Read the passage given below and answer the following question.
The pollen grains serve as the male gametophytes in flowering plants. Upon touching the opened anthers of flowers like Hibiscus, one can observe the deposition of yellowish powdery pollen grains on their fingers. When these grains are sprinkled on a glass slide with a drop of water and observed under a microscope, a fascinating variety of architecture, including sizes, shapes, colours, and designs, can be seen among the pollen grains from different species. Pollen grains are generally spherical and have a diameter ranging from 25 to 50 micrometers. They possess a two-layered wall, with the outer layer composed of sporopollenin, which exhibits intricate patterns and designs. The inner wall of the pollen grain is a thin and continuous layer. When mature, the pollen grain contains two cells: the larger vegetative cell and the smaller generative cell. The vegetative cell holds abundant food reserves and a large, irregularly shaped nucleus, while the generative cell floats within the cytoplasm of the vegetative cell. In the majority of angiosperms (over 60 per cent), pollen grains are shed at the 2-celled stage, where they contain vegetative and generative cells. However, in the remaining species, the generative cell undergoes mitotic division to produce the two male gametes before the pollen grains are shed, resulting in a 3-celled stage.
Pollen grain exine has prominent apertures where sporopollenin is absent. What are these known as?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Germ pores
The pollen grain has two wall layers. The hard outer layer, the exine, is made of sporopollenin, one of the most resistant organic materials known. At some places the exine has openings where sporopollenin is absent. These are the germ pores. When the pollen grain germinates on the stigma, the pollen tube grows out through one of the germ pores.
NCERT Extract:
Stamen, Microsporangium and Pollen Grain – “… The hard outer layer called the exine is made up of sporopollenin which is one of the most resistant organic material known. It can withstand high temperatures and strong acids and alkali. No enzyme that degrades sporopollenin is so far known. Pollen grain exine has prominent apertures called germ pores where sporopollenin is absent.”