.)

ii.               Rancid oils have a foul odour and unpleasant taste.

iii.              Thus, rancid oil is of no use.

iv.              Edible oils is not allowed to stand exposed to air for long to avoid rancidity.

Q5. We feel fresh while on a morning walk in natural surroundings. Why don’t we feel the same after 10 a.m. and during rush hours? Write a chemical reaction to support you statement?

Ans.

i.                 Early in the morning the air is fresh, has less pollutants due to low vehicular traffic. Breathing less polluted air gives us the feeling of freshness.

ii.               After 10 a.m. vehicular traffic increases. Fast moving vehicles raise dust in the air, and the partially burnt fuels set free carbon particles and carbon monoxide. The air also gets polluted with oxides of nitrogen and sulphur dioxide (diesel, petrol contains certain amount of sulphur.

iii.              Inhaling polluted air makes us feel tired.

iv.              (a) sulphur burns in the air to produce sulphur dioxide: S + O₂ → SO₂↑.

v.                Partial burning of carbon (petrol, diesel, being hydrocarbon contain carbon) which produced carbon monoxide: .

Q6. Explain the following terms:

Ans.

1.     Rancidity: Rancidity is a chemical process in which edible oils or fats get oxidized over a period of time and become inedible (unfit for human consumption) is called rancidity.

2.     Endothermic reactions: The reactions in which heat is absorbed are called endothermic reactions. The reactants absorb heat for form products.

3.     Redox reaction: The chemical reactions in which oxidation and reduction takes place simultaneously are called redox reactions. ‘Red’ stands for reduction and ‘ox’ stands for oxidation.

4.     Neutralization: The chemical reaction in which an acid and alkali (base) react together to form salt and water is called neutralization. The resulting solution is neither acidic nor basic but is neutral. This reaction is known as neutralization reaction.

Q7. Take finely powdered Zinc and allow it to react with CuSO₄ solution. Then take Zinc granules and carry out the same reaction. Which reaction will take place faster and why?

Ans.

i.                 The reaction between powdered zinc and copper sulphate solution is faster than that between zinc granules and copper sulphate solution.

ii.               This is because one of the factors that controls the rate of reaction is the size of the particles. The smaller the particles, the faster s the reaction.

iii.              Zinc granules are larger than powdered zinc. Hence, the rate of reaction is faster when powdered zinc is used.

Chemical Reaction between two elements.

Ch. No. 3. THE ACID BASE CHEMISTRY

Q1. Fill in the blanks:

1.     Most of the acidic substances are sour in taste.

2.     Phenolphthalein is synthetic type of indicator.

3.     The strength of basic substance is represented by pH.

4.     pH scale ranges from zero to fourteen.  

5.     Acids and bases neutralize each other to form salt and water.

6.     Sodium or potassium salts of higher fatty acids are termed as ­­­­­­­soap.

7.     In FeSO₄. 7H₂O.H₂O represents water of crystallization.

8.     10% NaCl is known as brine.

Q2. Name the carboxylic acids present in

	Acid		Acid
Tamarind Butter Roots of plant valerum Lemon	Tartaric acid Butyric acid ------------- Citric acid	Milk Orange Red ants Honey bee sting	Lactic acid Citric acid Formic acid Formic acid

Q3. Write short notes on

1.     Indicators (with proper example).

Ans. The acidic and basic nature of the compounds can also be indicated by some natural as well as chemical substances. These substances are known as indicators.

·       Rose petals

·       Turmeric

·       Beetroot are natural indicators.

i.                 Acid – base indicators: Some chemical substances such as phenolphthalein, methyl orange, eosin are synthetic indicators.

ii.               Olfactory indicators: Substances whose odour changes in acidic or basic solution are called olfactory indicator. An olfactory indicator works on the principle that when an acid or base is added to it, then its odour cannot be detected. Examples: onion and clove extract.

iii.              Universal indicators: Universal indicator is a mixture of several indicators which gives different colours at different pH values of the pH scale.

iv.              Uses of indicators: The acidic or basic nature of a compound can be judged. It is used in agriculture to determine the pH of the soil.

2.     pH scale (with proper diagram).

Ans.

i.                 The pH scale helps in measuring the concentration of hydrogen irons in a substance.

ii.               The pH scale has a range between 0 and 14.

iii.              pH 7 represents a neutral substance, i.e., a substance that is neither acidic nor basic.

iv.              An acidic substance has a pH value between 0 and 7. Whereas a basic substance has a pH between 7 and 14.

v.                Lower the pH of an acid, greater is the concentration of H+ ions, greater the pH of a base, greater is the concentration of OH ions.

3.     Water of crystallization (with proper example)

Ans.

i.                 Water of crystallization is the fixed number of water molecules present in the crystal structure.

ii.               For example, chemical formula of hydrated copper sulphate is CuSO₄.5H₂O. Copper sulphate has 5 molecules of water of crystallization.

iii.              Sodium carbonate is Na₂CO₃.10H₂O. Sodium carbonate has 10 molecules of water of crystallization.

iv.              On heating or on exposure to air, the above salts lose water of crystallization and form anhydrous substances.

Q4. Answer the following:

1.     How do metal carbonates react with acids?

Ans. When a metal carbonate or metal hydrogen carbonate reacts with an acid, it forms corresponding salt and carbon dioxide gas.

2.     Explain in detail about hydronium ion.

Ans.

i.                 The strength of an acid is measured in terms of the extent of ionization of the acid in aqueous solution.

ii.               Higher the H⁺ ions concentration stronger is the acid.

iii.              Hydrogen ion (H⁺) does not exist alone. H⁺ ion being unstable, it combines with H₂O to form hydronium ion (H₃O⁺).

3.     What is universal indicator? Does Mg(OH)₂ react with sodium hydroxide? If not, why?

Ans.

i.                 Universal indicator is an indicator which is a mixture of several indicators.

ii.               It has a very wide range and can indicate pH value almost from 0 to 14.

iii.              When one or two drops of universal indicator is added to a solution, it changes its colour. This colour is matched against the colour on a standard colour chart (usually given on its bottle) to find the pH, and the pH value can be read. This indicates the strength of the solution too.

iv.              Universal indicator is available as a solution or in the form of paper strips.

Mg(OH)₂ does not react with sodium hydroxide as both are bases.

4.     State application (uses) of baking soda.

Ans. Baking soda, also called sodium bicarbonate (NaHCO₃), has many applications.

i.                 It is used in preparing soft, fluffy food items such as loaves of bread, cakes and dhokla.

ii.               Being used to treat slightly alkaline hyperactivity in the stomach.

iii.              Its solution is used in fire extinguishers to produce carbon dioxide and water.

Q5. How do acids and bases react with each other? What is the name of the process? What product is obtained out of these reaction?

Ans.

i.                 Acid reacts with base to form salt and water.

ii.               It is known that, acid generates H⁺ and base generates OH^- ions.

iii.              The H⁺ ions of an acid and OH^- ions of a base react with each other to form unionized water. The process is termed as neutralization.

iv.              The product obtained out of this reaction is salt and water.

Ch. No. 4. THE ELECTRIC SPARK

Q1. Choose the correct alternative and rewrite the following:

1.     1mA = ___________ A

a.     10³A

b.    10 ^{– 3} A

c.      10⁶A

d.     10 ^{– 6} A

2.     To increase the effective resistance in a circuit, the resistors are connected in _________

a.     Series

b.     Parallel

c.      Both ways

d.     None of these

3.     1 kilowatt hr = ____________ Joules.

a.     4.6 x 10⁶ Joule

b.    3.6 x 10⁶ Joule

c.      30.6 x 10⁶ Joule

d.     3.6 x 10⁵ Joule

4.     If a P.D. of 12 V is applied across a 3Ω resistor, then the current passing through it is _______

a.     36A

b.    4A

c.      0.25A

d.     15A

Q2. State True or False. If false correct it.

1.     The SI unit of charge is volt.

False: The SI unit of charge is the coulomb and the SI unit of P.D. is Volt.

2.     A voltmeter is always connected in series with the device.

False: A voltmeter is always connected in series with the device.

3.     The conventional direction of flow of current is from positive terminal to negative terminal of the cell.

Ans. True

4.     Silver and copper are good conductors.

True

5.     Resistivity of pure meal is more than alloys.

False: Resistivity of pure metals is less than that of alloys.

6.     The electric bulb consists of the filament whose melting point is low.

False: The electric bulb consists of the filament whose melting point is high.

Q3. Match the column.

I	II	III
Heat generated	Is used to reduce effective resistance in a circuit	V = IR
Resistance in parallel	Proportional to the square of current
Resistivity	Gives relation between V and I
Ohm’s law	Depends on the material of the conductor

Ans.

I	II	III
Heat generated	Proportional to the square of current
Resistance in parallel	Is used to reduce effective resistance in a circuit
Resistivity	Depends on the material of the conductor
Ohm’s law	Gives relation between V and I

Q4. Give scientific reasons.

1.     The material used for fuse has low melting point.

Ans.

i.                 A fuse is used to protect a circuit and the appliances connected in the circuit by stopping the flow of an excess electric current. For this, a fuse is connected in series in the circuit.

ii.               When the current in the circuit passes through the fuse, its temperature increases. When the current exceeds the specified value, the fuse must melt to break the circuit. For this, the material used for a fuse has low melting point.

2.     Wood and glass are good insulators.

Ans.

i.                 When a current flows through a conductor, the free electrons in the atoms move from one end of the conductor to the other.

ii.               Certain materials have less free electrons in their atoms and the current does not easily flow through the material.

iii.              There are no such free electrons in wood and glass. Hence they cannot conduct electricity. Hence, they are good insulators.

3.     The melting point of filament of a bulb is very high.

Ans.

i.                 The bulb begins to glow only when the filament is heated to a high temperature, and it becomes incandescent (bright) without melting.

ii.               This happens only when the material of the filament has a high melting point.

iii.              Hence, the material used in the filament of an electric bulb must have a high melting point.

4.     Connecting wires in a circuit are made of copper and aluminium.

Ans.

i.                 Copper and aluminium offer a low resistance to the flow of current and hence they are good conductors of electricity.

ii.               Copper and aluminium are highly ductile and hence can be used for preparing this wire.

iii.              Copper being more ductile, it is used in making thing wires, and aluminium is used for making thicker wires.

iv.              Thus, they are suitable for making wires used in electrical circuit.

Q5. Define

1.     1 volt: The potential difference between two points is said to be 1 volt if 1 joule of work is done in moving 1 coulomb of electric charge from one point to another.

2.     1 ampere: 1 coulomb of charge passing through a cross – section of a conductor in 1 second is one ampere. It is the S.I. unit of an electric current.

3.     1 ohm: If one ampere current flows through the conductor, and 1 volt potential difference is applied across it, then its resistance is 1 ohm.

4.     Potential: Electric potential is the electrical level.

5.     Resistivity: The resistivity of a conductor is defined as the resistance of a conductor of unit length and the unit area of the cross – section.

6.     Electric power: Electric power is the rate at which electric energy is consumed. It is the electrical work done per unit time.

Q6. Differentiate between.

1.     Resistances in series and parallel.

Resistance in series

Resistance in parallel

1.     If a number of resistances are connected in such a way that the same current flows through each resistance, then the arrangement is called resistances in series. 2.     The effective resistance is a series combination is greater than the individual resistances. 3.     This combination is used to increase resistance in a circuit. 4.     This combination decreases the current in the circuit.

1.     If a number of resistances are connected between two common points such that the potential difference across each is the same then that arrangement is called resistances in parallel. 2.     The effective resistance of the combination is less than the individual resistances. 3.     This combination is used to decrease resistance in the circuit. 4.     This combination increases the current in the circuit.

2.     Conductors and insulators.

Conductors	Insulators
1.     Those substances through which electricity can flow are called conductors. 2.     Electrical resistances of conductors are very low. 3.     They contain large number of free electrons. 4.     Generally metals are conductors. E.g. silver, copper, aluminium	1.     Those substances through which electricity cannot flow are called insulators. 2.     Electrical resistances of insulators are infinitely very high. 3.     They do not contain free electrons. 4.     Generally non – metals are insulators. E.g. wood, rubber, plastic

3.     Resistance and resistivity.

Resistance	Resistivity
1.     The property of the conductor due to which it opposes flow of current through it is called resistance. 2.     The SI unit of resistance is Ohm ( ) 3.     The resistance of a conductor is inversely proportional to its area of cross section. This means that a thick wire has less resistance.	1.     Resistivity of a conductor is the resistance of a conductor of unit length and unit area of cross section. 2.     The SI unit of resistivity is Ohm metre ( m) 3.     Resistivity is independent of the shape and size of the conductor.

4.     High resistance and low resistance.

High resistance	Low resistance
1.     A high resistance indicates a material that hardly allows the movement of electrons. 2.     It is due to the less number of free flowing electrons in the outer most orbit of an element. 3.     Substances with infinitely high electrical resistance are insulators. 4.     High resistance provides low conductivity.	1.     A low resistance indicates a material that readily allows the movement of electrons. 2.     It is due to large number of electrons in the outer most orbit of an element. 3.     Substances with low electrical resistances are good conductors. 4.     Low resistance provides high conductivity.

Q7. State the laws:

1.     Ohm’s law: Ohm’s law states that the electric current flowing in a metallic conductor is directly proportional to the potential difference across its terminals, provided physical conditions of the conductor such as length, area of cross section, temperature and material remain constant.

If I is the current and V is the potential difference across the ends of a conductor then,

R is the resistance which is constant for given conductor. The SI unit of resistance is ohm (W)

2.     Joule’s law: - Joule’s law states that the quantity of heat generated (H) is a conductor of Resistance (R), when a current (I) flows through it for a time (t) is directly proportional to:

i.                 The square of the current.

ii.               The resistance of the conductor, and

iii.              The time for which the current flows.

Q8. Find the following.

a.     Find the expression for the resistors connected in series and parallel.

Ans.  

i.                 Resistors connected in series: - If the number of resistance are connected one after another in such a way that the same current flows through each resistance, then the arrangement is called resistance in series.

1.      LetR_1, R₂ and R₃ are three resistances connected in a series combination and let R be their equivalent resistance.

Let V_1, V₂ and V₃ be the P.D. across resistances R_1, R₂ and R₃ respectively.

Let ‘V’ be the P.D. of the cell.

Let ‘I’ be the current flow through each resistance.

2. According to Ohm’s Law,

                                                       

Conclusion

Therefore, equivalent resistance in series(R) is equal to the sum of the individual resistances

ii.               Resistors connected in parallel: If the numbers of resistance are connected between two common points, such that the potential difference across each resistance is the same, then the arrangement is called resistance in parallel.

Three resistances R_1, R₂ and R₃ are connected in parallel between the points A and B. Let R be the equivalent resistance of the parallel combination.

               A Cell E, Key K and the ammeters A are also connected with resistances.

               Let the current passing through R1 be I_1, R₂ be I₂, and R₃ be I_3­ and that of R be I.

 Conclusion

Thus, the reciprocal of the equivalent resistance is equal to the sum of the reciprocal of the individual resistance.

b.     Find the expression for resistivity of a material.

Ans. Resistance R of a conductor depends on the length ‘  and area of cross section  of the conductor.

Where (rho) is called resistivity of the conductor it is also called as specific resistance.

If we put  and  then

Conclusion

Thus, resistivity of a conductor is defined as the resistance of a conductor of unit length and unit area of cross section.

Q9.  Answer the following:

1.     P and Q are the two wires of same length and different cross sectional areas and made of same metal. Name the property which is same for both the wires and that which is different for both the wires.

Ans.

i.                 The property which is same for both the wires is resistivity. 

ii.               The property which is different for both the wires is resistance.

2.     Resistivity of some material is given below. State which one will be the best conductor.

Material	Copper	Aluminium	Silver	Nickel
Resistivity (Ωm)	1.62 x 10 – 8	2.63 x 10 – 8	1.60 x 10 – 8	6.48 x 10 – 8

Ans. From the above table we find that of all the metals, silver has the lowes resistivity (1.60 x 10 ^{– 8} Ωm), which means that silver offers the least resistance to the flow of current through it. Thus, silver metal is the best conductor of electricity.

3.     If the resistance of wire A is four times the resistance of wire B, find the ratio of their cross sectional areas.

Ans. Let resistance of wire  be  and that of wire B be .

   

  ----------------------equation number (1)

 

  (  is a constant called resistivity)

 

 

 

  --------------------------- from equation number (1)

 

 ratio of cross sectional areas of wires is 1:4.

4.     Two dissimilar bulbs are connected in series, which bulb will be brighter? (Hint: consider the resistance of the bulb).

Ans. When two bulbs are connected in series the first bulb will receive more current. As the bulb has its own resistance, less current will flow to the next bulb. Hence the first bulb will glow more.

Do you know?

James Joule

James Prescott Joule (December 24, 1818 - October 11, 1889) was an English physicist, born in Salford, near Manchester, England. Joule studied the nature of heat, and discovered its relationship to mechanical work (see energy). This led to the theory of conservation of energy (the First Law of Thermodynamics). The SI unit of work, the joule, is named after him. He worked with Lord Kelvin to develop the absolute scale of temperature, made observations on magnetostriction, and found the relationship between the flow of current through a resistance and the heat dissipated, now called Joule's law.

Ch. No. 5. All about Electromagnetism

Q1. (A) Choose the correct alternative and rewrite the following.

1.     The device used for producing current is called a ___________

a.     Voltmeter

b.     Ammeter

c.      Galvanometer

d.     Generator

2.     At the time of short circuit, the current in the circuit __________

a.     Increases

b.     Decreases

c.      Remains the same

d.     Increases in steps

3.     The direction of the magnetic field around a straight conductor carrying current is given by ____________

a.     Right hand thumb rule

b.     Fleming’s left hand rule

c.      Fleming’s right hand rule

d.     None of these.

(B) Say true or false. If false, write the correct sentence.

1.     Magnetic poles exist in pairs.

Ans. True

2.     Magnetic field increases as we go away from a magnet.

Ans. False:- Magnetic field decreases as we go away from a magnet.

3.     Magnetic lines of force always cross each other.

Ans. False:- Magnetic lines of force never cross each other.

4.     Electric generator is used to generate current.

Ans. True

(C) Find the odd one out.

1.     Loudspeaker, microphone, electric motor, bar magnet.

Ans. Bar Magnet: - It is a magnet while the rest are devices working on electromagnetism.

2.     Armature coil, brushes, commutator, direct current.

            Ans. Direct current: - The rest are parts of a generator.

3.     Fuse, insulating material, rubber shoes, generator.

Ans. Generator: - The rest are safety measures in using electricity.

4.     Voltmeter, ammeter, galvanometer, thermometer.

Ans. Thermometer: - The rest are dives working on electromagnetism.

Q2. Define

1.     Magnetic field: - The region around magnet, in which the force of attraction and repulsion exists, is called as ‘magnetic field’.

2.     Solenoid: - A coil of many turns of insulated copper wire wrapped in the shape of cylinder is called a solenoid.

3.     Electric motor: - A device which converts electrical energy into mechanical energy is called an electric motor.

Q3. State the rules

1.     Fleming’s right hand rule

Ans.

i.                 Stretch the thumb, forefinger and middle finger of the right hand so that they are perpendicular to each other.

ii.               If the forefinger indicates the direction of the magnetic field and the thumb shows the direction of the motion of conductor, then the middle finger will show the direction of induced current.

2.     Right hand thumb rule

Ans.

Imagine that you are holding a current carrying straight conductor in your right hand such that the thumb points towards the direction current, then the curled fingers around the conductor will give the direction of the magnetic field. This is known as right hand rule.

Q4. Distinguish between electric motor and electric generator.

Electric motor	Electric generator
1.     Electric motor converts electrical energy into mechanical energy. 2.     It uses electricity. 3.     It is based on the principle that current carrying conductor placed in a magnetic field experiences a force.	1.     Electric generator converts mechanical energy into electrical energy. 2.     It generates electricity. 3.     It is based on the principle of electromagnetic induction.

Q5. State the characteristics of magnetic lines of force.

Ans. The characteristics of magnetic lines of force are:

1.     Magnetic lines of force are closed continuous curves. They start from North Pole and ends on South Pole.

2.     The tangent at any point on the magnetic lines of force gives the direction of the magnetic field at that point.

3.     No two magnetic lines of force can intersect each other.

4.     Magnetic lines of force are crowded where the magnetic field is strong and far from each other where the field is weak.

Q6. Give scientific reasons.

1.     Wires carrying electricity should not be touched bare footed.

Ans.

i.                 Our body is a good conductor of electricity.

ii.               If we touch the wire bare footed, a large current may pass through our body.

iii.              Due to this, we may receive severe electric shock and sometimes even death.

iv.              Therefore, wires, carrying electricity should not be touched bare footed.

2.     We should not use many electrical appliances simultaneously.

Ans.

i.                 Many of the electrical appliances that we use at home have a high power rating. E.g. grinder, A.C, Oven, washing-machine, etc.

ii.               When we use these electrical appliances simultaneously, it causes overloading, that is flow of large amount of current in the circuit, occurs.

iii.              This causes fire.

iv.              Hence, we should not use many electrical appliances simultaneously.

3.     Alloys like alnico or nipermag are used in industry.

Ans.

i.                 Alloys like alnico or nipermag are very hard and are used in the production of permanent magnets.

ii.               Permanent magnets of these alloys are used in microphones, loudspeaker, ammeters, voltmeters, etc.

iii.              Alnico is an alloy of iron containing aluminium, nickel and cobalt. Nipermag is an alloy of iron containing nickel, aluminium and titanium.

iv.              Hence, permanent magnets prepared from these alloys are most suitable for use in industries.

4.     A magnetic crane is used to load and transport scrap iron.

Ans.

i.                 It is not feasible to create a permanent magnet of a big size required to load and transport scrap iron.

ii.               It is also not possible to store such a big magnet.

iii.              Hence, we create a powerful electromagnet by passing a current through a big iron disc.

iv.              Therefore, a magnetic crane is used to load and transport scrap iron.

Q7. Explain the construction and working of

1.     Electric motor.

Ans.

      Principle: - An electric motor converts electrical energy into mechanical energy.

      Construction: - The main parts of an electric motor are

i.                 Armature coil: - It consists of a large number of turns of insulated copper wire wound around a rectangular iron core (ABCD)

ii.               Strong magnet: - The armature coil is placed between the poles of a strong magnet to create a strong magnetic field.

iii.              Split ring commutator:- A metallic ring divided into two halves (R­­₁ and R₂). The ends of the armature are connected to the two rings. This commutator helps to reverse the direction of the current in the armature coil.

iv.              Brushes: - Two carbon brushes B₁ and B₂, used to press upon the commutator.

v.                Battery: - it supplies the current (D.C.) to the armature coil.

Working: -

i.                 When current is passed through the coil ABCD, arms AB and CD experience force in the downward and upward direction respectively.

ii.               These equal and opposite forces rotate the coil in clockwise direction until the coil is vertical.

iii.              At this position, the contact between commutator and brushed breaks, the supply to the coil is cut off and no force acts on the coil.

iv.              But the coil goes on rotating due to inertia until the commutator again comes in contact with the brushed B₁ and B₂.

v.                Again the current starts passing through the coil and the arm AB rotates through 90⁰, 180⁰, 270⁰ and 360⁰.

vi.              Now, the force acting on arm AB and CD is downward and upward respectively which moves the coil again in clockwise direction.

2.     Electric generator.

Ans. An electric generator is a device used to convert mechanical energy into electrical energy. It works mainly on the principle of electromagnetic induction. There are two types of electrical generators – A.C. generator and D.C. generator.

Construction:-  The main components of an AC generator are: -

i.                 Armature coil: -  A large number of turns of insulated copper wire wound on iron core in rectangular shape forms an armature coil ABCD.

ii.               Strong magnet: -  the armature coil is placed in between two poles of a strong magnet which provides a strong magnetic field.

iii.              Split rings: - The two ends of the armature coil are connected to two brass split rings R₁ and R₂ which rotate along with the armature coil.

iv.              Brushes: - Two carbon brushes B₁ and B₂ are used to press the split rings.

Working: -

1.     When the armature coil ABCD rotates in the magnetic field provided by the strong magnets, it cuts the magnetic lines of forces.

2.     Thus, the changing magnetic field produces induced current in the coil.

3.     The current flows out through the brush B₁ in one direction in the first half of the revolution and through the brush B₂ in the next half revolution in the reverse direction, this process is repeated.

4.     Therefore, the induced current produced is of alternating nature.

Ch. No. 6. Wonders of Light Part – I

Q1. Fill in the blanks

1.     A ray of light parallel to principal axis after reflection from concave mirror passes through ________. (Focus)

2.     The focal length of ____________ lens is positive. (convex)

3.     The image of an object is formed behind __________ in hypermetropia. (retina)

4.     An optical device used by watch repairers is _____________. (simple microscope)

5.     The power of spectacle for myopic eye is _____________. (negative)

Q2. Rewrite the following table so as to match second and third column with first column.

Column I	Column II	Column III
1.     Myopia	Old age problem	Convex lens
2.     Hypermetropia	Near – sightedness	Bifocal lens
3.     Presbyopia	Long  - sightedness	Concave lens

1.     Myopia	Near sightedness	Concave lens
2.     Hypermetropia	Long sightedness	Convex lens
3.     Presbyopia	Old age problem	Bi-focal lens

Q3. Answer the following

1.     State the different positions of source of light with respect to concave mirror-

a.     In torches

b.     Projector lamps

c.      Flood lights.

Ans.

i.                 In torches: - The source of light is placed at the focus.

ii.               Projector lamps: - The object is placed at the center of curvature.

iii.              Flood lights: - The source of light is placed just beyond the centre of curvature.

2.     What is ray diagram? What are the rules used for drawing ray diagrams for the formation of image by spherical mirror?

Ans.  A ray diagram is a specialized pictorial representation used to trace the path of light rays.

The rules used for drawing ray diagrams are as follows.

i.                 If the incident ray is parallel to the principal axis, then reflected ray passes through the focus.

ii.               If the incident ray passes through the focus then the reflected ray becomes parallel to the principal axis.

iii.              If the incident ray passes through the centre of the curvature, the reflected ray traces the same path.

3.     What is meant by power of accommodation of eye?

Ans.

i.       The ability of the lens of adjusting focal length is known as power of accommodation.

ii.     The process of focusing the eye at different distances is called accommodation.  

4.     State the function of iris and ciliary muscles in human eye.

Ans.

                 I.          Iris in human eye controls and regulates the amount of light entering the eye by contracting and dialating the pupil.

               II.          Ciliary muscles adjust the focal length of eye lens by contracting and relaxing.

5.     If you are given a part of hollow spherical glass, how will you convert it into concave mirror?

Ans. The inner side or concave side of the hollow spherical glass will be polished to get a concave mirror.

Q4. Distinguish between.

1.     Myopia and Hypermetropia

Myopia	Hypermetropia
1.     In this defect human eye can see nearby objects distinctly but is unable to see distant objects clearly. 2.     Image of distant object is formed in front of retina. 3.     Eye ball is lengthened or lens is curved. 4.     This defect is corrected using concave lens.	1.     In this defect human eye can see distant objects distinctly but is unable to see nearby objects clearly. 2.     Image of nearby objects falls behind retina. 3.     Eye ball is shortened or lens is flattened. 4.     This defect is corrected using convex lens.

2.     Convex mirror and concave mirror.

Convex mirror	Concave mirror
1.     It is called as diverging mirror. 2.     The light is reflected from outer surface. 3.     Centre of curvature and focus lies behind the mirror. 4.     According to sign convention, focal length is positive.	1.     It is called as converging mirror. 2.     The light is reflected from inner surface. 3.     Centre of curvature and focus lies in front of the mirror. 4.     According to sign convention, focal length is negative.

Q5. Give reasons:

1.     You cannot enjoy watching a movie from a very short distance from the screen in a cinema hall.

Ans.

i.                 If the object is too close, the eye lens cannot curve enough to focus the image on to the retina.

ii.               Therefore, while watching a movie from a very short distance a blurred image is formed causing strain to the eyes.

iii.              Hence, one cannot enjoy watching a movie from a very short distance from the screen in a cinema hall.

2.     A simple microscope is used by watch repairers.

Ans.

i.                 A magnification of about 20 times is obtained by the convex lens of small focal length used in a simple microscope.

ii.               Therefore, it is used by watch repairers to see the minute parts of the watch clearly without causing any strain to the eyes.

3.     A concave lens is used to correct myopia.

Ans.

i.                 In myopia the image of distant object is formed in front of retina.

ii.               A concave lens causes light rays to diverge before they strike the lens of the eye so that the image is formed on the retina.

iii.              Hence, a concave lens is used to correct myopia.

4.     In old age bifocal lens is necessary for some persons.

Ans.

i.                 In old age, sometimes person suffers both myopia and hypermetropia and then the person needs bifocal lens.

ii.               In bifocal lens, upper part is concave lens to correct myopia and lower part is convex lens to correct hypermetropia.

5.     Concave mirrors are used in solar devices.

Ans.

i.                 Concave mirrors are used in solar devices to collect heat and radiations.

ii.               Heat radiations from the sun coming from infinity are brought to focus by concave mirror in its focal plane.

Q6. Draw well labeled ray diagrams for image formation by convex lens when

1.     Object is at 2F₁.

Position of image: -At 2F₂

Nature of image: - Real, Inverted and same size as that of the object.

2.     Object between F₁ and 2F₁

Position of image: - Beyond 2F₂

Nature of image: -  Real, inverted and magnified.

3.     Object between focus F₁ and optical center O.

Position of image: - On the same side of the lens as the object.

Nature of image: - Virtual, erect and magnified.

Q7. Draw ray diagram for concave mirror when

1.     Object at centre of curvature.

2.     Object at focus.

3.     Object between centre of curvature and focus.

Q8. Given below is a diagram showing a defect of human eye.

Study it and answer the following questions:

1.     Name the defect shown in figure.

2.     Give two possible reasons for this defect of eye in human being.

3.     Name the type of lens used to correct the eye defect.

4.     Draw a labeled diagram to show how the defect is rectified by using the lens.

Ans.

1.     The defect of vision is hypermetropia.

2.     The two possible reasons of hypermetropia are:

a.     Weak action of ciliary muscles cause low converging power of eye lens.

b.     The distance between eye lens and retina decreases on account of either shortening of eyeball or flattening of lens.

3.     The defect is corrected using convex lens.

4.     The convex lens converges the light rays and image is now formed on the retina.

Q9. Fill in the blanks for convex lens.

	0.2	…	0.1
P(D)	…	2	…

Ans.

	0.2	0.5	0.1
P(D)	5	2	10

	…	5	10
	- 30	- 20	….
M	-2	…	-0.5

Ans.

	15	5	10
	- 30	- 20	5
M	-2	-4	-0.5

Ch. No. 7. Wonders of light – part II

Q1. Fill in the blanks

1.     The phenomenon of splitting of light into its component colours is ____________ (dipersion)

2.     Very fine particles mainly scatter ___________ light. (blue)

3.     The phenomenon of change in the ___________ of light when it passes from one transparent medium to another is refraction. (direction)

4.     The refractive index depends upon the ___________ of propagation of light in different media. (relative speed)

Q2. Rewrite the following table in such a way that column 2 and column 3 matches column 1.

Column 1	Column 2	Column 3
Dispersion	Change in the direction of ray of light due to change in medium.	Blue colour of the sky.
Scattering	Splitting of white light into component colours	Twinkling of stars.
Refraction	Deflection of light by small particles	Spectrum of seven colours.

Ans.

Column 1	Column 2	Column 3
Dispersion	Splitting of white light into component colours	Spectrum of seven colours.
Scattering	Deflection of light by small particles	Blue colour of the sky.
Refraction	Change in the direction of ray of light due to change in medium.	Twinkling of stars.

Q3. Answer the followings.

1.     What do you mean by dispersion? Name the different colours of light in the proper sequence in the spectrum of light.

Ans.

i.                 The phenomenon of splitting of white light into its component colours is dispersion.

ii.               The various colours in the spectrum of light are in the sequence:  Violet, indigo, Blue, Green, Yellow, Orange and Red.

2.     Explain how the formation of rainbow occurs.

Ans.

1.     The beautiful phenomenon of the rainbow is a combination of different phenomena – dispersion, refraction and reflection of light.

2.     The rainbow appears in the sky after a rain shower.

3.     The water droplets act as a small prisms.

4.     When sunlight enters the water droplets present in the atmosphere, they refract and disperse the incident sunlight.

5.     Then they reflect it internally inside the droplet and finally again refract it.

6.     As a collective effect of all the phenomena, the seven coloured rainbow is observed.

3.     What is refraction of light? How is it related to refractive index?

Ans.

i.                 The phenomenon of change in the direction of light when it passes from transparent medium to another is called dispersion of light.

ii.               The extent of change in the direction of the light ray is different for different media and it is related to the refractive index of the medium.

Q4. Give reasons.

1.     The sky appears dark instead of blue to a person located in space.

Ans.

i.                 At very high altitudes, there is no atmosphere.

ii.               Since there is no atmosphere, the scattering of light does not take place at all.

iii.              Hence, the sky appears dark instead of blue to a person located in space.

2.     Stars twinkle at night.

Ans.

i.                 In the atmosphere, there are different layers of air with different refractive indices which keep on changing.

ii.               When we observe the stars through this air the light coming from them refract randomly so that the intensity of light varies due to which the apparent position of the star fluctuates.

iii.              When more light reaches our eyes the star is seen bright and when less light reaches our eyes, the star is seen dim.

iv.              Thus, due to change in refractive index of atmosphere, stars appear twinkling at night.

3.     The sun appears reddish early in the morning.

Ans.

i.                 At the time of sunrise, the blue and violet colours are scattered away from the path of sunlight as thickness of the atmosphere is more between the horizon and the observer.

ii.               The light that reaches to the observer is mostly red.

iii.              Hence the sun appears reddish early in the morning.

4.     It is possible to enjoy a rainbow at fountains in any season.

Ans.

i.                 One can observe and enjoy the rainbow by standing in front of a water fountain in the evening facing the east.

ii.               One can also enjoy it in the morning under the same conditions just by facing the west.

iii.              Therefore, it is possible to enjoy a rainbow at fountains in any season.

Q5. Write short notes on

1.     Refraction observed in the atmosphere.

Ans.

i.                 In the atmosphere, there are different layers of air with different refractive indices which keep on changing as the physical conditions of air are not stationary (still).

ii.               When we observe any object through this air, the light coming from them refract randomly due to which the apparent position of the object fluctuates.

iii.              The large scale effect of this phenomenon is the twinkling of stars, advanced sunrise and delayed sunset.

iv.              Due to change in the refractive index of atmosphere, the intensity of light that reaches our eyes from the stars varies and hence the stars appear twinkling at night.

v.                Advanced sunrise occurs as a ray of light from the sun enters the earth’s atmosphere; it follows a curved path due to refraction before reaching to the observer.

vi.              It appears to the observer as if the rays are coming from the position where the sun is seen by the observer, hence, the sun is seen earlier before it reaches the horizon.

2.     Dispersion of light.

Ans.

       i.          The phenomenon of splitting of light into its component colours is dispersion of light.

     ii.          The band of coloured components of a light beam is called it’s spectrum.

    iii.          When White light is dispersed into seven colours by a prism, different colours of light bend through different angles with respect to incident ray.

    iv.          Out of these seven colours, red light bend the least while violet light bends the most.

      v.          So the rays of each colour emerge along different paths and become distinct.

    vi.          Hence we get a spectrum of seven different colours in the sequence, Violet, Indigo, Blue, Green, Yellow, Orange and Red.

Ch. No. 8. Understanding Metals and Non – metals

Q1. Name the following:

1.     Metal which forms an amphoteric oxide?

Ans. Aluminium.

2.     An alloy of copper and zinc.

Ans. Brass

3.     A compound which is added to lower the fusion temperature of an electrolytic bath in extraction of aluminium.

Ans. Cryolite.

4.     A metal which does not react with cold water but reacts with steam.

Ans. Aluminium.

5.     A common ore of aluminium.

Ans. Bauxite.

Q2. From the list of characteristic given below select the five which are relevant to metals and their compounds.

1.     Ductile

2.     Conduct electricity

3.     Acidic oxide.

4.     Discharged at anode basic oxides.

5.     Brittle

6.     (1,2,3) valence electrons.

7.     Discharged at cathode.

8.     (5,6,7) valence electrons.

9.     Occurring in solid or gaseous state.

10.  Basic oxides.

Ans. Characteristic of metals are:

1.     Ductile

2.     Conduct of electricity.

3.     Basic oxides

4.     (1,2,3) valence electrons.

5.     Discharged at cathode.

Q3. Name one metal each occurring as,

1.     A sulphide.

Ans. Copper

2.     A carbonate

Ans. Zinc

3.     An oxide

Ans. Aluminium

Q4. Explain the following terms.

1.     Minerals: - The naturally occurring compounds of metals along with other impurities are known as minerals.

2.     Gangue: - Ores contain metal compounds with some of the impurities like soil, sand, rocky material etc. These impurities are called as gangue.

3.     Ores: -The minerals from which metals are extracted profitably and conveniently are called ores.

4.     Metallurgy: - The process used for extraction of metals in their pure form from their ores is called metallurgy.

5.     Roasting: - The sulphide ores are first converted into oxides by heating strongly in excess of air. This process is called as roasting.

Q5. Give scientific reasons for the following.

1.     Sodium is stored under kerosene.

Ans.

i.                 Sodium is a highly reactive metal.

ii.               Sodium reacts with oxygen in air at room temperature to form, sodium oxide.

iii.              Therefore, it catches fire and starts burning when open in the air.

iv.              Hence, sodium is stored under kerosene to prevent its reaction with oxygen, moisture and carbon dioxide.

2.     Gold and silver are used to make jewellery.

Ans.

i.                 Gold and silver are highly inactive metals. Therefore, they do not undergo corrosion due to attack by moisture and atmospheric gases.

ii.               Gold and Silver are very shiny metals (lustrous).

iii.              They are used to make jewellery because of its bright shiny surface and high resistance to corrosion.

3.     Calcium floats over water during the reaction with water.

Ans.

i.                 Calcium reacts with water less vigorously so that the heat evolved is not sufficient for the hydrogen formed, to catch fire.

ii.               Instead, calcium starts floating because the bubbles of hydrogen gas formed stick to the surface of the water calcium.

4.     Ionic compounds have high melting and boiling points

Ans.

i.                 Ionic compounds are solids and hard due to strong force of attraction between positive and negative ions in their molecules.

ii.               A considerable amount of energy is required to break the strong inter molecular attraction.

iii.              Hence ionic compounds have high melting and boiling points.

5.     Tarnished copper utensils are cleaned with lime juice or tamarind.

Ans.

i.                 When copper utensils are exposed to moist air, they get tarnished or corroded due to the formation of green copper carbonate.

ii.               When these tarnished vessels are rubbed with lime juice or tamarind the weak acids present in them dissolve the green copper carbonate and original shine returns.

Q6. Sudha dipped a copper coin in  a solution of silver nitrate. After some time she saw the silver shine on the coin. Why? Give the balanced chemical equation for the same.

Ans.

1.     Copper is more reactive than silver. Hence displacement reaction occurs.

2.     When copper coin is dipped in silver nitrate solution forming copper nitrate and silver metal.

3.     A shining white deposit of silver metal is formed on copper coin. Hence she saw a silver shine on the copper coin.

Balanced equation:-

2AgNO_3(ag) + Cu_(s) → Cu(NO₃)_2(ag) + 2Ag_(s)

Q7. Metal A has electronic configuration of 2,8,1 and metal B has 2,8,8,2 which is more reactive. Identify these metals and vie their reactions with dil HCl.

Ans. Metal A is Sodium (Na) : 2,8,1

Metal B is Calcium (Ca) : 2,8,8,2.

Metal A (Sodium) is more reactive than metal B (Calcium).

Reaction: -

i.                 Sodium metal reacts violently with dilute hydrochloric acid to form sodium chlorides and hydrogen.

2Na_(a) + 2HCl_(aq) → 2NaCl_(aq) + H_2(g)

ii.               Calcium reacts less vigorously to form calcium chloride and hydrogen.

Ca + 2HCl → CaCl₂ + H₂

Q8. To obtain (zinc) Zn from zinc sulphide two chemical reaction are involved

Write the equations for A and B.

Ans. Equation for A:  Roasting is the process in which a sulphide ore is strongly heated in the presence of air to convert it into metal oxide.

Equation for B : Zinc metal is extracted by the reduction of its oxide with carbon (or coke). Thus, when, Zinc oxide is heated with carbon, Zinc metal is produced.

Q9. Translate the following statements into chemical equation and then balance them.

1.     When steam is passed over aluminium.

Ans. Aluminium reacts with steam to form aluminium oxide and hydrogen gas.

2.     Extraction of copper from its sulphide ore.

Ans.

i.                 The concentrated copper sulphide ore is roasted in air when a part of copper sulphide is oxidized to copper oxide.

ii.               Copper oxide formed above reacts with the remaining copper sulphide to form copper metal and sulphur dioxide.

3.     Thermit reaction.

Ans. Iron oxide reacts with aluminium to give iron and aluminium oxide evolving lot of heat.

4.     When magnesium reacts with hot water.

Ans. Magnesium reacts with hot water to form magnesium hydroxide and hydrogen.

5.      What happens when aluminium oxide dissolves in aqueous sodium hydroxide?

Ans. Aluminium oxide being amphoteric in nature dissolves in aqueous sodium hydroxide to form water soluble sodium aluminate.

Q10. In the extraction of aluminium

1.     Name the process of concentration of Bauxite.

2.     Write the cathode reaction in electrolytic reduction of alumina.

3.     Write the function and formula of cryolite in the extraction of aluminium.

4.     Write an equation for the action of heat on aluminium hydroxide.

5.     Draw the diagram of extraction of aluminium.

6.     Why is it necessary to replace anodes time to time?

7.     What happens when aluminium ore is heated with concentrated caustic soda. Write the balanced chemical equation for the same.

Ans.

i.                 The process of concentration of Bauxite is done by Bayer’s Process.

ii.               The positively charged aluminium ions (Al³⁺) are attracted to the cathode (negative electrode). The aluminium ions accept electrons from the cathode and get reduced to form aluminium atoms (or aluminium metal).

Cathode reaction :

iii.              Alumina has a very high melting point (>2000⁰C). Cryolite lowers the fusion temperature from 2000⁰C to 1000⁰C and enhances conductivity.

Chemical formula of cryolite: 

iv.              Equation: 

v.                Diagram

vi.              As the anode gets oxidized during the electrolysis of alumina. It has to be replaced from time to time.

vii.            When aluminium or is heated with caustic soda  solution under high pressure for 2 to 8 hours at water soluble sodium aluminate is formed.

Q11. Write two methods of preventing rusting of iron.

Ans.

i.                 The most common method of preventing the rusting of iron is to coat its surface with paint or apply grease, oil or varnish.

ii.               Rusting of iron can be prevented by galvanization. The process of depositing a thin layer of Zinc metal on Iron objects is called galvanization.

Q12. What is an alloy? Give two examples with their chemical composition.

Ans. An alloy is a homogenous mixture of two or more metals or a metal and a non – metal in definite proportion.

Eg.

i.                 Brass – copper and zinc.

ii.               Stainless steel – iron, nickel and chromium.

Q13. Arrange the following metals in the decreasing order of chemical reactivity, Cu, Mg, Fe, Na, Ca, Zn.

Ans. The arrangement of metals in the decreasing order of their chemical reactivity are Na > Ca > Mg > Zn > Fe > Cu.

Q14. Explain the formation of an ionic compound between metal and a non – metal by transfer of electrons with Mg as the metal and Cl as a non – metal to illustrate your answer.

Ans. Magnesium is a metal whereas chlorine is a non – metal. Magnesium reacts with chlorine to form an ionic compound magnesium chloride.

The atomic number of magnesium is 12, so its electronic configuration is 2,8,2. It has 2 valance electrons. A magnesium atom donates its 2 valence electrons (to two chlorine atoms) and forms a stable magnesium ion,

The atomic number of chlorine is 17, and its electronic configuration is 2,8,7. Chlorine atom has 7 valance electrons, so it requires only 1 more electrons to complete its octet. Since, one magnesium atom donates 2 electrons, so, two chlorine atoms take these two electrons and form two chloride ions.

The positively charged magnesium ions and negatively charged chloride ions are held together by electrostatic force of attraction to form magnesium chloride  compound.

Q15. An element x on reacting oxygen forms an oxide X₂O. This oxide dissolves in water and turns red litmus blue. State whether element X is a metal or a non – metal. Explain with proper example.

Ans. The element X is very likely to be a non – metal because most of the oxides of non – metals are acidic and are soluble in water.

Note: - There are exceptions: -  A few oxides of metals are acidic, e.g., chromic oxide  and Manganese hypoxide. Also PbO, SnO_2­, ZnO and Al₂O₃ are amphoteric, hence, can behave like acids as well as like bases. 

DIPPING A COPPER COIN IN SILVER NITRATE

Ch. 9. Amazing world of carbon compounds

Q1. Fill in the blanks.

1.     The organic compounds having double or triple bond in them are termed as _______(unsaturated)

2.     The general formula of alkanes is _____________. )

3.     _____________ are known as parent organic compounds. (hydrocarbons)

4.     Covalent compounds are generally soluble in ____________ solvents. (organic)

5.     Triple bond can be obtained by sharing ____________ pairs or ________ electrons. (three, shared)

6.     Hydrocarbons necessarily contain _____________ and ______________. (hydrogen, carbon)

Q2. Give the IUPAC name of the following compounds.

1.      

Ans.

2.    

Ans.

Q3. Write short notes on

1.     Catenation

Ans.

i.                 The remarkable property of carbon atom to form bonds with itself and give rise to a single structure of chain is called catenation.

ii.               Such carbon chains can be straight or branched forming large molecules.

iii.              The two ends of some chains join together to form closed ring – like structures.

iv.              While catenating, the bonds between carbon atoms can be single, double or triple covalent bonds.

2.     Functional group

Ans.

i.                 The atoms or group of atoms present in the molecule which determines characteristic property of organic compounds are called the functional group.

ii.               Halides (F, Cl, Br, I) aldehyde (- CHO), Hydroxyl ( - OH), Carboxyl (- COOH), etc., are some of the functional groups.

iii.              The chemical properties of different compounds having the same functional groups are different.

iv.              There exists a homologous series of one particular type of functional group, e.g., alcohols, aldehydes, ketones, ethers, etc.

3.     Homologous series.

Ans.

i.                 A group of organic compounds containing same functional group which can be represented by the same general formula and which have similar trends in their properties are called a homologous series.

ii.               In the general formula of compounds of a homologous series, the symbol R is used to represent its functional group.

iii.              Alcohols (R – OH), Aldehydes (R – CHO), Carboxylic acid (R – COOH), Ketones(R-C(=O)-R') are some of homologous series and their general formulae.

iv.              The alkanes family is a homologous family which have linear molecules. Examples: Ethane C₂H₆, Propane C₃H₈, Butane C₄H₁₀, Pentane C₅H₁₂.

Q4. Differentiate between: Detergents and soaps

Detergents	Soaps
i.                 Detergents are generally ammonium or sulphonate salts of long chain carboxylic acids. ii.               Detergents have a strong cleansing action. iii.              Oils or fats are not used in their manufacture, usually petrochemicals are used to produce detergents. iv.              They function well in hard or soft water.	i.                 Soaps are sodium or potassium salts of long chain carboxylic acids. ii.               Soaps have relatively weak cleansing action. iii.              Vegetable oils or animal fats are used along with hydroxide of sodium or potassium to manufacture soaps. iv.              They do not work well in had water but work well in soft water.

Q5. Answer the following.

1.     Draw chain and ring structures of organic compound having six carbon atoms in them.

Ans. a) chain structure –

b) Ring structure: -

2.     Which organic compounds are named as Alkanol in IUPAC system?

Ans. In IUPAC method, alcohols are named as AlKanol. In naming the alcholols by IUPAC method the last ‘e’ of the parent alkane is replaced by ‘ol’ to indicate the presence of OH group.

3.     Explain: What do you understand by substitution reaction?

Ans.

i.                 Reaction where substitution of one or more atoms in a molecule for another atom takes place are called substitution reactions. Saturated hydrocarbons undergo substitution reaction.

ii.               In Substitution reaction one or more hydrogen atom of a hydrocarbon are replaced by some other atom (like chlorine)

iii.              Ex: Substitution reaction of methane with chlorine.

Methane reacts with chlorine in the presence of sunlight to form methyl chloride and hydrogen chloride.

4.     Which organic compounds readily undergo addition reactions? Why?

Ans. Unsaturated hydrocarbons undergo addition reactions, that is addition reactions are given by all the alkenes and alkynes. This is because reactants add to the carbon atoms of  double and  bond to form a single product of saturated hydrocarbon.

For Eg.

5.     State two examples of (organic) compound having covalent bond and two examples having ionic bond.

Ans.

i.                 Hydrocarbons like methane and ethane have covalent bonds.

ii.               In organic compounds line NaCl and KMnO₄ have ionic bonds.

6.     State and explain how alkanes are further classified.

Ans. Alkanes are saturated hydrocarbons with single bonds. Alkanes are further classified as:

i.                 Straight chain alkanes: The alkanes in which all the carbon atoms are attached by covalent bonds in a continuous chain are called straight chain alkanes or normal alkanes Eg. CH₃ – CH₂ – CH₂ – CH₃ is normal butane or n – butane.

ii.               Branched chain alkanes: - The alkanes in which all the carbon atoms are not in a continuous chain and some of them are linked to other carbon atoms to make the branch are called branched chain alkanes.

a.     The alkanes, in which there is only one carbon chain attached to the second carbon atom of the long chain are called iso – alkanes Eg.

b.     The alkanes, in which there are two single carbon branches, attached the second carbon atom of the long chain are called neo – alkanes. Eg.

7.     What are alkynes? Name the first member of alkyne family.

Ans. Hydrocarbons containing triple bonds between carbon atoms are alkynes. The first member of alkyne family is ethyne or acetylene

A wonderful image released by Michael Ströck under the GNU Free Documentation License: The structures of eight allotropes of carbon:

a) Diamond b) Graphite c) Lonsdaleite d) C60 (Buckminsterfullerene) e) C540 Fullerene f) C70 Fullerene g) Amorphous carbon h) Single-walled carbon nanotube

Ch. No. 10. Life’s Internal Secrets

Q1. Fill in the blanks.

1.     ________________ artery takes the blood to the lungs for oxygenation. (Pulmonary)

2.     ______________ is the largest gland in the body. (Liver)

3.     The digested food is absorbed by the __________ in the small intestine. (Villi)

4.     Lymph flows in ____________ direction. (one)

Q2. Correct the following statements.

1.     Aquatic animals breathe at a slower rate than the terrestrial animals.

Ans. Aquatic animals breathe faster than terrestrial animals.

2.     In human beings the blood goes to the heart in one cycle once.

Ans. In human beings the blood goes to the heart twice during each cycle of circulation.

3.     Plasma is called as tissue fluid.

Ans. Lymph is called as the tissue fluid.

4.     Carbohydrates are the body building nutrients.

Ans. Carbohydrates are the energy giving nutrients.

5.     Calcium oxalate crystals present in the cells of some plants are called as resins.

Ans. Calcium oxalate crystals present in the cells of some plants are called as raphides.

Q3. Give scientific reasons.

1.     Breathing rate increases during vigorous exercising.

Ans.

i.                 During vigorous exercise, the demand for oxygen increases due to increased energy production.

ii.               Therefore, breathing rate increases to provide more oxygen.

2.     Translocation is needed in all higher plants.

Ans.

i.                 Transport of nutrients from leaves to other parts of the plant is termed translocation.

ii.               It is needed in all higher plants because every part of the plant needs food for harnessing energy and for building and maintaining the organism.

3.     The plants are kept in dark before determining the factors essential for photosynthesis.

Ans.

i.                 When the plants are kept in dark all the starch stored in them gets used up and no new starch is produced.

ii.               Such destarched plants help to determine the factors essential for photosynthesis.

4.     It is necessary to separate oxygenated blood from the deoxygenated blood in mammals.

Ans.

i.                 Mammals have high energy needs since they constantly use energy to maintain their body temperature.

ii.               It is necessary to separate oxygenated blood from deoxygenated blood in mammals because such separation allows a high efficient supply of oxygen to the body required for high energy production.

Q4. Draw a well labeled diagram of the following.

1.     Human excretory system.

2.     Vertical section of the human heart.

3.     Digestive glands.

Q5. Answer the following.

1.     How are fats digested in the human body?

Ans.

i.                 Whenever food enters the small intestine, the bile and pancreatic juice enter there through a common duct.

ii.               Bile makes the food alkaline and breaks the large fat globules into smaller ones.

iii.              The enzyme lipase in the pancreatic juice breaks down the fats.

iv.              Various intestinal juices secreted by the walls of the small intestine complete the digestion of fat converting it into fatty acids.

2.     What would be the consequences of deficiency of haemoglobin in the human body?

Ans.

i.                 Haemoglobin in the blood performs a very important function of absorbing and carrying oxygen from lungs to the body tissues and CO₂  from body tissues to the lungs.

ii.               Therefore, due to the deficiency of haemoglobin, the body tissues do not get sufficient oxygen which leads to a state called anaemia.

iii.              Fatigue, palpitation, dizziness, headache, nausea, lack of concentration etc., are some of the symptoms of anaemia.

3.     How do plants get rid of their excretory products?

Ans.

i.                 Gaseous excretory materials are eliminated by diffusion.

ii.               Waste products stored in the vacuoles of the leaves, flowers, fruits and bark are removed by the periodical shedding of these parts.

iii.              Some waste products are stored as resins and gum in old xylem. When the trunks of these trees are cut, these substances ooze out.

iv.              Plants also excrete some waste substances into the soil around them.

Q6. Given below are the end products of different reactions involving glucose.

Write the reaction number in front of the following:

1.      Anaerobic reaction =  

2.      Reaction in human muscles =

3.      Aerobic respiration =

4.      Reaction in plant cells =

5.      Reaction in liver =

Ans.

1.      Anaerobic reaction =  5

2.      Reaction in human muscles =4

3.      Aerobic respiration = 3

4.      Reaction in plant cells = 1

5.      Reaction in liver = 2

Q7. Answer briefly:

1.     Explain the process of translocation in plants.

Ans.

i.                 Transport of nutrients from leaves to other parts of the plant is called translocation.

ii.               It takes place through phloem in upward as well as downward direction.

iii.              This process needs energy which is obtained from ATP.

iv.              When food materials like sucrose are transferred to phloem tissue, using ATP, the concentration of water molecules decreases in that area.

v.                This results in the movement of water into the cells due to osmosis.

vi.              The increased contents within the cells exert a high amount of pressure on their wall.

vii.            This pressure moves the food materials to the adjacent cells with low pressure.

viii.           This allows the phloem to move material according to the plant’s needs.

2.     Explain the structure and function of a nephron.

Ans.

i.                 The basic filtration unit in the kidney is a cluster of thin walled blood capillaries called as nephron.

ii.               Each nephron has a cup shaped thin walled upper and called Bowman’s capsule which contains a bundle of blood capillaries called glomerulus.

iii.              When blood containing urea enters the glomerulus it gets filtered through glomerular capillaries.

iv.              The selectively permeable wall of the Bowman’s capsule allows the water molecules and small molecules of the other substances to pass through them and forms glomerular filtrate.

v.                The blood, free from these materials is taken to the heart through the renal vein.

vi.              The glomerular filtrate collected in the Bowman’s capsule further passes through the nephron tubule where reabsorption of water and useful molecules take place.

vii.            The remaining fluid containing the waste forms the urine which eventually enters a long tube called the ureter.

viii.           It is further stored in the urinary bladder and from there it is thrown out through the urethra.

Ch. No. 11. The Regulators of Life

Q1. Fill in the blanks:

1.     The loss of water from the plants is known as _____________. (Transpiration)

2.     Nervous system is absent in _______ and ____________. (plants, unicellular organism)

3.     Response to the stimulus of touch is called __________ whereas response to the stimulus of chemicals is called as _____________. (eismonastic movement, chemotropism)

4.     Brain is the main ____________ centre of the body. (coordinating)

Q2.  Name the following:-

1.     Growth of plant in response to external factors.

Ans. Tropism

2.     Maintenance of steady state by different system in an organism.

Ans. Homoeostasis

3.     Cells that assist the neurons in their function.

Ans. Neuroglia

4.     The small gap between the consecutive neurons.

Ans. Synapse

5.     Part of the brain that co – ordinates the voluntary movements.

Ans. Cerebellum

6.     Name the sense organs.

Ans. Eyes, ears, nose, tongue and skin are the five sense organs.

Q3. Give scientific reasons.

1.     Roots of plants grow away from light.

Ans.

i.                 The root system of plants always grows downwards in response to the stimulus of gravity and water.

ii.               This makes sure that the roots will find soil and water.

iii.              Hence, the roots of plants grow away from light.

2.     Hormones secreted by the endocrine glands are present everywhere in the body.

Ans.

i.                 Endocrine glands do not have ducts to store or transport their secretions called hormones.

ii.               The hormones are directly released into the blood stream and reach concerned body parts through blood.

iii.              Hence, hormones secreted by the endocrine glands are present everywhere in the body.

3.     Insulin plays an important role in controlling the sugar level of blood.

Ans.

i.                 When the sugar level of the blood rises, it is detected by the cells of the pancreas which respond to the situation by producing more insulin.

ii.               As the sugar level of the blood falls, the secretion of insulin is reduced.

iii.              Thus, insulin plays an important role in controlling the sugar level of blood.

Q4. Answer the following questions:

1.     Explain the following terms:

a.     Hydrotropic movement: - The movement or growth of the root system of a plant in response to the stimulus of water is called hydrotropic movement.

b.     Chemical control in animals:  chemical control in animals is brought about by chemical substances called hormones. These hormones are secreted by the endocrine glands.

2.     Differentiate between:

Voluntary and Involuntary movements

Voluntary movements	Involuntary movements
i.                 Voluntary movements are controlled by cerebrum and cerebellum. ii.               We have thinking control over these movements.	i.                 Involuntary movements are controlled by medulla oblongata. ii.               We do not have thinking control over these movements.

3.     Write a short note on

a.     Reflex action

                                     i.          The sudden action in response to some happenings in the environment is called as reflex action.

                                   ii.          It is an involuntary action which we perform automatically.

                                  iii.          The path way taken by nerve impulses in a reflex action is called reflex arcs. Reflex arcs allow rapid response.

                                  iv.          A nerve from all over the body meet in a bundle in such a connection is commonly called as the spinal cord, before impulses are sent to the brain.

                                    v.          Hence, reflex arcs are formed in the spinal cord, although the messages reach the brain.

                                  vi.          Pulling away our hand on toughing a hot object, narrowing of the eyes in sunlight, watering of the mouth on smelling something delicious etc. are examples of reflex action.

b.     Co – ordination in plants.

                                   i.     Plants do not have a nervous system or muscular system and sense organs like eyes, ears, nose, etc.

                                 ii.     The plants can still sense the presence of stimuli like touch, light, gravity, water, etc., and respond to them by the action of hormones in them.

                               iii.     So, plants co – ordinate their behaviors against environmental changes by using hormones.

                                iv.     Hormones bring about various movement in response to stimulus.

                                 v.     It is the result of such co – ordination that the lotus opens in the morning and the tube rose at night; stem grow towards light and the root towards gravity; the leaflets of the mimosa plant close on being touched and the explosive fruit of balsam burst open to scatter the seeds.

Ch. No. 12 The Life Cycle

Q1. Fill in the blanks.

1.     The two main methods of reproduction are _____________ and ________________. (sexual reproduction, asexual reproduction)

2.     The functional unit in a plant’s sexual reproduction is ____________. (flower)

3.     The male reproductive part of a flower is _____________(stamen)

4.     When the transfer of pollen from an anther to the stigma occurs in the same flower, the process is called ____________. (self pollination (autogamy))

5.     ________ give rise to variety and diversity. (variation)

6.     Hydra uses regenerative cells for reproduction in the process of _________. (budding)

7.     Yeast reproduces by _____________.  (budding)

8.     During unfavourable conditions ___________ type of fission is seen in amoeba. (multiple)

9.     A basic process in reproduction is the creation of a _____________ copy. (DNA)

10.  _______________ is necessary to maintain the number of individuals of a species. (Reproduction)

Q2. Write the correlated terms:

1.     Amoeba: Simple binary fisson : : Paramoecium: ______________(Transverse binary fission)

2.     Planaria :  regeneration :  : Rhizopus : ________________(spore formation)

3.     Root, stem, leaf : Vegetative propogation :  : Flower : ______________(sexual reproduction)

4.     Asexual reproduction : similarity : : Sexual reproduction : ____________ (diversity)

Q4. Explain the following terms.

1.     Reproduction: - The fundamental characteristic of living things to produce new individuals of the same species, that is a new generation of the species from and existing individual is known as reproduction.

2.     Vegetative propogation: -When new plants are produced from the vegetative parts like roots, stems, leaves and buds it is known as vegetative propagation.

3.      Pollination:-  The process of transfer of pollen grains from anther to stigma is called as pollination.

Q5. Write the functions of the following organs in reproduction.

1.     Vagina

i.                 It provides the route for the menstrual blood to leave the body during menstruation.

ii.               It is a pathway through which sperms enters into woman’s body.

iii.              It is a pathway through which a baby comes out of the woman’s body during child birth.

2.     Stigma

i.                 It receives pollen grains and on which pollen germinates.

3.     Ovaries

i.                 Ovaries develop and release eggs into the oviduct.

ii.               It secretes hormone estrogen.

4.     Seminal vesicle and Prostate glands

i.                 Produce ejaculatory fluid which helps the sperm in transport and provides nutrition.

5.     Uterus

i.                 It accommodates a growing foetus.

ii.               It push the baby during labour.

Q6. Draw a well labeled diagram of: [refer to text book]

1.     Longitudinal section of flower.

2.     Binary fission in amoeba.

3.     Spore formation in Mucor.

4.     Human female reproductive system.

Q7. Answer the following.

1.     What are the advantages of sexual reproduction over asexual reproduction?

Ans.

i.                 The offsprings produced by sexual reproduction are different from parents.

ii.               Variations give rise to variety and diversity.

iii.              Variation enables organisms to adapt and survive in the changing environment.

iv.              It helps to prevent the complete extinction of animal and plant species.

2.     Why does menstruation occur?

Ans.

i.                 A woman’s ovaries usually release one egg each month.

ii.               When the egg is not fertilized, menstruation occurs to leave out the unfertilized egg along with blood and mucous from the uterus.

3.     Describe sexual reproduction in plants.

Ans.

i.                 In plants, flower is the functional unit concerned with sexual reproduction.

ii.               In a flower, the ovary produced female germ cell or egg and the pollen grains produces male germ cells.

iii.              When the pollen lands on stigma, it germinates producing a pollen tube which grow downwards to reach ovary.

iv.              Each pollen tube contains two male gametes and are released near the egg,

v.                One male gamete fuse with the egg cell to form zygote.

vi.              The second male gamete fuse with the secondary nucleus in the embryo sac to form endosperm. This is called as double fertilization.

vii.            The zygote develops into embryo and the endosperm serves as nutritive tissue for the growing embryo.

4.     Describe the modes of reproduction in unicellular organisms.

Ans. Binary fission, multiple fission and budding are the modes of sexual reproduction in unicellular organisms.

a.     Binary fission: -

                                                              i.     It is employed by most prokaryotes, some protozoa and some organelles within eukaryotic cells.

                                                            ii.     In it, the living cell divides into two equal parts which have the potential to grow to the size of the original one.

b.     Multiple fission: -

                                                              i.     During unfavourable condition, the amoeba withdraws its pseudopodia and form a cyst.

                                                            ii.     Inside the cyst, nucleus divides into many nuclei and as a result many daughter cells are formed.

                                                           iii.     The cyst bursts to release the daughter cells during favourable condition.

c.      Budding: -

                                                              i.     Yeast reproduces by budding in which a small outgrowth is formed on the parental cell.

                                                            ii.     The nucleus of the parental call divides and one daughter nucleus migrates into the bud. The bud increases in size separates and grows further.

5.     Explain disadvantages of large family size.

Ans.

i.                 There is a strong relation between high national fertility rate and measures of poverty.

ii.               As the population density increases, decrease in per capital income and natural resources takes place.

iii.              General health goes down and creates an economical burden on the nation.

iv.              Large families affect both the individual as well as the community life.

v.                Economic pressure, mother’s poor health, children neglected at home, poor nourishing, malnutrition, insufficient medical care, lack of better education, etc., are some of the disadvantages of large family size.

Q8. Write short notes on the following:

1.     Pollination: -

                           i.          The process of transfer of pollen grains from anther to stigma is called as pollination.

                         ii.          If this transfer of pollen occurs in the same flower or another flower of the same plant, it is known as self pollination.

                        iii.          On the other hand, if pollen is transferred from one flower to the flower of another plant, it is known as cross pollination.

                        iv.          The agents of cross pollination are wind, water or animals.

2.     Regeneration: -

i.                 The capacity to regenerate is very high among some animals.

ii.               They can reconstruct the entire body from the isolated body cells.

iii.              Regeneration is carried out by specialized cells.

iv.              These cells proliferate and make large number of cells which later developed into various cell types and tissues, and helps in production of new organism.

v.                Eg. When Planaria is cut into many pieces, each piece develops into a whole Planaria. This process occurs only if the Planaria body gets cut up into pieces. But animals cannot wait to be cut to reproduce. So regeneration is not the same as reproduction.

3.     Germination of seeds : -

i.                 After fertilization, the zygote divides several times to form an ambryo within the ovule.

ii.               The ovule develops into a seed and ovary develops into the fruit.

iii.              The seed contains the future plant. It develops into the seedling under appropriate condition. This process is known as germination.

4.     Multiple fission: -

i.                 During unfavourable condition, the amoeba withdraws its pseudopodia, becomes almost round and secretes a hard covering called cyst.

ii.               Inside the cyst nucleus divides into many nuclei by repeated division, follow by division of cytoplasm.

iii.              As a result many daughter cells are formed.

iv.              The cyst bursts to release the daughter cells during favourable condition.

5.     Importance of variation.

i.                 Changes in ecological system, which are beyond our control like varying temperature, varying water level can wipe out the population species.

ii.               But, if variations in some individuals are suitable for new environment, there is a chance of survival of that species.

Ch. No. 13. Mapping our Genes

Q1. Fill in the blanks

1.     In ___________ mode of reproduction the offsprings are with minor differences. (asexual)

2.     Both the parents contribute equal amount of ___________ material to the offspring. (genetic)

3.     Dominant character masks the ___________ characters. (recessive)

4.     Selection by nature is not ____________ but ____________. (deliberate, natural)

Q2. Give scientific reasons:

1.     In sexual mode of reproduction greater diversities are generated.

Ans.

i.                 In sexual mode of reproduction two parents are involved.

ii.               Each one has its own DNA copies that are passed on through their nuclei at the time of fertilization of gametes.

iii.              Therefore more diversity is produced.

iv.              Moreover, the process of meiosis at the time of gamete formation, also produces variations. Hence in sexual mode of reproduction greater  

2.     Phenotypic and genotypic ratios are different.

Ans.

i.                 Phenotype is the appearance or any detectable characteristic feature of an individual life red and white flowers.

ii.               Genotype is the genetical composition of individuals like RR, Rr and rr.

iii.              Hence, phenotypic and genotypic ratios are different.  

3.     In human beings the gametes from the male parent decides the sex of the baby.

Ans.

i.                 In human male gametes, two dissimilar chromosomes XY are present whereas in females two similar chromosomes XX are present.

ii.               All children inherit ‘X’ chromosomes from their mother and ‘X’ or ‘Y’ from their father.

iii.              Hence the gametes from the male parent decide the sex of the baby.

4.     Paleontological evidence suggests that invertebrates came into existence before the vertebrates.

Ans.

i.                 A systematic study of fossils and its occurrence revealed that the deepest layers of land were found to have fossils of invertebrates.

ii.               In layers above them were found vertebrates such as fish – like animals, amphibians, reptiles, birds and mammals.

iii.              This suggests that invertebrates came into existence before the vertebrates.

Q3. With the help of a diagram (Punnett square) show a Mendelian experiment where tall pea plant bearing red flowers is crossed with a short pea plant bearing white flowers. Write both the phenotypic and genotypic ration for F2 generation.

Q4. Write a short note on:

Darwin’s theory of evolution.

i.                 Darwin’s theory of evolution is based on natural selection.

ii.               Darwin’s theory of natural selection suggests that only the fittest survive.

iii.              All those plants and animals which are not fit die.

iv.              These fit species reproduce and pass on the relevant characteristics to the following generation which in turn would make them fit for survival.

v.                This process of selection of characteristics that contribute to the fitness for survival was called natural selection by Darwin.

vi.              The criterion for the natural selection is the only one i.e. successful adaptation for growth and reproduction in the given environment.

Do You know?

Charles Darwin (Feb. 12, 1809 - April 19, 1882) was an English naturalist renowned for his documentation of evolution and for his theory of its operation, known as Darwinism. His evolutionary theories, propounded chiefly in two works--On the Origin of Species by Means of Natural Selection (1859) and The Descent of Man, and Selection in Relation to Sex (1871)--have had a profound influence on subsequent scientific thought.

Darwin was the son of Robert Waring Darwin, who had one of the largest medical practices outside of London, and the grandson of the physician Erasmus Darwin, the author of Zoonomia, or the Laws of Organic Life, and of the artisan-entrepreneur Josiah Wedgwood. Darwin thus enjoyed a secure position in the professional upper middle class that provided him with considerable social and professional advantages.