write a short note on the structure of pollen grains ??
Answers
Answer:Pollen is a fine to coarse powder containing the micro gametophytes of seed plants, which produce the male gametes (sperm cells). Pollen grains have a hard coat that protects the sperm cells during the process of their movement between the stamens to the pistil of flowering plants or from the male cone to the female cone of coniferous plants.
When pollen lands on a compatible pistil of flowering plants, it germinates and produces a pollen tube that transfers the sperm to the ovule of a receptive ovary. The individual pollen grains are small enough to require magnification to see detail.
Pollen itself is not the male gamete. Each pollen grain contains vegetative (non-reproductive) cells (only a single cell in most flowering plants but several in other seed plants) and a generative (reproductive) cell containing two nuclei: a tube nucleus (that produces the pollen tube) and a generative nucleus (that divides to form the two sperm cells).
The group of cells is surrounded by a cellulose-rich cell wall called the intine, and a resistant outer wall composed largely of sporopollenin called the exine. The pollen wall protects the sperm nucleus while the pollen grain is moving from the anther to the stigma, it protects the vital genetic material from drying out and solar radiation.
The pollen grain surface is covered with waxes and proteins, which are held in place by structures called sculpture elements on the surface of the grain. The outer pollen wall prevents the pollen grain from shrinking and crushing the genetic material during desiccation and it is composed of two layers.
These two layers are the tectum and the foot layer, which is just above the intine. The tectum and foot layer are separated by a region called the columella, which is composed of strengthening rods. The outer wall is constructed with a resistant biopolymer called sporopollenin. The pollen tube passes through the wall by way of structures called apertures.
Explanation: