Bhagya

S Chand Biology Class 10 Solutions Model Test Paper 4

Question 1.
Name a reducing agent that may be used to obtain manganese from manganese dioxide.
Answer.
Aluminium powder is used as the reducing agent to obtain manganese from its oxide.
2Al(s) + 3MgO → Al₂O₃ + 3Mg(s)

Question 2.
Why does a ray of light bend when it travels from one medium into another?
Answer.
When a light ray travels from one medium to another, then due to change in the density of the medium, speed of light changes. Change in the speed of the light at the boundary of two media force the light ray to bend from its original path.

Question 3.
A compound which is prepared from gypsum has the property of hardening when mixed with a proper quantity of water. Identify the compound. Write the chemical equation for its preparation. For what purpose is it used in hospitals?
Answer.
When gypsum is heated at 373 K, it gives plaster of paris,

Plaster of paris becomes hard when the appropriate amount of water is available.

In hospitals, it is used as a plaster to support broken or fractured bones.

Question 4.
What is the minimum number of rays required for locating the image formed by a concave mirror for an object. Draw a ray diagram to show the formation of a virtual image by a concave mirror.
Answer.
Only two rays are required for the image to be located.
Image diagram to show the formation of a virtual image formed by a concave mirror.

Question 5.
Name the type of respiration in which the end products are.
(a) ethanol, carbon dioxide and energy.
(b) carbon dioxide, water and energy.
Answer.
(a) ethanol, carbon dioxide and energy – Anaerobic respiration
(b) carbon dioxide, water and energy – Aerobic respiration

Question 6.
Name the functional group of organic compounds that can be hydrogenated. With the help of suitable example, explain the process of hydrogenation mentioning the conditions of the reaction and any one change in physical property with the formation of the product. Name any one natural source of organic compounds that are hydrogenated.
Answer.
Functional group that can be hydrogenated is alkene.
Hydrogenation of oils(unsaturated alkene).

Vegetable oil is unsaturated fatty acids having a double bond in between some of their carbon atoms. When vegetable oil is heated in the presence of nickel catalyst, then a saturated fatty acid called vegetable ghee is formed. This reaction is known as a hydogenation reaction.
When vegetable oil is hydrogenated, it changes from liquid state to solid state.

Vegetable ghee is generally produced by hydrogenation of vegetable oil or animal oil.

Question 7.
No chemical reaction takes place when granules of a solid, A, are mixed with the powder of another solid, B. However, when the mixture is heated, a reaction takes place between its components. One of the products, C, is a metal and settles down in the molten state while the other product, D, floats over it. It was observed that the reaction was highly exothermic.
(a) Based on the given information, make an assumption about A and B and write a chemical equation for the chemical reaction indicating the conditions of reaction, physical state of reactants and products and thermal status of the reaction.
(b) Mention any two types of reactions under which above chemical reaction can be classified.
Answer.
(a) Solid A is assumed to be aluminium (Al) and solid B to be manganese oxide. When the mixture of manganese oxide and aluminium is heated, manganese is produced in the molten state and aluminium oxide floats over it. Manganese produced in the molten state as a lot of heat energy is released in the process. Therefore, C is manganese and D is aluminium oxide.
Al(s) + MnO₂(s) → Mn(s) + Al₂O₃(s)
(b) The type of reaction under which the above reaction is classified are.
1. Redox reaction
2. Displacement reaction

Question 8.
Atoms of eight elements A, B, C, D, E, F, G and H have the same number of electronic shells but different number of electrons in their outermost shells. It was found that elements A and G combine to form an ionic compound which can also be extracted from sea water. Oxides of the elements A and B are basic in nature while those of E and F are acidic.
The oxide of element D is almost neutral. Answer the following Qs based on the information given herein.
(a) To which group or period of the periodic table do the listed elements belong?
(b) Which one of the eight elements is likely to be a noble gas?
(c) Which one of the eight elements would have the largest atomic radius?
(d) Which two elements amongst these are likely to be non-metals?
(e) Which one of the these eight elements is likely to be a semi-metal or metalloid?
Answer.
(a) A and G form an ionic compound so A must be a metal of group 1 and G must be a non-metal of group 17. As the ionic compound of A and G is obtained from seawater so that ionic compound must be sodium chloride. Therefore, A and G belong to the third period of the periodic table.
(b) Because all the given elements belong to the third period and H being the last element of the third period will be the noble gas.
(c) A belongs to the first group of the periodic table, so it has the largest radius.
(d) Oxides of E and F are acidic in nature, so they are non-metals.
(e) The oxide of D is almost neutral, so it is a metalloid.

Question 9.
State, giving reasons, which of the following reactions will occur and which will not.
(a) MgSO₄ (aq) + Cu(s) → CuSO₄ (aq) + Mg(s)
(b) CuSO₄ (aq) + Fe (s) → FeSO₄ (aq) + Cu(s)
(c) MgSO₄ (aq) + Fe (s) → FeSO₄ (aq) + Mg(s)
Answer.
(a) MgSO₄ (aq) + Cu(s) → CuSO₄ (aq) + Mg(s)
Copper is less reactive than magnesium, so copper cannot displace magnesium. Hence, this reaction will not occur.
(b) CuSO₄ (aq) + Fe (s) → FeSO₄ (aq) + Cu(s)
Iron is more reactive than copper, so it will displace copper from copper sulphate and form iron sulphate.
(c) MgSO₄ (aq) + Fe (s) → FeSO₄ (aq) + Mg(s)
Iron is less reactive than magensium, so iron can not displace magnesium. Hence, this reaction will not occur.

Question 10.
Draw three labelled ray-diagrams to show the defect of vision called hypermetropia and how it is corrected by using a lens. Also name the lens used.
Answer.
Hypermetropia or long-sightedness is a common eye defect, in which a person is not able to nearby objects whereas the farther objects appear clear to the person.
Hypermetropia deffect.

Correction made with a convex lens for the hypermetropic eye.

A convex lens is used to correct the defect of hypermetropia.

Question 11.
At what distance should an object be placed from a convex lens of focal length 18 cm to obtain an image at 36 cm from it on the other side? What will be the magnification produced in this case?
Answer.
The focal length of the convex lens, f = +18 cm
Image distance, v = + 36 cm
Using lens formula, \(\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\)
⇒ \(\frac{1}{36}-\frac{1}{u}=\frac{1}{18}\)
⇒ \(\frac{1}{u}=\frac{1}{36}-\frac{1}{18}=-\frac{1}{36}\)
⇒ u = -36 cm
Magnification of the lens = m = \(\frac{v}{u}=\frac{36 \mathrm{cm}}{-36 \mathrm{cm}}\) = -1

Question 12.
The magnetic field associated with a current carrying straight conductor is in an anticlockwise direction. If the conductor was held along the east-west direction, what will be the direction of current through it? Name and state the rule applied to determine the direction of the current.
Answer.
The direction of the flow of current can be found out by Maxwell’s Right Hand Thumb Rule. It states that if we point our right-hand thumb in the direction of current then the fingers of our hand curl along the direction magnetic field.
Now it is given that the magnetic field is in the anti-clockwise direction. If we look at the conductor from the right and apply the Thumb rule, the direction of current would be towards the East. However, if you look at the field from the left and apply this rule, the direction of current would be towards the west.

Question 13.
Explain analogous organs and homologous organs. Identify the analogous and homologous organs amongst the following.
Wings of an insect, wings of a bat, forelimbs of frog, forelimbs of a human.
Answer.
Analogous orgAnswer: These are organs that have different origins, but perform similar functions.
Homologous orgAnswer: These are organs that are similar in origin (or are embryologically similar), but perform different functions.
The wings of an insect and wings of a bat are examples of analogous organs.
The forelimbs of frog and forelimbs of humans are examples of homologous organs.

Question 14.
(a) Explain the terms.
(i) implantation (ii) placenta
(b) What is the average duration of human pregnancy?
Answer.
(a) (i) Implantation is the process wherein a fertilised egg (zygote) formed in the fallopian tube gets embedded on the walls of the uterus, inside the female body.
(ii) Placenta is a vascular structure present in the inner lining of the uterus. It is connected to the foetus by the umbilical cord. The embryo receives nutrition and oxygen from the mother’s blood via the placenta.
(b) The average duration of human pregnancy is nine months.

Question 15.
Explain the mechanism of reflex action with a suitable example.
Answer.
The automatic action or response provoked by a stimulus is known as reflex action. The sensory nerves that detect the stimulus are connected to nerves that move the muscles. Such a connection is called reflex arc. The reflex arc connections meet in a bundle in the spinal cord. The signal and the response that has taken place reach the brain but the brain does not coordinate the reflex response.
For example, we withdraw our hands on touching any hot article.

Question 16.
(a) Why did Mendeleev leave gaps in his periodic table?
(b) State any three limitations of Mendeleev’s classification.
(c) How does electronic configurations of atoms change in a period with increase in atomic number?
Answer.
(a) When Mendeleev developed the periodic table, he realized that many elements are missing in the periodic table and yet to be discovered. So, left gaps in his table for such elements and also predicted their properties.

(b) Limitations of Mendeleev’s classification.

• He could not explain the position of isotopes in the periodic table.
• He could not assign a proper position to the element hydrogen in the periodic table.
• He failed to explain the wrong order of atomic masses of some elements.

(c) As we move from left to right in a period, the atomic number will increase due to the increase of electrons in the shell.

Question 17.
What is meant by refining of a metal? Name the most widely used methods of refining impure metals produced by various reduction processes. Describe with the help of a labelled diagram how this method may be used for refining of copper.
Answer.
Refining of metals. Refining of metals is nothing but the removal of impurities from crude metals or purifying the crude metal.
Electrolytic refining is the most widely used method for the refining of metals.
Electrolysis of copper.

Electrolysis of copper from copper sulphate solution is done using copper electrodes. The crude copper serves as the anode while the thin sheet of pure copper serves as the cathode.
At anode: Cu → Cu⁺² + 2e⁻
At cathode: Cu⁺² + 2e⁻ →Cu
As the anode dissolves away, the cathodes on which the pure metal is deposited grow in size.

Question 18.
Explain the process of digestion of food in mouth, stomach and small intestine in human body.
Answer.
The process of digestion of food in mouth, stomach and small intestine is described as follows.
1. Mouth – Digestion of food begins in the mouth. Saliva present in mouth contains a digestive enzyme, called salivary amylase, which breaks down starch into sugar.

2. Stomach – Stomach stores and mixes the food received from the oesophagus with gastric juices. The main components of gastric juice are hydrochloric acid, mucus and pepsinogen.
Hydrochloric acid dissolves bits of food and creates an acidic medium. In this medium, pepsinogen is converted to pepsin, which is a protein-digesting enzyme. Mucus protects the inner lining of the stomach from the action of HCl.

3. Small intestine – Small intestine is the site for complete digestion of carbohydrates, proteins and fats. It produces intestinal juice from the glands present in its wall. The intestinal juice helps in further digestion of food. Small intestine also obtains digestive juices from liver and pancreas that helps in mixing of food.
The liver produces bile juice that causes emulsification of fats and the pancreas produces pancreatic juice for digesting proteins and emulsified fats.
This digested food is finally absorbed through the intestinal walls.

Question 19.
(a) Define ‘Photosynthesis’. Apart from sunlight, what other conditions are necessary for the process of photosynthesis.
(b) Describe an experiment to show that “sunlight is essential for photosynthesis”.
Answer.
(a) Photosynthesis is the process by which plant cells prepare food (carbohydrates) from inorganic raw materials such as carbon dioxide and water in presence of sunlight and chlorophyll.

The factors other than sunlight affecting the rate of photosynthesis are.

• Carbon dioxide − Carbon dioxide acts as the substrate for photosynthesis. During this process, carbon dioxide and water are converted into carbohydrates.
• Water − During photosynthesis, water is photolysed into oxygen and hydrogen and it provides the energy for photosynthesis.
• Chlorophyll − Chlorophyll is the green pigment present in the leaves which absorbs sunlight.

(b) Experiment to demonstrate that light is necessary for photosynthesis.

• Take two potted plants. Place one plant in a dark room and the other in a room receiving sufficient sunlight.
• After 3-4 days, take one leaf each from both the plants. Bathe the two leaves first in hot water and then in alcohol.
• Add some drops of iodine solution on the leaves.

Observation.
It can be observed that the leaf taken from the plant kept in sunlight develops blue-black patches whereas the leaf taken from the plant kept in the dark room does not show any patches.

Reason for the observation.
Plants which receive sunlight prepare their own food through the process of photosynthesis. It is the presence of starch that turns the colour of iodine solution blue-black. Therefore, blue-black patches are observed on the leaf taken from the plant kept in sunlight. In contrast, the leaf of the plant kept in the dark room does not produce any starch. Therefore, no patches are observed on it.

Question 20.
(a) What is a magnetic field? How can the direction of magnetic field lines at a place be determined?
(b) State the rule for the direction of the magnetic field produced around a current-carrying conductor. Draw a sketch of the pattern of field lines due to a current flowing through a straight conductor.
Answer.
(a) The magnetic field is defined as the space surrounding a magnet in which magnetic force is exerted. The direction of magnetic field lines at a place can be determined by finding the deflection in the needle of a magnetic compass.
(b) The rule for determining the direction of the magnetic field of a current carrying wire is the right-hand thumb rule.

Right-hand thumb rule. The right-hand thumb rule indicates the direction of the magnetic field for a know direction of the current. If the thumb of the right-hand points along the direction of current then the curled fingers of that hand gives the direction of the magnetic field due to the current.

Question 21.
Explain with the help of a labelled circuit diagram how will you find the resistance of a combination of three resistors, of resistance R₁, R₂ and R₃ joined in parallel. Also mention how you will connect the ammeter and the voltmeter in the circuit when measuring the current in the circuit and the potential difference across one of the three resistors of the combination.
Answer.

Applied voltage = V
Let the current in the circuit = I
If total resistance of the circuit is R_net, then
I = \(\frac{V}{R_{\mathrm{net}}}\)
As all the resistances are connected in parallel, so all of the resistors will get an equal voltage across their ends.
The total current in the circuit is simply the sum of the current passing through each resistance.

An ammeter is low impedance device which is always connected in the series with the circuit so that maximum of the current can pass through it and it can give a more accurate value of the current flowing in the circuit.
A voltmeter is a high impedance device which is always connected in parallel in the circuit so that it does not draw any current and can give the actual voltage drop across the component.

Question 22.
Draw the given diagram in your answer book and complete it for the path of a ray of light beyond the lens.

(a) What type of lens is shown in this diagram?
(b) Is it a converging lens or a diverging lens?
Answer.

(a) A convex lens is shown in the diagram.
(b) It is converging in nature.

Question 23.
A student connects a coil of insulated wire to a galvanometer. What would be seen if a bar magnet with its north pole towards one face of the coil is.
(a) moved quickly towards it?
(b) moved quickly away from the coil?
(c) placed near the face of the coil?
Name the phenomenon involved.
Answer.
(a) When the bar magnet is moved quickly towards the coil, a deflection is observed in the galvanometer. This deflection indicates that some current is produced in the coil.

(b) When we move the magnet quickly away from the coil, this time the deflection is indicated in the opposite direction. It indicates the current produced in the coil is in the opposite direction.

(c) When we simply move the magnet near the face of the coil then no deflection is found in the galvanometer, because of the absence of relative motion between the coil and the magnet.

The phenomenon involved is known as Electromagnetic induction.

Question 24.
A student was working in a chemistry laboratory. He found that a bottle contained a white powdery substance but half of the label on the bottle was torn. The part of label still sticking to the bottle had NaH written on it. The student took this powdery substance in a test-tube and added dil. HCl to it. A gas was evolved which extinguished a burning match-stick.
(a) Name the gas evolved.
(b) Write the formula of white powdery substance.
Answer.
When dilute hydrochloric acid is mixed with that salt a gas is produced which extinguished a burning match-stick that means the gas produced is carbon dioxide.
So, the salt must be sodium bicarbonate.
HCl + NaHCO₃ → NaCl + H₂O + CO₂
(a) Hence, the gas produced is carbon dioxide.
(b) White powdery salt is sodium bicarbonate(NaHCO₃).

Question 25.
Ravi placed a zinc plate in a glass container having a blue coloured solution of a metal sulphate MSO4 for a considerable time. He found that the blue colour of solution got lighter and lighter, and finally the solution became colourless. A red-brown deposit was also formed on the zinc plate.
(a) Which metal, zinc or M, occurs lower in the reactivity series?
(b) Name the substance which forms colourless solution.
Answer.
When Ravi places zinc plate in a blue colored solution of metal sulphate, he found that colour of the solution is fading that means zinc is more reactive than that metal and displacing it from the solution. As the solution becomes colourless after some time it shows that metal M will be copper.
(a) Zinc is more reactive than metal M.
(b) Due to the formation of zinc sulphate solution becomes colourless.

Question 26.
A student is performing an experiment to show that sunlight is necessary for photosynthesis. In the first stage, he keeps a potted plant with green leaves in a dark place for about 3 days. Towards the end of the experiment, he boils one leaf in alcohol before using iodine for testing starch.
(a) Why is the plant kept in a dark place for about 3 days?
(b) Why is the leaf boiled in alcohol before testing for starch with iodine?
Answer.
(a) The plant is kept in dark so as to destarch it, so that in the beginning of the experiment itself, the leaves do not have any starch.
(b) After the plant is destarched by keeping it in dark, it is again placed in sunlight so that photosynthesis can occur. This would result in the synthesis of starch. The leaves are again destarched by boiling them in alcohol before testing them with iodine.

Question 27.
Pure-bred pea plants A are crossed with pure-bred pea plants B. It is found that the plants which look like A do not appear in F₁ generation but re-emerge in F₂ generation.
(a) Which of the plants A and B are. (i) tall, and (ii) dwarf?
(b) Give reason for your answer.
Answer.
(a) (i) Tall – Plant B
(ii) Dwarf – Plant A

(b) In pea plants, tallness is a dominant trait whereas dwarfness is a recessive trait. Plants like A do not appear in the F₁ generation but reappear in the F₂ generation which means that plant A is dwarf whereas plant B is tall.

We can see from the cross that, tall plants appear in the F₁ generation but no dwarf plants are seen.
The dwarf plants are seen in F₂ generation.

Lakhmir Singh Biology Class 10 Solutions

S Chand Biology Class 10 Solutions Model Test Paper 3

Question 1.
Why is the red color selected for danger signal lights?
Answer:
The wavelength of red light is the longest in visible light, so the red color is scattered the least by air molecules of the atmosphere and therefore it can reach to a longer distance. That’s why the red color is used for danger signal lights.

Question 2.
Balance the following chemical equation.
MnO₂ + HCl → MnCl₂ + Cl₂ + H₂O
Answer:
Balanced chemical equation.
MnO₂ + 4HCl → MnCl₂ + Cl₂ + 2H₂O

Question 3.
What is the common name of CaSO₄. \(\frac{1}{2}\)H₂O ? Also name the compound from which it is prepared.
Answer:
The common name of CaSO₄. \(\frac{1}{2}\)H₂O is plaster of paris. Plaster of paris is obtained by heating gypsum (CaSO₄.2H₂O) at 373 K.

Question 4.
What is the resultant resistance of the three resistors of 5 Ω, 4 Ω and 10 Ω connected as shown in the figure? What is this combination of resistors known as?

Answer:
This given combination of resistors is known as parallel combination.
In a parallel combination, the reciprocal of the resultant resistance is equal to the sum of reciprocals of the individual resistances present in the combination. For the three resistors connected in parallel,

Question 5.
Define variation in relation to a species. Why is variation beneficial to the species?
Answer:
The occurrence of differences among the individuals of the same species is known as variation.
Variation helps in the survival of species by bringing about changes in the basic body design, thereby providing the organisms with a better adaptability against predators.

Question 6.
(a) Show on a diagram the transfer of electrons between the atoms in the formation of MgO.
(b) Name the solvent in which ionic compounds are generally soluble.
(c) Why are aqueous solutions of ionic compounds able to conduct electricity?
Answer:
(a) Transfer of electrons between atoms in the formation of magnesium oxide.

(b) Water is the best solvent in which ionic compounds are generally soluble.
(c) The aqueous solution of ionic compounds can conduct electricity because of the presence of free ions. These ions are responsible for the conduction of electricity in aqueous solutions.

Question 7.
Explain why, the blue colour of copper sulphate solution fades when an iron nail is kept dipped in it. Write chemical equation of the reaction involved. What does this reaction tell us about the relative reactivities of copper and iron?
Answer:
When an iron nail is put in the blue colour copper sulphate solution, then the iron displaces copper from copper sulphate and forms green coloured iron sulphate solution, that’s why the blue colour of the solution fades. The reaction involved is as follows.

As iron displaces copper from its sulphate solution, so, we can conclude that iron is more reactive than copper.

Question 8.
Why are decomposition reactions called the opposite of combination reactions? Explain by giving one example (with equation) of each type of reaction.
Answer:
Decompositon reaction are those in which a compound breaks down to form two or more substances. These reaction require a source of energy to proceed. Thus, they are the exact opposite of combination reactions in which two or more substances combine to give a new substance with the release of energy.
Decomposition reaction. \(2 \mathrm{H}_{2} \mathrm{O} \stackrel{\text { electrolysis }}{\longrightarrow} 2 \mathrm{H}_{2}+\mathrm{O}_{2}\)
Combination reaction. 2H₂ + O₂ → 2H₂O + energy

Question 9.
The atom of an element has the electron structure 2, 7.
(a) What is the atomic number of the element?
(b) To which of the following would it be chemically similar?
₇N, ₁₅P, ₁₇Cl, ₁₈Ar
(c) Why would you expect it to be similar?
Answer:
(a) The atomic number of the element is 9.
(b) Out of given options, ₁₇Cl has similar properties with this element.
Electronic configuration of Cl is 2, 8, 7. So, valence shell contains 7 electrons.
(c) The modern periodic table assumes that elements with the same number of valence electrons have similar properties.

Question 10.
The position of hand shown in the figure corresponds to one of the Fleming’s rules.

(a) Which Fleming’s rule is illustrated by this hand?
(b) In this figure of hand, what is indicated.
(i) by the direction of forefinger?
(ii) by the direction of center finger?
(iii) by the direction of thumb?
Answer:
(a) Fleming’s left-hand rule is illustrated by the hand.
(b) (i) The magnetic field is indicated by the direction of fore-finger.
(ii) Electric current is indicated by the direction of the center finger.
(iii) By the direction of thumb, the motion of the conductor is indicated in the given figure.

Question 11.
Two resistors, with resistances 5 Ω and 10 Ω respectively are to be connected to a battery of emf 6 V so as to obtain. (i) minimum current flowing (ii) maximum current flowing.
(a) How will you connect the resistances in each case?
(b) Calculate the strength of the total current in the circuit in two cases.
Answer:
(a) In a parallel combination of resistances, the net resistance is less as compared to a series combination of resistances. As the current flow is indirectly proportional to the resistance of the circuit, so to obtain maximum current flowing in the circuit the given resistances should be connected in parallel combination and to obtain the minimum current flowing the given resistances should be connected in series combination.

(b) Case (i) For minimum current flow, the resistance of the circuit should be maximum. i.e. resistances should be connected in Series.
Net resistances of given resistances when connected in series = 5 Ω + 10 Ω = 15 Ω
The voltage of the battery = 6 V
Hence, current = \(\frac{6 \mathrm{V}}{15 \Omega}\) = 0.4 A
Case (ii) For maximum current flow, the resistance of the circuit should be minimum. i.e. resistances should be connected in parallel.
Net resistances of given resistances when connected in parallel = \(\frac{5 \Omega \times 10 \Omega}{5 \Omega+10 \Omega}=\frac{10}{3} \Omega\)
The voltage of the battery = 6 V
Hence, current = \(\frac{6 \mathrm{V}}{\frac{10}{3} \Omega}\) = 1.8 A

Question 12.
What is hypermetropia? State the two causes of hypermetropia. With the help of ray diagrams, show.
(a) the eye-defect hypermetropia
(b) correction of hypermetropia by using a lens
Answer:
Hypermetropia or long-sightedness is a common eye defect, in which a person is not able to see nearby objects whereas the farther objects appear clear to the person.
Two causes of hypermetropia.
(i) Eyeball being too short.
(ii) The increased focal length of the eye lens.
(a) Hypermetropic eye.

(b) Correction made with a convex lens for the hypermetropic eye.

Question 13.
Distinguish between biodegradable and non-biodegradable substances. List two effects of each of them on our environment.
Answer:

Effects of biodegradable substances on environment –

• Decomposition of biodegradable wastes is accompanied by foul smell which spreads in the environment and affects the people in nearby areas.
• Heaps of biodegradable wastes act as breeding grounds for houseflies etc, which act as vectors of various diseases.

Effects of non-biodegradable substances on environment –

• Excessive use of non-biodegradable pesticides and fertilizers affect the fertility of soil.
• Certain non-biodegradable wastes enter the food chains, get biomagnified and affect the various biotic components of environment.

Question 14.
Why are bacteria and fungi called decomposers? List any two advantages of decomposers to the environment.
Answer:
Bacteria and fungi are called decomposers as they obtain nutrients by breaking down the remains of dead plants and animals.
Role of decomposers

• They help in the breakdown of organic matter or biomass of dead plants and animals into simple inorganic raw materials such as CO₂, H₂O and nutrients.
• They help in the natural replenishment of soil.

Question 15.
(a) Name two different ways in which glucose is oxidized to provide energy in various organisms.
(b) Write any two differences between the two ways of oxidation of glucose in organisms.
Answer:
(a) Glucose can undergo either aerobic or anaerobic respiration to provide energy.
(b)

Question 16.
(a) Which two criteria did Mendeleev use to classify the elements in his periodic table?
(b) State Mendeleev’s periodic law.
(c) Why could no fixed position be given to hydrogen in Mendeleev’s periodic table?
(d) How and why does the atomic size vary as you go.
(i) from left to right along a period?
(ii) down a group?
Answer:
(a) Two criteria used by Mendeleev in creating his periodic table.
(i)Mendeleev’s periodic table was based on the observation that the properties of elements are the function of their atomic masses. This means that if elements are arranged in the increasing order of their atomic masses, then their properties get repeated after regular intervals.
(ii) Relative atomic mass and similarity of chemical properties.

(b) Mendeleev’s periodic law states that the physical and chemical properties of elements are the periodic function of their atomic weights.

(c) hydrogen has atomic mass 1 so definitely, it must be in the first period but the group was confusing. He found that hydrogen forms oxides like alkali earth metals with formula H₂O as Na₂O. He also found that hydrogen is similar to halogens in forming diatomic molecules H₂ like Cl₂, Br₂. So, he could not assign a fixed position to hydrogen.

(d)
(i) On moving left to right in a period, atomic size decreases because of the number of electron increases due to which attractive forces towards nucleus increases and atomic size decreases.
(ii) On moving down the group, atomic size increases due to the increase in valence shells.

Question 17.
Write the names and symbols of the two most reactive metals belonging to the Group I of the periodic table. Explain by drawing electronic structure how either one of the two metals reacts with a halogen. With which name is the bond formed between these elements known and what is the class of the compound so formed known? State any four physical properties of such compounds.
Answer:
The two most reactive elements of group 1 are cesium (Cs) and rubidium(Rb). Since valence shell of cesium contains only 1 electron, so it can lose it and form positive Cs+ ion. The electron lost by cesium can be accepted by halogen atom like chlorine and form negative chloride ions. The positive and negative ions attract each other to form electrostatic bond also called ionic bond. This type of compound formed is called an ionic compound.
Electronic configuration of cesium chloride.

Properties of the ionic compound are.

• High melting and boiling point.
• Good electrical conductivity in the molten state and aqueous solution.
• Physical state is usually crystalline solid.
• Soluble in water.

Question 18.
(a) What is a solenoid? Draw a sketch of the pattern of field lines of the magnetic field through and around a current carrying solenoid.
(b) Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right hand rule to find out the direction of the magnetic field inside and outside the loop.
Answer:
(a) A solenoid is a long coil that contains a large number of close turns of insulated copper wire. The magnetic field pattern produced by a current-carrying solenoid is similar to the magnetic field produced by a bar magnet.

(b)

We can apply the right-hand thumb rule to determine the direction of magnetic field lines around a current caring circular wire.
Here, the current is flowing into the clockwise direction, hence the direction of magnetic field lines inside the loop is going inward the table and the direction of the magnetic field outside the loop is coming out of the table. As shown in the above figure.

Question 19.
Derive the expression for the heat produced to a current ‘I’ flowing for a time interval ‘t’ through a resistor ‘R’ having a potential difference ‘V’ across its ends. With which name is the relation known? How much heat will an instrument of 12 W produce in one minute if it is connected to a battery of 12 V?
Answer:
Heat energy = power consumed × time
∴ H = P × t
Let ‘I’ is the current flowing for a time interval ‘t’ through a resistor ‘R’ having a potential difference ‘V’ across its ends.
Power = I²R or \(\frac{V^{2}}{R}\)
∴ H = I²Rt or \(\frac{V^{2}}{R} t\)
This relation is known as Joule’s law of heating.
Power of the instrument = 12 W
Time for which the instrument is used = 1 minute = 60 Seconds
Heat produced = P × t = 12 W × 60 s = 720 J

Question 20.
(a) Draw a diagram of human alimentary canal and label on it.
Oesophagus, Gall bladder, Liver and Pancreas
(b) Explain the statement, ‘Bile does not contain any enzyme but it is essential for digestion.’
Answer:
(a)

(b) Bile does not contain any enzyme, but it plays an important role in digestion as it performs the following functions.

• The bile salts break down large fat globules into smaller globules so that the pancreatic enzymes can easily act on them. This is referred to as emulsification of fats.
• The food entering the small intestine is acidic which has to be made alkaline so that the pancreatic enzymes can act on it. This function is also performed by bile juice.

Question 21.
(a) Draw a diagram of excretory system in human beings and label on it.
Aorta, vena cava, urinary bladder, urethra.
(b) List two vital functions of the kidney.
Answer:
(a)

[Note. Aorta and vena cava are components of the circulatory system.]
(b) The two vital functions of kidney are.

• filters the wastes out of the blood and forms urine
• maintains the water balance of the body

Question 22.
Draw the following diagram in your answer-book and show the formation of the image of the object AB with the help of suitable rays.

What type of reflecting surface is shown in the above diagram?
Answer:
Image formation is as follows.

The above-shown reflecting surface is a converging surface of a concave mirror.

Question 23.
A student was given three resistors of 2 ohms, 3 ohms and 5 ohms by his teacher. The teacher asked him to connect these three resistors in such a way so as to obtain the minimum resistance.
(a) In what way should the student connect the resistors?
(b) Draw a diagram of the combination of resistors.
Answer:
In a parallel combination, the resultant resistance is always less than or equal to the smallest resistance in the combination. So, a parallel combination of resistances gives the minimum resistance.
(a) Hence, in order to get minimum resistance, the student needs to arrange them in a parallel combination.
(b) A parallel combination of given resistors is shown below.

Question 24.
When a student adds some dilute hydrochloric acid to baking soda taken in a test-tube, a gas is evolved.
(a) Name the gas evolved.
(b) How can this gas be tested?
Answer:
When a student add dilute hydrochloric acid to baking soda(NaHCO₃), the aqueous solution of sodium chloride, carbon dioxide gas, and water are obtained.
HCl(aq) + NaHCO₃(aq) → NaCl(aq) + CO₂(g) + H₃O(l)
(a) So, the gas evolved is carbon dioxide.
(b) When we pass this gas from lime water, it turns the lime water milky and its presence is confirmed.

Question 25.
A student was given two test-tubes A and B each containing a colourless solution. When a few drops of universal indicator were added to the two test-tubes, one by one, then the colour of solution in test-tube A changed to blue whereas the colour of solution in test-tube B changed to orange.
(a) Which test-tube has a solution of pH higher than 7?
(b) Which test-tube has a solution of pH lower than 7?
(c) Which test-tube has an acidic solution?
(d) Which test-tube has an alkaline solution?
Answer:
(a) The universal indicator changes its color towards violet in basic or alkaline medium. This, the pH of the solution in test tube A is greater than 7, that’s why the universal indicator shows blue colour.
(b) The universal indicator changes its color towards red in acidic medium. So, the pH of the solution in test tube B is less than 7, that’s why the universal indicator is giving an orange colour.
(c) The pH of the solution in the test tube B is less than 7, so the test tube “B” has an acidic solution.
(d) The pH of the solution in test tube A is greater than 7, so test tube “A” has an alkaline solution.

Question 26.
A student conducted an experiment to show that carbon dioxide is released during respiration. State two precautions that the student must take for obtaining correct observations.
Answer:
Two precautions which should be taken during performing the experiment to show that carbon dioxide is produced during respiration are

• The conical flask should be air tight so that the CO2 produced during the experiment does not escape and a partial vacuum can be created in the flask.
• Germinating seeds should be used in the experiment because germinating seeds produce CO2 which has to be tested in this experiment.

Question 27.
A star-shaped figure was cut in the black paper strip used for covering a part of the leaf of a destarched plant used for demonstrating that light is necessary for photosynthesis. At the end of the experiment (after the removal of chlorophyll), the leaf was tested for starch with iodine solution.

(a) What colour, if any, will be produced on the part of leaf under the star-shaped figure?
(b) Give reason for your answer.
Answer:
(a) The part of leaf under the star region will show blue black colour upon testing with iodine.
(b) The appearance of blue colour in that part indicates the presence of starch.

Lakhmir Singh Biology Class 10 Solutions

S Chand Biology Class 10 Solutions Model Test Paper 2

Question 1.
How is the increase in demand for energy affecting our environment adversely?
Answer:
As the population increases, so does their demand for energy. More and more of fossil fuels are being used to generate electricity and for transportation purposes. Use of fossil fuels in large amounts, add heat and pollution to the environment thus affecting the climatic conditions and the environment adversely.

Question 2.
Balance the following chemical equation.
\(\mathrm{FeSO}_{4} \stackrel{\text { Heat }}{\longrightarrow} \mathrm{Fe}_{2} \mathrm{O}_{3}+\mathrm{SO}_{2}+\mathrm{SO}_{3}\)
Answer: Balanced chemical equation.
\(2 \mathrm{FeSO}_{4} \stackrel{\mathrm{Heat}}{\longrightarrow} \mathrm{Fe}_{2} \mathrm{O}_{3}+\mathrm{SO}_{2}+\mathrm{SO}_{3}\)

Question 3.
Draw ray diagrams to represent the nature, position and relative size of the image formed by a convex lens for the object placed.
(a) at 2F₁
(b) between F₁ and the optical center O of the lens
Answer:
(a) When the object is at 2F₁

Nature of the image formed. Real and inverted
Position of the image formed. At 2F₂
Size of the image formed. Same as that of the object

(b) When the object is placed between the focus F₁ and optical center O.

Nature of the image formed. Virtual and erect
Position of the image formed. Same side of the object, beyond the 2F₁
Size of the image formed. Enlarged

Question 4.
Give an example of a decomposition reaction. Describe an activity to illustrate such a reaction by heating.
Answer:
A decomposition reaction is a chemical reaction in which a single compound breaks down to simpler products.
Example. Decomposition of ferrous sulphate crystals.

Heat the ferrous sulphate crystals, the colour of ferrous sulphate crystals is green. On heating, the ferrous sulphate crystals lose their water molecules. Therefore, the colour of the crystals change.

Question 5.
Write one function each of the following components of the transport system in human beings.
(a) Blood vessels
(b) Blood platelets
(c) Lymph
(d) Heart
Answer:
(a) Blood vessels help in transporting oxygenated and deoxygenated blood to different parts of the body.
(b) Platelets help in the process of blood clotting.
(c) Lymph carries digested and absorbed fats from the intestine. It also provides immunity to the body.
(d) Heart acts as a pump and helps circulate blood throughout the body.

Question 6.
Name two metals which react violently with cold water. Write any three observations you would make when such a metal is dropped into water. How would you identify the gas evolved, if any, during the reaction?
Answer:
Sodium and potassium are two metals that react violently with cold water.
Observations made when such a metal is dropped in water.

• The reaction is highly exothermic, i.e. a huge amount of heat is produced.
• Hydrogen gas is evolved in the reaction
• Little explosions take place because the heat produced in the chemical reaction burns the hydrogen gas.

Hydrogen gas can be identified by the pop sound produced during the reaction of metal with cold water.

Question 7.
(a) Why are covalent compounds generally poor conductors of electricity?
(b) Name the following compound.

(c) Name the gas evolved when ethanoic acid is added to sodium carbonate. How would you prove the presence of this gas?
Answer:
(a) As covalent bonds do not break easily (dissociate), so they do not form ions which help in conduction of electricity. Therefore, covalent compounds don’t conduct electricity as they don’t have free electrons or ions.
(b) The given compound contains 3 carbons and a ketone functional group so it would be called as ‘propanone’.
(c) When ethanoic acid reacts with sodium carbonate, sodium ethanoate, carbon dioxide, and water are formed.
\(2 \mathrm{CH}_{3} \mathrm{COOH}+\mathrm{Na}_{2} \mathrm{CO}_{3} \rightarrow \mathrm{CH}_{3} \mathrm{COONa}+\mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O}\)
To test the presence of formed gas, we pass this gas from lime water. Upon reaction, lime water turns milky, which confirms the presence of carbon dioxide in the reaction.

Question 8.
(a) What is the difference between washing soda and baking soda?
(b) Write the chemical formula for bleaching powder. How is bleaching powder prepared? For what purpose is it used in paper factories?
Answer:
(a) Washing soda: Chemical formula of washing soda is Na₂CO₃. 10H₂O Washing soda used as a cleansing agent in domestic household purposes.
Baking Soda: Chemical formula of baking soda is NaHCO₃. Baking soda is used as an antacid to remove acidity in the stomach.

(b) The chemical formula of bleaching powder is CaOCl₂.
Bleaching powder is prepared by passing chlorine gas over dry calcium hydroxide.

Bleaching powder is used in paper factories for bleaching wood pulp, as bleaching powder is a strong oxidizing agent.

Question 9.
In the electrolysis of acidified water.
(a) Name the gas collected at (i) anode, and (ii) cathode
(b) Why is the volume of gas collected at one electrode double than that at the other electrode?
(c) What would happen if dilute sulphuric acid is not added to water?
Answer:
(a) Electrolysis of acidified water.
At cathode: 2H⁺ + 2e^– → H₂
At anode: OH^– → OH + e^–
4OH → 2H₂O₂
Hence, the gas produced at cathode is hydrogen and the gas produced at anode is oxygen.

(b) A water molecule contains two atoms of hydrogen and one atom of oxygen. Therefore, during the electrolysis of water, the ratio of the amount of hydrogen gas and oxygen gas produced is 2.1. Hence, we can say that the volume of gas collected at one electrode is double than that at the other electrode

(c) As electrolysis of water is a slow process, to increase the rate of electrolysis we add dilute sulphuric acid.
Dilute sulphuric acid increases the rate of breakdown of ions.

Question 10.
Two lamps, one rated 40 W at 220 V and the other 60 W at 220 V, are connected in parallel to the electric supply at 220 V.
(a) Draw a circuit diagram to show the connections.
(b) Calculate the current drawn from the electric supply.
(c) Calculate the total energy consumed by the two lamps together when they operate for one hour.
Answer:
(a)

(b) Using, I = \(\frac{P}{V}\)
Current drawn by 60 W lamp is, I = \(\frac{220}{60}\) = 3.67 A
Current drawn by 40 W lamp is, I = \(\frac{220}{40}\) = 5.5 A
So, the net current drawn by the combination is = 3.67 A + 5.5 A = 9.17 A
(c) Net power of the combination = 60 W + 40 W = 100 W
So, the energy consumed in 1 h = E = P × t = 100 × 1 × 60 × 60 J = 360000 J

Question 11.
(a) Why is a series arrangement not used for connecting domestic electrical appliances in a circuit?
(b) Draw a diagram to show the magnetic field lines around a bar magnet. List any two properties of magnetic field lines.
Answer:
(a) A series arrangement not used for connecting domestic electrical appliances in a circuit because if any one of the components connected in series stops working or get damaged, then the whole circuit would break up and no current will flow further in the circuit and none of the other devices would work.
(b)

Two properties of magnetic field lines.

• They originate from the north pole of the magnet and end at the south pole of the magnet.
• They do not intersect each other.

Question 12.
Name the electric device which converts mechanical energy into electrical energy. Draw the labelled diagram and explain the principle involved in this device.
Answer:
An electric generator converts mechanical energy into electrical energy.

MNST → Rectangular coil
A and B → Brushes
C and D → Two slip rings
X → Axle, G → Galvanometer
The principle of working of an electric generator is that when a loop is moved in a magnetic field, an electric current is induced in the coil. It generates electricity by rotating a coil in a magnetic field. The above figure shows a simple AC generator.

Question 13.
Write any three differences between aerobic and anaerobic respiration.
Answer:

Question 14.
How is ozone formed in the upper atmosphere? Why is damage to ozone layer a cause of concern to us? What causes this damage?
Answer:
Ultraviolet radiations split the oxygen molecules present in stratosphere into free oxygen atoms. These free oxygen atoms then combine with molecular oxygen to form ozone.
O₂ → O + O
O₂ + O → O₃
Ozone layer is a protective layer which protects the earth from harmful UV radiations. Any damage to the ozone layer would result in UV rays entering the earth’s atmosphere. These UV rays can cause diseases such as skin cancer and cataract.
They can also adversely affect the crops.
The ozone layer is damaged as a result of chlorofluorocarbons. These are often used in refrigerators, air conditioners and fire extinguishers.

Question 15.
(a) State one difference between arteries and veins.
(b) Name any two sexually transmitted diseases. What advice is given to prevent them?
Answer:
(a)

(b) Syphilis and AIDS are two sexually transmitted diseases. Such diseases can be prevented by the use of condoms.
Condoms are made of thin rubber and are used to cover the penis and the vagina in males and females, respectively.

Question 16.
(a) What is meant by the dispersion of white light? Describe the formation of the rainbow in the sky with the help of a diagram.
(b)What is hypermetropia? Draw ray diagrams to show the image formation of an object by.
(i) Hypermetropic eye
(ii) Correction made with a suitable lens for the hypermetropic eye.
Answer:
(a) The splitting of white light into seven colors on passing through a transparent glass prism is called dispersion of white light.
A rainbow is formed in the sky because of the dispersion of sunlight by millions of water droplets in the atmosphere. Every single water droplet behaves like a tiny glass prism that splits the white light into different colors. Different colors bend at different angles on passing through the water droplets, thus separating the white light into a natural spectrum of seven colors, as Violet, Indigo, Blue, Green, Yellow, Orange, and Red. The diagram below shows the formation of a rainbow.

(b) Hypermetropia or long-sightedness is a common eye defect, in which a person is not able to nearby objects whereas the farther objects appear clear to the person.
(i) Hypermetropic eye.

(ii) Correction made with a convex lens for the hypermetropic eye.

Question 17.
(a) Give reasons for the following.
(i) Colour of the clear sky is blue.
(ii) The sun can be seen about two minutes before the actual sunrise.
(iii) We cannot see an object clearly if it is placed very close to the eyes.
(b) What is Presbyopia? Write two causes of this defect.
Answer:
(a) (i) The sky appears blue when viewed from Earth, because of the scattering of the light. When sunlight strikes molecules in our atmosphere, the light is redirected in many directions. The blue light is scattered more than the red light because blue color has the smallest wavelength i.e. comparable to the size of the particles present in our atmosphere. So, it is scattered the most, causing the sky to be blue.

(ii) The Sun is visible to us two minutes before the sunrise and two minutes after the sunset because of the bending of the light due to atmospheric refraction. The light from the Sun gets refracted by the atmospheric layers and reaches the observer. This causes the observer to think that the light is coming straight from the Sun.

(iii) If an object is placed very close to the eyes, the light reflected from it does not fall on the retina to form a clear image. The minimum distance for seeing an object clearly is 25 cm for the human eye.

(b) Presbyopia is a common defect of vision, which generally occurs at old age. A person suffering from this type of defect of vision cannot see the nearby objects clearly and distinctively. A presbyopic eye has its near point greater than 25 cm and it gradually increases as the eye becomes older.
Presbyopia is caused by the.
1. The weakening of the ciliary muscles.
2. Reduction in the flexibility of the eye lens.

Question 18.
(a) Why do we classify elements?
(b) What were the two criteria used by Mendeleev in creating his Periodic Table?
(c) Why did Mendeleev leave some gaps in his Periodic Table?
(d) In Mendeleev’s Periodic Table, why was there no mention of Noble gases such as Helium, Neon and Argon?
(e) Would you place the two isotopes of chlorine, Cl-35 and Cl-37 in different slots because of their different atomic masses or in the same slot because their chemical properties are the same? Justify your answer.
Answer:
(a) The need to classify elements into families with similar properties arose because, lacking this basic tool, the chemist had to deal with each of the 45 or so known elements one at a time, as if there were no rhyme or reason to them.

(b) Two criteria used by Mendeleev in creating his periodic table.
(i)Mendeleev’s periodic table was based on the observation that the properties of elements are the function of their atomic masses. This means that if elements are arranged in the increasing order of their atomic masses, then their properties get repeated after regular intervals.
(ii) Relative atomic mass and similarity of chemical properties.

(c) As at the time of Mendeleev some elements are not discovered, so he realized this fact and left gaps in his table for such elements and also predicted their properties.

(d) Because at the time of Mendleeve these elements are not discovered, so he did not mention about them.
(e) In the modern periodic table, all isotopes are placed in the same position as in modern periodic table is based on the atomic number not on atomic masses.

Question 19.
(a) Show the formation of Na2O by the transfer of electrons between the combining atoms.
(b) Why are ionic compounds usually hard?
(c) How is it that ionic compounds in the sold state do not conduct electricity but they do so when in molten state?
(d) What type of chemical bonds are present in CCl4?
(e) What type of chemical bonds are present in MgCl2?
Answer:
(a) Electronic configuration of Na₂O.

Formation of ionic bond.

(b) Ionic compounds are usually hard because of inter-atomic attractive forces between them. Positively charged ion and negatively charged ion are strongly attracted towards each other and their lattice enthalpy increases.

(c) Electricity can be conducted only in the presence of free electrons/ions. In the solid state, there will be no free electrons but in the molten state, ions are free to conduct electricity.

(d) In carbon tetrachloride, four single bonds are formed. Hence, covalent bonding is present in CCl4.

(e) In magnesium chloride, magnesium will lose its electrons and chlorine will accept those electrons to form magnesium chloride. Hence. ionic bonding is present in magnesium chloride.

Question 20.
(a) Draw the structure of a neuron and label the following on it.
Nucleus, Dendrite, Cell body and Axon
(b) Name the part of neuron.
(i) where information is acquired.
(ii) through which information travels as an electrical impulse.
Answer:
(a)

(b)
(i) Dendrites acquire stimulus or information from the other cells.
(ii) Axon carries away information from the cell body to the dendrite of the next neuron.

Question 21.
(a) What is (i) phototropism, and (ii) geotropism? With labelled diagrams, describe an activity to show that light and gravity change the direction that plant parts grow in.
(b) Mention the role of each of the following plant hormones.
(i) Auxin
(ii) Abscisic acid
Answer:
(a) (i) The bending of shoots or other plant parts in response to light is known as phototropism.
(ii) The bending or growth of roots towards gravity is known as geotropism.
Activity –
Fill a conical flask with water and then cover the neck of the flask with a wire mesh. Place few germinating seeds on the wire mesh. Then, take a cardboard box that is open from one side. Place the flask in the box and keep this setup near a window. After 3-4 days, you will notice the shoots start bending towards light, while the roots bend away from light.

(b) (i) Auxin helps cells grow longer.
(ii) Abscisic acid inhibits growth and causes wilting of leaves.

Question 22.
(a) How will you test for the gas which is liberated when hydrochloric acid reacts with an active metal?
(b) Name any two active metals which can be used with hydrochloric acid to liberate the same gas.
Answer:
(a) When hydrochloric acid is treated with an active metal then hydrogen gas is released.
\(2 \mathrm{M}+2 \mathrm{HCl} \rightarrow 2 \mathrm{MCl}+\mathrm{H}_{2}\)
When this hydrogen gas comes in contact with burning match stick then the gas burns with a pop sound.
(b) Sodium and potassium are two active metals which can be used with hydrochloric acid to liberate the hydrogen gas.

Question 23.
Sunita performs two sets of experiments to study the formation of lather(foam) by using liquid soap.
Set 1 . She takes 10 ml of distilled water in test tube ‘A’, adds 5-6 drops of liquid soap in it and shakes the test tube vigorously.
Set 2 . She takes 10 ml of distilled water in test tube ‘B’, adds 5-6 drops of liquid soap in it alongwith half spoonful of CaSO4, and shakes the test tube vigorously.
(a) In which test tube, A or B, less lather is formed? Why?
(b) In which test tube, A or B, more lather is formed? Why?
Answer:
(a) Test tube “B” has less lather due to the presence of calcium ions. Due to the presence of calcium ions water become hard and in hard water, lather formation decreases.
(b) Test tube “A” has more lather because it is soft water. In soft water, lather formation increases and cleansing action increases.

Question 24.
(a) Copy this figure in your answer-book and show the direction of the light ray after reflection.

(b) What type of mirror is shown in the above figure. a converging mirror or a diverging mirror?
Answer:
(a) The ray will get reflected from the mirror and will go parallel to the principal axis of the mirror.

(b) The mirror shown in the given figure is a converging mirror or a concave mirror.

Question 25.
A student is performing an experiment to verify Ohm’s Law in the laboratory. The ammeter given to him for this purpose has 10 divisions between 0 and 0.5 A on its scale. If the pointer shows 22 divisions on the ammeter scale while taking a reading, what is the value of current according to this position of pointer?
Answer:
The given ammeter has 10 division between 0 and 0.5 A.
Value of one division on the ammeter scale = 0.05 A
If the pointer shows 22 division for the main scale reading, then the actual reading = 22 × 0.05 A = 1.1 A
Hence, the value of the current according to the given pointer is 1.1 A.

Question 26.
In the test tubes A and B shown below, yeast was kept in sugar solution. Which products of respiration would you expect in tubes A and B?

Give reason for your answer.
Answer:
In test tube A, anaerobic respiration will occur. The top of test tube A is covered with a film of oil which means no oxygen would be available to the yeast cells for respiration. In this case, the product of respiration will be ethanol, carbon dioxide and energy.
Glucose → Pyruvate → 2C₂H5OH + 2CO₂ + 2ATP
In test tube B, aerobic respiration will occur. The products of aerobic respiration will be carbon dioxide, water and energy.
Glucose → Pyruvate → 6CO₂ + 6H₂O + 38ATP

Question 27.
Before testing the leaf for starch at the end of the experiment “Light is necessary for photosynthesis”.
(a) In which liquid the leaf should be boiled?
(b) Why should the leaf should be boiled in this liquid?
Answer:
(a) The leaf should be boiled in alcohol (ethanol).
(b) The leaf is boiled in alcohol to destarch it (remove the chlorophyll from the leaf) as the chlorophyll interferes with the testing of starch with iodine.

Lakhmir Singh Biology Class 10 Solutions