Reproduction
Step 1. In anthers (male flower parts), diploid microsporocytes divide by meiosis to make haploid microspores
Step 2. In carpels (female flower parts, and consist of a stigma, style, ovary, and ovule), a single diploid microsporocyte divides meiotically to create 4 haploid megaspores, but only 1 survives Step 3. Microspores have a mitotic division and make a pollen grain (called a microgametophyte) Step 4. The surviving megaspore divides to make 7 haploid cells. One large one contains two nuclei, and another is the egg. (the 7–celled structure is called the megagametophyte) Step 5. The pollen grain pollinates the female part by landing on the stigma. The grain germinates, and the tube grows down the style to meet the female gametophyte Step 6. Two sperm from the pollen grain travel through the pollen tube and enter the female gametophyte. One fertilizes it, making a diploid zygote, and the other fertilizes the polar nuclei (double nuclei cell) forming a triploid cell. This stage is called double fertilization. Step 7. The zygote develops into the embryo, and the triploid cell becomes a nutritive endosperm of the seed. The seed germinates and when the sporophyte matures, the cycle begins again. |