Our model organism for the Phaeophyta life cycle is Fucus (rockweed), which, like its relative Saprolegnia, has a diplontic life cycle.
Observe the displayed Fucus thallus. Note the dichotomous branching (forking into two equal branches) and the swollen, heart-shaped reproductive tips of the branches. These swollen branch tips are called receptacles. The receptacles are covered in small bumps, each with a pore at the center of the bump called an ostiole. The bumps are conceptacles, chambers that house the male and female gametangia.
View prepared slides of a cross section through a Fucus receptacle to view inside the conceptacles. The male and female gametangia are housed within the conceptacle chamber. The antheridia are branched structures that look like small trees. These produce sperm with heterokont flagella.
The oogonia are globose structures divided into sections as eggs are produced. The eggs will be fertilized by sperm that swim in through the ostiole, forming a diploid zygote that will be released in the marine water. This zygote will grow by mitosis into a multicellular, diploid thallus. Label the bolded structures in the life cycle diagram on the following page.
In the Fucus life cycle below, label any important structures, indicate where meiosis and fertilization occur, and color the haploid and diploid tissues differently. Draw arrows that show where mitosis is occuring.