Plant Characteristics

A plant refers to any of the eukaryotes that belong to the biological kingdom Plantae. Plants, in the strictest sense, are embryophytes that include vascular plants, liverworts, hornworts, and mosses. Some references that are less strict considered green algae as plants. The green algae are comprised of unicellular and multicellular species that have chloroplasts and cell wall. The fundamental characteristics listed below focus on the embryophytes. They are as follows:

• Plants are autotrophs. They make their own food through photosynthesis. They are capable of capturing energy via the green pigment (chlorophyll) inside the chloroplast, and using carbon dioxide and water to produce sugars as food and oxygen as by-product. As autotrophs, plants are often placed at the start of the food chain. They are labeled as producers. They serve as food to other organisms, including animals. Animals, in contrast, are heterotrophs and they need to consume other organisms for sustenance. Some animals (particularly, herbivores) depend exclusively on plants while others eat only meat or a mix of animal or plant material. Since plants are capable of making their own food, they do not feed on animals to grow and survive. The exception is a group of carnivorous plants (e.g. Venus flytrap) that catch and feed on animal prey, especially when conditions are less favourable for photosynthesis.
• Plants are eukaryotes. Similar to animals, plants have distinct, membrane-bound nucleus inside the cell. The nucleus is an organelle that contains chromosomes that bear genes. Other organelles suspended in the cytoplasm of a plant cell are Golgi apparatus, endoplasmic reticulum, lysosomes, peroxisomes, and plastids.
• Plants have plastids. The presence of plastids inside a eukaryotic cell is an indication that it is more likely a plant rather than an animal. There are different types of plastids. Chloroplasts are plastids containing chlorophyll (green pigments) and involved in photosynthesis. Chromoplasts contain pigments apart from green and involved in the synthesis and storage of pigments. The chlorophyll systems absorb light energy at particular wavelengths of the electromagnetic spectrum. The pigments are also responsible for the coloration of plant structures (e.g. green leaves, red flowers, yellow fruits). Leucoplasts (e.g. amyloplasts, elaioplasts, proteinoplasts) are non-pigmented plastids. Their function is primarily for food storage. Plants store food in the form of sugar, e.g. starch.
• Plants have a large vacuole inside the cell. This cytoplasmic structure is involved in the regulation of turgor pressure.
• Plants have rigid cell walls apart from the plasma membrane. The cell wall confers added structural support to a plant cell. Plants may not have a skeletal system as that in animals but their cell wall is comprised primarily of cellulosic material that aids in providing structural support.
• Plants have a distinctive cell division where a cell plate (phragmoplast) separates daughter cells.
• Plants are not as motile as animals. They do not have the capacity to move from one location to another at will. As such, they have to deal with harsh conditions, such as heat. One of the ways they are able to withstand heat is through their cell walls that prevent their body from drying up. In spite of this, plants do still exhibit movement but in another form. For example, nastic movement is exemplified by the folding of the leaflets of the plant Mimosa pudica when touched and the closing of the leaf of the Venus flytrap when capturing prey. Some plants (e.g. Betula pendula – silver birch) would even droop their branches and leaves at night as if they are “sleeping”. Another form of plant movement is tropism. Tropism, though, is more of growth response to a stimulus rather than a movement. For instance, plants tend to grow towards the source of light (phototropism).
• Plants have plasmodesmata. While animals have cell junctions that hold cells in an animal tissue, plants have plasmodesmata that act as if like cell junctions between plant cells. The cell wall forms these cytoplasmic bridges between adjacent cells. These “bridges” facilitate communication between cells and allow the circulation of fluid, thereby help maintain the tonicity of plant cells.
• Plants are multicellular, being made up of many cells organized into tissues and organs that perform a specific function as a unit. Plant organs are specialized for anchorage, support, and photosynthesis (e.g. roots, stems, leaves, etc.)
• Plants are capable of unlimited growth through meristematic tissues. The tissue is comprised of indeterminate, actively dividing cells that give rise to differentiated tissues such as epidermis, trichomes, phellem, and vascular tissues.
• Plants lack sense organs but they can perceive their surroundings albeit differently. Plants can “see”, “hear”, and “smell” despite the lack of eyes, ears, and nose. They seem to “feel” and respond in ways not as obvious as in animals. Plants may not have a nervous system as that of animals but they apparently have a system of their own based on how they respond to their surroundings. Arabidopsis, for example, despite lacking eyes, possesses photoreceptor (at least 11 types) that help the plant detect light. In another example, herbivory could instigate the release of certain chemicals on the affected plant part. Plants have also been observed to release defense chemicals that deter herbivores. Tomatoes were observed to release volatile signals to warn nearby plants of an impending attack of herbivores.
• Plants reproduce by asexual and sexual means. Asexual reproduction in plants is carried out by budding, fragmentation, fission, spore formation, vegetative propagation, apomixis, etc. Sexual reproduction involves male and female gametes that fuse at fertilization. In general, the plant life cycle incorporates alternation of generations, i.e. the alternating phases of sporophyte and gametophyte.
• Plants “breathe”. Through stomata, carbon dioxide from the atmosphere enters the plant cell. Through photosynthesis, carbon dioxide is converted into oxygen, which the plant releases as a metabolic by-product into the atmosphere through the stomata.
• Plants may not have other well-defined biological systems but they produce chemicals involved in plant defense and immune functions and plant hormones that act as signaling molecules.