Virus & Algae

Virus

  Virus is an obligate  intracellular parasites. It means that they will only be activated inside living host cells. It only contain one single type of nucleic acid, either DNA or RNA but not BOTH. Based on Internstional Committee on Taxonomy of Viruses (ICTV). It is grouped based on three aspects, the nucleic acid type, strategy of replication and lastly morphology. Host range means the type of organism that can be infected by virus. Outer surface of virus will form hydrogen bond with specific receptor sites on host cell. In addition, nucleic acid is protected by protein coat called capsid made up of capsomeres. In certain virus, capsid will be covered by envelope. Envelope may or may not have spikes. Lastly, there are 4 general morphology of virus:
(I) Helical viruses
(II) Polyhedral viruses
(III) Enveloped viruses
(IV) Complex viruses

Algae
Algae can be found in aquatic or terrestrial environment. In algae, there are 7 divisions from 2 kingdoms which is kingdom Protista and kingdom Plantae based on a few things:

•  the living habitat
• presence of cell wall
• reproductive structure
• type of chlorophyll present
• morphology of cells
• flagella number and location
• form of food and assimilatory products stored in pyrenoids

Chrysophyta, Euglenophyta, Pyrrhophyta, Charophyta and Chlorophyta are belongs to kingdom Protista since they are single cell while Phaeophyta and Rhodophyta are belongs to kingdom Plantae as they are multicellular eukaryotic. The reproduction of algae includes sexual and asexual. I would like to emphasize more on sexual reproduction. In our notes, there are isogamy and heterogamy(which is also known as anisogamy).

In isogamy, the morphology of gametes is similar. They got the similar shape and size which makes us difficult to differentiate whether it is male or female. They are only differs in allele expression. With the touching of flagella poles, pairs of isogametes fused to form diploid zygote. It is either non motile gamete fused with non motile gamete or motile gamete fused with motile gamete. The motility of both isogametes will be the same.

In anisogamy, gametes of different shape and size will fuse together. The smaller gamete (sperm) will be male while the larger gamete (egg cell) will be representing female. Oogamy is a form of anisogamy. However, it only involves the fusion of non motile egg cell and highly motile sperm cell. Motile sperm cell needs to compete for fertilisation of non motile egg cell.

Figure above shows the characteristic of algae from different division.