Q33 of 805 Page 180

Distinguish between pollination and fertilisation. Mention the site and product of fertilisation in a flower. Draw a neat, labelled diagram of a pistil showing pollen tube growth and its entry into the ovule.

OR


Reproduction is essentially a phenomenon that is not for survival of an individual but for continuation of a species. Justify

Pollination is the process of transfer of pollen grains from anther to the stigma of the carpel by various pollinating agents like wind, insects etc. Whereas the process of mixing of male and female gametes to form a zygote is called fertilization. The site of fertilization is inside embryo sac which is present within ovary. The product of fertilization is a zygote.


OR


For an organism to survive it has to perform various life processes like nutrition, respiration, circulation, excretion etc. Reproduction is not required for survival of an organism. During reproduction there is replication of DNA and only genetic material is transferred from one generation to the next producing certain variations in the offsprings. This process helps in maintaining the continuity of a species.


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31

Explain the following

(a) The reactivity of a piece of aluminium metal decreases if it is dipped in HNO3


(b) Carbon cannot reduce the oxides of Na or Mg


(c) NaCl does not conduct electricity in solid state whereas it does conduct electricity in aqueous solution as well as in molten state


(d) Necessity of galvanisation of iron articles


(e) Metals like Na, K, Ca and Mg are never found in their free state in nature.


OR


Given below are the steps for extraction of copper from its ore.


(a) Write the equations of the reactions involved in roasting of copper (I) sulphide followed by its reduction.


(b) Draw a neat labelled diagram for electrolytic refining

 32

You are given the balls and sticks models of six carbon atoms and fourteen hydrogen atoms and sufficient number of sticks. In how many ways one can join the models of six carbon atoms and fourteen hydrogen atoms to form different molecules of C6H14.

OR


Draw structural formulae of all the possible isomers of the compound with molecular formula C3H6O and also give their electron dot structures.

 34

(a) Draw ray diagrams showing the image formation by a convex lens when an object is placed

(i) at twice the focal length of the lens


(ii) at infinity


(b) The image of a candle flame formed by a lens is obtained on a screen placed on the other side of the lens. If the image is three times the size of the flame and the distance between lens and image is 80 cm, at what distance has the candle been placed from the lens? What is the nature of the image and the lens?


OR


Write laws of refraction of light. Explain the same with the help of ray diagram, when a ray of light passes through a rectangular glass slab

 35

How will you infer with the help of an experiment that the same current flows through every part of the circuit containing three resistances in series connected to a battery?

OR


Find out the following in the electric circuit given in the Figure.



(a) Effective resistance of two 8 Ω resistors in combination.


(b) Current flowing through 4 Ω resistor.


(c) Potential difference across 4 Ω resistor.


(d) Power dissipated by 4 Ω resistor.


(e) Difference in ammeter readings, if any.