MODEL PAPER 3 Science - MODEL PAPER 3

Assertion (A): CFCs deplete the ozone layer.
Reason (R): CFCs are used as refrigerants and in fire extinguishers.

Assertion (A): The strength of the magnetic field produced at the centre of a current-carrying circular coil
increases on increasing the number of turns of the circular coil.
Reason (R): Magnetic field strength is directly proportional to the number of turns of the circular coil.

Assertion (A): XX chromosome give rise to female child whereas XY give rise to male child.
Reason (R): The Y chromosome in males is small than X chromosome.

In the following groups of materials, which group (s) contains only non-biodegradable items?
i. Wood, paper, leather
ii. Polythene, detergent, PVC
iii. Plastic, detergent, grass
iv. Plastic, bakelite, DDT

Assertion (A): XX chromosome give rise to female child whereas XY give rise to male child.
Reason (R): The Y chromosome in males is small than X chromosome.

Assertion (A): The strength of the magnetic field produced at the centre of a current-carrying circular coil
increases on increasing the number of turns of the circular coil.
Reason (R): Magnetic field strength is directly proportional to the number of turns of the circular coil.

Assertion (A): CFCs deplete the ozone layer.
Reason (R): CFCs are used as refrigerants and in fire extinguishers.

A person is unable to see clearly a poster fixed on a distant wall. He however sees it clearly when standing at a
distance of about 2 m from the wall.
a. Draw ray diagram to show the formation of image by his eye lens when he is far away from the wall.
b. List two possible reasons of this defect of vision.
c. Draw ray diagram to show the correction of this defect using appropriate lens.

Give reason to justify the following:
i. The existence of decomposers is essential in a biosphere.
ii. Flow of energy in a food chain is unidirectional.

Rearrange the following according to their ascending trophic levels in a food chain. Hawk, grass, snake, frog, grasshopper.

Draw ray diagram showing the image formation by a convex lens when an object is placed between optical centre and focus of the lens.

When and where does anaerobic respiration occur in man and yeast?

"A concave mirror of focal length f can form a magnified, erect as well as an inverted image of an object placed in front of it." Justify this statement stating the position of object with respect to the mirror in each case for obtaining these images.

A child questioned his teacher that why do organisms resemble their parents more as compared to grandparents. In which way will the teacher explain to the child?

a. Draw a diagram of human excretory system and label on it the following parts:
i. Kidney
ii. Ureter
iii. Urinary bladder
iv. Urethra
b. Write one main function each of the labelled parts.

A student focussed the image of a candle flame on a white screen using a convex lens. He noted down the position of the candle screen and the lens as under Position of candle = 12.0 cm Position of convex lens = 50.0 cm Position of the screen = 88.0 cm
i. What is the focal length of the convex lens?
ii. Where will the image be formed if he shifts the candle towards the lens at a position of 31.0 cm?
iii. What will be the nature of the image formed if he further shifts the candle towards the lens?
iv. Draw a ray diagram to show the formation of the image in case (iii) as said above.

i. List three points of difference between nervous and hormonal mechanisms for control and coordination in animals.
ii. How are auxins related with the bending of plant shoot towards unidirectional light? Explain.

The labelled diagram of a flower is shown below:


Using the above diagram, answer the following questions:
i. Where is the egg cell present in a flower?
ii. Which part of the flower produces pollen grains?
iii. What is the difference between a uni-sexual and a bisexual flower?
iv. What happens when a pollen grain falls on the stigma of the carpel?
v. How a zygote is formed in a flower?

What are carboxylic acids? Give the common names, IUPAC names and structural formula of first four members of the homologous series.

A magnetic field is described by drawing the magnetic field lines. When a small north magnetic pole is placed in the magnetic field created by a magnet, it will experience a force. And if the north pole is free, it will move under the influence of the magnetic field. The path traced by a north magnetic pole free to move under the influence of a magnetic field is called a magnetic field line.


Since the direction of the magnetic field line is the direction of the force on a north pole, so the magnetic field lines always begin from the N-pole of a magnet and end on the S-pole of the magnet. Inside the magnet, however, the direction of magnetic field lines is from the S-pole of the magnet to the N-pole of the magnet. Thus, the magnetic field lines are closed curves. When a small compass is moved along a magnetic field line, the compass needle always sets itself along the line tangential to it. So, a line drawn from the south pole of the compass needle to its north pole indicates the direction of the magnetic field at that point.
(a) Do the magnetic field lines intersect? if not why?
(b) A strong bar magnet is placed vertically above a horizontal wooden board. What would be the magnetic lines of force?
(c) The figure shows the magnetic field lines in a magnetic field. A, B., and C are three points in this field. At what point is the magnetic field strength?

OR
Draw the pattern of magnetic field lines for a bar magnet.

You must have noticed many dramatic changes in your appearance as well as that of your friends as you approached 10-12 years of age. These changes associated with puberty are because of the secretion of testosterone in males and oestrogen in females. Do you know anyone in your family or friends who has been advised by the doctor to take less sugar in their diet because they are suffering from diabetes? As a treatment, they might be taking injections of insulin. This is a hormone that is produced by the pancreas.
(a) Why is pancreas a dual gland?
(b) Name the hormone which is secreted by males and females during adolescence.
(c) What happens if Insulin is not secreted in the proper amount?
OR
From which cells of pancreatic islets insulin and glucagon hormone are secreted?

The dissolving of an acid or a base in water is a highly exothermic reaction. Care must be taken while mixing concentrated nitric acid or sulphuric acid with water. The acid must always be added slowly to water with constant stirring. If water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause burns. The glass container may also break due to excessive local heating. Look out for the warning sign on the can of concentrated sulphuric acid and on the bottle of sodium hydroxide pellets.


(a) What is the exothermic reaction?
(b) Write an example of an exothermic reaction.
OR
How will you obtain sulphuric acid from an acidic oxide?