Q20 of 61 Page 1

(a) Give one example each of a unisexual and a bisexual flower.

(b) Mention the changes a flower undergoes after fertilization.


(c) How does the amount of DNA remains constant though each new generation is a combination of DNA copies of two individuals?

(a) The example of a Unisexual Flower is Papaya. The example of a Bisexual Flower is Hibiscus.


(b) The various changes a flower undergoes after the process of fertilization are:


1. Division of fertilized eff several times to form the embryo within the ovule.


2. Development of a tough coat by around the ovule and conversion into seed.


3. Developing of ovary of flower and formation of a fruit.


4. Drying and falling off sepals, petals, stamens, stigma and style.


(c) The amount of the DNA of the sexually reproducing parents and their offspring is same through each generation. As we know, in case of sexual reproduction, the genetic material DNA constitutes both gametes i.e. of male and female. These are combined to form the a new cell known as zygote but the the amount of the DNA remains the same and doesn’t gets doubled. This is because gametes contains only half amount of DNA i.e. half number of chromosomes. SO, a zygote carry half chromosomes from male and half from female. Therefore, the new cell formed have normal amount of the DNA.


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18

"Our food grains such as wheat and rice, the vegetables and fruits and even meat are found to contain varying amounts of pesticide residues." State the reason to explain how and why it happens?

 19

State the reason why carbon can neither form C4+ cations nor C4- anions, but forms covalent compounds. Also state reasons to explain why covalent compounds:

(a) are bad conductors of electricity?


(b) have low melting and boiling points?

 21

(a) Name, the respective part of human female reproductive system:

(i) that produces eggs.


(ii) where fusion of egg and sperm takes place, and


(iii) where zygote get implanted.


(b) Describe in brief what happens to the zygote after it gets implanted.

 22

A student wants to project the image of a candle flame on the walls. of school laboratory by using a lens:

(a) Which type of lens should he use and why?


(b) At what distance in terms of focal length 'F' of the lens should he place the candle flame so as to get


(i) a magnified, and (ii) a diminished image respectively on the wall?


(c) Draw ray diagram show the formation of the image in each case.