Chemical Reactions and Equations Class 10 Notes Science Chapter 1

In our daily lives, physical changes involve alterations in appearance or state without creating new substances, like melting ice. On the other hand, chemical changes result in the formation of entirely new substances, such as cooking food or rusting iron. Recognizing these changes helps us understand when a chemical reaction occurs.

What is Chemical reaction?

A chemical reaction is a process in which one or more substances, the Reactants, are converted to one or more different substances, the Products.  

➤ The substances which take part in a chemical reaction are called Reactants. 

➤ The substances which are formed in a chemical reaction are called Products. 

These are the following changes to determine that the chemical reaction has taken place:

(i) Change in state : The combustion reaction of candle wax is characterised by a change in state from solid to liquid and gas. 

(ii) Change in colour : Shiny brown colored Copper on heating in air becomes a black colored compound. 

2Cu + O2 → 2CuO 

(iii) Evolution of gas : The chemical reaction between zinc and dilute sulphuric acid is characterised by hydrogen gas. 

Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g) 

(iv) Change in temperature : The reaction between quicklime and water to form slaked lime is characterised by an increase in temperature. 

Ca(OH)2 + CO2 → CaCO3 + H2O 

(v) Formation of a precipitate : When an aqueous solution of sodium sulphate is mixed with the aqueous solution of barium chloride, barium sulphate comes in the form of white precipitate 

Na2SO4 (aq) + BaCl2(aq) → BaSO4(↓) + 2NaCl(aq) 

Chemical equations 

A chemical equation is a symbolic representation of a chemical reaction using the symbols and formulas of the substances involved.

For example:

Magnesium + Oxygen  → Magnesium oxide 

         (Reactants)                          (Product)

The substances that undergo chemical change in the reaction, Magnesium and Oxygen, are the Reactants. When magnesium burns in air, it combines with oxygen to form magnesium oxide. 

Chemical equations can be made more concise and useful if we use chemical formulae instead of words. 

Example: The chemical formula for water is H2O, which indicates that it is made up of two hydrogen atoms and one oxygen atom.

Writing a chemical equation:

Representation of a chemical reaction in terms of symbols and chemical formulae of the reactants and products is known as a chemical equation. 

For solids, the symbol is “(s)”. 

For liquids, it is “(l)”. 

For gases, it is “(g)”. 

For aqueous solutions, it is “(aq)”. 

For gas produced in the reaction, it is represented by “(↑)”. 

For precipitate formed in the reaction, it is represented by “(↓)”. 

The reactants are on the left (LHS) of the arrow, while the products are on the right (RHS). A plus sign (+) links the different reactants and products together. 

Balancing the chemical Equation: 

The Law of Conservation of Mass states that in a chemical reaction, atoms can't be created or destroyed. This means that the total number of atoms for each element in the starting materials (reactants) must be the same as in the end products, keeping the overall mass the same.

Example 1 : 

Skeletal equation : Mg + O2 → MgO

Balanced equation : 2Mg + O2 → 2MgO 

Example 2 : 

Skeletal equation : Fe + H2O → Fe3O4 + H2 

Balanced equation: 3Fe+ 4H2O → Fe3O4 + 4H2

Example 3 : 

Skeletal equation : AgCl → Ag + Cl2 

Balanced equation : 2AgCl → 2Ag + Cl2 

Example 4 : 

Skeletal equation : Al + O2 → Al2O3

Balanced equation : 4Al + 3O2 → 2Al2O3

→ Types of Chemical Reactions 

I. Combination Reaction: 

The reaction in which two or more reactants combine to form a single product. 

A + B  → AB

Example:

(i) Burning of coal : C + O2 → CO2 

(ii) Formation of water: 2H2 + O2 → 2H2O 

 (iii)   Calcium oxide reacts vigorously with water to produce slaked lime (calcium hydroxide) releasing a large amount of heat.

CaO   +   H2O →   Ca(OH)2    +   Heat 

(Quick lime)       (Slaked lime) 

A solution of slaked lime produced by the reaction is used for white-washing walls. Calcium hydroxide reacts with carbon dioxide in the air to form calcium carbonate. Calcium carbonate is formed after two to three days of white washing and gives a shiny finish to the walls. It is interesting to note that the chemical formula for marble is also CaCO3.

Exothermic Reactions : Reaction in which heat is released along with formation of products. 

Example:

(i) Burning of natural gas. 

CH4 + 2O2 → CO2 + 2H2O + Heat 

(ii) Respiration is also an exothermic reaction. 

We need energy to live, and we get it from the food we eat. When we digest food, it's broken down into simpler forms. For instance, rice, potatoes, and bread have carbohydrates, which are turned into glucose. This glucose then mixes with oxygen in our cells to produce energy.

C6H12O6 + 6O2 → 6CO2 + 6H2O + energy 

II. Decomposition Reaction: 

The reaction in which a compound splits into two or more simpler substances is called decomposition reaction. 

A → B + C 

(a) Thermal decomposition: 

When decomposition is carried out by heating. 

Example:

                          Heat

(i)    2FeSO4    →      Fe2O3   +   SO2 + SO3 

 (Ferrous sulphate)   (Ferric oxide) 

      Green colour       Red-brown colour 

Ferrous Sulphate Ferrous sulphate crystals (FeSO4. 7H2O) lose water when heated and the green colour of ferrous sulphate crystals fades. It then decomposes to ferric oxide (Fe203), sulphur dioxide (SO2) and sulphur trioxide (SO3). Ferric oxide is a solid, while S02 and SO3 are gases.

                    Heat

(ii) CaCO3     →     CaO         +    CO2 

   (Lime stone)    (Quick lime) 

Heating calcium carbonate breaks it down into calcium oxide (lime) and carbon dioxide. This reaction is important in industries, with calcium oxide being used in cement production.

                        Heat

(iii) 2Pb(NO3)2 → 2PbO   +   4NO2      +   O2 

 (Lead nitrate)(Lead oxide) (Nitrogen dioxide) 

Emission of brown fumes is nitrogen dioxide (NO2). 

( 👉 Thermal decomposition of lead nitrate Experiment video)

(b) Electrolytic Decomposition: 

When decomposition is carried out by passing electricity. 

 Example: Electrolysis of water 

           Electric current

 2H2O          →           2H2   +   O2  

★ Pure water is a bad conductor of electricity. So to carryout electrolysis it is essential to add few drops of dil. H2SO4 ,before the electrolysis 

★ Gas collected at cathode is Hydrogen and at anode is Oxygen 

★Water contains two parts of hydrogen element as compared to one part of oxygen element by volume. Hence, volume of gas collected at one electrode is double of another

(c) Photolytic Decomposition: 

When decomposition is carried out in presence of sunlight. 

Example: 

(i) White silver chloride turns grey in sunlight. This is due to the decomposition of silver chloride into silver and chlorine by light. 

           Sunlight

2AgCl      →     2Ag      +      Cl2 

(White)           (Grey)

                  Sunlight

(ii)  2AgBr       →        2Ag + Br2 

These reactions are used in black and white photography.  

Endothermic Reaction: The reactions which require energy in the form of heat, light or electricity to break reactants are called endothermic reactions. 

III. Displacement Reaction: 

The chemical reactions in which more reactive element displaces less reactive element from its salt solution. 

Example:

(i)  The iron nail becomes brownish in colour and the blue colour of copper sulphate solution fades. In this reaction, iron has displaced or removed another element, copper from the copper sulphate solution.

Fe   +    CuSO4    →       FeSO4 +  Cu 

              (Blue)                (Green)

(ii) Zinc displaces copper forming zinc sulphate. Zn is more reactive than copper. 

Zn + CuSO4 → ZnSO4 + Cu    

IV. Double Displacement Reaction: 

A reaction in which new compounds are formed by mutual exchange of ions between two compounds. 

Example: 

Na2SO4 + BaCl2   → BaSO4  + 2NaCl  

white precipitate of BaSO4 is formed by ther eaction of  SO4^2- and Ba^2+

reaction that produces produces a precipitate can be called a precipitation reaction.

Example:

 Al2(SO4)3 + 3BaCl2 → 2AlCl3 + 3BaSO4 ↓  

V. Oxidation and Reduction: 

Oxidation: Gain of oxygen or loss of hydrogen. 

 2Cu + O2 → 2CuO 

Reduction: ​Reduction: Loss of oxygen or gain of hydrogen

Oxidation of Copper to Copper Oxide 

The surface of copper powder becomes coated with black copper(ll) oxide because oxygen is added to copper and copper oxide is formed. If hydrogen gas is passed over this heated material (CuO), the black coating on the surface turns brown as the reverse reaction takes place, and copper is obtained. During this reaction, the copper(ll) oxide loses oxygen and is reduced. The hydrogen gets oxygen and is oxidized.

CuO + H2 → Cu + H2O 

 In this reaction, CuO is reduced to Cu and H2 is oxidised to H2O.  

​Redox Reaction: A reaction where one reactant is oxidised while the other is reduced. 

​Effects of Oxidation Reaction in Everyday Life? 

The process where a metal is attacked by moisture, acids, etc.

Examples: 

Corrosion of iron is called rusting. Iron objects when left in moist open air for sometime get coated with a reddish brown powder. The process is known as rusting. 

4Fe(s) + 3O2(from air) + xH2O(moisture) → 2Fe2O3.xH2O(rust)

Green coating on copper articles and black coating on silver ornaments are other examples of corrosion.  

Cu(s) + H2O(moisture) + CO2(from air) → CuCO3.Cu(OH)2(green) 

Ag(s) + H2S (from air) → Ag2S(black) + H2(g)

 

  

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                 PART - A PHYSICS        

I. Multiple choice questions: 2 × 1 = 2

1. The diameter of the reflecting surface of a spherical mirror is    

 (A) pole of the mirror 

 (B) centre of curvature 

 (C) principal axis 

 (D) aperture

Ans: (D) aperture

2. When three resistors of different resistance are connected in parallel in an electric circuit and switched on, then the quantity that remains the same in all the resistors is 

(A)  current 

(B) potential difference 

(C) resistance 

(D) resistivity   

Ans: (B) potential difference

II. Answer the following questions: 2 × 1 = 2

3. What are the reasons for overload in an electric circuit?

Ans:

★ Accidental hike in the supply voltage.

★ Connecting too many appliances to a single socket.

★ When live wire and neutral wire come into direct contact. ( Any two )

4. Two situations of freely suspended parallel copper wires carrying current are shown in the figure given below.

In which of these situations, the wires attract each other? Justify your answer. 

Ans:

★ Situation – 1

★Parallel wires carrying currents in the same direction attract each other. Therefore, in this situation, the two wires attract each other.

III. Answer the following questions: 3×2 =6

5. What is the colour of danger signal lights? Why is that colour preferred?

Ans:

★ The colour of danger signal lights is red.

★ Because it has the longest wavelength among visible colours so, it gets scattered the least by dust, fog, or air molecules.

6. Among nichrome and copper wires, which of the wires is used in electric fan and in the coils of electric heater? Why?

Ans:

★ Copper wire is used in the electric fan because It has low resistivity.

★ Nichrome wire is used in the coils of the electric heater because It has high resistivity and high melting point.

7. Draw the diagram indicating the field lines of the magnetic field around a current carrying straight conductor.

Ans:

IV. Answer the following questions : 3×3=9

8. Draw the ray diagram to show the image formation when an object is kept between ‘C’ and ‘F’ of a concave mirror. Write the nature and size of the image formed. [C = Centre of curvature, F = Principal Focus]

Ans:

Size of the image: Larger

Nature of the image : read and inverted.

9. Explain an experiment to demonstrate that a current carrying conductor placed in a magnetic field experiences a force. 

OR 

Explain an activity to draw the magnetic field lines around a bar magnet using a compass needle.

Ans:

★ Take a small aluminium rod and suspend it horizontally using connecting wires.

★ Place a strong horse-shoe magnet in such a way that rod lies between the two poles with the magnetic field directed upwards. 

★ Connect the aluminium rod in series with a battery, a key and a rheostat. 

★ Now pass the current through the aluminium rod in one particular direction. 

★ The rod displaces towards one side. 

★ Reverse the direction of current flowing through the rod. The rod displaces towards the opposite side.  

OR

★ Place a bar magnet on a white paper and mark the boundary of the magnet 

★ Place the compass needle near the north pole of the magnet. The south pole of the compass needle directs towards the north pole of the magnet. Mark it with a point. 

★ Move the needle to a new position such that its south pole occupies the position previously occupied by its north pole. Mark it with a point. 

★ In this way proceed step by step till you reach the south pole of the magnet. 

★ Join the points marked on the paper by a small curve. 

★ This curve represents a field line

10. A student clearly reads letters of a textbook only when the book is kept at a distance more than 50 cm from his eyes without difficulty. Then, 

i) identify this defect of the eye. 

ii) suggest a remedy for this defect.

b) When sunlight passes through the trees of a dense forest on a foggy morning then the path of the beam of light appears between the trees. 

i) What is this phenomenon called? 

ii) The same phenomenon is not normally visible in an open field. Why? Write your analysis.

OR 

a) The position of the stars changes apparently in the clear sky. Why? Explain. 

b) White light is passed through the given arrangement of three glass prisms (X, Y, and Z) as shown in the figure given below.

i) Is spectrum of light seen on the screen? 

ii) What is the role of prism Z?

Ans:

a) 

i) defect is Hypermetropia

ii) This defect is corrected by using a  convex lens

b)

i) This is called the Tyndall effect

ii) In an open field, the air is usually clearer and contains fewer suspended particles. Since scattering is very low, the light does not become visible as a beam.

OR

a)

★ It is due to atmospheric refraction of starlight. 

★ The starlight on entering the earth’s atmosphere, undergoes refraction continuously before it reaches the earth. 

★ The atmospheric refraction occurs in a medium of gradually changing refractive index 

★ As the path of rays of light coming from the star goes on varying slightly, the apparent position of the star fluctuates and the amount of starlight entering the eye flickers. This is the twinkling effect of stars.  

b)

i) Yes / The spectrum of light forms on the screen

ii) Prism Z disperses this white light into 7 colours and hence we see the spectrum of light on the screen.  

V. Answer the following questions: 2×4 = 8

11. a) What is magnification? Write the formula to calculate magnification of the image produced by a lens.

b) State the laws of reflection of light.

Ans:

a)

★ It is the ratio of the height of the image to the height of the object.

★ M = h'/h = v/u

b)

i) The angle of incidence is equal to the angle of reflection. 

ii) The incident ray, the normal to the mirror at the point of incidence and the reflected ray, all lie in the same plane 

12. a) Two resistors of resistance 10Ω and 40Ω are connected in series and connected to a 12V battery. Calculate the equivalent resistance in the electric circuit and the total current flowing in the circuit. 

b) A washing machine rated 500W is used for 2 hours a day for 30 days. Calculate the cost of using this appliance at 3 Rs per 1 kWh. 

OR 

a) Resistance of a metal wire of length 2 m is 28 Ω at 20°C. If the diameter of the wire is 0.04 mm then, what will be the resistivity of the metal at that temperature? 

b) 1000 J of heat is produced each 2 seconds in a 5Ω resistor. Find the potential difference across the resistor.

Ans:

a)

Given: 

R1 = 10 Ω

R2 = 40 Ω

V = 12 V

Equivalent Resistance: 

Rs = R1 + R2 = 10 + 40 = 50 Ω

Total Current:

I = V / Rs

I = 12 / 50 

I =  0.24 A

b)

Given:

P = 500W = 0.5 kW

t = 2h × 30 days = 60h

E = P × t 

E = 0.5kW × 60h = 30kWh

Cost = 30kWh × 3Rs = 90Rs

OR

a)

b)

Given:

H = 1000j

R = 5Ω

t = 2s

H = I2 R T

I2 = H/Rt

I = √ 1000/5×2 = 10 A

V = I R = 10A × 5 = 50V

                  PART - B CHEMISTRY        

VI. Multiple choice questions:   3 × 1 = 3 

13. As the pH value of a neutral solution increases, 

(A)    basic property decreases and number of OH− ions increases. 

(B) acidic property increases and number of H+ ions decreases. 

(C)  basic property increases and number of OH− ions increases. 

(D) acidic property decreases and number of H+ions increases. 

Ans: (C) basic property increases and number of OH− ions increases. 

14. The X in the following reaction represents, 

(A)  K2Cr2O7               (B) KMnO4 

(C) NaOH                     (D) KOH 

Ans: (B) KMnO4

15. To make pure iron hard and strong, the substance that is to be added to it is 

(A)  carbon       (B)  zinc     

(C) nickel           (D) tin

Ans: (A) carbon

VII. Answer the following questions: 3×1= 3

16. What is rancidity?

Ans: Rancidity is the process of oxidation of oils and fats in food materials, which leads to a change in their smell and taste.

17. Write the structural formula of the compound obtained when one atom of hydrogen in ‘ethane’ is replaced by −CHO group. 

Ans:

18. Aluminium articles do not corrode easily like iron articles. Justify.

Ans:

Because aluminium reacts with the oxygen in the air to form a thin, strong, and protective layer of aluminium oxide  on its surface. This oxide layer is highly resistant to further corrosion.

VIII. Answer the following questions: 3×2=6

19. Analyze the list of experiments in the table given below. In which of the experiments the following salts will be produced? (i)  An acidic salt (ii) A neutral salt 

Ans:

i) Experiment No 1

ii) Experiment No 3

20. Name the catalyst used and the product obtained in the hydrogenation of ethene. 

OR 

The molecular formula of the first member of a homologous series of carbon compounds is CH2O(HCHO). Determine the name and the molecular formula of the third member of this group. Mention the general name of this group.

Ans: 

★ Nickel (Ni) / Palladium (Pd)

★ Ethane 

21. Draw the diagram to show the action of steam on metals.  

Ans:

IX. Answer the following questions: 3×3 = 9 

22. Write the balanced chemical equations for the following reactions. 

a) Calcium carbonate → Calcium oxide + carbon dioxide 

b) Hydrogen + chlorine → Hydrogen chloride 

c) Magnesium + hydrochloric acid → Magnesium chloride + Hydrogen 

Ans:

a) CaCO3    →   CaO  +  CO2

b) H2   +  Cl2  →   2HCl

c) Mg  +  2HCl   →   MgCl2   +  H2

23. What is neutralization? Name the acid present in the following substances. i) Curd ii)Gastric juice 

Ans:

Reaction in which an acid reacts with a base to form salt and water

i) Lactic acid

ii) Hydrochloric acid

24. Explain the formation of ionic bond between sodium and chlorine atoms. 

OR 

a) Write the chemical reactions to prove that aluminium oxide is an amphoteric oxide. 

b) How calcination differs from roasting?

Ans:

OR

a) 

★  Al2O3   +    6HCl → 2AlCl3   +  3H2O

★   Al2O3  + 2NaOH → 2NaAlO2   + H2O

b)

★ Carbonate ores are converted into oxides by heating strongly in limited air. This process is known as calcination. 

★ Sulphide ores are converted into oxides by heating strongly in the presence of excess of air. This process is known as roasting. 

X. Answer the following question: 1 × 4 = 4

25. a) Give reasons: 

i)  Carbon atoms neither form C4 - anion nor form C4+ cation. 

ii) Ethanoic acid known as glacial acetic acid.  

b) Write the structural formula of the following carbon compounds: i)  Butyne ii) Cyclohexane 

OR 

a) Explain the mechanism of cleansing action of soaps. 

b) Write the differences between saturated and unsaturated carbon compounds.

Ans:

a)

i)   

★ Carbon cannot form C4+ cation because of removal of 4 elections from a carbon atom would require a large amount of energy.

★ Carbon cannot form C4- anion because it would be difficult for the nucleus with 6 protons to hold on to 10 electrons.

ii)

The melting point of pure ethanoic acid is very low / 290 K and hence it freezes during winter / in cold climates. 

b)

i)

ii)

OR

a) 

★ The molecules of soap are sodium or potassium salts of long chain carboxylic acids.

★ The ionic end of soap interacts with water while the carbon chain interacts with oil.

★ The soap molecules thus form structure called micells. This forms an emulsion in water.

★ The soap micelles thus helps in pulling out the dirt in water and we can wash our clothes clean.

b)

                 PART - C BIOLOGY        

XI. Multiple Choice Questions: 3× 1 = 3 

26. The process of producing new individuals in rhizopus is 

(A)    spore formation  (B) fragmentation 

(C) budding                   (D) regeneration 

Ans: (A) spore formation

27. Part of flower that develops into fruit and part of the seed that develops into root respectively are 

(A)  Ovary and Plumule 

(B) Plumule and radicle 

(C)  Ovary and radicle 

(D) Ovary and ovule

Ans: (C) Ovary and radicle 

28. Organisms that reproduce sexually are more likely to survive in their environment. Because in sexual reproduction these organisms, 

(A)    do not produce any variations. 

(B) will not have any errors during DNA replication. 

(C) will have the same body structure in all generations. 

(D) will have the maximum number of successful variations in the subsequent generations. 

Ans: (D) will have the maximum number of successful variations in the subsequent generations. 

XII. Answer the following questions:3 ×1 = 3 

 

29. What is the function of synapse?

Ans:

It transmits chemical signals generated at the axon terminal to the dendrite

30. Is self-pollination possible in flowers that have only stamens? Justify your answer. 

Ans:

No, For self-pollination to occur, a flower must have both stamens (male part) and pistil/carpel (female part).

31. The respiration rate of aquatic animals is faster than that is found in terrestrial animals. Why?

Ans:

Because the amount of dissolved oxygen is fairly low as compared to the amount of oxygen in the air, the rate of breathing in aquatic organisms is much faster than that seen in terrestrial organisms. 

XIII. Answer the following questions: 2×2=4 

32. What is geotropism? Name the plant part that is positively geotropic. 

OR 

Name the hormones that perform the following functions in humans. 

i) Controlling the level of sugar in the blood. 

ii) Preparing the body to face the emergency situation. 

Ans:

★ The growth movement of a plant part in response to the force of gravity.

★ The root

OR

i) Insulin

ii) adrenaline

33. The approximate lengths of the small intestine of the animals A and B are given in the below table. Observe the data in the table and answer the question.  

Identify the herbivorous and carnivorous animal among A and B. Support your conclusion. 

Ans:

★ Animal X is herbivorous and animal Y is carnivorous.

★Because herbivores consume plant which is full of cellulose and the digestion of cellulose takes a long time. Herbivores need a longer small intestine to allow cellulose to be digested.

★ Whereas Meat is easier to digest, hence carnivores have shorter small intestine.

XV. Answer the following questions: 3×3= 9

34. a) Define the following: 

i)  Food chain 

ii) Biomagnification 

b) Mention the function of ozone. Name the chemical responsible for ozone depletion.  

Ans:

a)

i) It is the sequence of organisms through which energy is transferred from one trophic level to the next,

ii) It is the phenomenon where the concentration of a non-biodegradable  progressively increases at successive trophic levels in a food chain

b) 

★ Ozone protects the earth from harmful UV-radiation 

★ CFC‘s are responsible for the decrease in the amount of ozone layer.

35. a) A short pea plant (tt) is crossed with a tall pea plant (TT). Express the result obtained in the F2 generation with the help of checkerboard. 

b) How is the baby girl sex will be determined? 

 OR 

Round and yellow seeds (RrYy) producing pea plants are self-pollinated. Express the result obtained in this crossing with the help of a checkerboard. Mention the types of the plants obtained. 

Ans:

a)

b)

★ male has one X and one Y chromosome (XY).

★ The female produces only one type of gamete (ovum) with an X chromosome.

★ A child who inherits X chromosome from her father will be a baby girl.

OR

The plants obtained are

Round yellow — 9 ,

Wrinkled yellow — 3 ,

Round green — 3

Wrinkled green — 1

36. In a situation where we withdraw our leg when stepped on thorn unknowingly, 

i)  Write the sequences of events that occur to give the response in this situation. 

ii) Which part of human nervous system controls this action?

Ans:

i) 

★ Receptors receive the stimulus of pain

★Messages reach spinal cord through sensory neuron.

★Responses reach motor neuron through association neuron.

★Responses reach effectors through motor neuron.

★ Muscles withdraw the leg.

ii) Spinal cord controls this action  

XVI. Answer the following question: 1×4 = 4 

37. Draw the diagram showing the structure of the human heart. Label the following parts: i)  Superior vena cava ii) Left ventricle 

Ans:

XVII. Answer the following question :1x5= 5 

38. a) What happens if egg does not fertilize in human female reproductive system? Explain briefly. 

b) List any four advantages of vegetative propagation. 

c) Write two examples for the organisms that reproduce by binary fission.  

OR 

a) In women, how does a fertilized egg develop into an embryo in the uterus? 

b) Is surgical contraception a better method of contraception than physical contraception? Justify your answer. 

c) Write the function of testes in human male reproductive system. 

Ans:

a)

★Uterus prepares itself every month to receive fertilized egg. It makes its inner layer thick and spongy.

★ If fertilization doesn‘t occur the lining slowly breaks and comes out through the vagina as blood and mucous. ( Menstruation occurs )

b)

★Good qualities of a variety can be maintained indefinitely.

★Vegetative propagation gives a genetically uniform population.

★ Plants raised by vegetative propagation can bear flowers and fruits earlier.

★ This makes the propagation of plants that have lost the capacity to produce seeds 

c)

★ Amoeba

​

★ Paramecium 

★ Leishmania      (Any two)

OR

a)

★ The fertilized egg starts dividing and forms a ball of cells or embryo.

★ The embryo is implanted in the lining of the uterus where they continue to grow and develop organs to become foetus.

b)

★ Yes

★Surgical contraception more effective and permanent than physical (barrier) methods like condoms or diaphragms

c) They produce sperms and testosterone hormone which is responsible for male characters.