question_answer

What develops into a microspore mother cell in a flower? Trace the development of this cell into a pollen grain which is ready for germination.

OR

A woman has conceived and implantation has occurred within her uterus. Describe the sequence of changes that would take place in her body up to parturition under the influence of various hormones.

 

Answer:

The cells ofsporogenous tissue divide in different plants and finally separate to each other and function as microspore mother cells (microsporocytes).

Each cell of the sporogenous tissue is a potential pollen or microspore mother cell (PMC). The meiosis division occurs in microspore mother cell and gives four microspores. The process is called microsporogensis. The microspores, as they are formed are arranged in a group of four cells called microspore tetrad. As the anthers mature and dehydrated the microspores dissociate from each other in tetrad and develop into pollen grains. The pollen grains represent the male gametophytes. Apollen grain has two layered wall, outer thick exine and inner intine. The cytoplasm and haploid nucleus are surrounded by these wall layers and plasma membrane. Exine has germ pores. When pollen grain matures, it has two cells. The larger vegetative cell and smaller generative cell.

OR

After implantation the corpus luteum of ovary continues to secrete progesterone until the end of pregnancy.

(a) Progesterone controls development of foetus in the uterus. The placenta is formed partly by the embryo and partly by the uterine lining. No other Graafian follicle matures and there is no ovulation and menstruation. Placenta secretes many hormones, such as estrogen, progesterone and hCG (human chorionic gonadotropin). The hCG stimulates the corpus luteum to secrete progesterone during pregnancy.

(b) Piolactin hormone from pituitary stimulates the growth of milk glands during pregnancy.

(c) Oxytocin hormone released from pituitary induces contraction of muscles of uterus during birth.

(d) Relaxin hormone produced from corpus luteum at the end of gestation, relaxes the cervix of uterus and ligaments of pelvic girdle for easy birth of the young one.

(e) Oxytocin also acts as milk ejecting hormone by contracting muscles of mammary glands.