Plants are eukaryotes, composed of cells that have a nucleus, and membrane-bound organelles. But plants have a few different features than animal cells. Here's a summary.
Unlike animals, plants are photoautotrphs. “Photo” means that they can capture sunlight energy. “Autotroph” means that plants are able to take in carbon from carbon dioxide in the atmosphere to build their organic molecule; in short, they are self-feeders able to whip up their own grub. To accomplish this, plant cells are different from animals cells in a few important ways. The following is a list, with summaries of the different parts of a plant cell.
* Cell Wall: Structural Support of Plant Cells *
Plants have a cell wall beyond their plasma membrane. This structure surrounds the entire cell and provides support and shape. The cell wall prevents the plant cell from taking on too much water through osmosis. The pressure of the cell wall keeps a plant cell from exploding when in a hypotonic (watery) environment.
* Chloroplasts: Capture Sunlight Energy *
Plants are able to make their own food from sunlight, water and carbon dioxide. Chloroplasts are special organelles within a plant cell, which contain the pigment chlorophyll. Chlorophyll captures energy from red and blue wavelengths of sunlight. The leaves of most plants appear green, because chlorophyll is unable to capture green light, and instead reflects it back.
All cells of a plant don’t contain chloroplasts, only those that are exposed to sunlight. For example, the leaves of an onion plant are green, and are able to photosynthesize. The onion bulb and roots lie below the soil, and therefore do not contain any photosynthetic equipment.
* Cytoplasm: The Molecular Chowder *
The fluid matrix inside of all cells is called the cytoplasm. Composed of cytosol and the cellular organelles, cytoplasm fills the area between the nucleus and the plasma membrane.
* Endomembrane System: Production and Shipping Network *
Eukaryotic cells also include a system of internal membrane-bound organelles called the endomembrane system. This network, which produces and transports material within the cell, includes the:
* endoplasmic reticulum (rough and smooth), where proteins and lipids are made.
* Golgi apparatus, where cellular molecules undergo additional processing and where lysosomes are made.
* vesicles transport materials between the organelles of the endomembrane system.
* lysosomes; specialized vesicles that function to break down cellular waste.
* plasma membrane; the outer phospholiped membrane that surrounds the cell.
Since all of the endomembrane system organelles are made of phospholipids, parts of each organelle are able to break off into vesicles and travel to and fuse with other membrane bound organelles. The endomembrane system is how many materials are shipped into, out of, and around within eukaryotic cells.
* Mitochondria: ATP Energy Powerhouse *
The mitochondia are double membrane-bound organelles that function as the powerhouse of eukaryotic cells, transforming food energy into usable ATP (adenosine triphosphate) energy the cell can use to do work.
* Nucleus: Genetic Command Central *
The most noticeable feature that differentiates complex eukaryotes from more simple prokaryotic cells (bacteria and bacteria-like organisms called Archaea) 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.
* Ribosomes: Cellular Protein Factories *
Ribosomes are cellular organelles not bound by a membrane. They are the protein factories of the cell, translating the genetic instructions in proteins. Ribosomes can be found floating in the cytoplasm and also attached to the rough endoplasmic reticulum.
* Sources *
Bauman, R. (2005) Microbiology. Pearson Benjamin Cummings.
Starr, C. & Taggart, R. (1992) Biology: The Unity and Diversity of Life. Wadsworth Publishing.