Class 10 Science Case Study Worksheet (PDF + Answers)
Class 10 Science case study questions - 120 case studies with answers & free PDF. Physics, Chemistry and Biology for CBSE 2026-27.
This free Worksheet for CBSE Class X Science contains a structured worksheet with MCQs, short answer, case-based and HOTS questions in one place. It has been prepared by Sumeet Sahu at Unique Study Point, Indore, strictly following the latest NCERT syllabus for Session 2026-27.
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Science Case Study Questions
Class 10 · Physics, Chemistry & Biology · Practice Worksheet with Solutions
Part 1 · Physics (Q1–Q44)
4 Marks eachIn our laboratories we use compound microscopes to see the magnified image of a microscopic object. A compound microscope is made up of two lenses. The lens nearest to the object to be viewed, called objective lens, forms real, inverted and magnified image of the object. This image serves as an object for the second lens called eyepiece. The eyepiece forms virtual, erect and magnified image of its object. Thus, the resultant image formed by a microscope is virtual, inverted and magnified with respect to the microscopic object viewed.Case Study
(a)
For a real, inverted, magnified image the object lies between F and 2F.
- f = 2 cm, so 2f = 4 cm.
(b)
A convex lens gives a virtual, erect, magnified image when the object is between the optical centre and the focus.
(c)(i)
- Given: f = 18 cm, u = 12 cm, so u < f (object lies between O and F).
- Ray 1: a ray parallel to the principal axis refracts through the focus F2.
- Ray 2: a ray through the optical centre O goes straight.
- The refracted rays diverge, so they are produced backwards (dotted) to meet on the object side.
- Using lens formula: 1v = 1f + 1u = 118 − 112 = −136.
- v = −36 cm.
(c)(ii)
- Real, inverted image of the same size forms only when u = 2f and v = 2f.
- Distance between object and image = u + v = 2f + 2f = 4f.
- 4f = 60 cm.
- f = 604 = 15 cm.
A student took three concave mirrors of different focal lengths and performed the experiment to see the image formation by placing an object at different distances with these mirrors as shown in the following table.Case Study
| Case No. | Object-distance | Focal length |
|---|---|---|
| I | 45 cm | 20 cm |
| II | 30 cm | 15 cm |
| III | 20 cm | 30 cm |
(i)
Case I: u = 45 cm and f = 20 cm, so u > 2f (40 cm).
(ii)
Real image of the same size forms when u = 2f.
- Case I: 2f = 40 cm, but u = 45 cm, not equal.
- Case II: 2f = 2 × 15 = 30 cm, and u = 30 cm, equal.
- Case III: u = 20 cm is less than f = 30 cm, so the image is virtual.
(iii)
Dentists use a concave mirror.
When the tooth is placed within the focus (between P and F) the mirror forms a virtual, erect and magnified image, so the dentist sees an enlarged view of the tooth.
Shaving mirror
A shaving mirror is a concave mirror with the face placed between the pole and the focus, i.e. u < f. This is Case III (u = 20 cm, f = 30 cm).
- Mirror formula: 1v + 1u = 1f with u = −20 cm and f = −30 cm.
- 1v = −130 + 120 = 160.
- v = +60 cm (behind the mirror).
The ability of a medium to refract light is expressed in terms of its optical density. Optical density has a definite connotation. It is not the same as mass density. On comparing two media, the one with the large refractive index is optically denser medium than the other. The other medium with a lower refractive index is optically rarer. Also the speed of light through a given medium is inversely proportional to its optical density.Case Study
(i)
- Refractive index n = cv.
- v = cn = 3 × 1082.42.
(ii)
From Snell's law, sin r = sin θn, so a larger n gives a smaller angle of refraction.
- n: water 1.33 < glass 1.5 < carbon disulphide 1.62.
(iii)(a)
Speed in glass (2 × 108 m/s) is less than in water (2.25 × 108 m/s).
(iii)(b)
The ray falls normally, so the angle of incidence is 0°.
Speed of light
- Speed of light in vacuum c = ng × vg = 32 × 2 × 108.
- c = 3 × 108 m/s.
- Speed in water vw = cnw = c × 34.
- vw = 3 × 108 × 34 = 2.25 × 108 m/s.
A highly polished surface such as a mirror reflects most of the light falling on it. In our daily life we use two types of mirrors plane and spherical. The reflecting surface of a spherical mirrors may be curved inwards or outwards. In concave mirrors, reflection takes place from the inner surface, while in convex mirrors reflection takes place from the outer surface.Case Study
(a)
(b)
A ray parallel to the axis passes through the principal focus after reflection, so f = 10 cm.
- R = 2f.
- R = 2 × 10 = 20 cm.
(c)
- Convex mirror: f = +15 cm, u = −10 cm.
- Mirror formula: 1v + 1u = 1f.
- 1v = 115 + 110.
- 1v = 2 + 330 = 16.
- v = +6 cm.
Type of mirror
Virtual, erect and diminished images are always formed by a convex mirror.
Study the data given below showing the focal length of three concave mirrors A, B and C and the respective distances of objects placed in front of the mirrors:Case Study
| Case | Mirror | Focal Length (cm) | Object Distance (cm) |
|---|---|---|---|
| 1 | A | 20 | 45 |
| 2 | B | 15 | 30 |
| 3 | C | 30 | 20 |
(i)
Case 1: u = 45 cm and 2f = 40 cm, so u > 2f.
(ii)
Case 2: u = 30 cm = 2f (object at C).
(iii)
Mirror C: f = 30 cm and u = 20 cm, so u < f (object between P and F).
Image position
- Concave mirror: f = −12 cm, u = −18 cm.
- 1v = 1f − 1u.
- 1v = −112 + 118.
- 1v = −3 + 236 = −136.
- v = −36 cm.
The refraction of light on going from one medium to another takes place according to two laws which are known as the laws of refraction of light. These laws are 1. The ratio of sine of the angle of incidence to the sine of the angle of refraction is always constant for the pair of media in contact.Case Study
sin isin r = constant = μ This constant is called the refractive index of the second medium with respect to the first medium. The Refractive index is also defined as the ratio of the speed of light in a vacuum to the speed of light in the medium.
2. The incident ray, refracted ray and normal all lie in the same plane. This law is called Snell’s law of refraction.
(i)
Light going from air (rarer) to glass (denser) bends towards the normal.
(ii)
- n = sin isin r.
- n = sin 45°sin 30°.
- n = 0.7070.5.
(iii)
- n = cv, so v = cn.
- v = 3 × 1081.5.
Refractive index
- anb = 2.
- bna = 1anb.
- bna = 12.
The relationship between the distance of the object from the lens (u), a distance of the image from the lens (v) and the focal length (f) of the lens is called the lens formula. It can be written as 1f = 1v − 1u.Case Study
The size of the image formed by a lens depends on the position of the object from the lens. A lens of short focal length has more power whereas a lens of long focal length has less power. When the lens is convex, the power is positive and for the concave lens, the power is negative.
The magnification produced by a lens is the ratio of the height of the image to the height of the object as the size of the image relative to the object is given by linear magnification (m).
When m is negative, an image formed is real and when m is positive, an image formed is virtual. If m < 1, the size of the image is smaller than the object. If m >1, the size of the image is larger than the object.
(i)
- Convex lens: f = +20 cm, u = −10 cm.
- 1v = 1f + 1u.
- 1v = 120 − 110.
- 1v = −120.
- v = −20 cm.
(ii)
- m = vu.
- m = −20−10 = +2.
- Height of image h' = m × h.
- h' = 2 × 4 = 8 cm.
(iii)
- m = h'h, so h = h'm.
- The image is real and inverted, so h' = −6 cm.
- h = −6−2.
Power
- f = −5 cm = −0.05 m.
- P = 1f.
- P = 1−0.05.
Hold a concave mirror in your hand and direct its reflecting surface towards the sun. Direct the light reflected by the mirror on to a white card-board held close to the mirror. Move the card-board back and forth gradually until you find a bright, sharp spot of light on the board. This spot of light is the image of the sun on the sheet of paper; which is also termed as Principal Focus of the concave mirror.Case Study
(i)
(ii)
- Distance between mirror and principal focus is the focal length, f = 15 cm.
- R = 2f.
- R = 2 × 15.
(iii)
When the object is between P and F, the reflected rays diverge; the image formed is virtual, erect and magnified behind the mirror.
Focal length and magnification
- Object and image are at the same place: v = u = −100 cm.
- 1f = 1v + 1u.
- 1f = −1100 − 1100 = −2100.
- f = −50 cm.
- m = −vu.
- m = −−100−100.
Many optical instruments consist of a number of lenses. They are combined to increase the magnification and sharpness of the image. The net power (P) of the lenses placed in contact is given by the algebraic sum of the powers of the individual lenses P1, P2, P3 ... as P = P1 + P2 + P3 ...Case Study
This is also termed as the simple additive property of the power of lens, widely used to design lens systems of cameras, microscopes and telescopes. These lens systems can have a combination of convex lenses and also concave lenses.
(i)
- Net power P = P1 + P2.
- P = +4 D + (−2 D).
- P = +2 D.
(ii)
- f = 1P.
- f = 12.5 m.
- f = 0.4 m.
(iii)
- Power P = +0.1 D, so f = 10.1 = 10 m = 1000 cm.
- Object distance u = 20 cm, which is much smaller than f, so the object is between O and F.
- Lens formula: 1v = 11000 − 120.
- v ≈ −20.4 cm.
Virtual images
Convex lens: virtual image is erect and magnified; formed only when the object is between the optical centre and the focus (u < f).
Concave lens: virtual image is erect and diminished; formed for every position of the object, between the focus and the optical centre.
The spreading of light by the air molecules is called the scattering of light. The light having the least wavelength scatters more. The sun appears red at sunrise and sunset, the appearance of the blue sky is due to the scattering of light. The colour of the scattered light depends on the size of the particles. The smaller the molecules in the atmosphere scatter smaller the wavelengths of light. The amount of scattering of light depends on the wavelength of light. When light from the sun enters the earth’s atmosphere, it gets scattered by the dust particles and air molecules present in the atmosphere. The path of sunlight entering in the dark room through a fine hole is seen because of the scattering of the sunlight by the dust particles present in its path inside the room.Case Study
(i)
(ii)
(iii)
At sunrise and sunset the Sun is near the horizon, so its light travels a longer path through the atmosphere.
Most of the blue and shorter wavelengths are scattered away, and the red light (least scattered) reaches the eye, so the Sun appears reddish.
Danger signal
The students in a class took a thick sheet of cardboard and made a small hole in its centre. Sunlight was allowed to fall on this small hole and they obtained a narrow beam of white light. A glass prism was taken and this white light was allowed to fall on one of its faces. The prism was turned slowly until the light that comes out of the opposite face of the prism appeared on the nearby screen. They studied this beautiful band of light and concluded that it is a spectrum of white light.Case Study
(i)
(ii)
(iii)(A)
- The Sun must be behind the observer.
- Water droplets (rain or mist) must be present in the air in front of the observer.
(iii)(B)
Sunlight enters a raindrop: (a) refraction and dispersion occur at the first surface; (b) the colours are reflected internally at the back of the drop; (c) final refraction occurs when the light leaves the drop.
Atmospheric refraction is the phenomenon of bending of light on passing through earth’s atmosphere. As we move above the surface of earth, density of air goes on decreasing. Local conditions like temperature etc. also affect the optical density of earth’s atmosphere. On account of atmospheric refraction, stars seen appear higher than they actual are; advanced sunrise; delayed sunset, oval appearance of the sun at sunrise and sunset; stars twinkle, planets do not.Case Study
(i)
(ii)
(iii)
Stars are point sources of light. As their light passes through layers of air of changing density, the apparent position and the amount of light reaching the eye keep changing, so stars twinkle.
Planets are nearer and act as extended sources (many point sources); the variations cancel out, so they do not twinkle.
Without an atmosphere
A person allowed a narrow beam of white light from the sun to enter a dark room through a small aperture and placed a glass prism in its path in such a manner that the beam falls on the face AB of the prism as shown in the figure.Case Study
A screen S is placed on the other side of the prism, facing AC. On turning the prism slowly, a beautiful band of colours is obtained on the screen. It is the spectrum of sunlight.
(a)
(b)
(c)(i)
Place a second identical prism in inverted position close to the first one so that the spectrum from the first prism falls on it.
The second prism bends the colours back in the opposite way, and they emerge together as a beam of white light.
(c)(ii)
Two or more resistances are connected in series or in parallel or both, depending upon whether we want to increase or decrease the circuit resistance.Case Study
The two or more resistances are said to be connected in series if the current flowing through each resistor is the same.
(i)
- Rs = R + R + R.
(ii)
- Each piece has resistance = 204 = 5 Ω.
- Four pieces in series: Rs = 5 + 5 + 5 + 5.
(iii)
All five resistors are in series between A and B.
- RAB = 5R.
- RAB = 5 × 2 Ω.
Current in each resistor
- Rs = 1 + 2 + 3 = 6 Ω.
- I = VRs.
- I = 186.
How do we express electric current? Electric current is defined by the amount of charge flowing through a particular area in unit time. In other words, it is the rate of flow of electric charges. In circuits using metallic wires, electrons constitute the flow of charges. However, electrons were not known at the time when the phenomenon of electricity was first observed. So, electric current was considered to be the flow of positive charges and the direction of flow of positive charges was taken to be the direction of electric current. Conventionally, in an electric circuit, the direction of electric current is taken as opposite to the direction of the flow of electrons, which are negative charges.Case Study
(i)
(ii)
(iii)
Current
- I = Qt.
- I = 124.
Study the following electric circuit in which the resistors are arranged in three arms A, B and C :Case Study
(i)
- Arm C: 10 Ω, 20 Ω and 30 Ω are in series.
- RC = 10 + 20 + 30.
(ii)
- Arm B: RB = 5 + 10 + 15 = 30 Ω.
- 1Rp = 130 + 160.
- 1Rp = 2 + 160 = 360.
(iii)
- Arm A: RA = 5 + 15 + 20 = 40 Ω.
- Total resistance R = RA + Rp.
- R = 40 + 20 = 60 Ω.
- I = VR.
- I = 660.
Arm B withdrawn
- Only arms A and C remain in series: R = 40 + 60 = 100 Ω.
- I = 6100.
Study the circuit shown in which two resistors X and Y of resistances 3 Ω and 6 Ω respectively are joined in series with a battery of 2 V.Case Study
I.
II.
III.(a)
- Rs = 3 + 6 = 9 Ω.
- I = VRs.
- I = 29.
III.(b)
- 1Rp = 13 + 16.
- 1Rp = 2 + 16 = 36.
The electrical energy consumed by an electrical appliance is given by the product of its power rating and the time for which it is used. The SI unit of electrical energy is Joule. Actually, Joule represents a very small quantity of energy and therefore it is inconvenient to use where a large quantity of energy is involved. So for commercial purposes, we use a bigger unit of electrical energy which is called kilowatt-hour. 1 kilowatt-hour is equal to 3.6 × 106 joules of electrical energy.Case Study
(i)
- E = P × t.
- Time doubled: E' = P × 2t = 2E.
(ii)
- E = P × t.
- E = 60 W × 60 s.
(iii)
- Energy per day = 0.4 kW × 8 h = 3.2 kWh.
- Cost = 3.2 × ₹ 5.
Energy transformed
- H = I2Rt.
- t = 30 min = 1800 s.
- H = 52 × 2 × 1800.
- H = 25 × 2 × 1800.
Study the following electric circuit in which the resistors are arranged in three arms A, B and C:Case Study
(i)
- Arm A: 5 Ω, 15 Ω and 20 Ω are in series.
- RA = 5 + 15 + 20.
(ii)
- Arm B: RB = 5 + 10 + 15 = 30 Ω; arm C: RC = 10 + 20 + 30 = 60 Ω.
- 1Rp = 130 + 160 = 360.
(iii)
- R = RA + Rp = 40 + 20 = 60 Ω.
- I = 660.
Arm B withdrawn
- R = RA + RC = 40 + 60 = 100 Ω.
- I = 6100.
The heating effect of current is obtained by transformation of electrical energy into heat energy. Just as mechanical energy used to overcome friction is covered into heat, in the same way, electrical energy is converted into heat energy when an electric current flows through a resistance wire. The heat produced in a conductor, when a current flows through it is found to depend directly on (a) strength of current (b) resistance of the conductor (c) time for which the current flows.Case Study
The mathematical expression is given by H = I2Rt.
The electrical fuse, electrical heater, electric iron, electric geyser etc. all are based on the heating effect of current.
(i)
(ii)
(iii)
- H = I2Rt.
- New current = 2I, new time = t2.
- H' = (2I)2 × R × t2.
- H' = 4 × 12 × I2Rt.
New radius
The wire has the same length L and material, so R = ρLπr2.
- The fuse melts when I2R reaches the same value, so I2 × 1r2 must stay the same.
- 52r2 = 102r'2.
- 25r2 = 100r'2.
- r'2 = 4r2.
We know that a battery or a cell is a source of electrical energy. The chemical reaction within the cell generates the potential difference between its two terminals that sets the electrons in motion to flow the current through a resistor or a system of resistors connected to the battery. To maintain the current, the source has to keep expanding its energy. Where does this energy go? A part of the source energy in maintaining the current may be consumed for useful work (like in rotating the blades of an electric fan). The rest of the source energy may be expended in heat to raise the temperature of the gadget. We often observe this in our everyday life. For example, an electric fan becomes warm if used continuously for a long time, etc. On the other hand, if the electric circuit is purely resistive, that is, a configuration of resistors only connected to a battery; the source energy continually gets dissipated entirely in the form of heat. This is known as the heating effect of electric current. This effect is utilized in devices such as an electric heater, electric iron, etc.Case Study
(i)
(ii)
(iii)
Nichrome and copper wires in series
The same current flows through both wires, so H = I2Rt depends on resistance.
When electric current flows in a purely resistive circuit electrical energy gets fully converted into heat energy. The amount of heat produced (H) in the circuit is found to be directly proportional to (i) the square of current I2 (ii) the resistance (R) of the conductor and (iii) the time (t) for which current flows. In other words H = I2Rt. Electrical devices such an electric fuse, electric heater, electric iron etc. are all based on this effect called heating effect of electric current.Case Study
a.
b.
c.
Principle: heating effect of electric current (Joule heating).
If the current rises above the safe value, the heat produced (H = I2Rt) melts the low-melting fuse wire and breaks the circuit, so the appliance is saved from damage.
Current in the heater
- P = VI, so I = PV.
- I = 1100220.
- I = 5 A.
In a domestic circuit five LED bulbs are arranged as shown. The source voltage is 220 V and the power rating of each bulb is marked in the circuit diagram. Based on the following circuit diagram, answer the following questions:Case Study
a.
b.
- I = PV.
- I = 1155.
c.
- RB = V2P.
- RB = 55 × 5511 = 302511.
- RB = 275 Ω.
- Four identical bulbs in series: R = 4 × 275.
Bulb C fused
In our homes, either the overhead electric poles or underground cables support the power supply flowing through the mains supply. One of the wires in this supply is covered with insulation in the colour red, and another wire colored black. At the meter board, these wires pass into an electric meter through the main fuse. The main switch, live wire, and the neutral wire are in connection to the line wires in our homes; these wires then supply electricity to separate electric circuits within the house.Case Study
(i)
(ii)
(iii)
Role of the fuse
As shown in the diagram, an electric circuit consisting of an ammeter, a voltmeter, 4 cells of 1.5 V each, a plug key with a gap XY was set up. Voltmeter and ammeter readings were recorded in the observation table for four arrangements as given below:Case Study
Arrangement No. 1 - only resistor R1 in gap XY
Arrangement No. 2 - only resistor R2 in gap XY
Arrangement No. 3 - Resistors R1 and R2 in series in gap XY
Arrangement No. 4 - Resistors R1 and R2 in parallel in gap XY
Based on the observations, four V - I graphs A, B, C and D as shown in figure were drawn. Study these graphs.
a.
The slope of an I–V graph is 1R. The series combination has the largest resistance, so the smallest slope.
b.
The parallel combination has the smallest resistance, so the largest slope.
c.(i)
- Connect two 10 Ω resistors in parallel: 1Rp = 110 + 110 = 210, so Rp = 5 Ω.
- Connect the third 10 Ω resistor in series with this combination.
- R = 10 + 5 = 15 Ω.
c.(ii)
- Resistors are in series: R = 0.1 + 0.2 + 0.3 + 0.4 + 0.5.
- R = 1.5 Ω.
- I = VR.
- I = 61.5.
Study the following electric circuit in which the resistors are arranged in three arms A, B and C:Case Study
(i)
- Arm B: 5 Ω, 10 Ω and 15 Ω are in series.
- RB = 5 + 10 + 15.
(ii)
- Arm C: RC = 10 + 20 + 30 = 60 Ω.
- 1Rp = 130 + 160.
- 1Rp = 360.
(iii)
- Arm A: RA = 5 + 15 + 20 = 40 Ω.
- R = RA + Rp = 40 + 20 = 60 Ω.
- I = 660.
Arm B withdrawn
- R = RA + RC = 40 + 60 = 100 Ω.
- I = 6100.
Study the following circuit:Case Study
On the basis of this circuit, answer the following questions:
a.
- RAB = 4 + 6 + 16.
b.
- Two 8 Ω resistors in parallel: 1RBC = 18 + 18 = 28.
c.
- Total R = RAB + RBC = 26 + 4 = 30 Ω.
- I = VR.
- I = 630.
More potential difference
The same current (0.2 A) flows through the 16 Ω resistor and through the parallel combination (4 Ω), since they are in series.
- V16 Ω = 0.2 × 16 = 3.2 V.
- Vparallel = 0.2 × 4 = 0.8 V.
Consider the following electrical circuit diagram in which nine identical resistors of 3 Ω each are connected as shown. If the reading of the ammeter A1 is 1 ampere, answer the following questions:Case Study
i.
ii.
The current 1 A divides equally among the four identical 3 Ω branches of the last block.
- A2 = 14 A = 0.25 A.
iii.
- First block: two 3 Ω in parallel, 1R1 = 13 + 13, so R1 = 1.5 Ω.
- V1 = I × R1.
- V1 = 1 × 1.5.
Total resistance
- Block 2: three 3 Ω in parallel: R2 = 33 = 1 Ω.
- Block 3: four 3 Ω in parallel: R3 = 34 = 0.75 Ω.
- R = R1 + R2 + R3.
- R = 1.5 + 1 + 0.75.
In 1827, a German physicist Georg Simon Ohm (1787-1854) found out the relationship between the current I, flowing in metallic wire and the potential difference across its terminals. He stated that the electric current flowing through a metallic wire is directly proportional to the potential difference V, across its ends provided its temperature remains the same.Case Study
The resistance of a circuit is defined as the ratio between the voltage applied to the current flowing through it. Rearranging the above relation, R = VI
Electric charge flows easily through some materials than others. The electrical resistance measures how much the flow of this electric charge is restricted within the circuit.
i.
ii.
iii.
The slope of an I–V graph is 1R, so the line with the least slope has the highest resistance.
Slope of V–I graph
If two or more resistances are connected in such a way that the same potential difference gets applied to each of them, then they are said to be connected in parallel.Case Study
The current flowing through the two resistances in parallel is, however, not the same. When we have two or more resistances joined in parallel to one another, then the same current gets additional paths to flow and the overall resistance decreases.
i.
- 1R = 12 + 16 + 18.
- 1R = 12 + 4 + 324 = 1924.
- R = 2419.
ii.
- Each piece = 123 = 4 Ω.
- The twisted ends join the three pieces in parallel: 1R = 34.
- R = 43.
iii.
The 6 Ω, 3 Ω and 1 Ω resistors are all connected between A and B, i.e. in parallel.
- 1R = 16 + 13 + 11.
- 1R = 1 + 2 + 66 = 96.
- R = 69.
Current in each resistance
The four 12 Ω resistors are in parallel, so each has the full 3 V across it.
- I = VR.
- I = 312.
The rate of flow of charge is called electric current. The SI unit of electric current is Ampere (A). The direction of flow of current is always opposite to the direction of flow of electrons in the current.Case Study
The electric potential is defined as the amount of work done in bringing a unit- positive test charge from infinity to a point in the electric field. The amount of work done in bringing a unit positive test charge from one point to another point in an electric field is defined as potential difference.
VAB = VB − VA = WBAq The SI unit of potential and potential difference is volt.
i.
- V = Wq.
- Since q = I t, V = WIt.
ii.
- n = I te.
- n = 1 × 11.6 × 10−19.
iii.
- V = Wq.
- V = 10020.
Current
- t = 100 ms = 0.1 s.
- I = qt.
- I = 20.1.
A student fixes a sheet of white paper on a drawing board using some adhesive materials. She places a bar magnet in the centre of it and sprinkles some iron filings uniformly around the bar magnet using a salt sprinkler. On tapping the board gently, she observes that the iron filings have arranged themselves in a particular pattern.Case Study
i.
ii.
iii.
The direction of the field at a point is the direction of the tangent to the field line at that point (direction in which the north pole of a compass needle points).
Two field lines never cross: at the point of intersection the compass needle would have to point in two directions, which is impossible.
Using a compass needle
Place the magnet on a sheet of paper and put a small compass near its north pole. Mark the two ends of the needle with dots. Move the needle so that its south end is on the previous north dot, mark the new position, and repeat. Join the dots to get one field line; repeat from other points.
A student fixes a sheet of white paper on a drawing board using some adhesive materials. She places a bar magnet in the centre of it and sprinkles some iron filings uniformly around the bar magnet using a salt sprinkler. On tapping the board gently, she observes that the iron filings have arranged themselves in a particular pattern.Case Study
i.
ii.
iii.
The direction of the field at a point is the direction of the tangent to the field line at that point (direction in which the north pole of a compass needle points).
Two field lines cannot cross: otherwise the field would have two directions at the point of intersection.
Using a compass needle
Place the compass near the magnet, mark both ends of the needle, move the needle so that its south end is at the marked north end, mark again, and repeat. Join all dots to get a field line. Field lines are drawn on both sides of the magnet (see figure).
An insulated copper wire wound on a cylindrical cardboard tube such that its length is greater than its diameter is called a solenoid. When an electric current is passed through the solenoid, it produces a magnetic field around it. The magnetic field produced by a current-carrying solenoid is similar to the magnetic field produced by a bar magnet. The field lines inside the solenoid are in the form of parallel straight lines. The strong magnetic field produced inside a current-carrying solenoid can be used to magnetize a piece of a magnetic material like soft iron when placed inside the solenoid. The strength of the magnetic field produced by a current-carrying solenoid is directly proportional to the number of turns and strength of the current in the solenoid.Case Study
i.
ii.
iii.
- B = μ0 n I.
- New current I' = 2I, new turns per cm n' = n2.
- B' = μ0 × n2 × 2I.
- B' = μ0 n I.
Face B
The battery drives the current into the coil at end A and out at end B (the current is anticlockwise when viewed from the B end).
A student was asked to perform an experiment to study the force on a current carrying conductor in a magnetic field. He took a small aluminum rod AB, a strong horse shoe magnet, some connecting wires, a battery and a switch and connected them as shown. He observed that on passing current, the rod gets displaced. On reversing the direction of current, the direction of displacement also gets reversed. On the basis of your understanding of this phenomenon, answer the following questions:Case Study
i.(a)
i.(b)
ii.
iii.
Field around a straight conductor
A magnetic field is described by drawing the magnetic field lines. When a small north magnetic pole is placed in the magnetic field created by a magnet, it will experience a force. And if the north pole is free, it will move under the influence of the magnetic field. The path traced by a north magnetic pole free to move under the influence of a magnetic field is called a magnetic field line.Case Study
Since the direction of the magnetic field line is the direction of the force on a north pole, so the magnetic field lines always begin from the N-pole of a magnet and end on the S-pole of the magnet. Inside the magnet, however, the direction of magnetic field lines is from the S-pole of the magnet to the N-pole of the magnet. Thus, the magnetic field lines are closed curves. When a small compass is moved along a magnetic field line, the compass needle always sets itself along the line tangential to it. So, a line drawn from the south pole of the compass needle to its north pole indicates the direction of the magnetic field at that point.
i.
ii.
iii.
Pattern for a bar magnet
A student was asked to perform an experiment to study the force on a current carrying conductor in a magnetic field. He took a small aluminum rod AB, a strong horse shoe magnet, some connecting wires, a battery and a switch and connected them as shown. He observed that on passing current, the rod gets displaced. On reversing the direction of current, the direction of displacement also gets reversed. On the basis of your understanding of this phenomenon, answer the following questions :Case Study
i.
ii.
iii.(i)
The U-shaped magnet is held vertically, so the field between its poles is horizontal (east-west); the current flows from B to A, i.e. from north to south.
- Apply Fleming's left-hand rule to the field and the current directions.
iii.(ii)
iv.
A student fixes a sheet of white paper on a drawing board using some adhesive materials. She places a bar magnet in the centre of it and sprinkles some iron filings uniformly around the bar magnet using a salt-sprinkler. On tapping the board gently, she observes that the iron filings have arranged themselves in a particular pattern.Case Study
i.
ii.
iii.
The direction at a point is along the tangent to the field line at that point (the direction of the north pole of a compass needle).
Two field lines never cross, because the field cannot have two different directions at one point.
Using a compass needle
Mark the positions of the two ends of a small compass needle, move it so that its south end sits at the earlier north mark, and repeat; join the marks to get a line. Draw lines on both sides of the magnet (N to S outside).
Take two different coils of copper wire having large number of turns, say 50 and 100 turns respectively. Insert them over a non-conducting roll as shown in the given figure. Connect the Coil-1, having large number of turns, in series with a battery and a plug key. Also connect the other Coil-2 with a galvanometer.Case Study
i.
ii.
iii.
N-pole and coil
In order to obtain magnetic field lines around a bar magnet, a student performed an experiment using a magnetic compass and a bar magnet. The magnet was placed on a sheet of white paper fixed on a drawing board. Using magnetic needle he obtained on the paper a pattern of magnetic field lines (as shown below) around the bar magnet.Case Study
a.
b.
c.A (i)
c.A (ii)
c.B
In a domestic circuit, six LED bulbs and a ceiling fan are arranged as per the circuit shown in the figure. The source voltage is 220 volts and the power rating of each device is marked in the circuit diagram. Two fuses F1 and F2 are also provided in the circuit. Based on the circuit diagram, answer the following questions :Case Study
a.
b.
- I = PV.
- I = 20220.
c.(i)
- RA = V2P.
- RA = 44 × 4410 = 193610.
- RA = 193.6 Ω.
- The five bulbs are in series: R = 5 × 193.6.
c.(ii)
Andre Marie Ampere suggested that a magnet must exert an equal and opposite force on a current-carrying conductor, which was experimentally found to be true. But we know that current is due to charges in motion. Thus, it is clear that a charge moving in a magnetic field experience a force, except when it is moving in a direction parallel to it. If the direction of motion is perpendicular to the direction of magnetic field, the magnitude of force experienced depends on the charge, velocity (v), strength of magnetic field (B), and sine of the angle between v and B. Direction of magnetic force is given by Fleming’s left-hand rule.Case Study
i.
Electron (negative) moving east; field vertically downward.
- The conventional current is towards the west.
- Apply Fleming's left-hand rule: forefinger down, middle finger west.
ii.
iii.
Electron moves down and the proton moves up in a field pointing to the right.
- Proton: current is upwards, field to the right; Fleming's left-hand rule gives the force into the plane of the paper.
- Electron: current is opposite to its motion, i.e. upwards; the force is also into the plane of the paper.
Electron beam
The electron beam moves downward, so the current is upward; the field is to the right.
A student was asked to perform an experiment to study the force on a current carrying conductor in a magnetic field. He took a small aluminum rod AB, a strong horse shoe magnet, some connecting wires, a battery and a switch and connected them as shown. He observed that on passing current, the rod gets displaced. On reversing the direction of current, the direction of displacement also gets reversed. On the basis of your understanding of this phenomenon, answer the following questions:Case Study
i.
ii.
iii.(a)
The magnet is held vertically, so the field is horizontal (east-west); current flows from B to A, i.e. north to south.
iii.(b)
Field around a straight conductor
In our homes, we receive the supply of electric power through a main supply also called mains, either supported through overhead electric poles or by underground cables. In our country the potential difference between the two wires (live wire and neutral wire) of this supply is 220 V.Case Study
a.
b.
- I = PV.
- I = 1000220.
- I = 4.54 A.
c.(i)
c.(ii)
Part 2 · Chemistry (Q45–Q70)
4 Marks eachRedox reactions are those reactions in which oxidation and reduction occur simultaneously. A redox reaction is made up of two half reactions. In the first half reaction, oxidation takes place and in second half reaction, reduction occurs. Oxidation is a process in which a substance loses electrons and in reduction, a substance gains electrons. The substance which gains electrons is reduced and acts as an oxidising agent. On the other hand, a substance which loses electrons is oxidised and acts as a reducing agent.Case Study
i.
ii.
iii.
Substance reduced
When the fats and oil present in the food material get oxidized by the oxygen (of air), their oxidation products have unpleasant smells and tastes. Due to this taste of food material containing fats and oil change and become very unpleasant. The condition produced by aerial oxidation of fats and oils in food marked by unpleasant smell and taste is called rancidity. Rancidity spoils the food material prepared in the fats and oils which have been kept for a considerable time and makes them unfit for eating.Case Study
The development of rancidity in food can be prevented in the following ways-
I. Rancidity can be prevented by adding an antioxidant to foods containing fats and oils.
II. Rancidity can be prevented by packaging fat and oil-containing food in Nitrogen gas.
III. Rancidity can be prevented by keeping food in a refrigerator.
i.
ii.
iii.
Food spoiled
Those reactions in which two compounds react by an exchange of ions to form two new compounds are called double displacement reactions. A double displacement reaction usually occurs in solution and one of the products, being insoluble, precipitate out (separates as a solid). Any reaction in which an insoluble solid (called precipitate) is formed that separates from the solution is called a precipitation reaction. The reaction in which acid or acidic oxide reacts with base or basic oxide to form salt and water is called neutralisation reaction.Case Study
For example, 2NaOH + H2SO4 → Na2SO4 + H2O
i.
ii.
iii.
Identify A
When oxygen combines with other elements or compounds, the process is called oxidation the substances that combine with oxygen are said to have been oxidized.Case Study
The reduction is exactly the opposite of oxidation. If a substance loses oxygen during a reaction, it is said to be reduced. When hydrogen burns the hydrogen combines with oxygen to form water 2H2 + O2 = H2O The hydrogen is oxidized in this reaction, but at the same time, the oxygen is reduced. Whatever oxidation occurs reduction must also occur.
i.
ii.
iii.
Molecules of water
- 2H2 + O2 → 2H2O.
- 4 molecules of H2 form 4 molecules of H2O.
When a more reactive element displaces a less reactive element from its compound, it is called a displacement reaction. The reaction is of two types. Single displacement reaction and double displacement reaction.Case Study
Iron being more reactive than copper displaces copper from an aqueous solution of copper sulphate. This is an example of a single displacement reaction.
On adding silver nitrate solution to sodium bromide, a yellow ppt of silver bromide and solution of sodium nitrate is formed. This is an example of a double displacement reaction.
i.
ii.
iii.
Displace aluminium
In a redox reaction, both oxidation, as well as reduction, takes place together, oxidation involves loss of electrons while reduction involves the gain of electrons. The redox- reaction may involve a combination of atoms and molecules, displacement of metals, or non-metals.Case Study
Example: CuSO4 + Zn → ZnSO4 + Cu displacement of Cu metal from its compound.
i.
ii.
iii.
Type of reaction
In a balanced chemical reaction, equal number of atoms are present on both sides of reaction. A balanced chemical reaction is based on law of conservation of mass which means that total mass of reactants and products participating in a reaction must be equal. For example, a balanced chemical equation of burning of magnesium in oxygen to form magnesium oxide is written as: 2Mg + O2 → 2MgO The mass of reactants (2 × 24 + 32 = 80) is equal to the mass of products [2 × (24 + 16) = 80].Case Study
i.
- Mass of Q = 35 g − 20 g.
ii.
iii.
Values of m and n
Copper sulphate crystal contains water of crystallisation when the crystal is heated the water is removed and salt turns white. The crystal can be moistened again with water. The water of crystallisation is the fixed number of water molecules present in 1 formula unit of copper sulphate. On heating gypsum at 373K, it loses water molecules and became calcium sulphate hemihydrate.Case Study
i.
ii.
iii.
Heating gypsum at 373 K
Acid-base indicators can be used to distinguish between an acid and a base. Universal indicator, a mixture of several indicators, shows different colours at different concentrations of acids and bases, thereby indicating their pH on the pH scale of 0 − 14. The pH of a solution is measured by pH paper, which is a paper impregnated with a universal indicator.Case Study
Answer the following questions:
a.
b.
c.(i)
c.(ii)
A scale for measuring hydronium ion in a solution is called the pH scale. The pH of a neutral solution is 7. A value of less than 7 on the pH scale represents an acidic solution. As the pH value, increases from 7 to 14 it represents OH- ion concentration in solution i.e a basic solution.Case Study
i.
ii.
iii.
Tooth decay
The teacher while conducting practicals in the laboratory divided the students into three groups and gave them various solutions to find out their pH and classify them into acidic, basic and neutral solutions.Case Study
Group A - Lemon juice, vinegar, colourless aerated drink Group B - Tomato juice, coffee, ginger juice Group C - Sodium hydroxide, sodium chloride, lime water
i.
ii.
iii.
Importance of pH
The dissolving of an acid or a base in water is a highly exothermic reaction. Care must be taken while mixing concentrated nitric acid or sulphuric acid with water. The acid must always be added slowly to water with constant stirring. If water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause burns. The glass container may also break due to excessive local heating. Look out for the warning sign on the can of concentrated sulphuric acid and on the bottle of sodium hydroxide pellets.Case Study
i.
ii.
iii.
Why acid to water
Salts play a very important role in our daily life. Sodium chloride which is known as common salt is used almost in every kitchen. Baking soda is also a salt used in faster cooking as well as in baking industry. The family of salts is classified on the basis of cations and anions present in them.Case Study
a.
b.
c.
pH scale
Common salt is a very important chemical compound for our daily life. It's chemical name is sodium chloride and it is used as a raw material in the manufacture of caustic soda, washing soda, baking soda etc. It is also used in the preservation of pickles, butter, meat etc.Case Study
i.
ii.
iii.A
iii.B
The strength of acid and base depends on the number of H+ and the number of OH- respectively. If we take hydrochloric acid and acetic acid of the same concentration, say one molar, then these produce different amounts of hydrogen ions. Acids that give rise to more H+ ions are said to be strong acids, and acids that give less H+ ions are said to be weak acids. Can you now say what weak and strong bases are?Case Study
i.
ii.
iii.
Saliva
Seawater contains many salts dissolved in it. Common salt is separated from these salts. Deposits of solid salt are also found in several parts of the world. These large crystals are often brown due to impurities. This is called rock salt and is mined like coal. The common salt is an important raw material for chemicals of daily use.Case Study
a.
b.
c.(i)
c.(ii)
The acidic behaviour of acids is due to the presence of hydrogen (H+) ions in them. They produce hydrogen ions in the presence of water. Water is a polar solvent and this property of water helps in weakening the bond between the ions and makes them soluble.Case Study
Hence, acids and bases produce ions in aqueous solutions. It may be noted that a dry HCl gas or a solution of hydrogen chloride in organic, non-polar solvents like toluene or benzene do not show acidic properties. This is because hydrogen chloride does not undergo ionization in toluene.
The reason why HCl splits into H+ and Cl- ions in presence of water lies in the fact that water molecules, being polar, pull the H+ and Cl- ions apart and thus, the bond in HCl is broken.
i.
ii.
- pH = −log [H+].
- [H+] = 10−8.
iii.
No H+ ions
Salt of a strong acid and strong base is neutral with a pH value of 7. NaCl common salt is formed by a combination of hydrochloride and sodium hydroxide solution. This is the salt that is used in food. Some salt is called rock salt, bed of rock salt was formed when seas of bygone ages dried up. The common salt thus obtained is an important raw material for various materials of daily use, such as sodium hydroxide, baking soda, washing soda, and bleaching powder.Case Study
i.
ii.
iii.
Permanent hardness
On the basis of reactivity metals are grouped into three categories-Case Study
i. Metals of low reactivity
ii. Metals of medium reactivity
iii. Metals of high reactivity
Therefore metals are extracted in pure form from their ores on the basis of their chemical properties. Metals of high reactivity are extracted from their ores by electrolysis of the molten ore. Metals of low reactivity are extracted from their sulphide ores, which are converted into their oxides. The oxides of these metals are reduced to metals by simple heating.
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ii.
iii.
Roasting and calcination
Almost all metals combine with oxygen to form metal oxides. Metal oxides are generally basic in nature. But some metal oxides show both basic as well as acidic behaviour. Different metals show different reactivities towards oxygen. Some react vigorously while some do not react at all.Case Study
i.
ii.
iii.
Burning sulphur
Non-metals are either solids or gases. Non-metal can exist in different forms such as carbon. Each form is called allotrope. Alkali metal is so soft that it can be cut with a knife. They have low density and low melting point. Some metal can melt if they are kept in the palm.Case Study
i.
ii.
iii.
Sodium in kerosene
Non-metals are highly electronegative in nature. They have a tendency to gain electrons in their valence shell to achieve nearest noble gas configuration. Thus, they form anions and act as good oxidising agents.Case Study
X + ne- → Xn− (non-metal atom → anion) They react with air or oxygen on heating to form oxides which react with water to form acids. Thus, non-metal oxides are acidic in nature. Non-metals do not react with dilute acids at all. This is because they are electronegative and therefore, cannot displace hydrogen from acids but they form covalent hydrides when heated with hydrogen.
i.
ii.
iii.
Dilute acids
Three metal samples of magnesium, aluminium and iron were taken and rubbed with sand paper. These samples were then put separately in test tubes containing dilute hydrochloric acid. Thermometers were also suspended in each test tube so that their bulbs dipped in the acid. The rate of formation of bubbles was observed. The above activity was repeated with dilute nitric acid and the observations were recorded.Case Study
Answer the following questions:
a.
b.
c.
Reactivity
Metals are required for a variety of purposes. For this we need their extraction from their ores. Ores mined from the earth are usually contaminated with many impurities which must be removed prior to the extraction of metals. The extraction of pure metal involves the following steps:Case Study
1. Concentration of ore 2. Extraction of the metal from the concentrated ore 3. Refining of the metal
i.
ii.
iii.
Sodium
The metals produced by various reduction processes are not very pure. They contain impurities, which must be removed to obtain pure metals. The most widely used method for refining impure metals is electrolytic refining.Case Study
i.
ii.
iii.
Zinc and silver in CuSO4
Many pure metals like copper, iron and gold are very soft and as such are considered unsuitable for certain uses. Metallic objects around us such as cooking utensils, statues, ornaments, guns etc. are actually not made up of pure metals. Instead of pure metals, alloys are used in the design of most of the useful objects. Making alloys enhances the basic properties of a metal which is the primary constituent (metal) of an alloy.Case Study
I.
II.
III.a
An alloy is a homogeneous mixture of two or more metals, or of a metal and a non-metal, made by melting them together and cooling.
III.b
Part 3 · Biology (Q71–Q120)
4 Marks eachThe maintenance functions of all living organisms must go on even when they are not doing anything particular. Even when we are just sitting in a class or even asleep, this maintenance job has to go on. These maintenance processes require energy to prevent damage and break-down of cells and tissues, which is obtained by the individual organism from the food prepared by the autotrophs, called producers.Case Study
a.
b.
c.(i)
- Absorption of light energy by chlorophyll.
- Conversion of light energy into chemical energy.
- Reduction of carbon dioxide to carbohydrates.
Desert plants take up CO2 at night (stomata open) and form an intermediate compound; during the day the energy absorbed by chlorophyll acts on it to form carbohydrate.
c.(ii)
Nutrition is the process of taking food by an organism and the utilization of food for energy. This is a vital process that helps living beings obtain their energy from various sources.Case Study
Nutrients are substances that provide nutrition.
The mode of nutrition varies from one species to another. Plants do photosynthesis to prepare their own food. Animals depend on plants for food.
i.
ii.
iii.
Common feature
Kidneys are vital organs for survival. Several factors like infections, injury or restricted blood flow to kidneys reduce the activity of kidneys. This leads to accumulation of poisonous wastes in the body, which can even lead to death. In case of kidney failure, an artificial kidney can be used. An artificial kidney is a device to remove waste products from the blood through dialysis.Case Study
a.
b.
c.
Selective reabsorption
Human digestive system is a tube running from mouth to anus. Its main function is to breakdown complex molecules present in the food which cannot be absorbed as such into smaller molecules. These molecules are absorbed across the walls of the tube and the absorbed food reaches each and every cell of the body where it is utilised for obtaining energy.Case Study
a.
b.
What will happen if
Bile juice
The green plants make their food, through photosynthesis and are therefore called autotrophs. All other organisms depend upon green plants for food and are referred to as heterotrophs. Green plants carry out photosynthesis by using light energy of sun. The first phase of reactions are directly light driven therefore called light reactions. The second phase of reactions are not directly light driven but are dependent on the products of light reactions and are called dark reactions.Case Study
i.
ii.
iii.
Parts X, Y and Z
In animals, control and coordination are provided by nervous and muscular tissues. Touching a hot object is an urgent and dangerous situation for us. We need to detect it and respond to it. How do we detect that we are touching a hot object? All information from our environment is detected by the specialised tips of some nerve cells. These receptors are usually located in our sense organs, such as the inner ear, the nose, the tongue, and so on. So gustatory receptors will detect taste while olfactory receptors will detect the smell. This information, acquired at the end of the dendritic tip of a nerve cell, see figure, sets off a chemical reaction that creates an electrical impulse. This impulse travels from the dendrite to the cell body, and then along the axon to its end.Case Study
i.
ii.
iii.
Parts of a neuron
Adrenaline is secreted directly into the blood and carried to different parts of the body. The target organs or the specific tissues on which it acts include the heart. As a result, the heart beats faster, resulting in the supply of more oxygen to our muscles. The blood to the digestive system and skin is reduced due to contraction of muscles around small arteries in these organs. This diverts the blood to our skeletal muscles. The breathing rate also increases because of the contractions of the diaphragm and the rib muscles. All these responses together enable the animal body to be ready to deal with the situation. Such animal hormones are part of the endocrine system which constitutes the second way of control and coordination in our body.Case Study
i.
ii.
iii.
Response to adrenaline
In life there are certain changes in the environment called 'stimuli' to which we respond appropriately. Touching a flame suddenly is a dangerous situation for us. One way is to think consciously about the possibility of burning and then moving the hand. But our body has been designed in such a way that we save ourself from such situations immediately.Case Study
i.
ii.
iii.A
iii.B
Animals have a nervous system for controlling and coordinating the activities of the body. But plants have neither a nervous system nor muscles. So, how do they respond to stimuli? When we touch the leaves of a chhui-mui (the ‘sensitive’ or ‘touch-me-not’ plant of the Mimosa family), they begin to fold up and droop. When a seed germinates, the root goes down, the stem comes up into the air. What happens? Firstly, the leaves of the sensitive plant move very quickly in response to touch. There is no growth involved in this movement. On the other hand, the directional movement of a seedling is caused by growth. If it is prevented from growing, it will not show any movement. So plants show two different types of movement - one dependent on growth and the other independent of growth.Case Study
i.
ii.
iii.
Tropic movement
You must have noticed many dramatic changes in your appearance as well as that of your friends as you approached 10-12 years of age. These changes associated with puberty are because of the secretion of testosterone in males and oestrogen in females. Do you know anyone in your family or friends who has been advised by the doctor to take less sugar in their diet because they are suffering from diabetes? As a treatment, they might be taking injections of insulin. This is a hormone that is produced by the pancreas.Case Study
i.
ii.
iii.
Islet cells
A person while climbing up a rocky hill comes into a panic state and fear. His body starts reacting in a "flight-or-flight" condition to adjust to the dangerous and stressful situation.Case Study
Based on the above facts, answer the questions that follow.
a.(i)
a.(ii)
b.
c.
We have seen that the different parts of our body have specific functions. Our mouth waters when we see the food we like without our meaning to. Our heart's beat without our thinking about it. In fact, we cannot control these actions easily by thinking about them even if we wanted to. So, in between the simple reflex actions like change in the size of the pupil, and the thought out actions such as moving a chair, there is another set of muscle movements over which we do not have any thinking control. Many of these involuntary actions are controlled by the mid-brain and hind-brain. All these involuntary actions including blood pressure, salivation and vomiting are controlled by the medulla in the hind-brain. Think about activities like walking in a straight line, riding a bicycle, picking up a pencil. These are possible due to a part of the hind-brain called the cerebellum. It is responsible for the precision of voluntary actions and maintaining the posture and balance of the body. Imagine what would happen if each of these events failed to take place if we were not thinking about it.Case Study
i.
ii.
iii.
Heart beat
In animals, control and coordination are provided by nervous and muscular tissues. Touching a hot object is an urgent and dangerous situation for us. We need to detect it and respond to it. How do we detect that we are touching a hot object? All information from our environment is detected by the specialised tips of some nerve cells. These receptors are usually located in our sense organs, such as the inner ear, the nose, the tongue, and so on. So gustatory receptors will detect taste while olfactory receptors will detect the smell. This information, acquired at the end of the dendritic tip of a nerve cell sets off a chemical reaction that creates an electrical impulse. This impulse travels from the dendrite to the cell body, and then along the axon to its end. At the end of the axon, the electrical impulse sets off the release of some chemicals. These chemicals cross the gap, or synapse, and start a similar electrical impulse in the dendrite of the next neuron. This is a general scheme of how nervous impulses travel in the body. A similar synapse finally allows the delivery of such impulses from neurons to other cells, such as muscles cells or glands.Case Study
i.
ii.
iii.
Synapse
Fill a conical flask with water. Cover the neck of the flask with a wire mesh. keep two or three freshly germinated bean seeds on the wire mesh. Take a cardboard box which is open from one side. Keep the flask a wire mesh. Kin the box in such a manner that the open side of the box faces light coming from a window as shown in the given figure. After two or three days, you will notice that the shoots bend towards light and roots away from light. Now turn the flask so that the shoots are away from light and the roots towards the light. Leave it undisturbed in this condition for a few days. Plants show tropism in response to other stimuli as well. The roots of a plant always grow downwards while the shoots usually grow upwards and away from the earth. This upward and downward growth of shoots and roots, respectively, in response to the pull of earth or gravity, is obviously, geotropism.Case Study
i.
ii.
iii.
Geotropism
Environmental triggers such as light, or gravity will change the directions that plant parts grow in. These directional, or tropic, movements can be either towards the stimulus or away from it. So, in two different kinds of phototropic movement, shoots respond by bending towards light while roots respond by bending away from it. How does this help the plant? Plants show tropism in response to other stimuli as well. The roots of a plant always grow downwards while the shoots usually grow upwards and away from the earth. This upward and downward growth of shoots and roots, respectively, in response to the pull of earth or gravity, is, obviously, geotropism. If ‘hydro’ means water and ‘chemo’ refers to chemicals, what would ‘hydrotropism’ and ‘chemotropism’ mean? Can we think of examples of these kinds of directional growth movements? One example of chemotropism is the growth of pollen tubes towards ovules, about which we will learn more when we examine the reproductive processes of living organisms.Case Study
i.
ii.
iii.
Stem and root
The growth movements of plant parts in which the direction of the stimulus determines the direction of the response is known as tropic movements or tropism. Plants also have non- directional movements which may not be growth dependent.Case Study
I.
II.
III.a
III.b
Following questions are based on the two tables given below. Study these tables related to blood sugar levels:Case Study
| Table A: Blood glucose chart | Mean Blood Glucose Level (mg/dL) |
|---|---|
| Doctor's advice needed | 380 |
| 350 | |
| 315 | |
| 280 | |
| 250 | |
| 215 | |
| Good | 180 |
| 150 | |
| Excellent | 115 |
| 80 | |
| 50 |
| Table B: Blood Report of Patient X and Y (mg/dL) | Patient X | Patient Y |
|---|---|---|
| Before breakfast (Fasting) | <100 | 70-130 |
| Before lunch, supper and snack | <110 | 70-130 |
| Two hours after meals | <140 | <180 |
| Bedtime | <120 | 90-150 |
i.
ii.
iii.
Table A
Animals have a nervous system for controlling and coordinating the activities of the body. But plants have neither a nervous system nor muscles. So, how do they respond to stimuli? When we touch the leaves of a chui-mui (the ‘sensitive’ or ‘touch-me-not’ plant of the Mimosa family), they begin to fold up and droop. When a seed germinates, the root goes down, the stem comes up into the air. What happens? Firstly, the leaves of the sensitive plant move very quickly in response to touch.Case Study
There is no growth involved in this movement. On the other hand, the directional movement of a seedling is caused by growth. If it is prevented from growing, it will not show any movement.
i.
ii.
iii.
Difference
The modes by which various organisms reproduce depend on the body design of the organisms. In asexual reproduction, a single individual parent produces offsprings without the involvement of gametes. This method is a common means of increasing the off-springs rapidly under favourable conditions. Asexual reproduction occurs mostly in unicellular organisms, some plants and certain simple multicellular animals.Case Study
i.
ii.
iii.
What happens
The modes by which various organisms reproduce depend on the body design of the organisms. In asexual reproduction, a single individual parent produces off-springs without the involvement of gametes. This method is a common means of increasing the offsprings rapidly under favourable conditions. Asexual reproduction occurs mostly in unicellular organisms, some plants and certain simple multicellular animals.Case Study
i.
ii.
iii.
What happens
All the reproductive methods of living organisms are broadly categorized into two types: 1. Asexual reproduction, and 2. Sexual reproduction.Case Study
Asexual reproduction involves the participation of a single parent without the formation of gametes, fertilisation and transfer of genetic material. This method is a common means of rapidly increasing off springs under favourable conditions.
i.
ii.
iii.
Dark green filaments
The modes by which various organisms reproduce depend on the body design of the organisms. In asexual reproduction, a single individual parent produces offsprings without the involvement of gametes. This method is a common means of increasing the offsprings rapidly under favourable conditions. Asexual reproduction occurs mostly in unicellular organisms, some plants and certain simple multicellular animals.Case Study
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What happens
Pollination is an important process in sexual reproduction of plants. It is an essential process that facilitates fertilisation in plants. Pollinating agents can be wind, water, insects and birds. Several changes take place in the flower after the fertilization has taken place.Case Study
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b.
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Germinating seed
Asexual reproduction involves a single parent to produce offsprings without the formation of gametes. It occurs by the following ways : Fission, Budding, Fragmentation, Spore formation and Regeneration. In one of the methods like regeneration, Planaria A is cut horizontally into three pieces -L, M and N and Planaria B is cut vertically into two equal halves -O and P.Case Study
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Difference
Renu collected some pond water which was dark green in colour in a test tube. She took out green coloured mass from it and separated its filaments by using needles. She broke some filaments into small fragments and put them in a Petri dish containing clean water. She observed that after few days the small fragments gave rise to complete filaments.Case Study
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Fragmentation
When a girl is born, the ovaries already contain thousands of immature eggs. On reaching puberty, some of these start maturing. One matured egg is released every month by one of the ovaries. The two oviducts unite into an elastic bag-like structure known as uterus.Case Study
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b.
c.(i)
c.(ii)
Pooja is very fond of gardening. She has different flowering plants in her garden. One day few naughty children entered her garden and plucked many leaves of Bryophyllum plant and threw them here and there in the garden. After few days, Pooja observed that new Bryophyllum plants were coming out from the leaves which fell on the ground.Case Study
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Leaf pieces
Plantation drives are often carried out especially during monsoon season for the protection of our environment. Such programmes need a lot of saplings for tree plantation. Plants are propagated by sexual or asexual means in fields and nurseries. Over the years horticulturists have developed asexual methods that use vegetative parts of the plants to multiply. Many plants can reproduce by this method naturally as well as by artificial means.Case Study
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b.
c.(i)
c.(ii)
Refer to the given table regarding results of F2 generation of Mendelian cross.Case Study
| Seed type | Number of plants |
|---|---|
| Plants with round and yellow coloured seeds (P) | 315 |
| Plants with round and green coloured seeds (Q) | 108 |
| Plants with wrinkled and yellow coloured seeds (R) | 101 |
| Plants with wrinkled and green coloured seeds (S) | 32 |
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YyRr self-pollinated
All human chromosomes are not paired. Most human chromosomes have a maternal and a paternal copy, and we have 22 such pairs. But one pair called the sex chromosomes, is odd in not always being a perfect pair. Women have a perfect pair of sex chromosomes. But men have a mismatched pair in which one is normal sized while the other is a short one.Case Study
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Female gametes
A student crossed pea plants having round and yellow seeds with pea plants having wrinkled and green seeds. He found that only one type of seeds were produced in the F1 generation. When these F1 generation pea plants were self-pollinated with each other, then in addition to the seed type of F1 generation, some new types of seed combinations were also obtained in the F2 generation.Case Study
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Dominant and recessive
Sex of an individual is determined by different factors in various species. Some animals rely entirely on the environmental cues, while in some other animal's the individuals can change their sex during their life time indicating that sex of some species is not genetically determined. However, in human beings, the sex of an individual is largely determined genetically.Case Study
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Flow chart
Refer to the schematic representation of albinism which is an inherited condition caused by a recessive allele (a). ‘A’ is the dominant allele for the normal condition. The inheritance of certain genetic traits for two or more generations is represented in a pedigree or family tree. Study the given pedigree chart and answer the following questions.Case Study
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X (Aa) × albino female (aa): gametes A, a and a, a.
- Offspring: Aa, Aa, aa, aa.
Y × normal homozygous male
Y (Aa) × AA: offspring AA, AA, Aa, Aa.
A purebred pea plant with smooth seeds (dominated characteristic) was crossed with a purebred pea plant with wrinkled seeds (recessive characteristic). The F1 generation was self-pollinated to give rise to the F2 generation.Case Study
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Alternative form of a gene
Pea plants can have smooth seeds or wrinkled seeds. One of the phenotypes is completely dominant over the other. A farmer decides to pollinate one flower of a plant with smooth seeds using pollen from a plant with wrinkled seeds. The resulting pea pod has all smooth seeds.Case Study
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- Rr × Rr gives smooth : wrinkled = 3 : 1.
- Smooth seeds = 34 × 1000 = 750.
- Wrinkled seeds = 14 × 1000 = 250.
F1 characters
Sex of an individual is determined by different factors in various species. Some animals rely entirely on the environmental cues, while in some other animals the individuals can change their sex during their life time indicating that sex of some species is not genetically determined. How ever, in human beings, the sex of an individual is largely determined genetically.Case Study
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Flow chart
Sex determination is the method by which distinction between males & females is established in a species. The sex of an individual is determined by specific chromosomes. These chromosomes are called sex chromosomes or allosomes. X and Y chromosomes are called sex chromosomes. The normal chromosomes other than the sex chromosomes of an individual are known as autosomes.Case Study
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Heterogamety
A student crossed pea plants having round and yellow seeds with pea plants having wrinkled and green seeds. He found that only one type of seeds were produced in the F1 generation. When these F1 generation pea plants were self-pollinated with each other, then in addition to the seed type of F1 generation, some new types of seed combinations were also obtained in the F2 generation.Case Study
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Dominant and recessive
Sex of an individual is determined by different factors in various species. Some animals rely entirely on the environmental cues, while in some other animals the individuals can change their sex during their life time indicating that sex of some species is not genetically determined. However, in human beings, the sex of an individual is largely determined genetically.Case Study
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Flow chart
The mechanism by which the sex of an individual is determined is called sex-determination. In human beings, sex of a newborn is genetically determined, whereas in some others it is not. There are 46 (23 pairs) chromosomes in human beings. Out of these, 44 (22 pairs) control the body characters and 2 (one pair) are known as sex chromosomes. The sex chromosomes are of two types- X chromosome and Y chromosome. At the time of fertilisation, depending upon which type of male gamete fuses with the female gamete, the sex of the newborn child is decided.Case Study
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Flow chart
In some families, either rural or urban, females are tortured for giving birth to a female child. They do not seem to understand the scientific reason behind the birth of a boy or a girl. In fact the mother is not responsible for the sex of the child and it has been genetically proved that the sex of a newborn is determined by what the child inherits from the father.Case Study
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Sex not genetically determined
In human beings, there are 23 pairs of chromosomes. Out of these 23 pairs of chromosomes (i.e. 46 chromosomes), 22 pairs of chromosomes are called autosomes and one pair of chromosomes. i.e. two chromosomes are called sex chromosomes. The sex chromosomes are of two types- 'X' chromosomes and 'Y' chromosomes. The sex of a child (i.e. progeny), is decided at the time of fertilisation. In other words, at the time of zygote formation the sex chromosomes inherited from the parents of a child decide whether the new born will be a boy or a girl.Case Study
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b.
c.A
c.B
Mendel crossed tall and dwarf pea plants to study the inheritance of one gene. He collected the seeds produced as a result of this cross and grew them to generate plants of the first hybrid generation which is called the first filial progeny or F1 Mendel then self-pollinated the tall F1 plants and he obtained F2 generation.Case Study
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- Rr × Rr gives round : wrinkled = 3 : 1.
- Wrinkled seeds are the non-parental type: 14 × 1600.
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Genotype of parents
Mendel worked out the rules of heredity by working on garden pea using a number of visible contrasting characters. He conducted several experiments by making a cross with one or two pairs of contrasting characters of pea plant. On the basis of his observations he gave some interpretations which helped to study the mechanism of inheritance.Case Study
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Inherited but not expressed
The cross that includes the inheritance of two pairs of contrasting characters simultaneously is referred to as a dihybrid cross. Mendel chose pure breeding plants for yellow and green seeds and round and wrinkled shape of seeds. He cross-pollinated the plant having yellow round seeds with the plant having green wrinkled seeds. All the plants produced in F1 generation were having yellow round seeds. The plants raised from these seeds were self-pollinated, which resulted in the production of plants having four phenotypically different types of seeds.Case Study
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Frequency of RrYY
- RrYy × RrYy has 16 combinations.
- RrYY occurs in 2 of the 16 combinations.
The mechanism by which the sex of an individual is determined is called sex-determination. In human beings, sex of a newborn is genetically determined, whereas in some others it is not. There are 46 (23 pairs) chromosomes in human beings. Out of these, 44 (22 pairs) control the body characters and 2 (one pair) are known as sex chromosomes. The sex chromosomes are of two types-X chromosome and Y chromosome. At the time of fertilisation, depending upon which type of male gamete fuses with the female gamete, the sex of the newborn child is decided.Case Study
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Flow chart
Mendel blended his knowledge of Science and mathe matics to keep the count of the individuals exhibiting a particular trait in each generation. He observed a number of contrasting visible characters controlled in pea plants in a field. He conducted many experiments to arrive at the laws of inheritance.Case Study
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F2 numbers
- Tall with round seeds = 916 × 1600 = 900.
- Short with wrinkled seeds = 116 × 1600 = 100.
The mechanism by which the sex of an individual is determined is called sex-determination. In human beings, sex of a newborn is genetically determined, whereas in some others it is not. There are 46 (23 pairs) chromosomes in human beings. Out of these, 44 (22 pairs) control the body characters and 2 (one pair) are known as sex chromosomes. The sex chromosomes are of two types - X chromosome and Y chromosome. At the time of fertilisation, depending upon which type of male gamete fuses with the female gamete, the sex of the newborn child is decided.Case Study
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Flow chart
Now a days chemical pesticides are excessively used to protect the crops from disease and pests. The chemical is washed down into the soil. From soil, these are absorbed by the plant along with water and minerals and from the water bodies. The human being occupies the top level in any food chain, the maximum chemical gets accumulated in their bodies.Case Study
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Decomposer
The good we eat acts as the fuel to provide energy to do work. The interaction among various components of environments involves the flow of energy from one component of the system to another. The green plant capture energy of sunlight and at each trophic level 10% can be taken as the average value for the amount of organic matter that is present at each step and reaches the next level.Case Study
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- Tertiary consumer has 10 J; secondary consumer has 10 J × 10 = 100 J.
- Primary consumer has 100 J × 10 = 1000 J.
10 per cent law
📋 Details
| Class | Class X (CBSE / NCERT) |
| Subject | Science |
| Resource Type | Worksheet |
| Last Updated | 03 October 2026 |
| Session | 2026-27 (Latest NCERT Syllabus) |
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| Prepared by | Sumeet Sahu, Unique Study Point, Indore |
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