1. Ch 2.2 Multicellular Organisms and Cell Specialization

2. Multicellular Organisms
living things made of more than one cell that rely on a variety of types of cells to perform cellular functions
rely on Specialized Cells, cells that perform a specific function and interact with other types of cells in the organism in order to carry out its task successfully

3. Cell Size
unicellular organisms are usually micro-sized because of limitations set by diffusion and osmosis
these activities are most efficient in small cells
ie. an oxygen particle can diffuse over a distance of 0.01 mm in a fraction of a second; to diffuse over a distance of 1 mm would take 100 times as long
so, the larger the cell, the more volume within the cell and more area that has to be covered to get water and gases to the organelles within the cell
in organisms made up of trillions of smaller cells, diffusion and osmosis can still happen in fractions of a second

4. The Cell as a “Community”
just as in a community, some people grow food, other transport that food, some people protect the community, and others help to keep it clean, the different cells in a multicellular organism have assigned tasks
specialized cells contain the same kinds of organelles, however, these organelles may be better adapted at performing a given task

5. Specialized Animal Cells
the number of types of cells in a multicellular organism depends on the complexity of the organism
the hydra is a simple multicellular organism that contains “skin” cells on the outside and digestive cells on the inside

6. Specialized Animal Cells
Humans, on the other hand, have hundreds of different types of cells
skin cells (protection and gatekeepers)
cells responsible for digestion
bone cells
muscle cells that convert energy
nerve and brain cells that transmit electrical impulses
cells in the eye that detect light
blood cells that transport oxygen and carry away waste
fat cells that store energy
and many, many others

7. Specialized Plant Cells
multicellular plants have their own set of specialized cells
some transform the Sun’s energy into sugars, found mostly in the leaves
cells in the stemtransport food and water to the rest of the plant, store some food, and support the plant
cells in the roots store food, absorb water from the soil, and transport water and nutrients to the stem

8. In-class Assignment
on a sheet of paper (with your name and date in the upper right hand corner – as always), answer the following questions:
in your own words, explain why diffusion and osmosis limit the size of cells
in your own words, explain why multicellular organisms have specialized cells
turn this in when complete