Q20 of 59 Page 1

What is placenta? Describe its structure. State its functions in case of a pregnant huma1n female.

After zygote implantation, there is a development of a disc like tissue known as Placenta which connects the mother and the Foetus through umbilical cord. The embryo gets nourishment inside the mother’s body by a disc-like tissue placenta which gets developed between the uterus wall and the embryo during the implantation. The nutrients, Oxygen and waste products are exchanged through this tissue.


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18

The activities of man had adverse effects on all forms of living organisms in the biosphere. Unlimited exploitation of nature by man disturbed the delicate ecological balance between the - living ' and non-living components of the biosphere. The unfavorable conditions created by man himself threatened the survival not only of himself but also the entire living organisms on the mother earth. One of your classmates is an active member of 'Eco-club' of your school which is creating. environmental awareness amongst the school students, spreading the same in the society and also working hard for preventing environmental degradation of the surroundings.

(a) Why is it necessary to conserve our environment?


(b) State the importance of green and blue dust-bins in the safe disposal of the household waste.


(c) List two values exhibited by your classmate who is an active member of Eco-club of your school.

 19

A carbon compound 'P' on heating with excess conc. H2S04 forms another carbon compound 'Q' which on addition of hydrogen in the presence of nickel catalyst forms saturated carbon compound 'R'. One molecule of 'R' on combustion, forms two molecules of carbon dioxide and three molecules of water. Identify P, Q and R and write chemical equations for the reactions involved.

 21

Define evolution. How does it occur? Describe how fossils provide us evidences in support of evolution.

 22

It is desired to obtain an erect image of an object, using concave mirror of focal length of 12 cm.

(i) What should be the range of distance of an object placed in front of the mirror? (ii) Will the image be smaller or larger than the object? Draw a ray diagram to show the formation of image in this case.


(iii) Where will the image of this. object be, if it is placed 24 cm in front of the mirror? Draw a ray diagram for this situation also to justify your answer.


Show the positions of the pole, the principal focus and the center of curvature in the above ray diagrams.