Life cycles Diatoms Flashcards
How do diatom cells reproduce?
Diatom cells reproduce both asexually and sexually
Species that reproduce sexually have:
- a diplontic life cycle with gametic meiosis
How do diatoms primarily reproduce asexually?
Diatoms reproduce asexually primarily by cell division:
- Before division, the cell contents swell, forcing the epitheca and hypotheca apart.
- The mitosis takes place
- Protoplast division
After mitosis, the formation of new wall elements in each daughter cell takes place.
Describe the process of new theca (cell wall) formation in daughter diatom cells.
Each daughter cell inherits one of the thecae from the mother cell and forms the new theca inside by the deposition of silica, facilitated by vesicles.
What is the result of the unique type of cell division in diatoms?
One daughter cell is the same size as the parent cell (upper cell in picture), while the other daughter cell is slightly smaller (lower cell in picture)
How does inheritance of the parental epitheca (upper part of cell) and hypotheca (lower part of cell) affect the size of daughter diatom cells?
- The daughter cell inheriting the epitheca is the same size as the parent cell,
- while the daughter cell inheriting the hypotheca is slightly smaller, as it reforms the internal theca.
So at each division half the daughter cells are smaller than their parents, what is the consequence of this?
Average cell size in a population decreases with each successive round of cell division
asexual reproduction scheme
What triggers sexual reproduction in diatoms?
- Sexual reproduction in diatoms is triggered when the size of individual cells reaches approximately 30% of their original diameter.
- Meiosis occurs to produce gametes
What is the genetic status of vegetative cells in diatoms?
- Vegetative cells in diatoms are diploid, containing two sets of chromosomes.
- The only haploid phase in the life cycle of the diatoms are gametes
Taxonomy of Diatoms based on..
The taxonomy of Diatoms
- valve simmetry
- kind of sexual reproduction
Centric diatoms
- Radial symmetry
- Oogamous sexual reproduction
When do centric diatom cells become potentially sexual and capable of producing gametes?
Centric diatom cells become potentially sexual and will produce gametes when they reach minimal sizes, if environmental conditions are suitable
All the potentially sexual cells (gametangia) can form either female or male gametes.
What determines whether a centric diatom cell produces male or female gametes?
- Smaller cells usually produce male gametes
- Larger cells typically produce female gametes.
What happens to the very smallest cells in the population?
They cannot be induced to form gametes and these tiny cells continue to divide and become smaller still until they die
What process occurs in male gametangia of centric diatoms before meiosis?
Male gametangia undergo two or three rapid mitotic divisions in rapid succession before meiosis occurs.