fertalisation in mammals
1.) sperm reach the ovum, chemicals released from the cells surrounding the ovum, trigger the acrosome reaction
2.) the acrosome swells fusing with the sperm cell surface membrane
3.) digestive enzymes in the acrosome are released
4.) the enzymes digest through the follicle cells, and the zona pellucida
5.) the sperm fuses with the ovum membrane and enters the ovum
6.) enzyme released from lysosomes in the ovum thicken the zona pellucida, preventing entry to other sperm
7.) nuclei of the ovum and sperm fuse forming a diploid cell (2n)
fertalisation in plants
1.)the pollen grain germinates on the style and a pollen tube grows down through the style towards the ovary.
2.) the pollen grain contains two nuclei the tube and generative nuclei, the growth is controlled by the tube nuclei
3.) on germination of the pollen, the generative nuclei divides into 2 haploid gametes which move down the pollen tube.
4.) pollen tube grows into the embyro sac, where the 2 male gametes enter
5.) one fuses with the egg cell and forms a diploid zygote (2n)
6.) the second fuses with the 2 polar nuclei to form the triploid cell or the endosperm which is a food store for the zygote.
prophase - chromatin condenses, getting shorter and fatter, sister chromatids make the chromosomes which are joined by the centromere
- centrioles migrate to opposite poles and begin to make the spindle fibres
- the nuclear envelope breaks down
metaphase - the chromosomes migrate to the equator