Living things are made of cells, the most basic unit of life. All cells fall into one of two major classifications. They are either prokaryotic or eukaryotic.
Prokaryotic cells are evolutionarily ancient and of simple construction, containing no nucleus or membrane-bound organelles. Modern day bacteria (Eubacteria) and bacteria-like Archaea are prokaryotic organisms.
Eukaryotic cells (Eukarya) are more complex, having evolved from a prokaryote-like predecessor. Most of the living things that people are familiar with (including the human body) are composed of eukaryotic cells. Both animals and plants are eukaryotes.
General Features of Eukaryotes
Eu = “true”, karyon = “nucleus”
Nucleus: The most noticeable feature that differentiates these more complex cells from prokaryotes is the presence of a nucleus, a double membrane-bound control center separating the genetic material, DNA (deoxyribonucleic acid), from the rest of the cell.
Membrane-bound organelles: Eukaryotic cell structure also include internal membrane-bound organelles. Organelles, such as mitochondria and chloroplasts, are believed to have evolved from prokaryotes that began living symbiotically within eukaryotic cells. These vital organelles are involved in metabolism and energy conversion within the cell. Other cellular organelles carry out the many additional functions required for the cell to survive, thrive, grow and reproduce.
Being eukaryotes, the cells of plants and animals have much in common. Both types of cells have a nucleus, membrane-bound organelles, ribosomes, and cytoskeleton.
Differences between Plant & Animals Cells
Cell wall: Plants have a cell wall beyond their plasma membrane which provides support and shape to the cell. The cell wall prevents the plant cell from taking on too much water through osmosis, and exploding when in a hypotonic environment. Animal cells are bound only by a plasma membrane, and if placed in a hypotonic environment, are prone to explode. Bottom line – plants have cell walls, animals don’t.
Chloroplasts: Plants are autotrophs, meaning that they make their own food from sunlight, water and carbon dioxide. In order to capture sunlight energy, plants have special organelles called chloroplasts which contain the pigment chlorophyll. Chlorophyll is able to capture energy from red and blue wavelengths of light. The leaves of most plants appear green, because chlorophyll is unable to capture green light, and instead reflects it. Animal cells are not able to capture sunlight energy. Animals are therefore heterotrophs, and must get their food directly or indirectly from plants. Bottom line – plants have chloroplasts, animals don’t.
Cytokinesis: All cells must divide in order to reproduce. Because plant cells have a cell wall, they can’t for ma cleavage furrow and pinch in half when dividing, like animal cells do. After duplicating and separating the genetic material, a plant cell builds a cell plate in the center of the dividing cell, which, when finished, becomes the cell wall between the two daughter cells. Bottom line – plant cells divide by building a cell plate. Animal cells divide by forming a cleavage furrow.
Centrioles: 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. Bottom line – for microtubule production, animal cells have centrioles. Plant cells have MTOCs.
Additional Cell Biology Information
To learn more about eukaryotic cellular structure and function see the Virtual Cell Biology Classroom.
Bauman, R. (2005) Microbiology. Pearson Benjamin Cummings.
Starr, C. & Taggart, R. (1992) Biology: The Unity and Diversity of Life. Wadsworth Publishing.