The S.I. unit od electric potential is volt. It is denoted by V.(Volt)

The part of the hindbrain that takes part in the regulation of respiration is medulla oblongata.

Brain and spinal cord.

Michael Faraday in 1831 discovered that mechanical motion can produce current.

C_nH_2n = Alkene
2nd member = C₃H₆ (Propene)

Female baby

(i) Oxygen enters the human body through the nasal passage and reaches the lungs.
(ii) Numerous alveoli are present in the lungs. These alveoli are surrounded by many blood capillaries. From the alveoli, 0₂ is taken up by the red blood cells present in the blood capillaries.
(iii) Similarly, the CO₂ from the various tissues is transported to the alveoli.
(iv) This CO₂ is then released through the nasal passage during exhalation. Alveoli are the sites of exchange of gases. Each lung contains 300- 350 million alveoli.
These alveoli increase the surface area for gaseous exchange, making the process of respiration more efficient.

The transport of soluble products of photosynthesis is known as translocation. Translocation in plants occurs by means of the vascular tissue known as phloem. Translocation is necessary because without it, the food prepared by the leaves cannot reach other parts of the plant.
(i)In plants, the synthesis of sugars takes place in the leaves by the process of photosynthesis.
(ii)Hormones are synthesised away from their targrt site.

The two ways in which non-biodegradable substances would affect the environment are
(i) They make the environment poisonous and unfit for survival of living forms of life.
(ii) They block the transfer of energy and minerals in the ecosystem.

(i) The acid is to be added slowly in water to prevent the mixture to be splashed. The reaction is highly exothermic, therefore, constant cooling should be done.
(ii) The process is called dilution.

(i) Bulb A and B do not glow but bulb C glows.
(ii) Glucose and alcohol solutions do not conduct electricity as they do not have ions. Dil. HCI contains ions so the flow of ions is responsible for the flow of current
(iii) After replacement, bulb glows in B as NaOH solution contains ions (Na⁺ and OH^- ions).

(i) Copper is more reactive than silver. Hence, when copper wire is dipped in silver nitrate solution, it displaces silver from AgNO₃ solution forming copper nitrate which is bluish green in colour.
\((ii)\quad Cu+2AgN{ O }_{ 3 }\longrightarrow \underset { Copperr\quad (II)\quad nitrate\\ bluish\quad green }{ Cu{ (N{ O }_{ 3 }) }_{ 2 } } +\underset { Silver }{ 2Ag } \)

A number of resistors are said to be connected in series, if these are joined end to end and the same, current flows through each one of them when a potential difference is applied across the combination. If we connect ammeter first between the point A and R₁, then between R1 and R₂:R₂ and R₃ and lastly between R₃ and the point B; it is same as current.

The salivary glands secrete saliva. The saliva contains water, salts, mucus and an enzyme ptyalin. The enzyme ptyalin, also glycogen and convert them into maltose. The mucus and water makes the food soft and slippery for the formation of bolus and also protects soft lining of alimentary canal. Thus the digestion of starch i.e., carbohydrate begins in the mouth. Since,the food remains in the mouth only for a short time and so, the digestion of food remains incomplete.
\(Starch(Carbohydrates)+Glycogen\overset { Ptyalin }{ \longrightarrow } Maltose\)
The partially digested food is further digested in the stomach. The food is broken down into smaller pieces and churned to form a semi-solid paste. The wall of the stomach contains three tubular glands. These glands secrete gastric juice. The gastric juice contains hydrochloric acid, mucus, pepsin, gastric lipase and rennin.
Hydrochloric acid:
It softens the food
It makes food acidic for the function of pepsin
It stops the action of salivary amylase
It kills germs and bacteria to disinfect the food
It converts inactive pepsinogen and prorennin into active pepsin and rennin.
\(InactivePepsinogen\overset { HCI }{ \longrightarrow } ActivePepsin\\ InactivePro-rennin\overset { HCI }{ \longrightarrow } Activerenin\)
Pepsin: It hydrolyses proteins into soluble proteoses and peptones only in presence of hydrochloric acid.
\(Protein\overset { Pepsin }{ \longrightarrow } Peptones+Proteoses\)
Rennin: It is active only in infants. The main function of rennin is that it converts soluble milk protein casein into insoluble protein called paracasein. Due to this, milk stays in stomach for longer duration.
\(\underset { (solublemilkprotein) }{ Casein } \overset { Rennin }{ \longrightarrow } \underset { (Insoluble) }{ Paracasein } \)
Mucus: The main function of mucus is to protect the inner lining of stomach from corroding action of hydrochloric acid as well as from pepsin enzyme.
Small Intestine: It is the seat of major digestion and absorption. Small intestine receives the secretion of two glands namely,
(i) Liver, (ii) Pancreas
Liver: It is the largest gland of the body. It is reddish brown in colour. It has soft pear - shaped sac called gall bladder. The gall bladder secretes bile juice. Bile is alkaline containing bile pigment. Thus, bile is stored in the gall bladder. It helps to emulsify or break the fats or lipids present in the food.
The bile performs the following functions:
(i) It breaks the larger globules of fat into small globules to make the enzyme to act and digest them.
(ii) It prevents putrefaction of food.
(iii) The bile creates a medium for the pancreatic juice to act on food by neutralizing the acidity in the food.
Pancreas: Pancreas secretes a digestive fluid called pancreatic juice. This juice contains digestive enzymes such as trypsin, nucleases, pancreatic lipase and pancreatic amylase. The enzyme trypsin digests the proteins, the enzyme pancreatic amylase breaks down the starch and the enzyme lipase breaks down the emulsified
facts. Pancreas produces two important hormones namely,
(i) Insulin, (ii) Glucagon
Insulin is essential for using glucose and storing it into glycogen. Glucagon is essential for conversion of glycogen into glucose. The alkaline medium is favourable
for the action of pancreatic enzymes.
\(Starch\xrightarrow [ ]{ Pancreaticamylase } Maltose\\ Fat\xrightarrow [ ]{ Lipase } Fattyacids+Glycerol\\ Proteins\xrightarrow [ ]{ Trypsin } Peptides\)
Secretion of intestinal juice by liver and pancreatic glands
The intestinal juice contains a number of enzymes which complete the digestion process. Here, the complex carbohydrates are converted into glucose, proteins are converted into amino acids and fats are converted into fatty acids and glycerol. All these end products i.e., amino acids, glucose, fatty acids and glycerol are small
and water soluble molecules. This complete digestion of food takes place by biological catalysts called enzymes. The intestinal juice includes - maltase, invertase, lactase etc.
\(Peptides\xrightarrow [ ]{ Trypsin } Aminoacids\\ Sucrose\xrightarrow [ ]{ Invertase } Glucose+Fructose\\ Maltose\xrightarrow [ ]{ Maltose } Glucose+Glucose\\ Lactose\xrightarrow [ ]{ lactose } Glucose+Galactose\)

Food is prepared in the green leaves of the plant by combining carbon dioxide and water in presence of sunlight and chlorophyll. The carbon dioxide required for photosynthesis is taken by the plants from air. The carbon dioxide enters the leaves through tiny pores called stomata. The water required is taken from soil. The sunlight provides the energy required to carry out the preparation of food. The green pigment called chlorophyll present in green leaves help to absorb energy from sunlight. The oxygen produced as a by-product goes into the air.
The food prepared by the green leaves is in the form of glucose. This glucose is sent to different parts of the plant. The excess glucose is changed into starch and is stored in the leaves of the plant. The food prepared by photosynthesis provides all the energy to a plant which it needs to grow. Thus, it is clear that the green plants convert sunlight energy into chemical energy. by making food. When we eat plant foods such as fruits, vegetables, food grains etc., the chemical energy stored in them is released in our body during respiration.
During the process of photosynthesis, the following three steps take place:
(i) Absorption of sunlight energy by chlorophyll.
(ii) Conversion of sunlight energy into chemical energy and splitting of water into hydrogen and oxygen using sunlight energy.
(iii) Reduction of carbon dioxide to form carbohydrates using the chemical energy.

Since the element B belongs to atomic number 17, it must be chlorine.
The element which burns golden flame in air is sodium. Therefore, the element A must be sodium.
When element sodium and chlorine reacts, it forms sodium chloride, the compound C. The compound C on electrolysis gives sodium hydroxide and hydrogen gas.
Thus, A = Na; B = CI₂; C = NaCI; D = NaOH.
         Chemical Reactions involved:
              \(2Na+{ CI }_{ 2 }\rightarrow 2NaCI\)
\(2NaCI(aq)+{ 2H }_{ 2 }O(I)\rightarrow 2NaOH(aq)+{ CI }_{ 2 }(g)+{ H }_{ 2 }(g)\)

(a) The arrangement of metals in a vertical column in the order of decreasing reactivity is called the 'activity series' of metals. 
Following is the order of decreasing order of reactivity:
Cu> Fe> Zn> AI> Mg
(b) (i) When some zinc is put into blue copper sulphate solution, the blue colour of the copper sulphate solution fades gradually due to the formation of colourless zinc sulphate and red-brown copper metal is deposited on the zinc strip.
                           \(\underset { Coppersulphate\\ \quad (blue) }{ { CuSO }_{ 4 }(aq) } +\underset { Zinc }{ Zn } \rightarrow \underset { Zincsulphate\\ (Colourless) }{ { ZnSO }_{ 4 }(aq) } +\underset { \quad Copper\\ (Red-brown) }{ Cu(s) } \)
(ii) No reaction will take place since copper is less reactive than iron and hence will not displace it from ferrous sulphate solution.
(c) Sodium metal combines with hydrogen gas to form sodium hydride.
                           \(\underset { Sodiummetal }{ 2Na(s) } +\underset { Hydrogengas }{ { H }_{ 2 }(g) } \rightarrow \underset { Sodiumhydride }{ 2NaH(s) } \)

Gamete is formed as a result of meiosis in gametogenic cells. Zygote is formed after fusion of two different kinds of gametes. Different types of gametes are formed by different parents. Zygote is formed in the female reproductive part only.
Role of gamete in sexual reproduction: Gamete formation results in halving of number of chromosomes which is necessary to maintain the number of chromosomes in an organism which reproduces sexually.
Role of zygote in sexual reproduction: Zygote formation makes the number of chromosome equal to the somatic cells. further, it is the zygote which undergoes mitosis to develop into an embryo and subsequently into a new individual.

(b) Refractive index of glass from air
\(_{ a }{ { n }_{ g } }=\frac { 3 }{ 2 } \)
Refractive index of air from glass:
\(_{ g }{ { n }_{ a } }=\frac { 1 }{ _{ a }{ { n }_{ g } } } \)
\(\Rightarrow \frac { 1 }{ 3/2 } =\frac { 2 }{ 3 } \)