The document discusses the process of crossing over during meiosis in plants and animals. It mentions stages in pollen and spore formation, including microspore pollen, megaspore mother cell and megaspore. It also references stages in animal cell formation like secondary spermatocyte and spermatid. The document then discusses mechanisms of permeability and active transport but does not provide details. It mentions numbered points but no further explanation is given.

1. crossing over
1. Microspore pollen
2. Megaspore mother cell megaspore
3. Secondary spermatocyte spermatid
4. Oogoniumprimary ppcyte
1. permeability
2. active transport
3.
4.
ก.
ข.
1.
2.
3. ,
4. ,
1.
2.

2. 3.
4.