Developmental Stages

  • Multicellular organisms begin their lives as a single cell – zygote 

  • Through embryological stages organisms develop the structures that make up the adult organism 

  • Some organisms begin life as smaller versions of their adult selves (e.g. humans) 

  • Others go through a metamorphosis (e.g. insects) and look very different at juvenile and adult stages 

  • Gamete formation – meiosis 

 

Fertilization 

  • Occurs when the sperm and egg fuse 

  • When the two nuclei fuse it is called a zygote 

  • A zygote is a single cell with a full complement of parental chromosomes 

Cleaving zygote 

  • The zygote immediately begins dividing by mitosis 

  • When you reach 16 cells, arranged in a compact ball, it is called a morula 

  • In the final stage you have a hollow ball of cells called a blastula 

Human embryogenesis 

  • Fertilization takes place at the end of the fallopian tube near the ovary 

  • Once fertilized, eggs take about 1 weel to implant into the uterus 

  • Development of the fetus will be completed in the uterus 

Gastrulation 

  • Division of cells into 3 cell types: 

  • Endoderm 

  • Eventually becomes organs 

  •  Mesoderm 

  • Eventually become bone, muscle, and cardiovascular system 

  • Ectoderm 

  • Becomes the nervous system, eyes, ears and nose 

Tobacco hornworm 

  • Undergo complete metamorphosis 

  • Egg: begins its development as a tiny egg 

  • Larva: the larva emerges 3-5 days after the egg was laid 
    solid white when it emerges, but gradually turns a green to blue-green color 

  • Grows through molting 

  • Pupa: the change from larva to pupa takes place over about 5 days, builds cocoon to transform into adult 

  • Adult: the adult tobacco hornworm is a medium to large moth with a wingspan of up to 4 inches 

Xenopus frog metamorphosis 

  • Eggs: have a darker side and lighter side 

  • Dark: gives rise to cells that form the tadpole 

  • Light: contains yolk for nourishment 

  • Tadpole will eventually form in the egg 

  • Once hatched, tadpoles will slowly develop legs and lose their tail 

  • Once they are adults they will live on the land and have lungs 

  • Females are larger than males 

Plant development: fruit producing plants 

  • Stamen: produces pollen 

  • Stigma: collects pollen 

  • Ovules (eggs) mature into seeds 

  • Ovary matures into a fruit 

Types of plant reproduction 

  • Dioecious: separate male and female plants 

  • Hermaphrodite with bisexual flower: male and female on same flower 

  • Monoecious hermaphrodite: male and female flowers are separate on same plant