Everything that is alive is made of one or more cells. The cell is the smallest unit of life, and there are two main types:
Prokaryotes = bacteria and their bacteria-like cousins Archaea
Eukaryotes = the more complex cells of animals, plants, fungi, protozoans, algae, and slime and water molds
Although eukaryotic cells share many characteristics, there are also specializations that make plant cells unique. The following is a rundown of the main features differentiating plant cells from other eukaryotes.
Article Summary: The cells of plants are eukaryotic, with a nucleus, a vacuole, membrane-bound organelles and a cell wall. Here's a summary of the structure and function of plant cells.
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VIDEO: How to Make a Wet Mount Slide of Elodea Plant Cells
Structures Present in Plant Cells and Absent in Animal Cells
Cell wall: Plant cells have protective cell walls, composed mainly of structural carbohydrates. The cell wall provides support, helps maintain cell shape, and prevents the cell from taking on too much water and bursting. The cell wall is not a feature unique to plants; bacteria, fungi and some protists also have cell walls. But unlike the cell walls of bacteria and fungi, plant cell walls are composed of different types of carbbohydrates—cellulose and hemicellulose—and structurally consist of three layers; an outer primary cell wall, a sticky pectin layer called the middle lamella, and a secondary cell wall, closest to the plasma membrane.
Central vacuole: The central vacuole takes up most of the space within a plant cell. Defined by a membrane called the tonoplast, the central vacuole functions as a holding tank for water and other molecules used by the cell. When full of water, the vacuole presses the other cell contents against the boundary of the cell.
Chloroplasts: These double membrane bound organelles contain the green pigment chlorophyll, which captures sunlight energy, so that the cell can produce its own food, a process called photosyntheses. Chloroplasts are just one type of plastid organelle common to plant cells. Some plastids function in food storage; others house different types of pigments that impart colors other than green to plants.
Structures Shared by Most Eukaryotic Cells
The presence of membrane-bound organelles is a defining characteristic of eukaryotic cells. Organelles, which are enclosed by the same type of material as the plasma membrane, divide the cell into different functional areas. The following are components of the endomembrane system of eukaryotic cells.
Nucleus: Bound by a double-layer nuclear membrane, the nucleus contains the genetic material (the genome) of the cell. It is also filled with fluid, called nucleoplasm and may contain one or more nucleoli--regions where ribonucleic acid (RNA) and ribosomes, the protein making machinery of the cell, are synthesized.
Endoplasmic reticulum: This network of hollow tubes extends off the nuclear membrane, and comes in two forms; rough endoplasmic reticulum, which is studded with ribosomes and produces protein molecules and smooth endoplasmic reticulum, which has no ribosomes, and is involved in making and transporting of lipids.
Vesicles: These small shipping organelles are spheres of membrane that break off from the plasma membrane or from membrane-bound organelles to ship materials into, out of, or within the cell.
Lysosomes: This special type of vesicle contains enzymes that can break down organic materials. Lysosomes are produced by the Golgi apparatus and function in cellular digestion as well as recycling broken cellular components.
Peroxisomes: These vesicles, derived from the endoplasmic reticulum, contain enzymes that break down free radicals and hydrogen peroxide that can be dangerous to the cell.
Golgi body: In addition to making lysosmes, the Golgi body (also known as the Golgi apparatus) packages and ships materials out of the cell.
Plasma membrane: This membrane—made mainly of phospholipids, proteins and sterols—is found in all eukaryotic cells, and serves as a barrier between the inside and the outside of the cell.
Other Eukaryotic Cell Components and Organelles
Mitochondria: Tiny powerhouses of the cell, these double membrane-bound organelles transform food energy into ATP (adesnosine-5’- triphosphate), an all-purpose cellular energy nucleotide, analogous to a rechargeable battery, that can be used for work within the cell.
Cytoplasm: The contents of the cell, between the nucleus and plasma membrane, consist of a gel-like fluid in which the organelles are suspended.
Cytoskeleton: This network of filaments and tubules spans the interior of the cell. The cytoskeleton provides support, anchors organelles, and helps with transport of materials within the cell.
Centrosomes: In plants cells, the centrosome does not contain centrioles like in animal cells, but does function to build microtubules (a component of the cytoskeleton) and is called the microtubule organizing center.
Sources and Helpful Plant Cell Resources
Becker, W. M. et. al. (2009) The World of the Cell. Pearson Benjamin Cummings.
Campbell, N. & Reece, J. (2002) Biology, Sixth Edition. Benjamin Cummings.
Starr, C. & Taggart, R. (1992) Biology: The Unity and Diversity of Life. Wadsworth Publishing.