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Ch.02. Acids, Bases and Salts
A. Answer the following questions in not more than 20 words.
1. Classify the following substances into acidic and basic substances.
Tomato juice, soap solution, tooth paste, lemon juice, vinegar
ANSWER: Acidic: Tomato juice, lemon juice and vinegar (they turn blue litmus red)
Alkaline: Toothpaste and soap solution (they turn red litmus blue)
2. Name three mineral acids and give their formulae.
ANSWER: Sulphuric acid (H2SO4), nitric acid (HNO3) and phosphoric acid (H3PO4) are examples of mineral (or inorganic) acids.
3. Define acids.
ANSWER: Acids are substances that taste sour and corrode metals. They react with bases and get neutralised to form salt and water. An acid furnishes H+ ions when dissolved in water.
4. Define bases.
ANSWER: Bases are substances that taste bitter and are slippery to the touch. They neutralise acids and form salt and water on reaction with acids. A base furnishes OH− ions when dissolved in water.
5. What are soluble bases called? Give two examples.
ANSWER: An alkali is a base that dissolves in water. When a base dissolves in water, it furnishes OH− ions. Examples: Sodium hydroxide and calcium hydroxide.
6. Define neutral substances.
ANSWER: A substance that has neither acidic nor alkaline character is termed chemically neutral or neutral substance.
B. Answer the following in not more than 40 words.
1. Name an acidic gas which is discharge into the atmosphere on the burning of fuels like coal and natural gas. How is this gas formed?
ANSWER: Fossil fuels like coal and natural gas, apart from carbon, contain impurities like sulphur and nitrogen. On burning the fossil fuels, these elements react with oxygen in air to form acidic oxides like sulphur dioxide, sulphur trioxide, nitric oxide and nitrogen dioxide. They are formed in accordance with following reactions:
S + O2 → SO2 (formation of sulphur dioxide)
2SO2 + O2 → 2SO3 (formation of sulphur trioxide)
N2 + O2 → 2NO (formation of nitric oxide)
2NO2 + O2 → 2NO2 (formation of nitrogen dioxide)
2. What are the general properties of basic substances?
ANSWER: Following are the characteristics of bases:
1. They have a bitter taste.
2. They are slippery to touch (like soap).
3. They furnish OH− ions when dissolved in water. (Soluble bases are called alkalis.)
4. They turn red litmus blue.
C. Answer the following in not more than 100 words.
1. Write the properties of an acid.
ANSWER: Properties of Acids:
• Acids are corrosive in nature. They damage the surface of metals when they make contact with them. Sour food items are not kept in metal containers because, such food items react with metal container and form metal salts and hydrogen gas.
H2SO4 + Zn → ZnSO4 + H2
H2SO4 + Fe → FeSO4 + H2
• When an acid is added to water, heat is generated. Almost all acids are readily soluble in water.
• Acids turn blue litmus red and show no effect on phenolphthalein and turmeric juice.
• Acids are sour in taste.
• Acids undergo neutralisation reaction i.e., they react with bases and get neutralised to form salt and water.
• Acids react with bicarbonates and carbonates to cause effervescence, releasing CO2 gas.
2. Describe an activity to show the effect of an acid on carbonates and hydrogen carbonates.
ANSWER: Carbonate salts contain a metal ion and a
3. What is acid rain? How is it formed? Mention three bad effects of acid rain.
ANSWER: When rainwater in clouds get mixed with sulphur dioxide and oxygen present in atmosphere, this mixture (i.e., sulphuric acid) is called acid rain. It is mainly due to burning of coal, which contains sulphur as impurity and emits sulphur dioxide on burning. This sulphur dioxide in the atmosphere reacts with oxygen to form sulphur trioxide; it then reacts with the water in the clouds to form sulphuric acid.
S + O2 → SO2
2SO2 + O2 → 2SO3
SO3 + H2O → H2SO4
Harmful Effects of Acid Rain:
• It damages metal structures like bridges, windows, door frames, railings, buildings and monuments made up of marble and cement.
• It increases the acidity of water bodies like ponds, lakes and oceans causing great damage to aquatic life.
• It increases the acidity of soil and decreases its fertility.
4. Write a note on the uses of bases.
ANSWER: Uses of Bases:
(a) Lime or calcium hydroxide [Ca(OH)2] is used for whitewashing.
(b) NaOH and KOH are used in the manufacturing of soaps and detergents. Sodium hydroxide is sometimes used to clear drain blockages.
(c) Ammonia (NH3) is used in the manufacturing of fertiliser like ammonium nitrate (NH4NO3) and ammonium sulphate (NH4)2SO4.
(d) Magnesium hydroxide [Mg(OH)2] (milk of magnesia) is used in antacids (a medicine that neutralises hyperacidity in our body).
(e) Oxides of iron, copper, chromium and cobalt are colourful and are used in manufacturing coloured glasses.
R/7
Ch.11 RESPIRATION IN PLANTS AND ANIMALS
A. Answer the following in not more than 20 words.
1. How do earthworms breathe?
Answer: - Earthworms do not have any special organ for breathing. They use
their skin to breathe.
2. How does an insect take in air and how does the air reach the different parts of its body?
Answer: - Insects have openings on the sides of their body called spiracles, through which they inhale air. The inhaled air gets distributed throughout the insect's body through the network of trachea.
3. What is respiration rate?
Answer: - The number of times we breathe air in and out in a minute can be defined as the rate of respiration.
4. How do the leaves of plant exchange gases with the atmosphere?
Answer: - In the leaves of plants, various small openings, called stomata, are present. Plants exchange gases through these openings.
5. Why do gardeners loosen the soil from time to time?
Answer: - Loosening of soil causes the gaps between soil particles to enlarge, which helps in the easy exchange of gases between the atmosphere and the roots of plants, which also breathe.
6. When does anaerobic respiration occur in our body?
Answer: - Strenuous activities, such as running, swimming and dancing, require a huge amount of oxygen. When this demand of oxygen is not fulfilled, the muscles start respiring anaerobically.
7. What roles do hair and the membrane of the nasal cavity play?
Answer: - The hair and nasal membrane present in the nasal cavity perform the following functions.
• They purify the air entering the nose.
• They moisten the air.
• They regulate the temperature of the air.
B. Answer the following in not more than 40 words.
1. How do fish and tadpole breathe?
Answer: - Tadpoles and fish have to utilise the oxygen dissolved in water. They have organs called gills for this purpose. The gills have several filaments supplied with numerous capillaries. Water enters through the mouth of a fish or a tadpole and flows over the filaments of the gills. The oxygen dissolved in the water diffuses into the capillaries and the carbon dioxide in the capillaries is released into the water.
2. Why does the respiration rate increase after exercise?
Answer: - The rate of respiration increases after exercise because, when we are engaged in strenuous activities, our body utilises much more energy than usual. This requirement of a higher amount of energy during exercise is met by an increase in the respiration rate, which increases the amount of oxygen made available to the body.
3. What are the two steps involved in respiration?
Answer: - Following are the steps involved in respiration:
(a) External respiration: Inhalation of oxygen by an organism from the atmosphere and exhalation of carbon dioxide back to the atmosphere is termed external respiration.
(b) Internal respiration: Internal respiration refers to breaking down of glucose by oxygen in all the cells of the body. Oxygen, from the respiratory organs of an organism, is distributed to all the cells of the body of the organism where it breaks down glucose to release energy.
4. What is anaerobic respiration? How do we make use of it?
Answer: - The type of respiration in which there is no requirement of oxygen is called anaerobic respiration. It occurs mostly in microbes. During anaerobic respiration, products such as lactic acid and alcohol are produced.
Glucose → Ethanol + CO2 + ATP (Energy)
Glucose → Lactic acid + ATP (Energy)
Anaerobic respiration in microbes is utilized in the industrial production of lactic acid and alcohol.
We make use of this process to provide instant energy to muscle cells during strenuous activities such as running, swimming etc., when the amount of oxygen in our body becomes insufficient to perform aerobic respiration.
C. Answer the following in not more than 100 words.
1. How would you so that exhaled air has carbon dioxide?
Answer: - Take two transparent glasses and fill them half with water. In both glasses, add lime powder and cover them with cardboard pieces. Make two holes in each cardboard piece and insert straws in all the four holes. Mark the straws 1, 2, 3 and 4. Straws 2 and 4 should be placed in such a way that they remain suspended in the air in half-filled glasses and do not touch the water surface.
Now, inhale from straw 2 using your mouth and exhale into the other glass using straw 3. Limewater in the second glass, into which air has been exhaled, turns milky because of the presence of a larger amount of CO2 in the exhaled air. This shows that exhaled air contains carbon dioxide.
2. Describe the path taken by inhaled air from the nostrils to the lungs.
Answer: - The path of air from the nose to the lungs is described below.
• Air from the atmosphere is inhaled through the two openings in the nose called nostrils.
• The nostrils lead the air to the nasal passage or nasal cavity. The nasal cavity contains numerous nasal hair and mucus membranes. These hairs filter the air we inhale by trapping the dust particles that enter the nose along with the air.
• The nasal cavity leads this filtered air to the pharynx that finally leads the air to the windpipe or trachea through the larynx.
• The larynx is also called the voice box, as it is responsible for the generation of speech.
• The trachea leads the air to the lungs through a pair of bronchi.
3. What makes air enter our lungs when we inhale?
Answer: - Our body has a circular, dome-like muscle present right below the lungs. This muscle is called the diaphragm. The diaphragm acts like a pump to create a vacuum in our chest cavity. When we inhale, the diaphragm gets flattened, and at the same time, the ribcage moves upward and outward. This leads to an increase in the volume of our thoracic/chest cavity. As the volume increases, the pressure of air outside the lungs increases and air rushes into our lungs through our nostrils.
4. How does oxygen from the air in the lungs reach the cells?
Answer: - Oxygen enters our lungs from the atmosphere through the nose. In the lungs, millions of balloon-like structures, called alveoli, are present. Air from bronchioles reaches these alveoli, which are surrounded by a very fine mesh of capillaries. These capillaries have very thin walls that allow oxygen to diffuse into the blood from each alveolus. Haemoglobin present in the red blood cells of blood combines with oxygen and is carried to each cell of the body through blood.
C. Fill in the blanks…
1. Oxygen combines with hemoglobin in the blood to form oxyhaemoglobin.
2. The lungs have millions of air sacs called alveoli.
3. Carbon dioxide and water are formed during internal respiration.
4. Anaerobic respiration is also known as fermentation.
5. The larynx is responsible for speech.
6. The tiny openings on stems and fruits that plants use for breathing are called stomata.
7. Alcohol is formed during anaerobic respiration.
8. The opening and closing of the stomata are controlled by guard cells.
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Ch.03 Changes and Reactions
A. Answer the following questions in not more than 20 words.
1. Define a physical change.
Answer: - A generally reversible change, in which no new substances are formed, is called a physical change.
2. Define a chemical change.
Answer: - An irreversible change in which new substances are formed under specific conditions is called a chemical change.
3. Classify the following into physical and chemical changes.
(a)The cooking of food
(b) The evaporation of a liquid
(c) The digestion of food
(d) Burning
(d) The condensation of water vapour
Answer: - (a) Chemical change
(b) Physical change
(c) Chemical change
(d) Chemical change
(e) Physical change
4. What are the following called?
(a) A reaction in which two or more reactants add up to form a product
(b) A reaction in which one substance breaks down into two or more simpler substances
(c) Reaction in which one element displaces another from a compound and takes its place
(d) A reaction in which an acid reacts with a base to form a salt and water
Answer: - (a) A reaction in which two or more reactants add up to form a product is called a combination reaction.
(b) A reaction in which one substance breaks down into two or more simpler substances is called a decomposition reaction.
(c) A reaction in which one element displaces another from a compound and takes its place in the compound is called a displacement reaction
(d) A reaction in which an acid reacts with a base to form salt and water is called a neutralisation reaction.
B. Answer the following in not more than 40 words.
1. How would you decide whether a change is physical or chemical? Mention two characteristics of each kind of change.
Answer: - In physical changes, generally no new substances are formed, whereas, in chemical changes, new kinds of molecules or new substances are formed.
Few characteristics are mentioned below:
Physical Changes | Chemical Changes |
No new substances are formed; only physical state changes. | New substances are formed. |
These changes are generally reversible. | These changes are irreversible. |
2. Discuss why the dissolving of salt in water is a physical change.
Answer: - Once salt is dissolved in water, it can be recovered from the salt solution by evaporating the water. This dissolution of salt in the fluid is reversible. Thus, it is a physical change
3. Discuss an example of physical and chemical changes happening together.
Answer: - A burning candle is an example of both physical and chemical changes. When a candle burns, the wax melts; on cooling, it solidifies. So, this is a physical change. However, burning of wax in candle is a chemical change.
C. Answer the following in not more than 100 words.
1. Giving one example of each kind, show that a change in energy takes place when a physical or a chemical change occurs.
Answer: - Energy is an important prerequisite for any change to take place. Both physical and chemical changes are accompanied with change in energy level. While energy is released during some changes, it is also absorbed during some other changes.
When a solid is converted into a liquid or gas, heat is absorbed. Similarly, when a liquid evaporates, it absorbs heat from the surroundings. Some solutes such as glucose, while dissolving, absorb heat.
Some chemical changes require release of energy. Photosynthesis is an example of such a change. Even cooking of food is a chemical change that requires heat.
On the other hand, there are processes that release heat during the process itself.
Physical changes such as conversion of a liquid into solid or condensation of a gas into liquid release heat into the environment. Similarly, certain chemical reactions (e.g., respiration) are accompanied with release of heat.
2. Describe an activity to find the conditions required for rusting.
Answer:- An activity to determine that moist air is important for rusting has been described below:
• Take a few rust-free iron nails in test tube A. Pour some water on the nails, so that the nails are submerged.
• Boil some distilled water over the burner in test tube B, so that no dissolved air is left in the water. Put some iron nails and cork the test tube after pouring some oil on the water surface to completely cut off oxygen supply.
• Put some anhydrous calcium chloride in test tube C, so that the air inside the test tube is moisture-free. Put a perforated disc in the test tube, put some nails over the disc and cork the test tube.
Observation: The nails in test tube A get rusted because of presence of both moisture and air. The nails in test tube B remain rust-free because of the absence of air. The nails in test tube C are rust-free because of the absence of moisture. Therefore, there is no rusting in test tubes B and C.
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Ch. 07 Electricity
A. ANSWER THE FOLLOWING IN NOT MORE THAN 20 WORDS.
1. What do you need to apply across a bulb to cause a current to flow through it?
Answer-We need to apply voltage across a bulb to cause a current to flow through it.
2. Why does a bulb get warmer than the wires that connect it to a battery?
Answer- A bulb gets warmer than the wires because the filament of bulb is made up of tungsten which provides greater resistance to the current than the wires, which are good conductors. Higher resistance leads to production of more heat. Radiation of heat from this heated up filament causes the bulb to heat up.
3. A magnetic needle gets deflected when brought near a current- carrying conductor. What does this show?
Answer- Deflection of magnetic needle on bringing it closer to a current carrying conductor shows that a current-carrying conductor behaves like a magnet.
4. What happens when you place an iron nail in a current -carrying coil?
Answer- Iron nails get magnetised when they are placed in a current-carrying coil.
5. Why do we use a soft iron core in an electromagnet?
Answer- We use a soft iron core in an electromagnet so that the electromagnet loses its magnetism as soon as the current is switched off.
6. Name four devices that use the heating effect of electric current.
Answer- Four devices that use the heating effect of current are an electric heater, an iron, a toaster and a bulb.
7. Mention four applications of electromagnets.
Answer- Electromagnets are used in motors, cranes, telephones and electric doorbells.
B. Answer the following in not more than 40 words.
1. What is a circuit diagram? Draw the circuit diagram of a torch which works on three cells.
Answer- A circuit diagram refers to the representation of a circuit showing its components using standard symbols.
2. Identify the following symbols. Also mark the positive and negative terminals in the symbols for the cell.
Answer- (a) Cell
(b) Bulb
(c) Battery
(d) Switch
Symbolic representation of positive and negative terminals in the symbol of a cell -
3. How is the heat produced by an electric current related to resistance and the magnitude of the current?
Answer- The amount of heat produced by an electric current depends upon the resistance of the conductor and the magnitude of the current. As the resistance of the conductor and the magnitude of the current increase, the heat produced by the electric current also increases.
4. Why is a long and thin tungsten filament used in a bulb?
Answer- A bulb has a long and thin tungsten filament because tungsten offers high resistance to the flow of current, moreover the length of the tungsten filament adds to this resistance which makes the bulb glow due to the generation of more heat.
5. Mention two problems associated with the heating effect of electric current.
Answer- Two problems associated with the heating effect of current are:
1. When electric current flows through a conductor, a part of the electrical energy is converted into heat energy. This causes wastage of energy.
2. The heat produced can cause fires by damaging the insulation on wires.
6. What is an electromagnet? Mention two properties of an electromagnet.
Answer- Electromagnets are magnets that are produced by passing an electric current through a coil wound around a soft iron core.
Two properties of an electromagnet are as follows.
1. Its strength depends on the number of turns of its coil and the amount of current passing through it.
2. Its magnetism lasts only as long as a current passes through its coil.
C. Answer the following in not more than 100 words.
1. What is electrical resistance? On what does the resistance of a piece of material depend? How does resistance affect current?
Answer- The electric resistance of a piece of a material is a measure of the hindrance or obstruction it creates to the flow of electric current.
The resistance of a piece of a material depends on two factors:
(a) Thickness of the material
(b) Length of the material
Electric resistance produces obstruction to the flow of electric current. Higher the value of resistance of a conductor, the lower the value of electric current that can flow through it and vice versa.
2. What is a fuse? How does it work?
Answer- A fuse is a safety device that opens an electric circuit when excessive current flows through it, threatening the wires to burn due to excessive heat and closes the circuit when there is no current flowing through it.
A fuse contains a special wire whose melting point is lower than those of other conductors in the circuit. When the current flowing through the circuit becomes excessive because of a short circuit or an overload, the wire of the fuse becomes hot and melts. This breaks the circuit and prevents any damage to the circuit.
3. Explain with the help of a diagram the construction and working of an electric bell.
Answer- An electric bell consists of a hammer, metal strip, gong and switch. It is made up of a coil of wire wound on an iron piece that acts as an electromagnet when electric current is passed through it. It works on the principle of electromagnetism.
The hammer of the bell is attracted towards the electromagnet when the circuit is complete. Further, the circuit breaks after the hammer moves towards the electromagnet. When the circuit breaks, the electromagnet does not attract the hammer, and the hammer returns to its original position because of a spring effect. As the hammer goes back to its original position, it touches the metal connector and the circuit is complete again. This cycle continues till the switch is kept in the 'on' position.
D. Fill in the blanks.
1. The greater the voltage across a device, the greater is the current through it.
2. The connections between components are represented by lines in a circuit diagram.
3. A long wire has a higher resistance than a short wire.
4. An overload is a condition in which a wire carries a current that is more than what is safe.
5. A closely wound length of wire is called a coil.
R/3
Ch. 06 Time, Motion and Speed
A. ANSWER THE FOLLOWING IN NOT MORE THAN 20 WORDS.
1. What is a unit of measurement?
Answer- A known fixed quantity is a unit of measurement. We compare an unknown quantity that we wish to measure with a fixed quantity.
2. Define speed and mention the SI unit of speed.
Answer- Speed of a body is defined as the distance travelled by the body in unit time. Its SI unit is metres/second (m/s).
3. When is a body said to be in motion?
Answer- A body is said to be in motion when its position changes with time.
4. How are stopwatches different from ordinary watches?
Answer- Stopwatches have electronic switches which can be used to stop or start these watches. This helps in measuring time intervals more accurately than ordinary watches which indicate continuous passage of time. This is how stopwatches are different from ordinary watches.
5. What property of a pendulum made it suitable to be used in the manufacture of clocks?
Answer- The periodic motion of pendulums makes them suitable for making clocks.
6. What is the time period of a pendulum?
Answer- The time period of a pendulum is the time taken by it to complete one oscillation.
7. Mention one factor that determines the time period of a pendulum.
Answer- One factor that determines the time period of a pendulum is the length of the pendulum.
8. When is a moving body said to be in uniform motion?
Answer- A moving body is said to be in uniform motion when its speed remains constant i.e., it covers equal distances in equal intervals of time.
9. Correct the following.
(a) 90 m. (b) 100 kgs (c) 10 secs (d) 50 kilos
Answer-(a) 90 m
(b) 100 kg
(c) 10 s
(d) 50 kg
Numericals
1. A car takes 20 minutes to cover a distance of 15 km. Calculate its speed in km/h and m/s.
2. The distance between two towns is 400 km. How much time would it take a car to cover this distance at an average speed of 50 km/h?
3. A man driving at an average speed of 40 km/h takes 6 hours to travel from one town to another. What is the distance between the towns?
4. Plot a distance-time graph for a body travelling at speed of 2.5 m/s.
5. The distance covered by a moving body over time is represented graphically in figure 6.9. Find its speed.
R/2
Ch. 09 Obtaining and Utilizing food
A. Answer the following questions in not more than 20 words.
1. All living beings procure energy from food. Name the three life processes which help them do this.
Ans.- Three life processes that help living organisms to procure energy from food are:
(i) Digestion (Nutrition)
(ii) Respiration
(iii) Transportation
2. What are autotrophs? Name an organism other than green plants that is an autotroph.
Ans.- Autotrophs are organisms that can prepare their own food. Chlamydomonas is a type of green algae which is an example of an autotroph, other than green plants.
Cyanobacteria are also an example of autotroph.
3. Name the three types of heterotrophic Nutrition.
Ans.- Three types of heterotrophic nutrition are:
(i) Saprophytic nutrition (ii) Parasitic nutrition (iii) Holozoic nutrition
4. What are enzymes?
Ans.- Enzymes are chemical substances that act as biological catalysts and are important for carrying out biochemical processes, such as digestion, in our body
5. Name the steps involved in the process of holozoic Nutrition.
Ans.- Holozoic nutrition involves the following steps:
(i) Ingestion (ii) Digestion (iii) Absorption (iv) Assimilation (v) Egestion
6. Name three things green plants need to order to photosynthesize.
Ans.- Green plants require the following three things to prepare their food:
(i) Carbon dioxide (CO2) (ii) Water (H2O) and (iii) Sunlight
7. What is the juice secreted by the liver called? What does it do?
Ans.- Juice secreted by the liver is called bile. It helps in digestion of fats by breaking them down into small droplets
8. Name a parasitic plant, and the parasite that lives in our intestine.
Ans.- Cuscuta is a parasitic plant. Tapeworm (Ascaris) is a parasite that lives in our intestines.
9. What is digestion?
Ans.- Digestion is the process of breaking down complex food material into simpler form so that they could be absorbed into the watery blood plasma.
10. Name a holozoic animal that is not a herbivore, carnivore or omnivore.
Ans.- Spider (also earthworm, mushroom is a Holozoic organism but not a herbivore or a carnivore or an omnivore
B. Answer the following in not more than 40 words.
1. What are saprophytes and parasites?
Ans.- Saprophytes: Saprophytes are the organisms that feed on dead and decaying organic matter. Example: Bread mold (a fungi)
Parasites: Parasites are organisms that derive their nutrition from other animals or plants by living inside their body or on it. Example: Round worm
2. Write about two special features related to the teeth of a herbivore.
Ans.- Herbivores feed on green plants, which are difficult to chew and digest due to cellulose in them. Herbivores have large, dull, flat teeth. These teeth are excellent for chewing and breaking down tough plant material. They also have sharp - edged incisors in the front to help them cut the grass.
3. Write briefly about the process of nutrition in the amoeba.
Ans.- Amoeba use fingers like projections called pseudopodia to engulfing the food. Then food reaches the food vacuole, where it gets digested by the action of enzymes.
4. Why does carnivorous plant trap insects? Explain how one such plant traps insects.
Ans.- Carnivore plants are found at places where there is lack of nitrogen in soil. Therefore they trap insects and digest them to fulfill their nitrogen requirement for making protein. For example, sundews and pitcher plants. Leaves of these of plants are modified to secrete sticky substance that attract and capture insects.
5. What are symbionts? Explain with an example.
Ans.- Symbionts are organisms that live together for mutual benefits.
An example of symbiont is nitrogen fixing bacteria. They live in the root nodules of plants to get food and fix atmospheric nitrogen into soluble form, which is useful for plants. They fix nitrogen for plants and plants provide them food and protection.
6. What is the digestive juice in the mouth called? What enzyme does it contain and what does it do?
Ans.- Digestive juice in the mouth is called saliva.
Saliva contains enzyme called amylase. This enzyme acts upon complex carbohydrates starch to convert them into simpler carbohydrates such as sugar (maltose) . Thus, saliva helps in partial digestion of carbohydrates.
7. What is peristalsis? Does it occur only in the oesophagus?
Ans.- The alternate relaxation and contraction of organs made of smooth muscles in our body is called peristalsis. For example food pushed down the oesophagus by peristalsis.
No, it occurs in the whole alimentary canal and not just in oesophagus.
8. The juice produced in the stomach contains an acid as well as an enzyme. Name the enzyme. What do the acid and enzyme do?
Ans.- The juice produced in the stomach contains hydrochloric acid and pepsin enzyme. Hydrochloric acid kills the bacteria and other pathogens, and pepsin helps in the digestion of proteins.
9. What happens to the undigested food that remains in the large intestine?
Ans.- At first some water is absorbed from the undigested food and remaining are thrown out of the body via the anus in the form of semisolid waste (faeces) .
C. Answer the following in not more than 100 words.
1. How would you show that chlorophyll is needed for photosynthesis?
Ans.- Take a leaf and put it in a test tube, half filled with alcohol. The leaf should be submerged in the alcohol in such a way that half of it remains outside. Put the test tube in a beaker filled with water and heat it.
Direct heating of the test tube containing alcohol should be avoided as it may catch fire.
The part of leaf submerged in the alcohol will start losing colour, as alcohol destroys its green pigment, chlorophyll. When this half leaf loses its colour completely, pull out the leaf and wash it gently to remove alcohol. After a few minutes, put some drops of iodine on the green and non green halves.
Observation: It is observed that the green part changes its colour to blueblack on dropping iodine. This indicates the presence of starch. The green pigment synthesises starch by trapping energy and gives blueblack colour on reaction with iodine. The colourless part of the leaf gives no such result.
Thus, it is confirmed that presence of chlorophyll is a must for photosynthesis to take place.
2. What happens to food in the small intestine?
Ans.- Complete digestion and absorption of food occur in the small intestine. As the food enters the small intestine, it is acted upon by a number of digestive juices secreted by the liver, pancreas and walls of small intestine.
Bile juice is secreted by the liver that breaks fat into smaller pieces to make it easily digestible.
Pancreatic juice secreted by pancreas act upon carbohydrates and proteins to digest them completely.
Walls of small intestine have many fingers like projections called villi, which help in increasing the surface area of the small intestine. This in turn helps in efficient absorption of digested food.
3. How many teeth does an adult (human being) have? Describe the different types of teeth and their function.
Ans.- An adult human has 32 teeth arranged in the upper and lower jaws.
We have four kinds of teeth in our oral cavity or mouth. They are:
(i) Incisors : They are flat teeth that act like scissors. They help in cutting food.
(ii) Canines: These are sharp teeth and are very prominent in carnivores. They are pointed and help
in tearing food. They function like knives in carnivores and help them capture their prey.
(iii) Premolars: These are teeth having broad surface. They help in grinding and chewing food.
(iv) Molars : They also help in grinding the food and chewing it. They are larger than premolars
4. How did Dr Beaumont study the functioning of the stomach?
Ans.- Dr. Beaumont, while treating one of his patients St. Martin, who was accidentally hit by a bullet in the stomach, found that after 18 months of treatment, a hole was left in St. Martin's stomach even though the wound had healed. When Dr. Beaumont experimented with the food from St. Martin's stomach for nine years, he found that digestion occurs in the stomach due to the action of juices, secreted by the stomach, on the food we eat.
5. What is special about a ruminant’s stomach? How does it help the animal digest vegetable matter?
Ans.- The stomach of a ruminant (grass eating herbivores) is divided into four chambers and is capable of digesting cellulose. The four parts of the stomach are the rumen, reticulum, omasum, and abomasum.
Ruminants chew the grass partially before swallowing it. This half or partially chewed food goes to the first chamber of the stomach called rumen, where bacteria and other micro organism act on it . Then it is sent to reticulum. This half digested food is sent back to the mouth for rechewing. This rechewing of half digested food is called cud chewing or rumination.
Now, complete chewed food goes to the omasum where some water gets absorbed. At last food reach to abomasums where final digestion occur b the action of enzymes.
D. Fill in the blanks:
1. The tube like mouth part of a butterfly is called a proboscis.
2. The process by which digested food enters the blood is called absorption.
3. Chemical substances produced in the body of an organism to help in the process of digestion are called enzymes.
4. The tube, starting from the mouth and ending in the anus, through which food passes is called the alimentary canal.
5. Digestion begins in the mouth.
6. The finger like folds in the wall of the small intestine are called villi
R/1
Ch. 01 Language of Chemistry
A. Answer the following in not more than 20 words.
1. What does the formula of a substance tell you?
Answer- Formula of a compound or an element represents the type and number of atoms present in one molecule of that compound or element
2. What do you mean by the valency of an element?
Answer- The number of electrons that can be donated, accepted or shared by an atom of an element during a chemical reaction is equal to the valency of that element. It represents the combining capacity of an atom.
3. What is the following called?
A group of atoms of two or more elements behaving like an atom and having a valency
Answer- A compound radical is a group of two or more elements that acts as a single atom with a specific valency, in a chemical reaction.
4. Name two elements that have variable valency.Give the formula and names of two compounds formed by each of these elements.
Answer- Two elements having variable valency and compounds formed by them are as follows:
(i) Copper (Cu):
Cuprous oxide [Copper(I)oxide] − Cu2O
Cupric oxide [Copper(II)oxide] − CuO
(ii) Iron (Fe):
Ferrous oxide [Iron(II)oxide] − FeO
Ferric oxide [Iron(III)oxide] − Fe2O3
5. What is a balanced chemical equation? Why should a chemical equation be balanced?
Answer- A balanced chemical reaction is one in which the number of atoms on the side of the products is equal to the number of atoms on the side of the reactants.
The number of atoms on the side of reactants is always equal to the number of atoms on the side of the products in a chemical reaction, i.e., no atom is lost during a chemical reaction. We balance a chemical reaction to represent this fact.
B. Find the valencies of the underlined elements or radicals in the following compounds.
BaCl2, PCl3, PCl5, NH3, MgSO4, CaCO3, Na2O, CaO, Ca(OH)2, FeSO4, FeCl3, Fe2O3, NaOH, Al(OH)3, Na2CO3.
Answer-
Compound | Valency of Underlined Elements of Radicals |
BaCl2 | 2 |
PCl3 | 3 |
PCl5 | 5 |
NH3 | 3 |
MgSO4 | 2 |
CaCO3 | 2 |
Na2O | 1 |
CaO | 2 |
Ca(OH)2 | 2 |
FeSO4 | 2 |
FeCl3 | 3 |
Fe2O3 | 3 |
NaOH | 1 |
Al(OH)3 | 3 |
Na2CO3 | 1 |
C. Answer the following in not more than 100 words.
1. What are compound radicals? Give examples of a few radicals, along with their valencies. Also mention some compounds containing compound radicals. Give the valencies of the parts that make up the compound.
Answer- Compound radical is a group of atoms of different elements that behave as an intact unit during a chemical reaction. Atoms in a compound radical do not break apart revealing the individual atoms but remain together forming an intact group of atoms having a valency. This unit behaves just like an atom or a molecule during a reaction.
Some compound radicals with their valencies are given below:
Compound Radical | Valency |
OH | 1 |
SO4 | 2 |
NO3 | 1 |
CO3 | 2 |
Some compounds containing compound radicals:
Compound | Name | Compound Radical | Valency |
NaOH | Sodium hydroxide | OH | 1 |
H2SO4 | Sulphuric acid | SO4 | 2 |
Na2CO3 | Sodium carbonate | CO3 | 2 |
(NH4)2SO4 | Ammonium sulphate | SO4 | 2 |
KNO3 | Potassium nitrate | NO3 | 1 |
D. Complete the following.
1. A symbol is an abbreviation of the name of an element.
2. A molecule of an element or a compound is represented by its formula.
3. The valencies of the two elements of a binary compound are transposed to obtain its formula.
4. Atoms are neither lost nor gained in a chemical reaction.
