Plants constitute one of the three major groups (kingdoms) of multicellular organisms in which living beings are distributed. The other two are animals and fungi. Nearly 2000 new species are discovered each year, and to date, about 400,000 plant species have been identified.
Are plants living beings?
Yes, because they feed, develop and reproduce just like human beings. Moreover, in biology, human beings are part of the animal kingdom.
All plants, fungi, bacteria and animals are made up of cells, the “basic units” of life. The information that makes it possible to build and operate cells is contained in a molecule called DNA. Since all living things have DNA that functions in the same way, and their cells have many things in common, biologists have managed to draw a “Tree of Life”, with the bonds of kinship between all living things.
The role of plants in ecosystems
Plants are at the base of the food chain, which gives them a fundamental role in the global functioning of the biosphere. They are called “primary producers” because they are capable of producing their own organic matter through photosynthesis. Whether on land or in water, plants are at the origin of any food chain.
It is worth remembering that human life depends entirely on plants, not only for the supply of oxygen, to satisfy its energy needs in the form of fossil resources accumulated over millions of years, and to provide medicines and food.
Why plants are living beings (like human beings)
Plants perceive environmental stimuli (rain, wind, cold, heat, aggression from herbivores or pathogens, etc.) and memorize over a sufficiently long time, not really these stimuli but rather the type of reaction they should cause.
This capacity is a valuable asset that allows plants to make a final integrated response to all these stimuli and their fluctuations. If a plant perceives a stimulus to which it has previously been subjected, its response will be stronger.
Thus, gradually, over the last three decades, a hidden complexity of the plant world has been uncovered thanks to the technological advances of recent years, thanks to the obstinacy of researchers who refuse to adopt dogmatic positions. New fields of study have emerged such as plant neurobiology and plant intelligence.
The incredible capabilities of plants
We might think that when a plant is attacked by an insect it has no choice but to let itself be eaten passively. However, they defend themselves from their predators with sophisticated strategies that often involve the intervention of other species. They know how to hunt or seduce animals.
When the larvae hatch, they devour the caterpillars from the inside. Now there are no more people to attack cabbage. But seduction can take many different forms. One of the most striking examples is the Ophrys bombyliflora orchid. It produces a large petal that mimics a bumblebee and it also produces molecules equivalent to pheromones to attract real bumblebees.
An air current sent by a fan, which predicted the location of a light source, directed the pea’s growth in the right direction. A behaviour that could be described as associative learning. These discoveries are mind-boggling, but even more important than knowing the extraordinary capacities of plants would be for me to understand their different ways of functioning, as well as their specificities.
Do plants have a memory like human beings?
No, they do not have any structure that can store information. However, some experiences can be confusing. If you shake a jar of Mimosa pudica (Mimosa pudica, also known as “sensitive”), it will suddenly fold its leaves. But if this gesture is repeated five or six times in a row, the reaction disappears.
Would the mimosa have learned that being shaken is not dangerous, and would it remember that?
The answer is much simpler. When the plant detects an aggression (in this case, shaking), the calcium ions stored in its cells are released and spread from cell to cell from top to bottom, changing the so-called osmotic pressure in the cells at the bottom of the leaf.
The rapid drop in this pressure allows the leaves to close almost instantaneously.
If the mimosa is shaken several times in a row, it will eventually stop reacting because its reserves of calcium ions will be exhausted. When the stock of ions is replenished, the closing reaction will occur again.
Do the plants sleep?
Like all living beings, plants are sensitive to the alternation of day and night. They can evaluate the duration of sunshine to bloom at the right time. Thanks to this process called photoperiodism, plants called “long day” plants wait for long days to bloom, and others called “short day” plants wait for shorter ones.
This difference is due to their adaptation to the specific sunshine in their area of origin. Thus, to bloom, the bougainvillea, native to Brazil, will need longer days than the azalea, native to China and Japan. This characteristic inscribed in the genes is maintained if the plant is moved from south to north, or vice versa. In Europe, the autochthonous plants are especially sensitive to the temperature in order to initiate their bloom.
But they remain synchronized with day-night alternation: in tamarind for example, darkness stops photosynthesis, which causes a decrease in the flow of sap in its leaves and induces their folding.
Conversely, in other species such as belle-de-nuit, baobab or durian, the flowers open at night because their most effective pollinators are nocturnal: moths for the former, bats in the case of baobab and durian.
Do plants do better than animals?
Yes, they have a considerable advantage: they are autotrophic, i.e. they produce the organic matter that makes them up themselves, from water, carbon dioxide and solar energy. From an evolutionary point of view, photosynthesis is a real advantage. Our planet is essentially vegetal, since plants make up 80% of its biomass.
Far from the clichés about the green and passive plant, plant biology has been observing for the last fifteen years or so surprising faculties that were thought to be reserved for the animal world.
Plants have multiple sensory capacities that allow them to communicate with each other and with insects, to adapt to crisis situations, to memorize, and to the great surprise of researchers, their biochemical activities are linked to mysterious electrical activities.
We explain why plants are indeed living beings, which have a well-defined system of functioning.