Science (English Medium) इयत्ता १२ - CBSE Important Questions

Some organisms suspend their metabolic activities to survive in unfavourable conditions. Explain with the help of any four examples.

Why are some seeds referred to as apomictic seeds?

Angiosperms bearing unisexual flowers are said to be either monoecious or dioecious. Explain with the help of one example each.

A flower of tomato plant following the process of sexual reproduction produces 240 viable seeds.

Answer the following questions giving reasons :

(a) What is the minimum number of pollen grains that must have been involved in the pollination of its pistil?

(b) What would have been the minimum number of ovules present in the ovary?

(c) How many megaspore mother cells were involved?

(d) What is the minimum number of microspore mother cells involved in the above case?

(e) How many male gametes were involved in this case?

A non biology person is quite shocked to know that apple is a false fruit, mango is a true fruit and banana is a seedless fruit. As a biology student how would you satisfy this person?

Describe the development of endosperm after double fertilisation in an angiosperm.

A flower of tomato plant following the process of sexual reproduction produces 200 viable seeds.

Answer the following questions giving reasons :

(a) What would have been the minimum number of ovules present in pre-pollinated pistil ?

(b) How many microscope mother cells would minimally be required to produce requisite number of pollen grains ?

(c) How many pollen grains must have minimally pollinated the carple ?

(d) How many male gametes would have used to produce these 200 viable seeds ?

(e) How many megaspore mother cells were required in this process ?

Name the part of the flower which the tassels of the corn- cob represent.

Sketch and label stages in the development of the angiospermic female gametophyte from the functional megaspore.

Mention two strategies that evolved to prevent self-pollination in flowers.

List the three stages the annuals and biennial angiosperms have to pass through during their life cycle.

In a flowering plant a microspore mother cell produces four male gametophytes, while a megaspore mother cell forms only one female gametophyte. Explain.

Read the statement and answer the questions that follow.

A flower of brinjal has 520 ovules in its ovary. However, it produces a fruit with only 480 viable seeds.

(a) What could have prevented the rest of the 40 ovules from maturing into viable seeds? Explain giving a reason.

(b) Describe the development of a dicot embryo in a viable seed.

(c) Why certain angiospermic seed albuminous while others are exalbuminous? Explain.

A capsicum flower has 240 ovules in its ovary. But, it produces a fruit with only 180 viable seeds.
 

Draw a diagram of a section of a megasporangium of an angiosperm and label funiculus, Micropyle, embryosac and nuclleus.

Why does endosperm development preceeds that of zygote ?

Describe the development of an endosperm in a viable seed. Why does endosperm development precedes embryo development?

Give an example of an angiosperm seed that has a perisperm. Name the part the perisperm develops from.

Compare the characteristic features of insect pollinated and wind pollinated flowers. Explain how the respective features assist in pollination.

Answer the following question.
You are conducting artificial hybridization on papaya and potato. Which one of them would require the step of emasculation and why? However, for both, you will use the process of bagging. Justify giving one reason.