question_answer

(i) Write the characteristic features of anthers, pollen and stigma of a wind pollinated flowers.

(ii) What is heterostyly and dioecy? Why some cross - pollinated plants develop such adaptations?

Or

(i) Give a schematic representation of oogenesis in humans. Mention the number of chromosomes at each stage. Correlate the life phases of the individual with the stages of the process.

(ii) A women passes out hCG in the urine during pregnancy, why?

Answer:

(i) Characteristic features of wind pollinated flowers are as follows

· The anthers are well exposed for the easy dispersal of pollen grains.

· Pollen grains are small, light, dry, dusty, nonstick and sometimes even winged.

· The stigmas are large, hairy and feathery or branched to catch the air-borne pollen grains.

· Flowers are small, colorless, inconspicuous and nectar less.

· Wind pollinated flowers often have a single ovule in each ovary and numerous flowers packed into an inflorescence like in tassels of corn cob.

(ii) Heterostyly In some plants species, the anther and stigma are placed at different positions, so that the pollen cannot come in contact with the stigma of same flower. This condition is called heterostyly. It prevents autogamy.

Dioecy In some plants,male and female flowers are present on different plants, i.e. each plant is either male or female . It is known as dioecy, e.g. papaya. It prevents both autogamy and geitonogamy.

Some cross-pollinated plants have developed such devices to discourage self-pollination and encourage cross-pollination. Continued self-pollination leads to chances of inbreeding depression.

Or

(i) Oogenesis in humans is the formation of a mature female gamete. The process occurs in ovary and begins before birth, i.e. during embryonic development but completes when fertilisation occurs.

(ii) The presence of human Chorionic Gonadotropin (hCG) is the basis of pregnancy test. Placenta forms during pregnancy releases hCG, Which comes in urine of pregnant woman.