Unicelluar vs. Multi-cellular Section 2.4

Unicellular Organisms An organism made up of only a single cell. Amoebas are common unicellular organisms that live in water. They move around using foot-like projections called pseudopods (false feet). They extend a pseudopod and the cytoplasm fills it. The also use their pseudopods to capture food by surrounding it between two pseudopods and absorbing it. Paramecium move swiftly through the fresh water where they live. They are covered in hair-like structures called cilia, which move back and forth like little oars, moving it through the water. Cilia also help gather food, by channeling the food to an oral groove, which is also lined with cilia, sweeping the food into the cytoplasm forming a food vacuole.

Unicellular Organisms Examples Diatoms Acetabularia Diatoms are a major group of algae, and are among the most common types of phytoplankton. Diatoms are unicellular, although they can form colonies in the shape of filaments or ribbons, fans, zigzags, or stars. Acetabularia is a genus of green algae, specifically of the Polyphysaceae family,[2] Typically found in subtropical waters, Acetabularia is a single-celled organism, but gigantic in size and complex in form, making it an excellent model organism for studying cell biology

Unicellular Organisms Unicellular organisms are simple because they lack tissues and organs. However, they are not simple because they have adapted the means to gather food, move, eat, respond to stimulus, get rid of waste, and reproduce – basically everything a multicellular organism can do – but with only one cell!

Multi-cellular Organisms An organism made up of two or more cells. Multi-cellular organisms can: live in a wide variety of environments grow very large obtain their energy from a wide variety of foods have complex bodies specialize functions and work in harmony with other cells

Think about It! Could a cell in a multicellular organism function on it’s own??

How Substances Move In & Out of Cells Section 2.3

The Cell Membrane A cell membrane allows some substances to enter or leave the cell, while stopping other substances. It is a selectively permeable membrane. (some stuff goes in, some can’t pass)

Diffusion Movement of particles from high concentration to low concentration.

Osmosis Diffusion of a substance through a selectively permeable membrane. Amoeba Sisters video: https://youtu.be/IaZ8MtF3C6M

Diffusion

Osmosis Water helps to dissolve many of the substances involved in cell processes. When water is lost (moves out of the cell) it leaves behind a high concentration of the dissolved substances. When water moves back into the cell, the substances become more diluted and can be used by the cell for it’s life functions.

The Effect of Osmosis on Cells