Floors

We explain everything about plants, their classification, parts, reproduction and other characteristics. Also, what is photosynthesis.

What are plants?

The plants are living beings members of the plant kingdom or phylum plantae . These are autotrophic organisms, lacking the ability to move, and composed mainly of cellulose. Trees, weeds, grass, algae, and shrubs are all members of this kingdom of life.

What we know today as plants descended from the first eukaryotic and photosynthetic algae that appeared on Earth approximately 1.5 billion years ago : Primoplantae (Archaeplastid), product of the symbiosis between a eukaryotic protozoan and a cyanobacteria.

From this ever closer collaboration the first chloroplast arose and the possibility of photosynthesis as an energetic process. Thus, these primitive algae conquered the sea and then colonized the land, where evolution made them into ferns, bushes, trees and the other plant forms that we know today.

So, Although they originated in water, plant species exist in practically all habitats of the world, as long as there is water and sunlight. Even in hot deserts (such as the Sahara) and frozen deserts (such as Antarctica) plant species adapted to adverse climatic conditions can be found.

General characteristics of plants

Three common and fundamental traits characterize plants, shared by all species of the kingdom without distinction:

• Autotrophic nutrition. Which means that they generate their own food from inorganic matter (water and substances from the soil and air) and sunlight (ultraviolet radiation). This complex process of manufacturing carbohydrates is known as photosynthesis.
• Absence of locomotion. That is, they are beings incapable of moving at will (unlike animals). Some of them change their habitat at the mercy of the waters (algae and other aquatic plants).
• Cells equipped with a cell wall. That is, their cells have a rigid cellulose structure that covers their plasma membrane, giving them hardness and resistance, but making the growth process slower and more complicated.

Types of plants

In general, it is possible to differentiate plants in two large groups: 1) green algae and 2) terrestrial plants . The first group is much earlier than the other evolutionarily, and for that reason some scholars include them within other kingdoms of life; but when they carry out photosynthesis, they act fundamentally like plants.

Terrestrial plants, at the same time, are divided into two different categories:

• Vascular land plants Known as “higher plants”, they have a complete body structure: stems, roots, leaves and internal transport mechanisms (vascular mechanisms) that connect their organs and travel the distance of their stems. At the same time, the upper floors are divided into:
  • Pteridophytes Higher seedless plants, commonly known as ferns. They have long, curled leaves known as fronds, and can grow to a considerable size.
  • Spermatophytes Higher seed plants, later than ferns on the evolutionary tree. This group is made up of angiosperms (plants with showy flowers and lots of pollen) and gymnosperms (woody plants), and is the predominant group on the planet.
• Non-vascular land plants Plants that do not have internal vascular structures, so they do not have a clear division between stem, root and leaves, nor do they reach much size. They are a group halfway between ferns and algae, like bryophytes, for example, commonly known as moss.

Parts of a plant

Depending on the type of plant, it may have one or other structures. But broadly speaking, plants are made up of:

• Root The fundamental organ of all types of plants, which serves to absorb water and nutrients from the medium in which they are found, whether liquid or solid. Generally the roots do not usually see the light, and they grow rhizomatically, that is, in a disorderly manner. In addition, nutrients and emergency substances are usually stored in their structures.
• Stem The stems are aerial extensions of the plant, which grow in the opposite direction from the root and generally have a system of conductive vessels to transport sap and nutrients to other organs, such as the leaves. Furthermore, the stem provides structural support to the organism, since in the case of trees (there they would no longer be called stems but trunks), branches arise from it, which are nothing more than secondary forks of the stem.
• Leaves Organs of different shape (round, elongated), color (between green and red) and texture in which photosynthesis takes place. They arise from the stem or branches, and depending on the plant species, they can dry out and fall when the cold arrives (autumn) to reduce the tree's water loss, or not.
• Flowers These are the reproductive organs of plants, from which fruits and seeds are then generated. They are generally composed of stamens (male sexual organs) and pistils (female sexual organs), although there are plants of a single defined sex. And plants, too, never bloom, since their reproduction occurs in another way. Flowers have attractive smells and colors, whose function is to attract animals (such as bees or certain birds), so that they serve to transport pollen from one flower to another, thus allowing insemination and genetic exchange between plants.
• Seeds Once the flowers are fertilized, the plants produce seeds, which are embryos ready to produce a new individual. Sometimes these seeds are produced without the need for flowers and fertilization, it all depends on the species. Likewise, some seeds come covered in fleshy things known as fruits, while others simply fall into the environment, or do so wrapped in different forms of protection and transport.
• Fruits Fleshy or dry coverings of the seeds of a plant, generally nutritious, thus guaranteeing the embryo fertile support for its germination when it falls or, on the contrary, helping it to move away from the shadow of the parent, when they are eaten and then defecated by some animals.

Importance of plants

Plants are essential for life on the planet as we know it, since are responsible for the oxygenation of the atmosphere without which the organisms we breathe would suffocate.

Besides, They are the first link in the food chains both terrestrial and marine (producing organisms), since they feed on inorganic matter and a source of energy (sunlight), thus feeding herbivores or primary consumers.

On the other hand, plants fix carbon from the atmosphere in their organisms since they consume CO₂ atmospheric, which if accumulated would increase the greenhouse effect and global temperature because they block heat radiation away from the planet. Seen this way, plants are the planet's cooling mechanism .

Plant photosynthesis

Plants make their own sugars or starches, that is, their own carbohydrates necessary to grow and maintain themselves, from the transformation of inorganic matter. This is its main metabolic activity and is called photosynthesis.

It consists of taking in carbon dioxide (CO₂) from air, soil water or other physical media, and photons from ultraviolet radiation from sunlight, in order to activate a chemical reaction that generates carbohydrates and underproduces oxygen expelled back into the atmosphere.

Every year plants convert about 100,000 million tons of carbon through photosynthesis, returning to the air the oxygen that living beings require to breathe.

Plant reproduction

Plants reproduce both sexually and asexually, but their exact mechanisms for doing so generally depend on the species.

sexual reproduction . It occurs in species that have flowering, since the sexual organs are found in the flowers. Some plants are hermaphrodites (they have both sexes) while others have a defined sex.

In both cases, pollination is required: the exchange of pollen grains from the male to the female organs (from the same plant or a different one) to fertilize the ovules within the pistil. This insemination can occur through the action of the wind or animals that feed on the flowers, such as bees.

Subsequently, a seed (a fertilized ovule) is formed and around it a fruit of some type, which contains the embryo ready for a new individual to germinate, when the external conditions are favorable.

Asexual reproduction. This mode of reproduction does not require flowers or pollination, but rather uses other parts of the plant. These mechanisms lack genetic variability and produce clonal individuals, rather than original individuals. There are various asexual modes of plant reproduction, such as:

• Stolons The plant produces horizontal stems, at the end of which a new plant emerges, connected to its parent as by an umbilical cord. Upon coming into contact with the soil, the new plant forms its own roots and begins to break the stolon to gain its autonomy.
• Rhizomes These are underground stems that the parent creates and that move away from it until allowing a new sprout, however keeping all the individuals connected, like a colony. This makes it difficult to distinguish between the first generation of individuals and the second.
• Tubers Another type of underground stems that the parent generates, sometimes through seeds, and which then thicken, storing nutritional substances, until new individuals germinate, which then sprout from the earth.

Continue in: Plant reproduction

Plant stratification

In the environment where various plant species proliferate, There is an organization of plant “layers” known as strata vegetables. This allows plants to be distributed in different ecosystems within the same environment, allowing trees, shrubs and grasses to coexist without competing fiercely.

The first layer is closest to the ground, where herbs and grasses grow to a low height. Higher up the bushes rise, in the second layer, already equipped with a firm stem and suspended above the ground. Above them is the third layer, made up of trees that rise several meters from the ground.

Environmental problems

Plants often face various environmental problems caused by humans. For example, monoculture impoverishes the soil the contamination of the latter with heavy chemical elements, forest fires or deforestation for industrial purposes (to obtain wood, paper or arable land).

These are some of the inconveniences that our lifestyle causes them daily, often causing irreparable damage to the plant community or damage that will take many years to repair, much longer than the few moments it took to cause it.

References

• “Plantae” on Wikipedia.
• “The kingdom of plants. Its characteristics and classification” (video) in Happy Learning Spanish.
• “Plants” in Ecology Today.
• “Kingdom Plantae” in BioEncyclopedia.
• “Photosynthesis” (video) on Khan Academy.
• “Plant (organism)” in The Encyclopaedia Britannica.