Reproduction in diatoms can take place by two different processes, sexual and asexual. The following article will help you to gain information regarding subject of reproduction in these tiny single-celled algal species.
Diatoms are unicellular organisms, which are covered with a cell wall containing silica, which is called frustule. They belong to the major algal group that consists of many types of phytoplankton. These diatoms can exist in colonies, and form shapes like filaments, zigzag and stellated patterns, and ribbon-shaped colonies.
Diatoms have a nucleus, cytoplasm, vacuoles, and chromatoplasts as cell components. The silicon wall is porous with different designs at various places for passage of gases and nutrients within the cell. These algae are classified into pinnate and centric groups. The ones belonging to the latter group are round in shape, and the former ones are elongated.
The reproduction process can occur by either sexual or asexual reproduction. All diatoms pass through a seed-like or a spore phase called the resting spore.
This is the primary form of reproduction, and it occurs by binary fission. In this process, the DNA undergoes replication that causes the chromosomes to divide into two identical halves. This leads to the formation of two frustules or theca. Each daughter cell receives one of the parent cell’s frustules, like other organisms that reproduce asexually. This causes the small frustule or hypotheca to form a larger frustule or epitheca. The parent cell grows larger to divide the two daughter cells by pushing out of the valve. Each daughter cell produces a new cell wall, and such units receive one valve each. This type of reproduction causes reduction in size of a daughter cell from the average size. It eventually leads to shrinkage in the size of cells, which are just one-third their maximum size. This ‘shrinking division’ is a unique mode of asexual reproduction in diatoms. The algae also need to restore their original cell size of population, and therefore undergo sexual reproduction.
Diatoms are non-motile organisms, and therefore the sperms have flagella. The vegetative cells of diatoms are diploid (2n), and hence, they undergo meiosis. The cells produce sexual gametes that fuse to form a zygote. The males produce sperms and females produce eggs. The female cells tend to bend, and create an opening in the cell wall. This helps the sperms to enter the female cell, and fertilize it. The egg gets encased in an envelope-like structure, which produces its own shell and nucleus. Soon, the diatom will grow to its full size. The parent cell and the new diatom form auxospores, and act as if it is in a dormant stage called ‘resting spores’. This helps the cells to survive long periods of time under unfavorable conditions. Once the cells get proper conditions to grow, they continue with their sexual reproduction.
- The word diatom is derived from Greek words, dia that means ‘across’ and tome that means ‘cut’. The reason being that diatoms are cut into half by the frustule.
- They can live in fresh as well as salt water, and even can survive in soil.
- Diatoms occur in hundreds of different shapes, and their size ranges from 10 millionths to 150 millionths of a meter.
- The diatomaceous ooze at the bottom of the water bodies is formed by the sedimentation of dead diatoms.
- Scientists have come across diatom fossils that are about 185 million years old, i.e., from the Jurassic age.
They initially follow the primary modes of reproduction, i.e., asexual reproduction. When the cell size in population decreases considerably, they switch over to sexual reproduction.