10th Science - 2nd Mid Term Exam 2024 - Original Question Paper | Tirupattur District | English Medium

Class 10 Science - Second Mid Term Test 2024 - Solutions

PART - I

I. Choose the correct answer. (10x1=10)

1. Speed of sound waves in air at NTP is

• a) 340 ms⁻¹
• b) 34 x 10⁴ ms⁻¹
• c) 3x10⁸ ms⁻¹
• d) none of these

Answer: a) 340 ms⁻¹
Explanation: The speed of sound in air at NTP (Normal Temperature and Pressure, 20°C) is approximately 343 m/s. The closest value given is 340 ms⁻¹.

2. Photolysis is a decomposition reaction caused by

• a) heat
• b) electricity
• c) light
• d) Mechanical energy

Answer: c) light
Explanation: The term 'photo' means light and 'lysis' means breaking down. Photolysis is the decomposition of a compound by light energy.

3. The frequency, which is audible to the human ear is

• a) 50 kHz
• b) 20 kHz
• c) 15000 kHz
• d) 10000 kHz

Answer: b) 20 kHz
Explanation: The audible range for a healthy human ear is from 20 Hz to 20,000 Hz (or 20 kHz). Among the given options, 20 kHz is the upper limit of the audible range.

4. Unit of Radioactivity is

• a) roentgen
• b) curie
• c) becquerel
• d) All the above

Answer: d) All the above
Explanation: Roentgen (measures exposure), Curie (older unit of activity), and Becquerel (SI unit of activity) are all units related to radioactivity.

5. In which of the following the mass number of daughter nucleus decreases by four

• a) α decay
• b) β decay
• c) γ decay
• d) Neutron decay

Answer: a) α decay
Explanation: In alpha (α) decay, an alpha particle (a helium nucleus, $_2^4$He) is emitted. This decreases the mass number by 4 and the atomic number by 2.

6. The use and disuse theory was proposed by

• a) Charles Darwin
• b) Ernst Haeckel
• c) Jean Baptiste Lamark
• d) Gregor Mendel

Answer: c) Jean Baptiste Lamark
Explanation: The theory of inheritance of acquired characters, also known as the use and disuse theory, was proposed by Jean Baptiste Lamark.

7. The pH of the solution is 3. Its [OH⁻] concentration is

• a) 1x10⁻³M
• b) 3M
• c) 1x10⁻¹¹M
• d) 11M

Answer: c) 1x10⁻¹¹M
Explanation: We know that $pH + pOH = 14$. Given $pH = 3$, so $pOH = 14 - 3 = 11$. The hydroxide ion concentration $[OH⁻]$ is $10^{-pOH}$, so $[OH⁻] = 10^{-11} M$.

8. We can cut the DNA with the help of

• a) scissors
• b) Restriction endonucleases
• c) Knife
• d) R.N. Aase

Answer: b) Restriction endonucleases
Explanation: Restriction endonucleases, also known as "molecular scissors," are enzymes that cut DNA at specific recognition sites.

9. The term Ethnobotany was coined by

• a) Khorna
• b) J.W. Harshberger
• c) Ronald Ross
• d) Hugo de Vries

Answer: b) J.W. Harshberger
Explanation: The term "Ethnobotany" was first coined by the American botanist John William Harshberger in 1895.

10. Pusa Komal is a disease resistant variety of

• a) Sugar cane
• b) rice
• c) cow pea
• d) maize

Answer: c) cow pea
Explanation: Pusa Komal is a high-yielding, disease-resistant variety of cowpea, developed to resist bacterial blight.

PART - II

II. Answer any Briefly (any 5). Q.No.18 is compulsory. (5x2=10)

11. What is a longitudinal wave?

A longitudinal wave is a wave in which the particles of the medium vibrate parallel to the direction of the propagation of the wave. Sound waves are a primary example of longitudinal waves.

12. Mention two cases in which there is no Doppler effect in sound?

There is no Doppler effect in sound under the following two conditions:

1. When the source (S) and the listener (L) are both at rest.
2. When the source (S) and the listener (L) move in such a way that the distance between them remains constant. For example, when they move in mutually perpendicular directions.

13. Difference between Nuclear fission and fusion.

Nuclear Fission	Nuclear Fusion
The process of breaking up of a heavy nucleus into smaller nuclei.	The process of combining two lighter nuclei to form a heavier nucleus.
It can be performed at room temperature.	It requires extremely high temperature and pressure.
It is a chain reaction.	It is not a chain reaction.
It produces radioactive waste.	It does not produce radioactive waste.

14. Define combination reaction. Give one example for an exothermic combination reaction.

Combination Reaction: A reaction in which two or more reactants combine to form a single product is called a combination reaction.
Example of Exothermic Combination Reaction: The formation of carbon dioxide from carbon and oxygen is an exothermic reaction, releasing heat.
$C(s) + O_2(g) \rightarrow CO_2(g) + Heat$

15. Why is Archaeopteryx considered to be a connecting link?

Archaeopteryx is considered a connecting link because it possesses features of both reptiles and birds.

• Reptilian features: Claws on its wings, teeth in its jaw, and a long tail with vertebrae.
• Avian (bird) features: Feathers on its wings and a beak.

This suggests that birds evolved from reptiles.

16. Define Genetic engineering.

Genetic engineering is the process of altering the genetic makeup (DNA) of an organism by introducing, deleting, or modifying specific genes using biotechnology. This is done to give the organism a new, desirable trait.

17. Name two maize hybrids rich in amino acid lysine.

Two maize hybrids rich in the amino acid lysine are:

1. Protina
2. Shakti

18. A Sound wave has a frequency of 200 Hz and the speed of 400 ms⁻¹ in a medium. Find the wavelength of the sound wave.

Given:
Frequency (f) = 200 Hz
Speed (v) = 400 ms⁻¹

Formula:
The relationship between speed, frequency, and wavelength ($\lambda$) is given by $v = f \times \lambda$.

Calculation:
Wavelength, $\lambda = \frac{v}{f}$
$\lambda = \frac{400 \, \text{ms}^{-1}}{200 \, \text{Hz}}$
$\lambda = 2 \, \text{m}$

Result: The wavelength of the sound wave is 2 meters.

PART - III

III. Answer any four questions. (Question number 24 is compulsory) (4x4=16)

19. a) Why does sound travel faster on a rainy day than a one a dry day? (2)

Sound travels faster on a rainy day because the presence of water vapor (humidity) in the air decreases the density of the air. The speed of sound is inversely proportional to the square root of the density of the medium ($v \propto 1/\sqrt{\rho}$). Since humid air is less dense than dry air, the speed of sound increases in it.

b) Why does empty vessel produce more sound than a filled one? (2)

When an empty vessel is struck, its walls are free to vibrate with a larger amplitude, producing a loud sound. When the vessel is filled with a substance (like water), the substance dampens these vibrations, reducing their amplitude. As the intensity of sound is proportional to the square of the amplitude, the sound produced by the filled vessel is much fainter.

20. State Soddy and Fajan's law.

Soddy and Fajan's Law, also known as the Radioactive Displacement Law, describes the change in atomic number and mass number of a nucleus during radioactive decay.

1. Alpha (α) Decay: When a parent nucleus emits an alpha particle, the atomic number (Z) of the daughter nucleus decreases by 2, and the mass number (A) decreases by 4.
   $_Z^A X \rightarrow _{Z-2}^{A-4} Y + _2^4 He$
2. Beta (β) Decay: When a parent nucleus emits a beta particle, the atomic number (Z) of the daughter nucleus increases by 1, while the mass number (A) remains unchanged.
   $_Z^A X \rightarrow _{Z+1}^{A} Y + _{-1}^{0} e$

21. Differentiate reversible and irreversible reactions.

Property	Reversible Reactions	Irreversible Reactions
Direction	Can proceed in both forward and backward directions.	Can proceed only in the forward direction.
Equilibrium	Attain a state of chemical equilibrium.	Do not attain equilibrium; they proceed to completion.
Completion	Never go to completion.	Reactions go to completion.
Example	Formation of ammonia: $N_2 + 3H_2 \rightleftharpoons 2NH_3$	Burning of coal: $C + O_2 \rightarrow CO_2$

22. State the applications of DNA finger printing technique.

The applications of DNA fingerprinting technique are:

• Forensic Science: It is used to identify criminals in crime investigations by comparing the DNA from a crime scene (e.g., blood, hair) with a suspect's DNA.
• Paternity and Maternity Tests: It is used to resolve disputes of parentage by comparing the DNA of the child with that of the potential parents.
• Medical Diagnosis: It helps in identifying and diagnosing inherited genetic disorders like cystic fibrosis, sickle cell anemia, and Huntington's disease.
• Conservation of Wildlife: It is used to track endangered species, identify poached animals, and manage breeding programs in zoos.

23. Define Ethnobotany and write its importance.

Definition: Ethnobotany is the scientific study of the relationship between people (of a particular culture or region) and plants. It explores how local people use plants for food, medicine, shelter, rituals, and other purposes.

Importance:

• Discovery of New Medicines: Traditional knowledge from indigenous communities has led to the discovery of many modern drugs (e.g., quinine from cinchona bark).
• Conservation: It helps in understanding the importance of plant biodiversity and promotes the conservation of traditional plant species and their habitats.
• Sustainable Agriculture: It provides insights into traditional farming methods and identifies hardy, locally-adapted crops, which can contribute to food security.
• Economic Development: It can lead to the development of new plant-based products, creating economic opportunities for local communities.

24. What is pH of 1x10⁻⁵ molar solution of KOH.

Step 1: Identify the substance.
KOH (Potassium hydroxide) is a strong base. It completely dissociates in water. $KOH \rightarrow K^+ + OH^-$

Step 2: Determine the hydroxide ion concentration [OH⁻].
Since KOH is a strong base, the concentration of hydroxide ions [OH⁻] will be equal to the concentration of the KOH solution.
Given [KOH] = $1 \times 10^{-5}$ M
Therefore, $[OH⁻] = 1 \times 10^{-5}$ M

Step 3: Calculate the pOH.
The formula for pOH is: $pOH = -\log_{10}[OH⁻]$
$pOH = -\log_{10}(1 \times 10^{-5})$
$pOH = 5$

Step 4: Calculate the pH.
The relationship between pH and pOH at 25°C is: $pH + pOH = 14$
$pH = 14 - pOH$
$pH = 14 - 5$
$pH = 9$

Result: The pH of the $1 \times 10^{-5}$ M KOH solution is 9.

PART - IV

IV. Answer Briefly: (2x7=14)

25. a) What do you understand by the term Ultrasonic Vibration ?
b) State 3 uses of Ultrasonic Vibrations?
c) Name 3 animals which can hear ultrasonic Vibrations.

a) Ultrasonic Vibration:
Ultrasonic vibrations (or ultrasound) are sound waves with frequencies higher than the upper audible limit of human hearing, which is typically 20,000 Hertz (20 kHz). These high-frequency vibrations are inaudible to humans.

b) 3 Uses of Ultrasonic Vibrations:

1. Medical Imaging: Used in ultrasonography to create images of internal body organs, such as monitoring a fetus during pregnancy, examining the heart (echocardiography), and detecting tumors.
2. SONAR Systems: Used in SONAR (Sound Navigation and Ranging) by ships and submarines to detect underwater objects, measure the depth of the sea, and map the seabed.
3. Industrial Cleaning: High-frequency ultrasonic waves are used to clean delicate objects like jewelry, electronic components, and surgical instruments by creating tiny cavitation bubbles that scrub surfaces clean.

c) 3 Animals that can hear Ultrasonic Vibrations:

1. Bats
2. Dolphins
3. Dogs

(OR)

Compare the properties of alpha, beta and gamma radiations.

Property	Alpha (α) Radiation	Beta (β) Radiation	Gamma (γ) Radiation
Nature	Helium nucleus ($_{2}^{4}He$)	Electron ($_{-1}^{0}e$)	Electromagnetic waves (photons)
Charge	Positive (+2e)	Negative (-1e)	Neutral (No charge)
Ionizing Power	Very High (about 100 times beta)	Moderate	Very Low
Penetrating Power	Very Low (stopped by a sheet of paper)	Moderate (stopped by an aluminum sheet)	Very High (requires thick lead or concrete to stop)
Speed	About 1/10 to 1/20 times the speed of light.	Up to 9/10 times the speed of light.	Travels at the speed of light.
Effect of Electric/Magnetic Field	Deflected	Deflected (in opposite direction to alpha)	Not deflected

26. How does pH play an important role in everyday life.

pH plays a crucial role in various aspects of our everyday life:

1. Human Digestion: The stomach produces hydrochloric acid (HCl), creating a highly acidic pH of about 1.5-3.5. This acidic environment is essential for the enzyme pepsin to function and break down proteins. Acidity issues (indigestion) are treated with antacids (bases) to neutralize the excess acid.
2. Tooth Decay: When we eat sugary foods, bacteria in our mouth break down the sugar to produce acids. If the pH in the mouth falls below 5.5, the acid starts to dissolve the tooth enamel, leading to cavities. Using toothpaste, which is basic, helps neutralize this acid.
3. Soil pH for Agriculture: Plants require a specific pH range in the soil for optimal growth. Most crops prefer a neutral or slightly acidic soil (pH 6.5-7.5). Farmers test soil pH and add substances like lime (basic) to treat acidic soil or gypsum (acidic) to treat alkaline soil.
4. Acid Rain: Pollutants like sulfur dioxide and nitrogen oxides dissolve in rainwater to form sulfuric and nitric acids, lowering the pH of the rain (below 5.6). This acid rain damages buildings, harms aquatic life by acidifying lakes and rivers, and affects forests.
5. Blood pH: The pH of human blood is tightly maintained in a narrow range of 7.35 to 7.45. Any significant deviation from this range can lead to serious health problems or even be fatal.
6. Aquatic Life: The pH of water bodies is critical for the survival of aquatic organisms. Most fish thrive in water with a pH between 6.5 and 8.5. Changes in pH, often due to pollution or acid rain, can be lethal to marine life.

(OR)

With neat labelled diagram explain the techniques involved in gene cloning.

Gene Cloning is the process of creating multiple, identical copies of a specific gene. The main techniques involved are as follows:

1. Isolation of DNA: The first step is to isolate the desired gene (the 'gene of interest') from the source organism's DNA and a plasmid vector from a bacterium (like E. coli). A plasmid is a small, circular piece of DNA separate from the chromosomal DNA.
2. Cutting DNA (Restriction Digestion): Both the gene of interest and the plasmid vector are cut with the same restriction enzyme. This enzyme acts like "molecular scissors," cutting the DNA at a specific recognition site, often creating "sticky ends" (short, single-stranded overhangs).
3. Ligation (Joining DNA): The cut gene of interest is inserted into the opened plasmid vector. The sticky ends of the gene pair with the complementary sticky ends of the plasmid. The enzyme DNA ligase is then added to permanently join the fragments by forming phosphodiester bonds, creating a recombinant DNA (or recombinant plasmid).
4. Transformation: The recombinant plasmid is introduced into a host bacterium (e.g., E. coli). This process is called transformation. The host cells are often treated with calcium chloride or heat shock to make their membranes more permeable to the plasmid DNA.
5. Screening and Selection: The bacteria are grown on a culture medium. It's necessary to identify which bacteria have successfully taken up the recombinant plasmid. This is often done using selectable markers. For example, the plasmid may carry a gene for antibiotic resistance. By growing the bacteria on a medium containing that antibiotic, only the transformed bacteria (which have the plasmid) will survive.
6. Gene Expression and Multiplication: The transformed host bacteria are cultured in large quantities. As the bacteria reproduce, they replicate the recombinant plasmid, thus making millions of copies of the gene of interest. If the goal is to produce a protein, the host cells will also transcribe and translate the gene to synthesize the desired protein (e.g., insulin).

Neat Labelled Diagram:

Caption: A diagram illustrating the process of gene cloning, showing isolation of the gene and plasmid, cutting with restriction enzymes, ligation to form recombinant DNA, transformation into a host bacterium, and subsequent replication.