Multicellularity Flashcards
Why is multicellularity so significant in evolutionary history
It has evolved separately across many species in different kingdoms of life
What is the life cycle of myxobacteria
-when nutrients are plentiful the cells divide normally through binary fission
-when nutrients are scarce they clump together forming a mound of cells
-the mound will eventually produce a fruiting body
-the fruiting body releases myxosores which develop into new bacteria
What are the benefits of multicellularity
Size increase means the organism is less vulnerable to predation. It also reduces the limitation of surface area to volume ratio that single cells face when increasing in size.
Labour is divided between the organisms with specialised cells carrying out specific processes more efficiently than a singled celled organism
Since cells are constantly being replaced, the overall lifespan of the organism is greater
What are the levels of multicellularity
Colonies
Aggregations
True multicellularity
Complex multicellularity
Define colony
A group of cells that are permenantly associated but do not communicate with each other
Define aggregations
A temporary collection of cells that come together for a period and then separate
Define true multicellularity
An organism composed of many cells that are permanently associated with one another. Cells can specialise into different functions
Define complex multicellularity
When the specialised cells are organised into tissues and organs. E.g. plants and animals
What are the two hypothesis to multicellularity
Colonial hypothesis
Syncytial hypothesis
What is the syncytial hypothesis of multicellularity
Syncytium forms as a result of incomplete cell decision leading to polynucleated cells. Eventually a cell membrane forms around the nuclei resulting in a separate cells that are joined together. Over time the different cells will specialise into performing different functions
What evidence supports the syncytial hypothesis of multicellularity
Many protists e.g. slime moles have several nuclei
What is the colonial hypothesis of multicellularity
Individual cells in a colony cooperate which results in an advantage. Eventually somatic and reproductive cells differentiate and an inside-outside polarity is formed
What makes an organisms multicellular
Cell to cell adherence and cohesion is required to keep the cells together
Cell to cell communication is required to coordinate development
Cell specialisation allows for more efficient processing and distinguishes multicellular organisms from colonies
The organisms has to undergo growth and development which is governed by genetic program
How do cells differentiate despite having identical genetic code
Differential gene expression
