Lakhmir Singh & Manjit Kaur 2020 Solutions for Class 9 Science Chapter 8 - Model Test Paper 2

Answer:

Smallest cell is Mycoplasma and the largest cell is an egg cell of Ostrich.

Answer:

Countries that are centres of megadiversity are India and USA. 

Answer:

Initial speed of the bus = 20 km/h = $20\times \frac{1000 \mathrm{m}}{60\times 60 \mathrm{s}}=\frac{50}{9} \mathrm{m}/\mathrm{s}$

Final speed of the bus = 50 km/h = $50\times \frac{1000 \mathrm{m}}{60\times 60 \mathrm{s}}=\frac{125}{9} \mathrm{m}/\mathrm{s}$

Time taken by the bus to change its speed = 10 seconds

Acceleration of the bus = $\frac{\mathrm{Final} \mathrm{Speed} - \mathrm{Initial} \mathrm{Speed}}{\mathrm{Time} \mathrm{taken}}=\frac{{\displaystyle \frac{125}{9}-\frac{50}{9}}}{10}=\frac{5}{6}\mathrm{m}/{\mathrm{s}}^2=0.83 \mathrm{m}/{\mathrm{s}}^2$

Hence, the correct answer is option D.

Answer:

Platelets are responsible for the clotting of blood. If all the platelets are removed, then the blood will not be able to clot in case of an injury.
This would result in uncontrolled bleeding and could eventually lead to death.

Answer:

Platelets are responsible for the clotting of blood. If all the platelets are removed from the blood, it would lose its ability to clot.
This means, in case of an injury, the blood will not clot and would lead to uncontrollable bleeding. This would eventually result in the death of the organism.

Answer:

(a) Sublimation can be defined as the process in which the solid phase of the matter directly converts to the gaseous phase. For eg. camphor, naphthalene.

(b) Setup to demonstrate the sublimation of ammonium chloride:

  

Answer:

(a) CaF₂
(b) H₂S
(c) NaH
(d) CCl₄
(e) Na₂O
(f) CO₂

Answer:

Niels Bohr proposed the following postulates regarding the model of the atom:

(i) Only certain orbits known as discrete orbits of electrons are allowed inside the atom.
(ii) While revolving in these discrete orbits, the electrons do not radiate energy.

These discrete orbits or shells are shown in the following diagram:



Bohr explained the stability of atom by proposing that electrons revolve around the nucleus in the definite circular paths having fixed energy and while moving in the same orbit they do not lose or gain energy.

Answer:

(a) Mass of a body is defined as the quantity of matter(Solid, liquid or gas) contained in the given volume of the body. Mass is a scalar quantity. SI unit of mass is kilogram.

(b) The force felt by a body towards the center of the earth due to earth's gravitational attraction is known as the weight of the body. The SI unit of weight is Newton.

(c) We know that Force = (Mass)$\times$(Acceleration).

The weight of a body is actually the gravitational force applied by the earth.

Hence, we can write, Weight = (Mass)$\times$(Acceleration due to gravity) = m$\times$g = mg

So, the weight of a body is given by the product of its mass and acceleration due to gravity. 

Answer:

(a) 'kWh' symbol means kilowatt hour. kWh is a unit of energy. 1 kWh means the energy consumed when 1-kilowatt is used for 1 hour.

(b) The electrical energy consumed  by the appliance = Power of the appliance $\times$ Time 

                                                                                      = 1000 W $\times$ 60 $\times$ 60 s
                                                                                    
                                                                                     = 3.6 $\times$ 10⁶ J

Answer:

(a) An echo is basically a reflection of a sound wave. When a sound wave gets reflected by a hard surface and comes back to the listener with a little delay, then the reflected sound heard by the listener is known as the echo of the original sound wave. 

An echo is formed when a sound wave reflects back towards its source after reflecting from a hard surface.

(b) The velocity of the sound at 20° C is 343 m/s.

Let the minimum distance in the air required to perceive an echo is 'x'

Minimum time required to perceive a sound by human, t = 0.1 s

Then,

$$\begin{gathered} v =\frac{2x}{t} \\ \Rightarrow x=\frac{vt}{2}=\frac{343\times 0.1}{2}=17.2 \mathrm{m} \end{gathered}$$

Hence, minimum distance in the air required from a sound reflecting surface to hear an echo is 17.2 m.

Answer:

The technique of growing crops with different nutritional requirements (e.g., soyabean and maize) in alternate rows, in a definite pattern, to ensure maximum utilisation of nutrients is called intercropping.
 

Answer:

(a) 

Answer:

Different modes of transmission of infectious diseases are -

(a) Through air − The microorganisms that cause diseases such as influenza, chicken pox, etc., are transmitted through air as and when the infected person sneezes or coughs.

(b) Through water − The microorganisms that cause diseases such cholera, typhoid, etc., spread through contaminated water containing the faeces of infected individuals.

(c) Blood to blood contact − This occurs during blood transfusion, pregnancy, etc. For example - AIDS.

(d) Animal vectors − Insects carry disease-causing microbes in their saliva and transmit them to the healthy individuals by biting them. Malaria and dengue are spread in this way

(e) Direct physical contact − AIDS and syphilis are sexually-transmitted diseases.

Answer:

Air is called breath of life because it contains oxygen which is essential for us to survive. We take in oxygen and use it for our vital life processes. Absence of oxygen can cause immediate death of an organism.

Air is a mixture of various other types of gases. Each of this gas plays an important role -

• oxygen is required by living organism to carry out their vital functions
• carbon dioxide is used by plants to produce their food
• air is used in the process of combustion

Answer:

The water is purified at a large scale in water treatment plants:
Following three steps are involved for purification of water at large scale:
1. Sedimentation: In this process, all the large impurities are removed from the water.
2. Filtration: In this process, the water is filtered through different types of filters that trap the minute impurities present in the water.
3. Disinfection: In this process, the water is disinfected to remove the remaining microorganisms from the water. 

Water purification on a large scale can be done as shown below:



Chlorine gas is passed through the water to kill germs in the drinking water supply.
 

Answer:

(i) Electronic configuration of sodium(Na) is 2, 8, 1. To attain noble gas configuration sodium atom will lose one electron and form sodium ion. As sodium loses one electron due to which sodium gets a positive charge on it.

Na = 2, 8, 1
Number of protons = 11
Number of electrons = 11
Na^$+$ = 2, 8
Number of protons = 11
Number of electrons = 10

(ii) Electronic configuration of chlorine(Cl) is 2, 8, 7. To attain noble gas configuration chlorine atom will gain one electron and form chloride ion. As chlorine gain one electron due to which chlorine gets a negative charge on it.

Cl = 2, 8, 7
Number of protons = 17
Number of electrons = 17
Cl^$-$ = 2, 8, 8 
​Number of protons = 17
Number of electrons = 18

Answer:

(a) Balanced forces are those forces whose resultant is zero. Unbalanced forces are those whose resultant is not zero.

When we push a box and it moves, that means it has some unbalanced forces working on it, or the resultant forces working on the box is not zero, that's why the box moved in the direction of the resultant force.

But, if we push a box and someone pushes the same box back from the other side with an equal and opposite force, then in that condition the box will not move. Because, the resultant force on the box would be zero, or we can say the forces are balanced on the box. So, there is no movement of the box.

(b) When we press a rubber ball between our hand, then forces acting on it are balanced, because the ball does not move when we press it. By pressing the ball between our hands, the ball gets deformed.
 

Answer:

First law: Kepler's first law states that the planets move in elliptical orbits around the sun, with the sun at two foci of the elliptical orbit. 

This law means that the motion of the planets around the sun follows an elliptical path, not a circle. As an ellipse has two foci, according to this law, the sun is considered to be situated at one of the foci.



Second law: Kepler's second law states that each planet revolves around the sun in such a way that the line joining the plant to the sun sweeps the equal areas in equal intervals of time. 

This law means that a planet while revolving around the sun situated at one of the foci of their elliptical orbit, travels faster when it's close to the sun and slower when it is away from the sun.


 

Answer:

Mitochondria -
Mitochondria are double membraned structures i.e. they are enclosed by double membranes. The outer membrane is porous while the inner membrane is deeply folded. These folds are called cristae. They have their own DNA and proteins and hence are semi-autonomous in nature. It performs various kinds of functions like -

• produce energy (in the form of ATP) required for the functioning of cells
• regulate free calcium ion concentration in cytosol
• participate in apoptosis or programmed cell death
• provide intermediates for the synthesis of various chemicals such as fatty acids, steroids and amino acids

• transport of lipids in cells
• formation of lysosomes
• takes part in glycosylation and phosphorylation  of certain proteins

Answer:

Characteristic features of phylum Platyhelminthes:

• The body is bilaterally symmetrical and flattened.
• The members of this phylum lack a body cavity. They are acoelomates.
• The digestive tract lacks an anus; an excretory pore is present instead.
• The members are mostly parasitic.
• Example − Taenia solium, Fasciola, etc.

Characteristic features of phylum Nematoda:

• They are parasitic animals which cause diseases such as elephantiasis (filarial worms) and usually live in the intestine.
• A nematode has a cylindrical body with tapering ends.
• Nematodes have an organ system level of organization, but no real organs are formed due to the absence of a true coelom.
• They are bilaterally symmetrical and triploblastic.
• A false body cavity or pseudocoelom is present.
• Examples of nematodes: Ascaris, Wuchereria (filarial worm)

Answer:

1 mole of oxygen = $6.022\times {10}^{23}$ atoms of oxygen

Mass of 1 mole of oxygen atom = 16 g

$$\begin{gathered} \mathrm{Mass} \mathrm{of} \mathrm{one} \mathrm{atom} \mathrm{of} \mathrm{oxygen}=\frac{\mathrm{Mass} \mathrm{of} \mathrm{one} \mathrm{mole} \mathrm{of} \mathrm{oxygen} \mathrm{atom}}{\mathrm{Number} \mathrm{of} \mathrm{atoms} \mathrm{in} \mathrm{one} \mathrm{mole}} \\ \mathrm{Mass} \mathrm{of} \mathrm{one} \mathrm{atom} \mathrm{of} \mathrm{oxygen}=\frac{16}{6.022\times {10}^{23}} \mathrm{g}=2.6569\times {10}^{-23 }\mathrm{g} \end{gathered}$$

Answer:

(a) When electricity is passed through gases, electrical energy pushes out some electrons from the atoms of the gas. These fast-moving electrons form cathode rays. Thus, the formation of cathode rays shows that one of the subatomic particle present in all the atoms is the negatively charged "electron".

(b) When electricity is passed through gases, electrical energy pushes out some electrons from the atoms of the gas and a positively charged particle proton is formed. These fast-moving protons form anode rays. Thus, the formation of anode rays shows that one of the subatomic particle present in all the atoms is the positively charged "proton".
 

Answer:

Applications of the universal law of gravitation are as follows:

(1) We use the universal law of gravitation to calculate the force that binds us to the surface of the earth. 

(2) We can also use this law to study the motion of planets around the sun or the motion of the moon around the earth. 

Answer:

(a) While lifting the boxes to a height of 1.5 m, the work is done by the man against the gravitational pull of the earth. 

Work done against the gravity is given by, $W = mgh$. (Where 'm' is the mass of the body, 'g'  is the acceleration due to gravity and 'h' is height  up to which the body is taken) 

In the given case, weight of one box = mg = 100 N

Height up to which the man lift the box = 1.5 m

Work done by the man = mgh = 100 N $\times$ 1.5 m= 150 J

(b) The work done by the man is stored in the box as the potential energy of the box by virtue of its height with respect to ground. So, when one box is lifted the total work done of 150 J is transfered to the box in form of energy.

Answer:

Epidermis provides protection to plants against the invasion of parasites. It forms an outer covering of plant organs which remains in direct contact with the environment. This epidermis is further covered by a layer of fatty substance called cuticle. The epidermis is interrupted only at regions where stomata are present. Anything that enters the plant, has to first cross this epidermal layer.

Answer:

A plant can easily be recognised as monocot/dicot by looking at its leafs.
The leafs of a monocot plant show parallel venation (arrangement of veins) wheres the leafs of a dicot plant show reticulate venation.