Chapter – 8
How Do Organisms Reproduce
Q. 1 A couple wants to space the birth of their second child. Suggest one preventive
method which could be observed 1 Mark
(a) By the husband (b) By the wife for the same.
Ans. (a) Use of condoms by the husband
(b) Use of oral pills or loop or Copper-T by the wife.
Q. 2 A girl attains her puberty at the age of 11 years and a boy at 13 years but, still
they are asked to refrain from sex, why? 2 Marks
Ans. They are asked to refrain from sex because:-
1. They are not physically, emotionally mature enough to be able to bear the
responsibility of the child.
2. They may suffer from reproductive tract infections.
Q.3 A pregnant woman visits a doctor to determine the sex of her child. The doctor
refused to perform the test. Why is she being denied? 2 Marks
Ans. The doctor refused to perform the test in order to prevent female foeticide which
leads to an alarming decline in child sex ratio.
Q. 4 Blue prints of body design are stored in the DNA. Why? 3 Marks
Ans. The chromosomes present in the nucleus of a cell contain information for inheritance
of features from parents to next generation in the form of DNA molecule. The DNA
is the information source for making proteins. Thus, blueprints of the body design
Chapter 6 Babies derive sexual pleasure from stroking, cuddling, bathing and other tactile stimulation. Cutaneous stage = the first stage of sexual development. Infants skin can be considered a single erogenous stage Infants also learn about their gender roles ex. The toys they play with or they way that they are handled childhood sexuality disguise their interests because they don't want to risk ...
are stored in the DNA.
Q. 5 Producing individuals by parents consume a lot of energy. So, why should an
individual organism waste energy in the process, it does not need to stay alive?
Ans. Reproduction, unlike other life processes is not essential to maintain the life of an
individual organism. But it is essential for providing stability to the population of
Maintaining the species is essential for maintaining balance in nature.
Q. 6 Protozoan reproduce by binary fission as well as by multiple fission. In your
opinion which process is better and why? 2 Marks
Ans. Multiple fission is better than binary fission because:-
1. More number of individuals is produced.
2. It helps to tide over unfavourable conditions.
Chapter – 10
Light: Reflection & Refraction
(1 Mark Questions)
Q 1.How does image changes when the face is slowly moved away from inner face of a
Ans. As the face is moved away than after a particular time image becomes inverted.
Q.2. Due to which property of light, sharp shadow of an object is obtained?
Ans. straight line property of the light.
Q.3. Identify the type of lens or mirror placed at XY where O is object and I is image.
Ans convex lens (when object is placed between pole and focus)
Q.4.What type of lens must be placed at XY so that image I shifts to I’
Ans. concave lens
Q.5. A ray AFB is incident on a spherical mirror whose centre of curvature is 2 F. In
which direction will it reflect?
Ans It will reflect towards the object side parallel to principal axis.
Q 6. A ray of light is incident at angle of 350 to a plane surface. What will the angle of
Q 7. A fish under water is viewing obliquely a fisherman standing on the bank of lake.
Does the man look taller or shorter?
Ans. As light travels from rarer to denser medium, it bends towards normal and appears
to come from greater height.. Therefore to fish under water man looks taller.
... placed beyond f from the lens would produce a real image. ... final image would occur at the same position as the object. The distance between the object and the lens gives the focal length of the convex lens. An object ...
(Two marks Questions)
Q 1. An Object is placed 15 cm in front of a lens ‘A’ and lens gives real, inverted ,
magnified image and formed at large distance. Lens ‘A’ is replaced by Lens ‘B’
and a real, inverted image of the same size as of object is formed.
i) What is the nature of Lens A&B?
ii) What is the focal length of A&B?
Ans i) A=Convex lens ,B=Convex Lens
ii) fA=15cm, fB=7.5cm
Q 2 Two lenses 1&2 are placed in contact .Focal length of lens 1 is 20 cm and of 2 is –
10 cm. Calculate
i) Total Power of combination
ii) What is the nature of combination..
Ans (i) P= -5 D ,(ii)Concave Lens
Q 3. For the same angle of incidence the angle of refraction in three different media
A, B and C are 300 , 450 and 600 respectively. In which medium will the velocity
of light be minimum?
Ans) μA=sin i/sin 30 , μB=sin i/sin45, μC=sin i/sin 60
μA >μB >μC , μ=c/v as μA= max. ,vA=min.
Q 4.You are given three lenses.
i) a concave lens of focal length 25 cm.
ii) a convex lens of focal length ¼ m and
iii) a convex lens of focal length 100 cm.
Which combination out of these three lenses will form a lens of zero power?
Ans ) Combination of concave lens of focal length of 25 cm and a convex lens of focal
length of 1/4m
(Three Marks Questions)
Q1.A rod of length 10 cm lies along the principal axis of a concave mirror of f= 10 cm
in such a way that the end closer to the pole is 20cm away from it. Find the length of
Ans. R =2f=20cm. Thus the nearer end B of the rod AB is at C and hence its image will be
formed at B itself
For end A u = -30 cm, f = -10 cm, v = -15cm
Length of image will be at 5 cm
Q 2. Absolute refractive Index of some of material is tabulated below
Material Rock salt Kerosene Water diamond
1.54 1.44 1.33 2.42
i) In which of these does light travel fastest and why? 2
ii) arrange these materials in ascending order of their optical densities. 1
Ans i) Water due to least refractive index.
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ii) Water ,Kerosene, Rock salt ,diamond
Q 3. A object is placed on the axis of a convex lens. Draw the neat ray diagrams for
formation of image when
i) Object is placed at a distance more than double of its focal length.
ii) The object is at a distance equal to double of its focal length and
iii)The object is at a distance more than focal length but less than double of its focal
Ans NCERT Book Pg. 18