Summarizing Reproductive Development and Structure

Summary

The flower contains the reproductive structures of a plant. All complete flowers contain four whorls: the calyx, corolla, androecium, and gynoecium. The stamens are made up of anthers, in which pollen grains are produced, and a supportive strand called the filament. The pollen contains two cells— a generative cell and a tube cell—and is covered by two layers called the intine and the exine. The carpels, which are the female reproductive structures, consist of the stigma, style, and ovary. The female gametophyte is formed from mitotic divisions of the megaspore, forming an eight-nuclei ovule sac. This is covered by a layer known as the integument. The integument contains an opening called the micropyle, through which the pollen tube enters the embryo sac.

The diploid sporophyte of angiosperms and gymnosperms is the conspicuous and long-lived stage of the life cycle. The sporophytes differentiate specialized reproductive structures called sporangia, which are dedicated to the production of spores. The microsporangium contains microspore mother cells, which divide by meiosis to produce haploid microspores. The microspores develop into male gametophytes that are released as pollen. The megasporangium contains megaspore mother cells, which divide by meiosis to produce haploid megaspores. A megaspore develops into a female gametophyte containing a haploid egg. A new diploid sporophyte is formed when a male gamete from a pollen grain enters the ovule sac and fertilizes this egg.

Glossary

androecium

sum of all the stamens in a flower

antipodals

the three cells away from the micropyle

exine

outermost covering of pollen

gametophyte

multicellular stage of the plant that gives rise to haploid gametes or spores

gynoecium

the sum of all the carpels in a flower

intine

inner lining of the pollen

megagametogenesis

second phase of female gametophyte development, during which the surviving haploid megaspore undergoes mitosis to produce an eight-nucleate, seven-cell female gametophyte, also known as the megagametophyte or embryo sac.

megasporangium

tissue found in the ovary that gives rise to the female gamete or egg

megasporogenesis

first phase of female gametophyte development, during which a single cell in the diploid megasporangium undergoes meiosis to produce four megaspores, only one of which survives

megasporophyll

bract (a type of modified leaf) on the central axis of a female gametophyte

micropyle

opening on the ovule sac through which the pollen tube can gain entry

microsporangium

tissue that gives rise to the microspores or the pollen grain

microsporophyll

central axis of a male cone on which bracts (a type of modified leaf) are attached

perianth

(also, petal or sepal) part of the flower consisting of the calyx and/or corolla; forms the outer envelope of the flower

polar nuclei

found in the ovule sac; fusion with one sperm cell forms the endosperm

sporophyte

multicellular diploid stage in plants that is formed after the fusion of male and female gametes

synergid

type of cell found in the ovule sac that secretes chemicals to guide the pollen tube towards the egg