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Page No 232:

Question 1:

Which of these is not a property of respiration?

(a) It occurs at high temperature.
(b) It occurs only in living cells.
(c) It releases energy in steps.
(d) It is a slower porcess than combustion.

Answer:

(a) It occurs at high temperature.
Respiration occurs only in living cells. It releases energy in steps and is a slower process than combustion.

Page No 232:

Question 1:

Which body process is responsible for releasing energy from food?

Answer:

Energy is released from digested food through the process of respiration. During respiration, the nutrients of the digested food react with oxygen in the body cells to release energy.  

Page No 232:

Question 2:

If reproduction in a plant occurs without seeds, is it sexual or asexual reproduction?

Answer:

If reproduction in a plant occurs without seeds, it is called an asexual reproduction. 

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Question 3:

A weight is tied to a string. The other end of the string is fixed to a support. If the weight is given a push, what kind of motion is observed in it?

Answer:

Uniform motion is observed because the time taken for one to-and-fro movement is always the same.

Page No 232:

Question 4:

What kind of image does a cinema porjector make-real or virtual?

Answer:

A cinema projector creates a real image and it is formed on a screen.

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Question 5:

Is the sun an exhaustible renewable resource or an inexhaustible renewable resource?

Answer:

Sun is an example of inexhaustible renewable resource.

Page No 232:

Question 1:

How does exchange of gases for respiration occur in insects?

Answer:

Insects have openings called spiracles on their bodies. Air enters through these openings and reaches all parts of the body through respiratory tubes called trachea and their branches called tracheoles. 

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Question 2:

How does transpiration help plants in transportation of water from the roots up the stem?

Answer:

Transpiration of water from leaves creates a suction pull which pulls water up to the plant from the roots. This pull is strong enough to force water up high trees.    

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Question 3:

What is a nephron?

Answer:

Nephrons are the tiny filtering units of the kidney. They filter out excess water, salts and urea from the blood when it passes through them. Each kidney contains about one million nephrons.

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Question 4:

Name the agents of dispersal of seeds.

Answer:

The agents of dispersal of seeds are wind, water, animals and explosion of fruits. 

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Question 5:

If a car takes 45 minutes to travel from point A to point B at a uniform speed of 60 km/h, what is the distance from A to B?

Answer:

Time taken = 4560=34hSpeed = 60 km/hDistance from point A to B = Speed ×Time=60 ×34=45 km

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Question 6:

Why do high speed winds often lift off roofs of houses with tin or thatch roofs?

Answer:

High-speed winds reduce the air pressure on the top of the roof, whereas the air pressure below the roof remains the same. Hence, due to this reduction in pressure, roofs of houses with tin or thatch roofs are often carried away by high-speed winds. 

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Question 7:

What is the relation between angle of incidence and angle of reflection when a ray of light strikes a mirror?

Answer:

When a ray of light strikes a mirror, the reflected ray leaves the mirror at the same angle at which the incident ray strikes. Therefore, we have:
Angle of incidence = Angle of reflection

Page No 232:

Question 8:

What is a miniature circuit breaker?

Answer:

Miniature circuit breaker is a switch that automatically stops the flow of current in a circuit if the current in it exceeds the specified maximum limit.

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Question 9:

In what forms does water exist in nature?

Answer:

In nature, water exists in all states. In the solid state, it exists as snow on high mountains. Most of the water on the earth exists in liquid form in rivers, lakes, seas, oceans, etc. In the gaseous state, water exists as water vapour in the air.

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Question 10:

How do forests help in maintaining the water table?

Answer:

Rainwater does not collect and stagnate on the forest floor. Instead, it drips down the forest floor slowly. The water is able to seep into the soil and thus helps in maintaining the water table.

Page No 232:

Question 1:

Describe the process of cellular respiration.

Answer:

Cellular respiration uses oxygen to break down food to release energy. It occurs in body cells. The sugar molecules in food are oxidised to form carbon dioxide and water and energy is released. This oxidation reaction is as follows:
 
C6H12O6   +    6O2    →     6CO2    +     6H2O    + Energy
Glucose         Oxygen       Carbon        Water
                                         dioxide

Page No 232:

Question 2:

Describe the structure of a cyclone.

Answer:

A cyclone consists of a low pressure region with higher pressure all around. The winds tend to blow towards the low pressure region and circulate violently around the centre with great speed. At the centre of the cyclone, there exists a calm and cloudless area called eye. There is no rain here and the winds are fairly light. The strongest winds and heaviest rains are formed in the thick clouds around the eye.

Page No 232:

Question 3:

An object is kept very far away from a convex lens and slowly brought close to it. Describe how the image formed by the lens will change.

Answer:

(a) When the object is very far away from a convex lens, the image is real and inverted.
(b) As the object is brought closer to the lens, image becomes bigger and moves away further from the lens.
(c) When the object is very close to the lens, the image can no longer be formed on screen. However, an erect, magnified and virtual image can be seen on looking through the lens on the same side as the object.

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Question 4:

Draw a labelled diagram of an electric bell.

Answer:


               
           Electric Bell

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Question 5:

What does rainwater harvesting consist of?

Answer:

Rainwater harvesting consists of conserving groundwater by allowing raindrops falling on roofs of buildings to flow into a deep trench on the ground. In this way, rainwater harvesting replenishes groundwater instead of flowing to the drains that empty into the rivers. 



Page No 233:

Question 2:

Through which of these does exchange of gases and digested food occur between blood and the surrounding cells?

(a) arteries
(b) veins
(c) capillaries
(d) all of these

Answer:

(c) capillaries
Capillaries are the thinnest blood vessels through which exchange of gases and digested food occurs between blood and the surrounding cells.

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Question 3:

Which of the following is not necessary for a seed to start germinating?

(a) water
(b) air
(c) light
(d) warmth

Answer:

(c) light
To start germinating, seed requires water, air and warmth.

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Question 4:

Which of these is NOT a standard unit in the SI system?

(a) metre
(b) gram
(c) second
(d) kelvin

Answer:

(b) gram
The standard unit of length is metre, standard unit of time is second and standard unit of temperature is kelvin. The standard unit of mass is kilogram and not gram.

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Question 5:

A convex lens works as a magnifying glass when the object is kept

(a) very far away
(b) at the focus
(c) between the lens and focus
(d) beyond the focus

Answer:

(c) between the lens and focus
A convex lens works as magnifying glass when the object is kept between the lens and focus.

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Question 6:

Which of these colours is not present in a spectrum formed by which light?

(a) blue
(b) brown
(c) violet
(d) orange

Answer:

(b) brown
Ordinary white light is made up of seven colours - violet, indigo, blue, green, yellow, orange and red.

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Question 7:

You want to make an electric circuit in which electric current makes a bulb glow. Which of the following is not absolutely necessary in the circuit?

(a) connecting wires
(b) switch
(c) electric cell
(d) electric bulb

Answer:

(b) switch
In an electric circuit, switch is used to put on or off a bulb. Since, we want to make an electric circuit in which electric current makes a bulb glow, switch is not required.

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Question 8:

In which of these processes in plants is water not required?

(a) germination
(b) transportation of nutrients
(c) respiration
(d) photosynthesis

Answer:

(c) respiration
Water is not required for respiration in plants.

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Question 9:

Which of these is not a produce of forests?

(a) foodgrains
(b) timber
(c) paper
(d) medicinal plants

Answer:

(a) food grains
Food grains are produce of agriculture and not forests.

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Question 10:

In which part of the wastewater treatment plant are oil and grease removed from water?

(a) grit chamber
(b) clarifier
(c) aeration tank
(d) vertical bars

Answer:

(b) clarifier
During wastewater treatment, wastewater passes through a sedimentation tank called clarifier in which floating materials such as oil and grease are removed with the help of a skimmer.



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