Multicellularity and cell specialisation Flashcards
what defines an organism as multicellular?
Except for reproductive cells, its cells must have the same DNA
Cells must be connected and communicate and cooperate to function as a single organism
Different cells must be specialised and be responsible for certain functions
Its cells must be dependent on each her for survival
what is the symbiotic theory for how organisms became multicellular? what is a limitation?
Developed when different species of unicellular organisms started to cooperate. It benefited the cells and over time they became dependent on each other. Began to specialise and carry out different functions. Eventually their DNA combined and a new species evolved.
Doesn’t explain how DNA was combined
what is the syncytial theory or cellularisation theory?
A single cell with multiple nuclei evolved internal membranes that separated them. They began to specialise and eventually became separate cells, forming a multicellular organism.
But nuclei tend to have different roles and they are only present in one stage of the organism’s life
what is the colonial theory?
Suggests that when a single cell divided, it didn’t split fully but cell division continued and the cells began to specialise and carry out different functions. It later formed reproductive cells and was capable of replicating itself.
Seems like best theory
It explains how DNA stayed the same also it has been observed before such as with the amoeba dictyostelium
how does a multicellular organism develop?
Multicellular organisms start as a single cell (zygote) that resulted from the fusion of gametes (ovum and sperm). These are specialised cells that can stick together and become one.
This cell has genetic information required to develop into a multicellular organism
By cell division it becomes an embryo
By cell replication and differentiation one cell becomes trillions of specialised cells- an organism
what is cell differentiation? with what cells does it occur and when?
Process in which unspecialised cells (stem cells) become specialised Stem cells are in embryos and in some adult tissue or in the meristem tissue in plants
Stem cells are always able to divide but specialised cells usually can no longer do so
Begins shortly after fertilisation
what are advantages of multicellularity?
Advantages
More energy efficient because functions and work is divided up across the cells
Have longer lifespan because they are more efficient
Sexual reproduction and genetic recombination promotes increasing complexity and specialisation over generations compared to clonal reproduction in unicellular organisms
Can be larger because unicellular organisms must be small to obtain nutrients and remove wastes through diffusion
More mobile due to increased size and specialisation of limbs and therefore more effective at locating resources and escaping predators
Can preform more functions
what are disadvantages of multicellularity?
Disadvantages
More cells means more energy is needed to survive
Cells cannot function independently
More energy is required of reproduction and most plants and animals need another plant or animal in order to mate
Take much longer to evolve and adapt to long term changes in their environment because they have longer generations
