Development Of Plant Gametes Flashcards
Briefly explain the formation of the male gamete.
Pollen cell mother (diploid) - meiosis - 4 pollen grains in a tetrad (haploid) - each nucleus undergoes mitosis - generative nucleus (haploid) and tube nucleus (haploid) - generative nucleus undergoes mitosis - 2 male nuclei (haploid)
Where does male gamete formation occur?
In the pollen sacs in the anthers.
What is the tapetum?
The layer of cells around the pollen sac which provides nutrients and regulatory molecules to developing pollen grains. Significant role in the formation of pollen cell walls.
What are some characteristics of pollen cell walls?
The outer exine is tough and resistant to chemicals. It resists desiccation so pollen grains can be transferred from one flower to another without drying out. UV light can’t penetrate the cell wall so DNA is protected from mutation. The inner intine is made of cellulose.
What happens when the pollen is mature?
The outer layers of the anther dries out, causing tension in the lateral grooves. Eventually, dehiscence occurs where tension pulls the walls of the anther apart and the edges of the pollen sacs curl away. An opening called the stomium exposes pollen grains and they’re carried away.
Briefly explain the formation of the female gamete.
Megaspore mother cell (diploid) - 4 megaspores (haploid) - 3 disintegrate - one undergoes 3 rounds of mitosis making 8 haploid nuclei - 2 fuse - 1 polar nucleus (diploid) - 1 oosphere (haploid) - 3 synergids - 2 antipodals (both haploid).
Describe the structure of the female part of the plant where development of the female gamete occurs.
The nuclei are in an embryo sac, which is surrounded by a nucellus which is a layer of cells providing nutrients. Around this are 2 layers of cells called integuments, which have a gap in them called the micropyll.
