Animals and plants are eukaryotes, composed of cells that have a nucleus, and membrane-bound organelles. But animal cells have a few different features than plant cells.
Unlike plants animals are heterotrophs, meaning that they must eat energy originally captured by plants and other autotrophs (photosynthetic self-feeders). The way that they obtain energy makes animal cells different from plant cells in a few important ways. The following is a list, with summaries of the different parts of an animal cell.
* Plasma Membrane *
The plasma membrane, or cytoplasmic membrane, is the boundary between the inside and outside of a cell. It is semi-permeable, meaning that some molecules, such as water, can freely move into and out of the cell, whereas other molecules cannot as easily pass through. All living cells have a plasma membrane, but prokaryotes (bacteria and other bacteria-like cells) and plants have a cell wall beyond the plasma membrane that give the cell structural stability. Animal cells do not have a cell wall, and therefore are more vulnerable.
* Cytoplasm of the Cell *
The fluid matrix within the cell is called the cytoplasm. It, and the cellular organelles, fill the area between the nucleus and the plasma membrane. All cells, prokaryotic and eukaryotic, have cytoplasm inside.
* Cytoskeleton *
All cells contain a network of structural elements known as the cytoskeleton (learn more on cytoskeleton function and structure). They give the cell support and shape, somewhat like the human skeleton gives the body structure and shape.
* Centrioles of Animal Cells *
Centrioles are the organelles that, in animal cells, produce microtubules (components of the cell’s cytoskeleton). Centrioles are involved in animal cell division; creating microtubule spindles which pull the chromosomes to opposite ends of the cell and create the cleavage furrow. Plant cells, instead, have microtubule organizing centers (MTOC) that produce their microtubules.
* Endomembrane System *
Eukaryotic cells also have a system of internal membrane-bound organelles, including the:
* endoplasmic reticulum (rough and smooth), where proteins and lipids are synthesized
* Golgi apparatus, where cellular molecules are further processed and lysosomes are made
* vesicles, which transport materials between organelles in the endomembrane system
* lysosomes, special vesicles that break down cellular waste
* plasma membrane, the outer membrane surrounding the cell
Since all of the endomembrane system organelles are made of the same thing — phospholipids — part of each organelle can break off into a vesicle and travel to and fuse with another membrane bound organelle. This is how many materials are shipped into, out of, and around within eukaryotic cells.
* Mitochondria and ATP *
The mitochondia are double membrane-bound organelles that transform food energy into usable ATP (adenosine triphosphate) energy that the cell can use to do work. Eukaryotic cells have many mitochondria, the powerhouses of the cell.
* Nucleus of Eukaryotes *
The most noticeable feature that differentiates the more complex, eukaryotic cells from prokaryotes (bacteria and bacteria-like organisms called Archaea) is the presence of a nucleus, a double membrane-bound control center that separates the genetic material, DNA (deoxyribonucleic acid), from the rest of the cell.
* Ribosomes of Cells *
Ribosomes are cellular organelle that are not bound by a membrane. They are the protein factories of the cell, translating the genetic instructions in polypeptides. Ribosomes are found floating in the cytoplasm and also attached to the rough endoplasmic reticulum. (They are what makes it “rough”).
* Sources *
Bauman, R. (2005) Microbiology. Pearson Benjamin Cummings.
Starr, C. & Taggart, R. (1992) Biology: The Unity and Diversity of Life. Wadsworth Publishing.
