14.1. Multicellular Life Flashcards
Low oxygen levels…
Under low atmospheric O2 levels, large masses of cells were not possible as cells in the middle would asphyxiate.
This is due to early organisms having poor circulatory systems and purely relying on diffusion.
High oxygen levels led to giant insects…
Because insects rely on diffusion.
They have a network of tubes (tracheae) that deliver oxygen to insect tissue.
Fossils show dragonflies with wingspans of 70cm.
Phylogenetic tree of life…
Most organisms are unicellular.
Eukaryotes include multicellular species.
Our close relatives are choanoflagellates:
- Unicellular eukaryotes that form colonies during part of their lifecycles.
- They consist of a cell body, flagellum and actin-filled tentacles that capture bacteria.
Sponges:
- The simplest animals.
- Their cells have different properties, division of labour.
- Composed of genetically identical cells.
Volvocaceae…
Resemble a unicellular eukaryote Chlamydomonas (estimated to have a common ancestor about 50 million years ago).
In this simple species, each cell can divide to produce a new organism. All the cells are identical.
Therefore, they are a colony but not a multicellular organism.
Volvox…
A true multicellular organism.
Only a few cells can reproduce to form new organisms, therefore it is a multicellular organism.
Weismann barrier…
The strict distinction between the immortal germ cell lineages producing gametes and disposable somatic cells.
Hereditary information moves only from germline cells to somatic cells.
