Question

What develops into a microscopic mother cell in a flower? Trace the development of this cell into a pollen grain that is ready for germination. Draw a labeled figure of a mature pollen grain.

Answer 1

Hint: The pollen grains are the male gametophytes that are produced by the flowers. Microscopic mother cells develop and mature to form the pollen grains.

Complete answer:
1) The androecium consists of a stamen. The stamen contains a stalk called the filament and a terminal structure called the anther; within the anther are chambers called microsporangia (pollen sacs) that produce pollen. As the stamens are produced, each anther develops four microsporangia, also called pollen sacs. Inside the microsporangia, there are numerous diploid cells which are known as microsporocytes or better known as microspore mother cells.
2) Each microsporocytes undergoes meiosis and then forms four haploid microspores. Each of these microspores then gives rise to a haploid male gametophyte. Each microspore undergoes mitosis and produces a haploid male gametophyte. The haploid male gametophyte consists of two cells: the generative and the tube cell.
3) The pollen grain is made up of these two cells and the spore wall. The process of development of male gametophyte from the pollen grain is called microgametogenesis.
4) The pollen grain typically consists of only the tube cell and the generative cell at the time of pollination. Absorption of water takes place in the pollen grain and a long cellular thin protuberance is formed for germination. This delivers sperm to the female gametophyte.

Additional information:
-Flowers are the reproductive parts of angiosperm sporophytes. They are typically composed of four different whorls: carpels, stamens, petals, and sepals.
-The microspore or the pollen grain is the first cell of male gametophyte. It is unicellular and haploid.
-The outer layer of the pollen grain is known as exine and is made up of sporopollenin. Sporopollenin provides pollen resistance to physical and biological damages.
-Microspores start germinating in situ (when they are still enclosed in the pollen sac) and the process is named as precocious.
-The pollen grains are shed from anther at this bicelled stage.

Mature pollen grain

Note:
-In insect-pollinated flowers, the exine of the pollen grain is covered with a sticky viscous and yellow substance known as pollenkitt.
-The smallest pollen is found in Myosotis and the largest pollen is found in Mirabilis.