1.
(c) Combine
Combine is a machine which is used for both harvesting (cutting) and threshing (gathering/separating grain).
2.
(b) Polio
Polio is caused by a virus. Typhoid, Tuberculosis and Cholera are bacterial diseases.
3.
(b) Coal tar
Coal tar is a black, thick liquid with an unpleasant smell obtained from coal. It is used to make naphthalene balls.
4.
(a) Kilojoule per kg (kJ/kg)
5.
(c) Vas deferens
Vas deferens is part of the male reproductive system (sperm duct).
6.
(c) Menarche
The first menstrual flow which begins at puberty is termed menarche.
7.
(c) 1000 times
An increase of 2 in magnitude means 1000 times more destructive energy. (Magnitude 4 to 6 is an increase of 2).
8.
(c) A man
Men have longer vocal cords which vibrate at a lower frequency compared to women and children.
10.
(c) 0.1 s
The sensation of sound persists in our brain for about 0.1 s.
11.
(b) Tap water
Tap water contains dissolved salts which make it a good conductor. Distilled water, oil, and honey are poor conductors.
13.
(d) Real, behind the mirror and of the same size as the object is INCORRECT. Correct answer is (b) Virtual, behind the mirror and of the same size as the object.
Note: Option (b) is the correct answer. Plane mirrors form virtual, erect images.
15.
(b) Estrogen
Testosterone is male hormone; Adrenaline is stress hormone; Thyroxine controls metabolism.
16.
(a) liquid A is a better conductor than liquid B
A brighter glow indicates more current flowing, which means lower resistance (better conductivity).
17.
(d) Increase in rainfall
Deforestation leads to reduced rainfall, not increased.
18.
(c) 80 dB
Noise becomes physically painful above 80 dB.
19.
(b) Kaleidoscope
It uses multiple mirrors inclined to each other to form beautiful patterns via multiple reflections.
21.
Sodium is a very reactive metal. It reacts vigorously with oxygen and water (moisture in air) generating a lot of heat. To prevent this accidental fire, it is kept immersed in kerosene.
22.
1. Cell Wall: Provides rigidity and protection.
2. Plastids (Chloroplasts): Essential for photosynthesis.
23.
Asexual Reproduction: The type of reproduction in which only a single parent is involved.
Methods:
1. Budding (e.g., Hydra)
2. Binary Fission (e.g., Amoeba)
24.
The retina acts as a screen on which the image is formed. It contains light-sensitive cells (rods and cones) that convert light energy into electrical signals sent to the brain via the optic nerve.
25.
Water is a good conductor of electricity. If used on electrical fires, it can conduct electricity and cause electric shock to the person fighting the fire.
OR (Requirements for Fire):
1. Fuel (Combustible substance).
2. Air (Supplier of Oxygen).
3. Heat (To raise temperature beyond ignition temperature).
26.
Red Data Book is the source book which keeps a record of all the endangered animals and plants. There are different Red Data Books for plants, animals and other species.
27.
Greenhouse Effect: It is the trapping of the sun's heat in the earth's atmosphere by gases like Carbon Dioxide (CO2). Without this, earth would be too cold. However, excess CO2 traps too much heat leading to Global Warming.
Main Gas: Carbon Dioxide (CO2).
28.
Zygote: It is a single cell formed by the fusion of male and female gametes (fertilization).
Foetus: It is the multicellular stage of the embryo in which all the body parts (hands, legs, head, eyes, ears etc.) can be identified.
OR (Sperm Diagram): [Diagram showing Head, Middle Piece, and Tail]. Head contains nucleus; Middle piece contains mitochondria for energy; Tail helps in motility.
29.
(a) Adam's Apple: The protruding part of the throat seen in boys during puberty. It is the enlarged voice box (larynx).
(b) During puberty, the larynx grows larger in boys. Sometimes the muscles of the growing voice box go out of control and the voice becomes hoarse. This state remains for a few days or weeks.
30.
Activity: Take a glass tumbler and place a cell phone in it. Suck the air out of the tumbler while your friend gives a ring to the phone. As you suck air out, the sound becomes fainter. If air is completely removed (vacuum), no sound is heard. This shows sound needs a material medium (air) to travel.
31.
During a thunderstorm, air currents move upwards while water droplets move downwards. This vigorous movement causes separation of charges. Positive charges collect near the upper edges of clouds and negative charges near the lower edges. Positive charges also collect on the ground. When the magnitude of accumulated charges becomes large, air (normally a poor conductor) cannot resist flow. Negative and positive charges meet, producing streaks of bright light (lightning) and sound (thunder).
32.
LEDs (Light Emitting Diodes) can glow even with a very weak electric current. In some liquids (like lemon juice or vinegar), the current produced is weak because they are weak electrolytes. An ordinary bulb requires a strong current to heat its filament to glow. Therefore, LEDs are preferred for detecting weak currents.
33.
Irrigation: The supply of water to crops at regular intervals.
Methods Conserving Water:
1. Sprinkler System: Rotating nozzles sprinkle water like rain. Useful for uneven land and sandy soil.
2. Drip System: Water falls drop by drop directly near the roots. It minimizes water wastage and is best for fruit plants/gardens.
34.
(a) Prokaryotic: No well-defined nucleus (nuclear material without nuclear membrane), e.g., Bacteria. Eukaryotic: Well-defined nucleus with nuclear membrane, e.g., Humans, Plants.
(b) [Diagram check: Rectangular shape, large central vacuole, cell wall outside cell membrane, chloroplasts].
OR
(a) (i) Mitochondria: Powerhouse of cell (energy production). (ii) Ribosomes: Protein synthesis. (iii) Nucleus: Controls all cell activities and contains inheritance material.
(b) Cells are structural units because all organisms are made of cells. They are functional units because all basic functions of life (respiration, digestion, etc.) take place inside cells.
35.
(a) Laws of Reflection: 1. Angle i = Angle r. 2. Incident ray, Reflected ray, Normal lie in same plane.
(b) Activity: Fix a white sheet on a drawing board. Place a mirror strip. Shine light using a comb/torch (Incident ray). Mark the reflected ray. If you fold the paper where the reflected ray falls, you won't see it on the folded part. This shows they lie on the plane of the sheet.
(c) Infinite number of images are formed due to multiple reflections.
36.
(a) Electroplating: The process of depositing a layer of any desired metal on another material by means of electricity.
(b) [Circuit Check: Battery, Copper Plate at Anode (+), Iron Spoon at Cathode (-), Copper Sulphate Solution].
(c) Uses: 1. Chromium plating on car parts/taps for shine and corrosion resistance. 2. Gold/Silver plating on cheaper jewelry. 3. Tin cans (Iron coated with Tin) for food storage (Tin is less reactive).
37.
(i) Preservatives (e.g., Sodium Benzoate, Sodium Metabisulphite).
(ii) Sugar reduces the moisture content which inhibits the growth of bacteria which spoil food.
(iii) Milk is heated to about 70°C for 15 to 30 seconds and then suddenly chilled and stored. This prevents the growth of microbes.
38.
(i) Tympanic membrane.
(ii) It sends the signals (vibrations converted to signals) from the inner ear to the brain.
(iii) When sound waves strike the eardrum, it vibrates. These vibrations are passed to the inner ear.
39.
(i) Petroleum Conservation Research Association.
(ii) Coke (It is used in the extraction of metals).
(iii) 1. Drive at a constant and moderate speed. 2. Switch off the engine at traffic lights. 3. Ensure correct tyre pressure.