Half Yearly Class 9 Science Set 1 (Solutions)

Time:  3 Hours
Maximum Marks: 80
General Instructions:

(i) The question paper comprises four sections: A, B, C, and D. 
(ii) All questions are compulsory. However, internal choices are provided in some questions. 
(iii) Section A consists of 20 objective type questions (MCQs/Assertion-Reason) carrying 1 mark each. 
(iv) Section B consists of 7 very short answer questions carrying 2 marks each. 
(v) Section C consists of 7 short answer questions carrying 3 marks each. 
(vi) Section D consists of 5 long answer questions carrying 5 marks each. 
(vii) Draw neat and labelled diagrams wherever necessary.

Syllabus: The half-yearly question paper is framed from the following chapters: Matter in our surroundings, Is matter around us  pure?, Fundamental unit of life, tissues, Motion, Forces and laws of Motion.

Section A

Q1. The process by which a solid changes directly into a gas is called:  (1 Mark) 
(a) Melting
(b)  Sublimation
(c)  Evaporation
(d)  Condensation

Ans: (b)
Sol: Sublimation is the process where a solid changes directly into a gas without passing through the liquid state.

Q2. Which of the following is a physical change?  (1 Mark) 
(a) Burning of coal
(b)  Rusting of iron
(c)  Boiling of water
(d)  Digestion of food

Ans: (c)
Sol: Boiling of water is a physical change as it involves a change in state without altering the chemical composition.

Q3. The smallest unit of life that can perform all life processes is:  (1 Mark) 
(a) Tissue
(b)  Organ
(c)  Cell
(d)  Organelle

Ans: (c)
Sol: The cell is the smallest unit of life capable of performing all life processes.

Q4.  Which tissue provides mechanical support to plants?  (1 Mark) 
(a) Parenchyma
(b)  Collenchyma
(c)  Sclerenchyma
(d)  Xylem

Ans: (c)
Sol: Sclerenchyma provides mechanical support to plants due to its thick, lignified cell walls.

Q5. An object moving with uniform velocity has:  (1 Mark) 
(a) Zero acceleration
(b)  Constant acceleration
(c)  Variable acceleration
(d)  Negative acceleration

Ans: (a)
Sol: An object moving with uniform velocity has constant speed and direction, so its acceleration is zero.

Q6. The SI unit of force is:  (1 Mark) 
(a) Joule
(b) Newton
(c) Watt
(d) Pascal

Ans: (b)
Sol: The SI unit of force is the Newton (N).

Q7. Which of the following is a mixture?  (1 Mark) 
(a) Distilled water
(b)  Salt solution
(c)  Carbon dioxide
(d)  Sugar

Ans: (b)
Sol: A salt solution is a mixture as it contains two or more substances mixed in variable proportions.

Q8. The plasma membrane is:  (1 Mark) 
(a) Fully permeable
(b)  Impermeable
(c)  Selectively permeable
(d)  Rigid

Ans: (c)
Sol: The plasma membrane allows selective passage of substances in and out of the cell.

Q9. Which of the following measures the shortest path covered by an object?  (1 Mark) 
(a) Speed
(b)  Distance
(c)  Displacement
(d)  Time

Ans: (c)
Sol: Displacement measures the shortest path between the initial and final positions of an object.

Q10.  The third law of motion states that:  (1 Mark) 
(a) An object remains at rest unless acted upon
(b)  Acceleration is proportional to force
(c)  For every action, there is an equal and opposite reaction
(d)  Force equals mass times acceleration

Ans: (c)
Sol: This is Newton's third law of motion

Q11. Assertion (A): Evaporation causes cooling.  (1 Mark) 
Reason (R): Particles with higher kinetic energy leave the liquid surface during evaporation. 
(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. 

Ans: (a)
Sol: Evaporation causes cooling because high-energy particles leave the liquid, reducing its average kinetic energy.

Q12. Assertion (A): A solution is a homogeneous mixture.   (1 Mark) 
Reason (R): The components of a solution cannot be separated by filtration. 
(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. 

Ans: (a)
Sol: A solution is a homogeneous mixture, and its components cannot be separated by filtration due to their uniform distribution at the molecular level.

Q13. Assertion (A): Mitochondria are called the powerhouse of the cell.   (1 Mark) 
Reason (R): They produce energy in the form of ATP through cellular respiration. 
(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. 

Ans: (a)
Sol: Mitochondria produce ATP through cellular respiration,  earning them the title "powerhouse of the cell."

Q14. Assertion (A): Blood is a connective tissue.   (1 Mark) 
Reason (R): It connects different parts of the body by transporting nutrients and oxygen. 
(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. 

Ans: (a)
Sol: Blood is a connective tissue as it connects different body parts by transporting nutrients and oxygen.

Q15. Assertion (A): An object can have zero displacement even after moving.   (1 Mark) 
Reason (R): Displacement depends on the initial and final position of the object. 
(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. 

Ans: (a)
Sol: Displacement is zero if the initial and final positions are the same, regardless of the path taken.

Q16. Assertion (A): Inertia depends on the mass of an object.   (1 Mark) 
Reason (R): A heavier object requires more force to change its state of motion. 
(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. 

Ans: (a)
Sol: Inertia depends on mass, as a heavier object requires more force to change its state of motion.

Q17. Which of the following is a chemical change?   (1 Mark) 
(a) Melting of ice 
(b) Burning of paper 
(c) Cutting of wood 
(d) Dissolving sugar in water 

Ans: (b)
Sol: Burning of paper is a chemical change as it forms new substances like ash and gases.

Q18. The function of the vacuole in a plant cell is to:   (1 Mark) 
(a) Synthesize proteins 
(b) Store nutrients and waste 
(c) Produce energy 
(d) Control cell division 

Ans: (b)
Sol: Vacuoles in plant cells store nutrients, waste products, and help maintain turgor pressure.

Q19. A car accelerates uniformly from rest to 20 m/s in 5 seconds. Its acceleration is:   (1 Mark) 
(a) 2 m/s² 
(b) 4 m/s² 
(c) 5 m/s² 
(d) 10 m/s² 

Ans: (b)
Sol: Acceleration = (Final velocity - Initial velocity) / Time = (20 - 0) / 5 = 4 m/s².

Q20. The process used to separate cream from milk is:   (1 Mark) 
(a) Filtration 
(b) Centrifugation 
(c) Distillation 
(d) Chromatography

Ans: (b)
Sol: Centrifugation is used to separate cream from milk based on differences in density.

Section B

Q1. Define latent heat of fusion.  (2 Marks) 

Ans: Latent heat of fusion: The amount of heat energy required to change 1 kg of a solid into a liquid at its melting point without a change in temperature.

Q2.  Differentiate between a mixture and a compound (any two points).  (2 Marks) 

Ans: Difference between mixture and compound:

• Mixture: Components retain their properties; variable composition.
• Compound: Components lose their individual properties; fixed composition.

Q3. Name two cell organelles that contain their own DNA.  (2 Marks) 

Ans: Two cell organelles with own DNA: Mitochondria and Chloroplasts.

Q4.  What is the function of xylem in plants?  (2 Marks) 

Ans: Function of xylem: Xylem transports water and minerals from roots to other parts of the plant and provides mechanical support.

Q5. Define uniform motion with an example.  (2 Marks) 

Ans: Uniform motion: When an object covers equal distances in equal intervals of time. Example: A car moving at a constant speed of 60 km/h on a straight road.

Q6.  State Newton's second law of motion  (2 Marks) 

Ans: Newton's second law: The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. Mathematically, F = ma.

Q7. What is evaporation? What are the factors affecting it?  (2 Marks) 

Ans: Evaporation is the process by which water (liquid) changes to vapours (gaseous form) at any temperature below its boiling point.
Factors on which evaporation depends:-

• Surface area
• Humidity
• Wind speed
• Temperature

Section C

Q1. Explain the process of evaporation and list two factors affecting it.  (3 Marks) 

Ans: Evaporation Evaporation is defined as the phenomenon of change of liquid into vapours at any temperature below its boiling point. It is categorized as a surface phenomenon. The process occurs because a small fraction of particles at the surface of the liquid, possessing higher kinetic energy, are able to break away from the forces of attraction of other particles and get converted into vapour.

Factors Affecting Evaporation (List two) The rate of evaporation increases with:

1. An increase of surface area: Since evaporation is a surface phenomenon, increasing the surface area (for example, by spreading clothes for drying up) increases the rate of evaporation because more liquid particles are exposed to the atmosphere.

2. An increase of temperature: With the increase of temperature, a greater number of particles get enough kinetic energy to overcome the forces of attraction and transition into the vapour state

Q2.  Describe the process of separating a mixture of sand and salt.  (3 Marks) 

Ans:  

1. Dissolution (Solution Formation): The sand and salt mixture is added to water, which acts as a solvent. The salt, being soluble, dissolves in the water to form a homogeneous mixture known as a salt solution. The sand, being insoluble, remains suspended in the liquid.

2. Filtration (Separation of Sand): The mixture is passed through a filter (like filter paper). The sand particles, which are large and do not dissolve, are left behind as the residue on the filter paper. The salt solution, now called the filtrate, passes through the filter.

3. Evaporation (Obtaining Salt): The salt solution (filtrate) is then heated. The water (solvent) converts into vapour (gas) through the process of evaporation, which is the change of liquid into vapour at any temperature below its boiling point. Since the salt does not vaporize, it is left behind as a solid residue (salt crystals) in the container

Q3. Draw a labelled diagram of a plant cell.  (3 Marks) 

Ans: 

Q4. Differentiate between meristematic and permanent tissues in plants .  (3 Marks) 

Ans: 

Q5. Derive the second equation of motion: s = ut + 1/2 at².   (3 Marks) 

Ans: Derivation of second equation of motion: Let initial velocity = u, acceleration = a, time = t, distance = s.
Average velocity = (u + v)/2, where v = u + at (first equation).
Distance = Average velocity × Time =
Thus, s = ut + 1/2 at².

Q6. Explain Newton's first law of motion with an example.  (3 Marks) 

Ans: The First Law of Motion states that an object remains in a state of rest or of uniform motion in a straight line unless compelled to change that state by an applied force.

This law is also known as the Law of Inertia. Inertia is the natural tendency of an undisturbed object to resist a change in its state of motion or of rest.

Example: When travelling in a motorcar, we tend to remain at rest with respect to the seat until the driver applies a braking force.

• When brakes are applied, the car slows down, but our body tends to continue in the same state of motion because of its inertia.

• A sudden application of brakes may thus cause us to be thrown forward.

(Alternatively, citing the starting motion): When we are standing in a bus and it suddenly begins to move, we tend to fall backwards. This occurs because the sudden start brings the bus and our feet into motion, but the rest of our body opposes this motion due to its inertia.

Q7.  (Internal Choice)   (3 Marks) 
Option 1: What is a colloid? Give two examples and one property. 
Option 2: Describe the process of sublimation with an example.

Ans: Option 1: Colloid

A colloid, or a colloidal solution, is a mixture where particles of one substance are dispersed in another. Its particles are too large to form a true solution but too small to settle out. Although the particles are uniformly spread throughout the solution, a colloidal solution is actually a heterogeneous mixture.

Two Examples:

1. Milk (an emulsion, liquid dispersed in liquid).

2. Fog (an aerosol, liquid dispersed in gas).

One Property: A colloid shows the Tyndall effect. This is because colloidal particles are big enough to easily scatter a beam of visible light passing through it, making the path of the beam visible. (Alternatively: A colloid is quite stable as the particles do not settle down when left undisturbed
OR  
Option  2 : Sublimation
Process of Sublimation Sublimation is the change of state directly from a solid to a gas (vapour) without changing into the liquid state. The direct change of gas back to solid without changing into liquid is called deposition.

Example: The sublimation of naphthalene balls is an example, as they disappear with time without leaving any solid residue. Another example is when camphor is heated, it changes directly from solid to gas.

Section D

Q1. (a)  Explain the process of boiling and how it differs from evaporation. (3 Marks) 
(b)  Why does the temperature remain constant during the change of state?  (2 Marks) 

Ans:  

(b) The temperature remains constant during the change of state (e.g., solid changing to liquid, or liquid to gas) because the heat energy supplied is used up in changing the state by overcoming the forces of attraction between the particles.

This heat is known as latent heat (meaning "hidden" heat). Since this energy is absorbed by the substance without showing any rise in temperature, it is considered hidden into the contents. Therefore, the average kinetic energy of the particles does not increase until the entire mass has undergone the state change.

Q2. (a)  Describe the structure and functions of the nucleus in a cell. (3 Marks) 
(b)  Differentiate between plant and animal cells (any four points). (2 Marks)

Ans:  (a) Structure and Functions of the Nucleus

Structure: The nucleus has a double layered covering called the nuclear membrane. The nuclear membrane has pores which allow the transfer of material from inside the nucleus to the cytoplasm (outside). The nucleus contains chromosomes, which are visible as rod-shaped structures only when the cell is about to divide. Chromosomes are composed of DNA (Deoxyribo Nucleic Acid) and protein. When the cell is not dividing, the DNA is present as chromatin material, which is visible as an entangled mass of thread-like structures.

Functions:

1. It plays a central role in cellular reproduction, the process by which a single cell divides and forms two new cells.

2. It contains information for the inheritance of characters from parents to the next generation in the form of DNA/genes.

3. It plays a crucial part in directing the chemical activities of the cell, determining how the cell will develop and what form it will exhibit at maturity

(b) Plant vs. Animal cells:

Q3.  (Internal Choice)
Option 1: 
(a) Derive the third equation of motion: v²  = u² + 2as. (3 Marks) 
(b) A car starts from rest and accelerates at 2 m/s² for 10 seconds. Calculate the final velocity and distance covered. (2 Marks)

Option 2: (a) Explain Newton's third law of motion with two examples. (3 marks) 
(b)  A force of 50 N acts on a body of mass 10 kg initially at rest.  Calculate the acceleration and the distance covered in 5 seconds. (2 Marks)

Ans: (a) Derivation of third equation of motion:
From first equation: v = u + at.
From second equation:  (since average velocity = (u + v)/2).
Multiply both sides by 2: 2s = (u + v)t.
From v = u + at, we get t = (v - u)/a.
Substitute t in 2s = (u + v)t: 2s
Thus, v  = u  + 2as.
(b) Calculation:
Given: u = 0, a = 2 m/s², t = 10 s.
Final velocity: v = u + at = 0 + 2 × 10 = 20 m/s.
Distance: s = ut + 1/2 at² = 0 + 1/2 × 2 × 10= 100 m.
OR Option 2:
(a) Newton's third law: For every action, there is an equal and opposite reaction. 
Examples: 

• When you push a wall, the wall pushes back with equal force. 
• A rocket moves forward as exhaust gases are expelled backward.

(b) Calculation:
Given: F = 50 N, m = 10 kg, u = 0, t = 5 s.
Acceleration: a = F /m = 50/10 = 5 m/s².
Distance: s = ut + 1/2 at² = 0 + 1/2 × 5 × 5  = 62.5 m.

Q4. Grass looks green, papaya appears yellow. Which cell organelle is responsible for this?  (5 Marks) 

Ans: Plastids are responsible. These are found in plant cells only. Plastids are the major cell organelles in plants. On the basis of pigments present in plastids, they are divided into two types;
i) the colourless leucoplasts and
ii)  the pigmented chromoplasts.
The colourless leucoplasts store starch, oil and protein granules whereas the pigmented chromoplasts have different colours and can be of several types. The most important ones are those containing the pigment chlorophyll, known as chloroplasts, which is responsible for the preparation of food by photosynthesis. Other chromoplasts contain non-green pigments, which are responsible for the characteristic colours of fruits and flowers.

Q5. i. Explain the Tyndall effect and name two mixtures that exhibit it. (3 Marks)
ii. How do the particles of a solution differ from those of a colloid? (2 Marks)

Ans:  The Tyndall effect is the scattering of a beam of light by the particles in a colloid or mixture. Colloidal particles are big enough to scatter a beam of light passing through the mixture, which makes the path of the light visible.

Two mixtures that exhibit the Tyndall effect (colloids) are:

1. Milk (an emulsion, where liquid is dispersed in liquid).

2. Fog/Mist (an aerosol, where liquid is dispersed in gas).

(ii) The particles of a solution differ from those of a colloid primarily in size, visibility, and stability, as detailed in the sources: