4.
(b) burns typically with external heat producing heat and light
8.
(c) 100 Pa (P = F/A = 10/0.1 = 100)
13.
(b) Virtual, behind the mirror and of the same size
14.
(d) Endangered species
17.
(b) Prokaryotic cells
21.
Sowing: The process of putting seeds into the soil is called sowing.
Tool: Seed drill (Modern) or Funnel (Traditional). As per question 'traditionally' -
Funnel.
22.
1. It enhances the water-holding capacity of the soil.
2. It makes the soil porous, which helps in the exchange of gases.
23.
Fossil fuels are exhaustible because they are formed from the dead remains of living organisms over millions
of years. Since their formation is a very slow process and their known reserves are limited, they will get
exhausted by continuous human use.
24.
1. Squeezing a toothpaste tube causes a change in its shape.
2. Stretching a rubber band changes its shape.
25.
Objects moving in fluids must have special shapes (streamlined) to reduce fluid friction (drag) so that they
can move through the fluid easily without losing much energy.
OR
Fluid Friction: The frictional force exerted by fluids (liquids and gases) is called fluid
friction or drag.
Factors: Speed of the object, Shape of the object, and Nature of the fluid.
26.
Electroplating: The process of depositing a layer of any desired metal on another material
by means of electricity is called electroplating.
Example: Chromium plating on car parts / Gold plating on silver ornaments.
27.
Characteristics: It is a tough, porous, and black substance. It is an almost pure form of
carbon.
Uses: It is used in the manufacture of steel and in the extraction of many metals.
28.
(Draw a labelled diagram of a candle flame showing 3 zones: Outer zone (Blue, non-luminous), Middle zone
(Yellow, luminous), Inner zone (Black, unburnt wax)).
29.
Causes: Procuring land for cultivation, building houses and factories, making furniture or
using wood as fuel.
Consequences: Increases temperature and pollution level, decreases rainfall leading to
drought, soil erosion, and loss of biodiversity.
30.
Asexual Reproduction: Reproduction in which only a single parent is involved. Gametes are
not formed. Offspring are identical clones.
Sexual Reproduction: Reproduction in which two parents (male and female) are involved.
Gametes fuse to form a zygote. Offspring show variation.
OR
Binary Fission: In Amoeba, the nucleus divides first into two nuclei. This is followed by
the division of the body into two, each part receiving a nucleus. Finally, two daughter amoebae are produced
from one parent amoeba.
31.
1. Increase in height.
2. Change in body shape (broadening of shoulders in boys, widening of hips in girls).
3. Voice change (Adams apple in boys).
4. Development of sex organs. (Any 3)
32.
Number of oscillations = 40
Time taken = 4 sec
Frequency = No. of oscillations / Time = 40 / 4 = 10 Hz.
Time Period = Time / No. of oscillations = 4 / 40 = 0.1 sec.
33.
Earthquake: A sudden shaking or trembling of the earth lasting for a very short time.
Effects: It can cause immense damage to buildings, dams, and people. It can cause floods,
landslides, and tsunamis.
Causes: It is caused by a disturbance deep inside the earth's crust, primarily due to the
movement of tectonic plates.
34.
(a) Organisms that are too small to be seen with the naked eye are called microorganisms.
Groups: Bacteria, Fungi, Protozoa, Algae.
(b) Microorganisms (decomposers) decompose dead organic waste of plants and animals converting them into
simple substances which are mixed into the soil, thus cleaning the environment.
OR
(a) [Schematic Diagram Description]: Atmospheric Nitrogen -> Nitrogen Fixing Bacteria -> Nitrates in soil ->
Plants -> Animals -> Excretion/Death -> Decomposers -> Soil Nitrates -> Denitrifying Bacteria -> Atmospheric
Nitrogen.
(b) Rhizobium.
35.
(a) Laws: (i) The angle of incidence is equal to the angle of reflection. (ii) The incident
ray, the normal, and the reflected ray, all lie in the same plane.
(b) [Diagram showing mirror, normal, incident ray, reflected ray, i=r].
(c) Characteristics: Virtual, Erect, Same size as object, Laterally inverted, Distance
behind mirror equals distance in front.
36.
(a) Friction: The force that opposes the relative motion between two surfaces in
contact.
Advantages: Helps us walk, enables writing on paper.
Disadvantages: Produces heat causing wear and tear, reduces efficiency of machines.
(b) Ball bearings reduce friction by converting sliding friction into rolling friction (which is much
smaller).
37.
(i) Larynx (Voice Box).
(ii) Two vocal cords stretch across the larynx such that it leaves a narrow slit for the passage of air.
When lungs force air through the slit, cords vibrate producing sound.
(iii) Due to the difference in the length and thickness of vocal cords. Men have longer and thicker cords
producing lower pitch.
38.
(i) The process of decomposing an ionic liquid (electrolyte) by passing electric current through it.
(ii) Oxygen.
(iii) Electroplating: Coating a metal object with a thin layer of another metal using
electricity. Application: Coating zinc on iron to prevent rust (Galvanization).
39.
(i) 45 degrees (Since angle i = angle r).
(ii) It retraces its path (reflects back along the same line) because angle of incidence is 0.
(iii) (1) Angle of incidence = Angle of reflection. (2) Incident ray, reflected ray and normal lie in the
same plane.