Amoebas are single-celled organisms. Humans are multicellular organisms. In humans and animals it’s easy to distinguish between the different characteristics of life. For multicellular organisms, different cells perform different jobs, while amoebas have to do it all in one cell. Amoebas are unique from most other types of life, but with the same characteristics as humans. Although amoebas are microscopic, it is one of the most curious life forms on Earth.
An amoeba eats living food by engulfing (surrounding) it. As it moves to the food, such as ciliate, it forms a “U” shape. The opening is called the food cup. It then closes off the opening with its prey in it. A food vacuole is formed that contains the prey and a small amount of water. Digestive enzymes within the cell break down the prey for absorption. The parts it can’t digest simply fall through the outer membrane as waste.
Amoebas breathe oxygen. The amoeba's outer surface is permeable, which allows the gases in the water to penetrate and diffuse throughout the cell. Oxygen is absorbed and used while it removes the carbon dioxide from its system, releasing it back into the water. The chemical reactions from breathing produce nitrogen-containing waste that are excreted in the same manner. It does not take in air, it is simply absorbed through the whole body of the cell.
Amoebas move by stretching a portion of its outer layer, or ectoplasm, forward. It then squeezes all its inner fluid, or endoplasm, into the forward projection called a pseudopodium. As this happens the endoplasm liquefies allowing it to flow forward away from the contractions. It then solidifies once more and the process starts over again. The pseudopodium can be formed in any direction, which allows the amoeba to move at random.
Reproduction is most often achieved by binary fission, although sometimes it can be by multiple fission. The amoeba contracts all of its protrusions and creates a hard shell or cyst during severe cold spells or droughts. The cyst is very light and is called a spore, which is blown to new surroundings. The nucleus of the spore divides making numerous smaller amoebulae. The cyst eventually breaks down releasing them into the environment.
While the amoeba does not have any specific organs used for sensing its surroundings, it can sense the outside world. The entire surface of the amoeba detects minute changes in its surroundings and will quickly move to an area where it is more favorable. It will move away from things such as acidic or alkaline water or strong sunlight. This sensing ability is also what allows the amoeba to find its food.