1.
(b) Harvesting and Threshing
14.
(b) Light Emitting Diode
19.
(b) Opposite to motion
21.
Plastic is a bad conductor of electricity, so it protects the user from electric shock.
22.
The pressure exerted by the weight of air (atmosphere) on the earth's surface is called atmospheric
pressure.
23.
Thermosetting plastics (like Bakelite) are poor conductors of heat and do not soften on heating, making them
suitable for handle grips to protect hands from burns.
24.
1. Muscular Force.
2. Frictional Force.
25.
Eardrum (Tympanic membrane).
OR
Larynx (Voice box).
26.
Gas: Carbon dioxide (CO₂).
Cause: Produced by burning of fossil fuels (coal, petrol, diesel) and deforestation.
27.
Prokaryotic Cells: Nuclear membrane absent, primitive nucleus, usually unicellular (e.g.,
Bacteria).
Eukaryotic Cells: Well-defined nucleus with nuclear membrane, complex organelles,
unicellular or multicellular (e.g., Onion peel cell).
28.
The fusion of a sperm (male gamete) with an ovum (female gamete) to form a zygote is called fertilization.
It occurs in the fallopian tube (oviduct) of the female reproductive system.
29.
Crop Rotation: Growing different crops alternately in the same field. (e.g., Legumes and
Wheat).
Benefit: It helps in replenishment of soil nutrients (especially nitrogen) naturally
without using much fertilizer.
30.
Take a plastic bottle. Drill holes at different heights. Fill it with water. Observe that water coming out
from holes near the bottom falls farther than water from holes near top. This shows pressure increases with
depth.
31.
Noise pollution can cause lack of sleep (insomnia), hypertension (high BP), anxiety, and temporary or
permanent impairment of hearing.
32.
Infinite images will be formed. This is because light reflects back and forth repeatedly between the two
parallel mirrors.
33.
1. Making Jewellery.
2. Electroplating cheap metals.
3. In electronics (as good conductors).
34.
(a) [Diagram of Animal Cell showing Membrane, Cytoplasm, Nucleus, Vacuole].
(b) (i) Nucleus: Controls all activities of the cell; contains hereditary info. (ii)
Cell Membrane: Controls entry/exit of substances; provides shape.
OR
(a) Differences: (1) Plant cell has cell wall, Animal cell doesn't. (2) Plant cell has
large vacuole, Animal cell has small/none. (3) Plant cell has plastids (chloroplasts), Animal cell
doesn't.
(b) Genes: Units of inheritance. They are located on chromosomes in the nucleus.
35.
(a) Kaleidoscope: Three rectangular mirror strips produced to form a prism. Put in a tube.
One end closed with ground glass plate. Coloured bangles pieces put inside. Other end with viewing hole.
Multiple reflections form beautiful patterns.
(b) Periscope Uses: (1) To see above obstacles/walls. (2) Used in submarines to see objects
on the surface of the sea.
36.
(a) Food Preservation: The process of treating and handling food to stop or slow down
spoilage caused by microorganisms.
(b) Salt, Sugar, Vinegar, Sodium Benzoate. (Any two)
(c) Pasteurization: Milk is heated to about 70°C for 15-30 seconds and then suddenly
chilled and stored. This kills most bacteria. Discovered by Louis Pasteur.
37.
(i) Hertz (Hz).
(ii) The time taken by a vibrating body to complete one oscillation is called Time Period.
(iii) Frequency = No. of oscillations / Time = 20 / 1 = 20 Hz.
38.
(i) Gravitational Force / Magnetic Force.
(ii) Muscular Force.
(iii) The ball changes its direction and speed. Force applied by the bat changes the state of motion of the
ball.
39.
(i) Tin is less reactive than iron. It prevents food from coming in contact with iron and getting
spoiled.
(ii) Zinc (Galvanization).
(iii) Because it contains pollutants and heavy metals which can contaminate soil and water bodies, affecting
aquatic life.