Answer:
Yes, when a body moves in a circular path with constant speed. It has acceleration, which is constant in magnitude but changes in direction at every point. (1 mark)

Answer:
When we vigorously shake a tree, its branches move while because of inertia its leaves remain at rest. Because of this mutual movement between branches and leaves of a tree, the leaves get detached from a tree. (1 mark)

Answer:
The density of an iron nail is more than the density of water. This means the up thrust of water on iron nails is less than the weight of the nail. So it sinks. (1 mark)

Answer:
The amount of sound energy passing each second through unit area is called the intensity of sound. (1/2 mark)

Loudness is a measure of the response of the ear to the sound. Even when two sounds are of equal intensity, we may hear one as louder than the other simply because our ear detects it better. (1 mark)

Answer:
Suppose the total distance covered by the body is 2s, out of which first half is covered with speed 'a' and other half is covered with speed 'b'. Let us suppose that t1 and t2 are the times taken for the first and the second half respectively. Then the average speed (v) for the whole journey is given as ((1/2 mark)
v = (Total distance)/(Total time) (1/2 mark)
t₁ = s/a, t₂ = s/b (1/2 mark)
= 2s/(s/a + s/b) = 2ab/(a + b) m/s. (1/2 mark)

Answer:
The effects, that may occur when a force is applied on an object are:
(i) It can change the speed of an object making it to move faster or slower. (1/2 mark)
(ii) It can change the direction of the motion of an object. (1/2 mark)
(iii) It can change the shape of the object. (1/2 mark)

Example- A stone tied to one end of a string whirling at a constant speed in a horizontal circle changes its direction of motion continuously. (1/2 mark)

Answer:
Universal law of gravitation states that the force of attraction between two bodies is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. (1/2 mark)
(1/2 mark)

Let the two bodies ‘A’ and ‘B’ of masses ‘M’ and ‘m’ are separated by a distance ‘r’.

Answer:
Relative density of silver = 10.8

Relative density = Density of silver / Density of water (1/2 mark)
Density of silver = Relative density of silver x density of water (1 mark)
= 10.8 x 103 kg m^–3. (1/2 mark)

Answer:
Given: υ₁(in air) = 344 m/s, υ₂ (in iron) = 5130 m/s

Let l be the length of the pipe and t₁ and t₂ are time taken by sound in air and in iron respectively to reach the other end of the pipe. (1 mark)

Answer:
Law of conservation of energy: It states that whenever energy changes from one form to another, the total amount of energy remains constant, i.e., energy can neither be created nor destroyed. (2 mark)

Let a ball of mass 'm' at height 'h' from the ground level starts falling down from rest.

At point A :
Potential energy = mgh
Since the velocity here is zero, K.E. = 0
Therefore total energy = mgh + 0 = mgh . …………………………(i) (1 mark)


At point B :
It falls through a distance 's' from A to B. Hence potential energy = mg (h - s)
Now, v² = u² + 2gs
or v² = 2gs (u = 0)
Kinetic energy = (1/2) mv²
= (1/2) m x 2gs
= mgs
Total energy = mg (h - s) + mgs
= mgh ....................................(ii) (1 mark)

At point C :
v² - u² = 2gh
or v² = 2gh (u = 0)
Kinetic energy = (1/2) mv² = (1/2) m x 2gh = mgh
and potential energy = 0
Total energy = mgh + 0 = mgh ………………………………………(iii)

It is clear from expressions (i), (ii) and (iii) that the total energy of the ball is constant at every point. (1 mark)

Answer:
a) Hydrogen (1 mark)

Answer:
i)Au :Gold (1/2 mark)
ii)Ag: Silver (1/2 mark)

Answer:
Plants loose water through their leaves by a process called transpiration. Transpiration keeps the plant cool. During summers when the temperature is high, plants must transpire more in order to keep themselves cool. Thus they require more leaves to do the transpiration. Hence plants acquire more leaves during summer. (2 marks)

Answer:
i)

Physical Changes	Chemical Changes
1) Those changes that involve transformation of state and do not change chemical nature of substance are physical change. (1/2 mark)	1) Those changes that involve conversion of a substance into one or several different substance are chemical changes. (1/2 mark)
2) Substance retain their chemical nature. (1/2 mark)	2) Properties of new substance are different from those of the original components (1/2 mark)

ii)
a) Sol: Paints or milk of magnesia (1/2 mark)
b) Solid Sol: Colored gems or rock salt (1/2 mark)

Answer:
i) Molar mass of H₂O₂
= (2x1) + (2x16)
= 34g/mol (1 mark)

34 g H₂O₂ = 1mole
∴ 16 g H₂O₂ = 0.47 mole of H₂O₂ (1 mark)

The number of moles in 16 g of H₂O₂ is 0.47 moles.

ii) Formula unit mass of a substance is the sum of the atomic masses of all atoms in a formula unit of a compound. Only difference is that we use the word formula unit for that substance whose constituents are particularly ions. (1 mark)

Answer:
i) Chadwick discovered neutrons present in the atom.
ii) Mass of an atom is determined by two particles namely protons and neutrons.
iii) K-shell or first energy level is closest to the nucleus.
iv) Since the isotopes of an element have different number of neutrons, their mass numbers are different
v)

OR

Ans 16:
Conclusions of Rutherford’s model of an atom from the α -particle scattering experiment (3 marks)

1) Most of the space between inside atoms is empty; hence it allows the particles to pass straight through it without any deflection.
2) Very few particles were deflected from their path which suggests that the positive charge of the atom occupies very little space.
3) A very small fraction of α particles were defected by 180° indicating that all the positive charge and mass of the gold atom were concentrated in a very small volume within the atom.

Rutherford’s model of an atom (2 marks)

1) There is positively charged centre in an atom called the nucleus and the entire mass of atom resides in the nucleus.
2) Electrons revolve around the nucleus in well defined orbits.
3) Size of nucleus is very small as compared to size of atom.

Answer:
Chloroplast is semiautonomous because it has its own DNA and ribosomes.

Answer:
Kala-azar is caused by Leishmania.
Causative agent of Sleeping sickness is Trypanosoma

Answer:
The taste and colour of honey depends on the quality and quantity of pasturage or flowers that are available to the bees for nectar collection.

Answer:
Yes, we can ‘fool’ the immune system. This process is followed during immunization when we inject something inside the body that mimics the microbe we want to vaccinate against. (1 mark)

These substances are weakened or killed microorganisms or their purified parts that do not actually cause the disease. But, when that particular microbe or its close relatives enter the body, the immune system responds with even greater vigour. This eliminates the infection even more quickly than the first time around and protects the body from the disease. (1 mark)

Answer:
Farmers are advised to use fertilizers carefully because:

a) The excess of fertilizers that gets washed away from the fields causes water pollution.
b) Continuous use of fertilizer depletes the organic matter of soil.
c) It also destroys microorganism in the soil.
d) Excessive use of fertilizer damages the soil texture.
(1/2 X4 = 2 marks)

Answer:
Viruses are on the borderline between living and non-living organisms. They do not contain cytoplasm, or organelles like mitochondria and ribosomes. All they have is a capsid or head made up of proteins, in which there is some genetic material in the form of DNA or RNA. (1 mark)

The virus is said to become 'living' when it enters a host cell. There it takes control of the cell's mitochondria to build up the energy the virus needs, and takes control of its ribosomes as well to build its own proteins. Therefore, the virus replicates inside the host using the host’s cellular machinery. Outside a host cell, a virus can not perform any of these things so it is considered as non-living. (1 mark)

Answer:
Clouds are formed when air containing water vapour is cooled below a critical temperature and the resulting moisture condenses into droplets on microscopic dust particles called the condensation nuclei in the atmosphere. (1 mark)

A large amount of water vapour enters the atmosphere through the process of evaporation and transpiration. The warm air carrying this water vapour rises up. It cools and expands as it goes up. As a result water vapour in the air forms tiny droplets that form clouds. (1 mark)

Answer:
A prokaryotic cell

Eukaryotic cells	Prokaryotic cells
1. They have a true nucleus, bound by a double membrane.	1. Nucleus is absent. The undefined nuclear region containing only DNA is called nucleoid.
2. DNA is linear	2. DNA is circular.
3. Single chromosome is present	3. More than one chromosome is present.

(1 ½ marks)

Answer:
a)
1. Cell Wall
2. Golgi apparatus
3. Chloroplast
4. Vacuole
(1/4 X 4 = 1 mark)

b) Plasmolysis will occur in the given circumstances. (1/2 mark)

Since salt solution is hypertonic to the plant cell, it will lose water through osmosis and its cell membrane will separate (shrink) from the cell wall. (1/2 mark)

c) Plasmolyzed plant cell

Answer:
a)

Reptiles	Aves
1. They have an exoskeleton of scales. 2. They are cold-blooded animals.	1. They have an exoskeleton of feathers. 2. They are warm-blooded animals.

b)

Annelida	Arthropoda
1. They possess a closed circulatory system. 2. Exoskeleton is absent.	1. They possess an open circulatory system. 2. They have a protective exoskeleton formed of chitin.

c)

Monocots	Dicots
1. Their seeds have a single cotyledon. 2. Leaves show parallel venation.	1. Their seeds have two cotyledons. 2. Leaves possess reticulate venation.

(1 +1+1=3 marks)

Answer:
a) Aquatic organisms are used to a certain range of temperature in the water body. A sudden increase or decrease in water temperature is harmful for them as it alters their metabolic rate. Eggs or larvae of aquatic organisms are particularly susceptible to these changes. (1 mark)

Also warm water typically decreases the level of dissolved oxygen in the water. Therefore, change in the temperature of water bodies is considered water pollution. (1 mark)

b) Water contributes to soil formation in 2 ways:
i) Water gets into the cracks in the rocks. When this water freezes, it causes widening of this crack.
ii) Fast flowing water carries big and small pieces of rocks. These rocks rub against each other. The resultant abrasion causes the rock to break down into smaller particles. (1+1=2 marks)

c) Air is a bad conductor of heat, so it prevents sudden increase or decrease in the temperature of earth. (1 mark)