CBSE Sample Papers for Class 10 Science Set 12 with Solutions

Students must start practicing the questions from CBSE Sample Papers for Class 10 Science with Solutions Set 12 are designed as per the revised syllabus.

CBSE Sample Papers for Class 10 Science Set 12 with Solutions

Time: 3 Hours
Maximum Marks: 80

Instructions

• This question paper consists of 39 questions in 5 sections.
• All questions are compulsory. However, an internal choice is provided in some questions. A student is expected to attempt only one of these questions.
• Section A consists of 20 objective-type questions carrying 1 mark each.
• Section B consists of 6 Very Short questions carrying 2 marks each. Answers to these questions should be in the range of 30 to 50 words.
• Section C consists of 7 Short Answer type questions carrying 3 marks each. Answers to these questions should be in the range of 50 to 80 words.
• Section D consists of 3 Long Answer type questions carrying 5 marks each. Answers to these questions should be in the range of 80 to 120 words.
• Section E consists of 3 source-based/case-based units of assessment of 4 marks each with sub-parts.

Section A

Select and write the most appropriate option out of the four options given for each of the questions 1-20.

Question 1.
Which of the following two combinations is correct?

(a) P – Sodium, Q – Aluminium
(b) P – Aluminium, Q – Zinc
(c) Q – Potassium, R – Lead
(d) Q – Copper, R – Silver
Answer:
(a) P – Sodium, Q – Aluminium
Metal like potassium and sodium reacts violently with cold water.

Metal like aluminium, iron, and zinc do not react either with cold or hot water. They react with steam and form the metal oxide and hydrogen gas.

Lead, copper, silver, and gold do not react with water at all.

Question 2.
A student learns that magnetic field strength around a bar magnet is different at every point which of the following diagrams shows the correct magnetic field lines around a bar magnet?

Answer:

Explanation: The Magnetic lines of forces are continuous curves and originate from the N-pole and end at the S-pole.

Question 3.
Chlorine forms a diatomic molecule, Cl ₂ . The electron dot structure for this molecule is




Answer:

In a chlorine molecule, both chlorine atoms contribute one electron and thus, share a single electron pair to form a single covalent bond. As electrons are shared by both atoms, they acquire the inert gas configuration of the argon atom in the valence shell.

Question 4.
By removing the inducing magnets, the induced magnetism is:
(a) Diminishes overtime
(b) Immediately diminishes
(c) It persists for a significant duration
(d) It remains unchanged
Answer:
(b) Immediately diminishes
Explanation: Induced magnetism takes place, as long as the induced magnet is present.

Question 5.
Which of the following are the correct structural isomers of butane?

(a) (i) and (iii)
(b) (ii) and (iv)
(c) (i) and (ii)
(d) (iii) and (iv)
Answer:
(a) (i) and (iii)
Structure (i) is n-butane. Structure (iii) is iso-butane.
Since the molecular formula is the same, only the structures are different. So, (i) and (iii) are isomers while structures (ii) and (iv) have molecular formula C ₄ H ₈ .

Question 6.
Which among the following is not the function of the testes at puberty?
(i) Formation of germ cells
(ii) Secretion of testosterone
(iii) Development of placenta
(iv) Secretion of estrogen
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (i) and (iv)
Answer:
(c) (iii) and (iv)
Explanation: The development of the placenta and secretion of estrogen are related to the female reproductive system and, hence, are not the function of the testes at puberty.

Question 7.
Which of the following reactions involved the combination of two elements?
(a) CaO + CO ₂ → CaCO ₃
(b) 4Na + O ₂ → 2Na ₂ O
(c) SO ₂ + \(\frac{1}{2}\)O ₂ → SO ₃
(d) NH ₃ + HCl → NH ₄ Cl
Answer:
(b) 4Na + O ₂ → 2Na ₂ O
In this reaction, two elements sodium and oxygen participate and form sodium oxide. However, in other reactions, the compounds are combined and form a single product.

Question 8.
The process where characteristics are transmitted from parent to offspring is called:
(a) Variation
(b) Heredity
(c) Gene
(d) Allele
Answer:
(b) Heredity
Explanation: Characteristics from the parents are passed down to the offspring during sexual reproduction. These are the combinations of female and male parents. This is known as heredity.

Question 9.
Identify the phase of digestion which is represented in the diagram in Amoeba. The arrow indicates the flow of stages of the nutrition process.

(a) The pseudopodia form the food vacuole for the egestion of undigested food
(b) The pseudopodia fuses over the food particle forming a food vacuole for the absorption of the food
(c) The pseudopodia forms the food vacuole for the excretion
(d) The pseudopodia fuses over the nucleus forming a food vacuole for the absorption of food
Answer:
(b) The pseudopodia fuses over the food particle forming a food vacuole for the absorption of the food.
Amoeba takes in food using temporary finger-like extensions of the cell surface, which fuse over the food particle forming a food vacuole. Inside the vacuole, complex substances are broken down into simpler ones which then diffuse into the cytoplasm, The remaining undigested material is moved to the surface of the cell and thrown out.

Question 10.
A student wrote a chemical equation of the reaction between carbon monoxide and hydrogen as,
CO ₂ + 2H ₂ O → CH ₃ OH.
How can the reaction be classified?
(a) An example of a combination reaction as a compound separated into two compounds.
(b) An example of a decomposition reaction as a compound dissociates into two compounds.
(c) An example of a combination reaction as two compounds react to form a single compound.
(d) An example of a decomposition reaction as two compounds react to form a single compound.
Answer:
(c) An example of a combination reaction as two compounds react to form a single compound.
Explanation: The equation CO ₂ + 2H ₂ O → CH ₃ OH. represents the combination of carbon monoxide (CO) and hydrogen (H ₂ ) to produce methanol (CH ₃ OH). The reactants (CO and H ₂ ) combine to form a single compound, methanol. This reaction does not involve the dissociation of any compound or the formation of multiple compounds.

False

False

False

False

Question 11.
What is the correct sequence of components of the reflex arc?
(A) Sensory afferent nerve
(B) Relay neuron
(C) Motor nerve
(D) Receptor organ
(E) Effector, e.g. muscle
(a) D → C → B → A → E
(b) D → A → B → C → E
(c) E → B → E → A → D
(d) E → C → A → D → B
Answer:
(b) D → A → B → C → E
The sequence of events in the reflex arc is as follows:
(D) Receptor organ-like skin perceives the stimulus and activates a sensory nerve impulse.
(A) The sensory (afferent) nerve carries messages in the form of sensory impulses to the spinal cord.
(B) The neurons of the spinal cord (relay neurons) analyze sensory impulses and transmit them to motor neurons.
(C) The Motor (efferent) nerve conducts these impulses from the central nervous system to the effectors.
(E) Effector-like muscles respond by pulling back the organ away from the stimulus.

Question 12.
Which of the following obeys Ohm’s law?
(a) Filament of a bulb
(b) LED
(c) Nichrome
(d) Transistor
Answer:
(c) Nichrome
Explanation: In conductors, resistance remains constant when the current passing through them is increased, they are known as Ohmic conductors. Nichrome which is an alloy is made in such a way that its resistance remains constant for a wide range of temperature. Hence, nichrome obeys Ohm’s Law. Whereas, transistors, LEDs, and bulb filaments do not obey Ohm’s law because with the varied change in temperature their resistance changes.

Question 13.
No matter how far you stand from a mirror, your image appears erect. The mirror is likely to be
(a) plane
(b) concave
(c) convex
(d) either plane or convex
Answer:
(d) either plane or convex
Plane mirrors and convex mirrors always form an erect image.

Question 14.
The electrical resistivity of an alloy of copper and nickel is …………….. when compared with the electrical resistivity of an alloy of copper, manganese, and nickel.
(a) same
(b) double
(c) more
(d) less
Answer:
(c) more
Explanation: The electrical resistivity of an alloy of copper and nickel is greater when compared with the electrical resistivity of an alloy of copper, manganese, and nickel. The electrical resistivity of Cu-Ni alloys with increasing temperature rises steeply. At 200°C, the electrical resistivity of Cu-Ni alloy is 49 × 10 ^-8 Ω-m whereas of copper, manganese, and nickel 44 × 10 ^-8 Ω-m.

Question 15.
The main function of abscisic acid in plants is to
(a) increase the length of cells
(b) promote cell division
(c) inhibit growth
(d) promotes the growth of stems
Answer:
(c) inhibit growth
The main function of abscisic acid in plants is to inhibit growth.

Question 16.
A student has traced the path of a ray of light through a glass slab as follows. If you are asked to label 1,2,3 and 4, the correct sequencing of labeling ∠i, ∠e, ∠r and lateral displacement respectively is :

(a) 2, 1, 3, 4
(b) 1, 2, 3, 4
(c) 1, 3, 2, 4
(d) 1, 3, 4, 2
Answer:
(c) 1, 3, 2, 4
Explanation: Here, 1 is the angle of incidence, 3 is the angle of emergence, 2 is the angle of refraction, and 4 is the lateral displacement.

Directions (Q.Nos. 17-20) These consist of two statements – Assertion (A) and Reason (R). Answer these questions by selecting the appropriate option given below.

(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.

Question 17.
Assertion (A): Denatured alcohol is not suitable for drinking purposes.
Reason (R): Because denatured alcohol does not same taste and smell as drinkable alcohol.
Answer:
(c) A is true, but R is false.
Denatured alcohol is not suitable for drinking purposes because it contains some poisonous substances like methanol, copper sulphate, etc. which results in coagulation of protoplasm causing nausea, blindness, and even death. Hence, A is true but R is false.

Question 18.
Assertion: It is possible to correct the refractive defects with contact lenses or through surgical interventions.
Reason: The eye lens is composed of fibrous jelly-like material.
Answer:
(b) Both A and R are true and R is not the correct explanation of A
Explanation: The refractive defects can be corrected by contact lenses and the eye lens is composed of fibrous jelly-like material.

Question 19.
Assertion (A): Photosynthesis is the opposite biochemical reaction of respiration.
Reason (R): Energy is utilized during respiration.
Answer:
(c) A is true, but R is false.
Respiration is defined as the process of biochemical oxidation of nutrients at the cellular level during which energy is released whereas photosynthesis is the synthesis of glucose molecules.

Question 20.
Assertion: The rate of photosynthesis will be lowered if the leaves are coated with oil.
Reason: Stomata gets blocked and thus gaseous exchange is affected.
Answer:
(a) Both A and R are true and R is the correct explanation of A
Explanation: Stomata is a tiny pore in leaves that helps in gaseous exchange, so if the stomata gets blocked due to oil, gaseous exchange will be affected and hence the rate of photosynthesis gets lowered.

Section B

Questions No. 21 to 26 are Very Short Answer Questions.

Question 21.
Compound A oxidizes in the presence of a strong oxidizing agent to produce an acid that is present in ants. Write the formula and IUPAC names of both compounds. Give the formula and IUPAC names of the next two members of their homologous series.
Answer:
CH ₃ OH; IUPAC name – Methanol
The general formula of an alcohol can be written as R—OH (where R is an alkyl group).
Here, CH ₂ and (CH ₂ ) ₂ are added to CH ₃ OH, the next two members are
C ₂ H ₅ —OH; IUPAC name – Ethanol
C ₃ H ₇ —OH; IUPAC name – Propanol (1)
An acid present in ants is HCOOH; IUPAC name – Methanoic acid
The next two members are (in the same manner as before)
CH ₃ COOH; IUPAC name – Ethanoic acid
C ₂ H ₅ —COOH; IUPAC name – Propanoic acid (1)

Question 22.
(i) One half of a convex lens of focal length 10 cm is covered with black paper. Can such a lens produce an image of a complete object placed at a distance of 30 cm from the lens? Draw a ray diagram to justify your answer.
(ii) A 4 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 20 cm. The distance of the object from the lens is 15 cm. Find the nature, position, and size of the image.
Answer:
(i) Yes, it can produce an image of a complete object placed 30 cm from the lens.

(ii) Given: h ₁ = 4 cm, f = + 20 cm, u = – 15 cm
We know that,
\(\frac{1}{f}=\frac{1}{υ}-\frac{1}{u}\)
⇒ \(\frac{1}{υ}=\frac{1}{f}+\frac{1}{u}=\frac{1}{20}-\frac{1}{15}=\frac{3-4}{60}=\frac{-1}{60}\)
∴ Image distance, υ = – 60 cm. The image will be virtual and erect.
Now, Magnification, m = \(\frac{h_2}{h_1}=\frac{υ}{u}\)
⇒ h ₂ = \(\frac{υ}{u}\) × h ₁ = \(\frac{-60}{-15}\) × 4 = + 16cm
Hence, an erect and virtual image is formed having a size of 16 cm.

Question 23.
What is the role of leaves, glomerulus, and ureter in excretion by various organisms?
Or
In birds and mammals, the left and right sides of the heart are separated. Give reasons.
Answer:
Leaves: Plants can accumulate some of their wastes in leaves. These leaves fall off and the plant gets rid of the waste. (1)
Glomerulus: In nephrons, it filters the blood passing through it.
Ureter: Transports urine from the kidney to the urinary bladder. (1)
Or
The heart of mammals and birds is four-chambered. It helps them in various ways as these are warm-blooded animals. Their metabolism is complex and the body temperature is to be maintained throughout. The separation keeps the oxygenated and deoxygenated blood away from the mixing, allowing a highly efficient supply of oxygen to the body. (2)

Question 24.
A student is viewing under a microscope a permanent slide showing various stages of asexual reproduction by budding in yeast. Draw a diagram of what he observes in proper sequence.
Answer:

Question 25.
What are the advantages of connecting electrical appliances in parallel with the battery instead of connecting them in series?
Or
In the arrangement shown in the figure, there are two coils wound on a non-conducting cylindrical rod. Initially, the key is not inserted in the circuit. Later the key is inserted and then removed shortly after.

What are the two observations that can be noted from the galvanometer reading?
Answer:
The following are the advantages of connecting electrical devices in parallel with the battery:
(i) Parallel circuits divide the current among the electrical devices so that they can have the necessary amount of current to operate properly. (1)
(ii) If one of the devices in a parallel combination fuses or fails, then the other devices keep working without being affected. (1)
Or
The magnetic field lines around a straight current-carrying conductor are concentric circles whose centers lie on the wire (as shown in the figure).

In the above figure, I and B represent the current and magnetic field, respectively. (2)

Question 26.
What is ozone and how does it affect any ecosystem?
Answer:
Ozone is a triatomic molecule made of three oxygen atoms. It is present as a layer in the stratosphere that prevents the harmful UV radiations of the sun from entering the earth’s surface, thus protecting us from skin cancers, genetic mutations, eye diseases like cataracts, etc. Ozone is a molecule made from three atoms of oxygen.

False

Section C

Questions No. 27 to 33 are Short Answer Questions.

Question 27.
P, Q, and R are 3 elements that undergo chemical reactions according to the following equations.

Answer the following questions.
(a) Which element is most reactive?
(b) Which element is least reactive?
(c) State the type of reaction listed above.
Answer:
(a) The most reactive element is Q as it has replaced both P and R from their compounds.
(b) Element R is least reactive as it has been replaced by both P and Q.
(c) Displacement reaction. (1 × 3)

Question 28.
The figure represents the human brain. Study the figure given below and answer the following:
(i) Name the parts labeled (a), (b) and (c)
(ii) Give one function of each parts labelled (a), (b) and (c)
(iii) The largest part of the brain comprising two hemispheres is known as …………….. .

Study the diagrams given below and answer the following questions:

(i) Name the structures shown as X and Y in the figures (A) and (B), respectively.
(ii) Write the functions performed by the structures X and Y.
(iii) Name the phenomenon depicted and define it.
(iv) How do the structures X and Y differ from each other?
(v) Give examples of the plants which show the said phenomenon.
Answer:
(i) (a) – Cerebrum, (b) – Cerebellum, (c) – Medulla oblongata

Cerebrum is the seat of intelligence, memory, will power, and consciousness . it is divided into two halves called cerebral hemispheres . corpus callosum is connected by a sheet of fibres called corpus callosum .

True

Medulla oblongata controls the functioning of internal organs and involuntary actions like the beating of heart, breathing movement, peristalsis movement etc.

(iii) The largest part of the brain comprising two hemispheres is known as Cerebrum.
OR
(i) X: Stem tendrils, Y: Leaf tendrils.
(ii) Functions of X and Y: Stem and leaf tendrils enable the plant to climb up support.
(iii) Thigmotropism is depicted here in the figure. It is the growth movement of plant parts in response to a touch stimulus.
(iv) Stem tendrils (X) arise from the stem while leaf tendrils (Y) arise from the leaf of the plant.
(v) Sweet peas, vines and Cuscuta.

Question 29.
Mustard was growing in two fields A and B. Field A produced brown coloured seeds, while field B produced yellow-coloured seeds. It was observed that in field A, the offspring showed only the parental trait for consecutive generations, whereas in field B, the majority of the offspring showed a variation in the progeny. What are the probable reasons for these?
Answer:
In field A, the reason for parental traits in consecutive generations of the offspring is self-pollination. In self-pollination, the pollen from the stamen of a flower is transferred to the stigma of the same flower. The parent plant remains the same, so there will be no or very little variation seen. (1)

True

Question 30.
Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also?
Answer:
Soap may be represented by the formula RCOONa where R is an alkyl group that represents a long chain of carbon with fifteen or more atoms. Oil drops containing dirt particles and water do not mix. Soap helps in their mixing by reducing interfacial tension or friction. It forms a sort of bridge between oil drops and water in which the alkyl portion (hydrophobic end) points towards the oil drop while the other portion (hydrophilic end) is directed towards water. This is known as micelle formation. Thus, soap helps in the formation of a stable emulsion between oil and water. Ethanol and other similar solvents are organic, and they do not help in micelle formation because soap is soluble in them.

Question 31.
(a) In the figure below, a light ray travels from the air into the semi-circular plastic block. Give a reason why the ray does not deviate at the semi-circular boundary of the plastic block.

(b) Complete the ray diagram of the above scenario when the light ray comes out of the plastic block from the top flat end.
Answer:
(a) The ray of light is undergoing normal incidence at the air-plastic block interface. For normal incidence, there is no deviation. (1)

Question 32.
(i) How will you infer with the help of an experiment that the same current flows through every part of a circuit containing three resistors in series connected to a battery?
(ii) Consider the given circuit and find the current flowing in the circuit and the potential difference across the 15 Ω resistor when the circuit is closed.

Answer:
(i) Let three resistors R ₁ , R ₂ and R ₃ be connected in series which are also connected to a battery, an ammeter and a key as shown in the figure.

When the key is closed, an electric circuit is completed and current starts flowing through the circuit. Take the reading of the ammeter. Now change the position of the ammeter to anywhere in between the resistors and take its reading. We will observe that in both cases reading of the ammeter will be the same showing the same current flows through every part of the electric circuit,

(ii) Given, R ₁ = 5 Ω, R ₂ = 10 Ω, R ₃ = 15 Ω, V = 30 V
Total resistance, R = R ₁ + R ₂ + R ₃
[As 5 Ω, 10 Ω, and 15 Ω are connected in series]
⇒ R = 5 + 10 + 15
⇒ R =30 Ω
Potential difference, V = 30 V
Current in the circuit, I = ?
From Ohm’s law, I = \(\frac{V}{R}\)
⇒ I = \(\frac{30}{30}\)
⇒ I = 1A
Therefore,
Current flowing in the circuit = 1 A
Potential difference across 15 Ω resistors = IR ₃ = 1 A × 15 Ω = 15V

Question 33.
A student fixed a straight thick copper wire between two terminals of a battery. He placed a magnetic compass near the current carrying copper wire. Then, he observed that the position of the compass needle changed slightly.
(a) What is the phenomenon by which the compass needle gets deflected?
(b) What does the change in the position of the compass needle indicate?
(c) If we change the direction of current through the wire, then how does the position of the compass needle change?
Answer:
(a) When a magnetic compass is placed near a current-carrying conductor, the position of the compass needle changes. This phenomenon is known as the magnetic effect of current. (1)
(b) The change in the position of the compass needle near a current-carrying conductor indicates that a magnetic field is produced around the conductor. (1)
(c) If we reverse the direction of current through the wire, then the change observed in the position of the compass needle is also in the opposite direction. (1)

Section D

Questions No. 34 to 36 are Long Answer Questions.

Question 34.
(i) A 10 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 12 cm. The distance of the object from the lens is 18 cm. Find the nature, position and size of the image formed.
(ii) The absolute refractive index of Ruby is 1.7. Find the speed of light in Ruby. The speed of light in vacuum is 3 × 10 ⁸ m/s.
OR
A 6 cm tall object is placed perpendicular to the principal axis of a concave mirror of a focal length of 30 cm. The distance of the object from the mirror is 45 cm. Use mirror formula to determine the position, nature and size of the image formed. Also, draw a labelled ray the diagram to show the image formation in this case
Answer:
(i) Height of object, h ₁ = + 10 cm
Focal length, f = + 12 cm
Object distance, u = – 18 cm
From the lens formula,

The position of the image formed is at a distance of 36 cm from the convex lens.

(ii) We know that,

= 1.76 × 10 ⁸ ms ^-1
Thus, the speed of light in ruby is 1.76 × 10 ⁸ ms ^-1
OR
Given the height of the object = 6 cm
Focal length, f = – 30 cm
Object distance, u = – 45 cm
Image distance, υ =?
Height of image, h _i = ?
We have, \(\frac{1}{f}=\frac{1}{υ}+\frac{1}{u}\)
⇒ \(\frac{1}{-30}=\frac{1}{υ}+\frac{1}{-45}\)
⇒ \(\frac{-1}{30}+\frac{1}{45}=\frac{1}{υ}\)
⇒ \(\frac{1}{υ}=\frac{-3+2}{90}\)
⇒ υ = – 90 cm
Thus the image position is at 90 cm on the same side of the mirror where the object is placed, we have magnification (m),
⇒ m = \(\frac{h_i}{h_0}=\frac{-v}{u}\)
⇒ \(\frac{h_i}{6}=\frac{-(-90)}{-45}\)
⇒ \(\frac{h_i}{6}\) = – 2
⇒ h _i = – 12 cm
Thus the height of the image formed is 12 cm.

The image formed is real and inverted.

Question 35.
(a) Explain the barrier and chemical method of contraception by giving an example of each.
(b) Explain the structure of the carpel with the help of a labelled diagram.
Or
(a) Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.
(b) How does chemical coordination occur in plants?
Answer:
(a) (i) Barrier method: It involves the usage of certain products or devices that prevent the meeting of gametes and help in birth control, e.g. condom, diaphragm, etc. (1)
(ii) Chemical method: It involves the usage of chemicals called spermicides, which are applied in the vagina to kill sperm. It can only be used with condoms or diaphragm (1)

: (a) Carpel or Pistil is the female reproductive part and is present in the centre of a flower. (b) Carpel or Pistil is the female reproductive part and is present in the centre of a flower. It is made up of the following three parts: (a) Carpel or Pistil is the female reproductive part and is present in the centre of a flower. (b) Carpel or Pistil is the female reproductive part and is present in the centre of a flower. (c) Carpel

• Stigma: the sticky terminal part of the carpel which helps in receiving the pollen grains.
• Style: the middle elongated part of the carpel which helps in the attachment of stigma to the ovary.
• Ovary: the swollen bottom part of the carpel which contains ovules having an egg cell.

Or
(a) Comparison between hormonal mechanisms are as follows:

Basis	Hormonal Mechanism/Endocrine System	Nervous Mechanism
Passage of information	It is through chemicals called hormones.	It is through electrical conduction.
Sensory Receptors	Absent	Present
Rapidity	The system is comparatively slower.	The system is rapid.
Connection	The system is not connected to target sites directly.	The system is directly connected to every part under its control.
Response	The response is slow and produced by all the cells of the target tissues.	The response is quick and limited to those cells that are innervated with nerves.
Role in growth and development	The system controls growth and development.	It has little role in growth and development.
Components	It consists of glands and their secretions.	It consists of neurons, nerves, and nervous organs.
Effects	The effect of chemical messages lasts for a longer period.	The effect of a nervous message is for a short duration.
Action	It is involuntary.	It can be voluntary or involuntary.

plant hormones are the chemical compounds that help the plant to coordinate the growth, development, and responses to the environment . the plant contains the following plant hormones: melatonin, melatonin, melatonin, melatonin, melatonin, melatonin, melatonin, melatonin, melatonin, melatonin, melatonin, melatonin, melatonin,

• Auxins help in cell elongation.
• Gibberellins help in the growth of the stem.
• Cytokinins promote cell division.
• Abscisic acid inhibits plant growth. (2)

Question 36.
Describe the alimentary canal of human beings.
OR
Describe the internal structure of the human heart.
Answer:
The alimentary canal of human beings starts with the mouth and ends at the anus.

(1) Mouth: We ingest food through the mouth. Teeth are present in the mouth which helps in chewing and mastication of food. Tongue helps in mixing food with saliva. Mouth has salivary glands which secrete saliva. Saliva contains the enzyme ptyalin or salivary amylase which helps in breaking down complex food (starch) into simpler substances.

True

False

True

(5) Large intestine: It receives undigested and unabsorbed food from the small intestine. Most of the water is absorbed here and the remaining is converted into a semi-solid waste material called faece. The faecal matter is stored in rectum and is removed through the anus from time to time.
OR
(1) Human heart is four-chambered. It consists of two upper chambers called auricles or atrium and two lower chambers called ventricles.

Falk: right atrium receives deoxygenated blood from all parts of the body through two venacava . Falk: right atrium receives deoxygenated blood from all parts of the body through two venacava . Falk: right atrium receives deoxygenated blood from all parts of the body through two venacava . Falk: right atrium receives deoxygenated blood from all parts of the body through two venacava .

(3) Pulmonary artery carries deoxygenated blood from right ventricle to the lungs for oxygenation.

True

True

(6) Human heart is enclosed by the pericardium membrane.

Section E

Questions No. 37 to 39 are case-based/data-based questions with 2 to 3 short sub-parts. Internal choice is provided in one of these sub-parts.

Question 37.
The table given below shows the hints given by the quiz master in a quiz.

Hints

(i) Compound ‘A’ is widely used as a preservative in pickles.

(ii) ‘A reacts with ethanol to form a sweet-smelling compound ‘S’.

Based on the above hints answer the following questions.
(a) Identify the compound A and compound B.
(b) Which gas is produced when compound ‘A’ reacts with washing soda? Write the chemical equation.
Or
How can we get the sodium salt of compound A from compound B? Name the process and write the corresponding chemical equation.
Answer:
(a) A = Ethanoic acid, B = Ester (2)
(b) CO ₂ gas is produced.

Or
The sodium salt of the compound ‘A’ can be obtained from compound ‘B’ by the action of a base. This process is called saponification.

Question 38.
When growing plants detect light, a hormone called auxin, is synthesized at the shoot tip, which helps the cells to grow longer. When light is coming from one side of the plant, auxin diffuses towards the shady side of the shoot. This concentration of auxin stimulates the cells to grow longer on the side of the shoot which is away from light. Thus, the plant appears to bend towards the light. Other examples of plant hormones are gibberellins which, like auxins, help in the growth of the stem. Cytokinins promote cell division, and it is natural then that they are present in greater concentration in areas of rapid cell division, such as in fruits and seeds. These are examples of plant hormones that help in promoting growth. But plants also need signals to stop growing. Abscisic acid is one example of a hormone that inhibits growth. Its effects include wilting of leaves.

(a) What is the function of cytokines?
(b) What are plant growth inhibitors? Give an example.
(c) Where is auxin synthesized?
OR
What is the function of gibberellins?
Answer:
(a) Cytokinins promote cell division, and it is natural then that they are present in greater concentration in areas of rapid cell division, such as in fruits and seeds.
(b) Plant growth inhibitors are regulating substances which retard such processes as root and stem elongation, seed germination, and bud opening. For example, Abscisic acid.
(c) Auxin is synthesized at the shoot tip and helps the cells to grow longer.
OR
Gibberellins help in the growth of the stem.

Question 39.
A student experiments and plots the V-I graph of a sample of nichrome wire at three temperatures T ₁ , T ₂ , and T ₃ as shown in the figure.

(a) Which temperature, V-I graph obeys Ohm’s law?
(b) Which temperature, the resistance of nichrome wire is minimum?
(c) What is the correct relation among temperatures T ₁ , T ₂ , and T ₃ ?
Or
Give two examples of the application of the heating effect of electric current.
Answer:
(a) The V-I curve of a given wire at temperatures T ₁ , T ₂ , and T ₃ obeys Ohm’s law because each V-I curve is a straight line. (1)
(b) Resistance of nichrome wire is directly proportional to temperature. Since, T ₁ < T ₂ < T ₃ , hence, resistance of nichrome wire is minimum at temperature T ₁ . (1)
(c) The slope of the V-I graph for the nichrome wire is directly proportional to its temperature. Hence, correct relation among T ₁ , T ₂ and T ₃ is given as T ₃ > T ₂ > T ₁ (2)
Or
Electric iron and electric bulbs are two examples of the application of the heating effect of electric current. (2)

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