We explain what a plant cell is, its classification, its parts and the types that there are. Also, its differences with an animal cell.
What is a plant cell?
The plant cell is one that makes up many of the tissues of the organisms belonging to the kingdom Plantae, that is, the plants. Plant cells, like animal cells, are eukaryotes, so they have a core defined (in which the genetic material is found), a cell membrane and different organelles located in the cytoplasm.
However, although they share some characteristics, a typical plant cell is perfectly differentiable from an animal. These differences are not only due to morphological criteria, due to the structural needs of plants, but also to the functions they perform and the type of metabolism they own. The plant cell has distinctive structures that allow it to carry out the process of photosynthesis.
All organisms belonging to the plant kingdom are photoautotrophs, that is, they are capable of synthesizing their own food through photosynthesis. During this process, from inorganic material (Water, carbon dioxide) and the use of Energy of Sun, the plants elaborate organic material (glucose) that they use or store, and oxygen, that they release into the atmosphere. Unlike vegetables, animals are heterotrophs, so they need to feed on others living beings to obtain its source of organic matter.
Despite this difference in the way they get their food, both plant and animal cells carry out cellular respiration, a process by which they obtain energy (ATP) from the oxidation of organic matter.
Plants evolved into various types of cells, each specialized for particular functions. Plant cells are organized into tissues, and these tissues, in turn, are organized into three tissue systems, each of which extends throughout the body. Most of the plant body is made up of the fundamental system, which has various functions, including photosynthesis, storage, and support.
The vascular system, an intricate conduction system that runs throughout the plant body, is responsible for conducting various substances, including water, dissolved minerals, and food (dissolved sugar). The vascular system also works to strengthen and support the plant. The epidermal system provides a covering to the body of the plant. Roots, stems, leaves, flower parts, and fruits are organs, because each is made up of the three tissue systems.
Plant cell types
Organisms in the plant kingdom have many different types of cells. Botanists distinguish, on the one hand, initial or meristematic cells (those found in the main centers of growth and division, where mitotic activity is constant) from differentiated cells (derived from meristematic cells) and are classified as:
- Parenchyma cells. They are responsible for the support of the body, the secretion of many compounds such as resins, tannins, hormones, enzymes and sugary nectar, from the transport and storage of substances, as well as photosynthesis itself. They are the most abundant, but the least specialized of the plant organism.
- Collenchyma cells. Endowed with only one primary wall, they are alive during maturity and are typically elongated, giving them traction, flexibility Y endurance to tissues, that is, they are plastic structural support cells. Plants lack the usual skeletal skeletal system of many animals; Instead, individual cells, including cholenchymal cells, support the plant body.
- Sclerenchyma cells. They are hard, rigid cells, whose secondary walls have lignin, making them waterproof. At maturity the plant is usually already dead, without cytoplasm, leaving only an empty central cavity. His main role is defensive and mechanical support. They can be sclereids and fibers. Sclereids are cells of variable shape, common in the shells of walnuts and in the pits of fruits such as cherries and peaches. The fibers are long tapered cells, often occurring in patches or groups, they are particularly abundant in the wood, inner bark and veins of the leaf.
- Xylem cells. They are cells that conduct water and minerals dissolved from the roots to the stems and leaves, and provide structural support. Xylem cells can be of two types: tracheids and vessel elements. Tracheids and glass elements conduct water and dissolved minerals. They are highly specialized for driving. As they develop, both types of cells undergo programmed cell death and as a result are hollow, only their cell walls remain.
- Phloem cells. They are cells that conduct food materials, that is, carbohydrates in solution that are formed in photosynthesis throughout the plant and provide structural support. They can be of two types: sieve tube elements and companion cells. The sieve tube elements are joined end to end to form long sieve tubes. The sieve tube elements are alive at maturity but many of their organelles, including core, vacuole, mitochondria and ribosomes, disintegrate or shrink as they mature. The sieve tube elements are among the few eukaryotic cells that can function without nuclei. Adjacent to each sieve tube element is a companion cell that assists in the operation of the sieve tube element. The companion cell is a complete, living cell with a nucleus. This nucleus is believed to direct the activities of both the companion cell and the sieve tube element.
- Cells of epidermis. In most plants, the epidermis consists of a single layer of flattened cells. Epidermal cells usually do not contain chloroplasts and are therefore transparent so that light can penetrate the inner tissues of stems and leaves. In both stems and leaves, photosynthetic tissues are found under the epidermis. The epidermal cells of the aerial parts secrete a waxy cuticle on the surface of their outer walls; This waxy layer greatly restricts water loss from plant surfaces.
- Peridermis cells. They are the cells that form several thick cell layers under the epidermis to provide a new protective covering as the epidermis is destroyed. As a woody plant continues to increase in girth, it sheds its epidermis and exposes the peridermis, which forms the outer bark of the older stems and roots. They form complex structures composed of cork cells and cork parenchymal cells. Cork cells die at maturity, and their walls are covered with a substance called suberin, which helps reduce water loss. Cork parenchymal cells function primarily as storage.
Parts and functions of a plant cell
A typical plant cell is made up of:
- Plasma membrane. Like all cells, plant cells have a membrane composed of a double layer of lipids Y protein that distinguishes the inside of the cell from its outside, and allows them to maintain their pressure ranges and pH. Besides, the plasma membrane regulates the entry and exit of substances between the inside and outside of the cell.
- Cell nucleus. Like all eukaryotic cells, plant cells have a well-defined cell nucleus, where the genetic material is found (DNA) organized in chromosomes. The main function of the nucleus is to protect the integrity of DNA and control cellular activities, which is why it is said to constitute the control center of the cell.
- Cellular wall. Plant cells have a rigid structure that lines the plasma membrane, composed mainly of cellulose, whose function is to provide protection, rigidity, support and shape to the cell. Two walls can be distinguished: a primary and a secondary, separated by a structure called the middle lamella. The presence of the cell wall prevents the growth of the cell as such and forces it to thicken, depositing cellulose microfibers.
- Cytoplasm. Like all cells, the cytoplasm is the interior of the cell, and is composed of the hyaloplasm or cytosol, an aqueous suspension of substances and ions, and cell organelles.
- Plasmodesmata. They are the continuous units of cytoplasm that can cross the cell wall and connect the plant cells of the same organism, allowing communication between cell cytoplasms and the direct circulation of substances between them.
- Vacuole. It is present in all plant cells, and it is a group of closed compartments without a defined shape surrounded by a plasma membrane called the tonoplast, which contain Water, enzymes, sugars, salts, proteins, pigments and metabolic residues. In general, mature plant cells have a large vacuole, which can occupy up to 90% of the cell volume. The vacuole is a multifunctional organelle that participates in the storage of substances, digestion, osmoregulation and the maintenance of the shape and size of plant cells.
- Plastos. They are organelles that are responsible for the production and storage in the cell of essential substances for primordial processes, such as photosynthesis, the synthesis of amino acids or of lipids. There are different types of plastos, including:
- Chloroplasts. They store chlorophyll (responsible for the characteristic green coloration of plant tissues) and constitute the organelle in which photosynthesis takes place.
- The leukoplasts. They store colorless substances (or little colored), and allow the conversion of glucose into more complex sugars.
- Chromoplasts. They store pigments called carotenes, which determine, for example, the color of fruits, roots and flowers.
- Golgi apparatus. It is a set of flattened saccules surrounded by a membrane, which is responsible for the processing, packaging and transport (export) of different macromolecules, like proteins and lipids.
- Ribosomes. They are macromolecular complexes of proteins and RNA, located in the cytoplasm and in the rough endoplasmic reticulum, where protein synthesis occurs from the information contained in DNA. Is Genetic information it leaves the nucleus in the form of mRNA (messenger), and reaches the ribosome where it is "read and translated" into a specific protein.
- Endoplasmic reticulum. It is a complex system of cell membranes that encompasses the entire cell cytoplasm of eukaryotes, in the form of flattened sacs and interconnected tubules that continue with the nuclear membrane. The endoplasmic reticulum is usually divided into two parts that have different functions: the smooth reticulum, involved in lipid metabolism, calcium storage and cell detoxification, and the rough reticulum, on whose surface multiple ribosomes are embedded, and which it is responsible for the synthesis of certain proteins and some modifications on them.
- Mitochondria. They are large organelles present in all eukaryotic cells, which function as the energy center of the cell. In mitochondria, the cellular respiration, by means of which the cell manages to generate the energy (ATP) it needs for its functions.
Animal cell
Animal cells, unlike plant cells, do not have a cell wall (which makes them more flexible) or plasmodesmata, or a central vacuole (they usually have several much smaller vesicles). They also do not have any plastids, which makes sense if we remember that they do not photosynthesize.
Just as there are organelles that are exclusive to plant cells, there are others that are only present in animal cells, depending on their metabolic requirements and needs. This is the case, for example, of centrioles, peroxisomes and lysosomes. In some cases, animal cells are provided with cilia and flagella to move about, something that plant cells do not have.
It is worth clarifying, however, that when dealing with eukaryotic cells, plant and animal cells have structures in common: they both have a cell nucleus (which houses DNA), plasma membrane, cytoplasm, free ribosomes and membranous organelles in common, such as the apparatus of Golgi, the smooth and rough endoplasmic reticulum and the mitochondria.