PLANT LIFE CYCLE: STAGES AND THEIR CHARACTERISTICS - BIOLOGY - 2025

The life cycle of plants describes the different stages that these living beings go through from the beginning of their life until it ends. It begins with a seed that germinates and continues with a small plant that develops roots.

Unlike humans, who can reproduce sexually in only one way, plants are capable of reproducing by various methods, both sexual and asexual.

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The asexual reproduction of plants requires a single parent, that is, a plant gives rise to another genetically identical plant, so in this case, we are not talking about "males" or "females".

The sexual reproduction of plants, on the other hand, always requires two different parents, usually a " male " vegetable and a " female " vegetable, who mix their genes to produce genetically different offspring of both.

In the plant kingdom, the same plant that reproduces asexually at one time can do so sexually at another time, but that depends on several factors that we will not mention in this text.

However, there are also plants that reproduce exclusively sexually or exclusively asexually.

The sexual reproduction of many plants is usually related to special structures with which we are very familiar: flowers and seeds. The plants in whose sexual reproduction we see these structures belong to a large group known as the angiosperms or flowering plants.

Life cycle of a flowering plant (sexual reproduction)

1- A seed that germinates

The life cycle of almost all flowering plants begins with a seed, but what is a seed? A seed is the structure where the embryo of a plant is enclosed, which we can identify as a "baby plant".

This embryo is the result of the fusion of two very special sex cells: a pollen grain (microspore) and an ovum (megaspore), which are equivalent to the sperm and ovum of animals.

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The seeds generally contain enough food to maintain the life of the embryo inside them until the external conditions are suitable for their germination. In addition, they also have a resistant cover, which we call the seminal cover, which protects everything that is inside.

It is important that we comment that there are other plants that do not have flowers and whose sexual reproduction does not begin with the germination of a seed, but of a very small spore.

- The dispersion

The seeds can be dispersed over great distances in different ways. Some are transported inside fruits, which can be uprooted from the plants by different animals, which can eat them and disperse them with their waste or water them wherever they go.

Others are spread by the wind or by water and others are spread by birds, insects and mammals. Human beings also participate in the dispersal of seeds and normally we use them to grow the food that sustains us on a daily basis.

- Germination

Once the seeds of a plant reach their final destination, they can germinate, that is, the embryo inside receives certain signals from the outside and begins to grow.

Among these signs we can mention the presence of water, sunlight, oxygen and the right temperature, although these vary depending on the type of plant.

When the embryo begins to grow, it begins to "push" the seminal cover until it breaks it and leaves it.

Normally, the first thing we see when a seed germinates is a very tiny root. Shortly after we can see one or two simple leaves, which we call cotyledons and which will help the growing seedling to photosynthesize to feed.

2- A seedling that roots

Roots of a plant

The growth of the seedling is made possible thanks to the fact that its roots go deep into the soil and branch out in it, increasing its capacity to find and absorb water and other mineral nutrients.

It is very common for growing seedlings to “seek” to orient themselves in the direction of the sun's rays, since it is thanks to the energy contained in these that they can be fed by photosynthesis through a pigment known as chlorophyll.

3- A growing adult

As the seedling grows, it becomes an adult plant. Adult plants generally develop deeper roots, branches and new “true” leaves, increasing in size and area of ​​coverage.

Through their roots, adult plants can "suck" water and nutrients from the soil, driven by forces arising in the stems and leaves. These nutrients are transported to the other structures of the plant's body, in order to nourish and hydrate them.

4- A blooming adult

When an adult plant begins to flower we say that it has "entered" its reproductive stage, since the flowers (which grow at the apices or the tips of the stems) are the reproductive organs of plants, as are the genitalia in humans.

There are different types of flowers: some are male and others female, while there are others that are hermaphrodites, that is, they are both male and female. Hermaphrodite flowers are very common and are generally made up of the same basic elements:

- a " foot " or stem that supports the entire structure, - some petals that have different colors, with which they “seek” to attract the animals that help pollination (usually insects and birds), - Stamens, formed by filaments and anthers, which are the sites where pollen is produced by meiosis, so we could say that they are the "male" part of the flower and

- a pistil, made up of a stigma, a style and an ovary, which are the sites where pollen grains are received, the channel through which they germinate and the container that contains the ovules (produced by meiosis), respectively. We can say that this corresponds to the "feminine part of the flower".

Some flowers also have a kind of "containers" in which they produce sugary substances, which attract the attention of the insects that pollinate them and can be seen as a "reward" for them.

5- A flower that pollinates

The process of transferring pollen from the stamen of one flower to the stigma of another is called pollination. This depends, to a great extent, on those insects, birds or other animals that visit the flowers and take the pollen with them, leaving it "by accident" on other flowers they visit.

This can also occur without the participation of another living organism, but it can occur through wind or water, for example.

Pollination usually leads to the germination of one or more pollen grains on the stigma, which produce a tube that "grows" until it reaches the ovary and the ovules inside.

Through this structure, known as the pollen tube, the pollen grains discharge their internal content into the ovules. Let us remember that both pollen grains and ovules have half the genetic load of the plant that gave rise to them.

When the nucleus of a pollen grain fuses with the nucleus of an ovum through fertilization, the genetic load is restored in a cell known as a zygote, from which an embryo is formed.

6- The cycle that begins again

The embryo produced by sexual reproduction is "sequestered" inside a seed and, sometimes, inside a fruit.

The cycle begins again when this seed is dispersed in some way, reaches the soil and the right conditions and germinates, leaving a new seedling with the characteristics shared between two different plants.

The plant that gave rise to this seed can die after reproducing, but it can also continue to live and carry out many other flowering and fruiting cycles, as is the case with perennial fruit trees, for example.

Life cycle by asexual or vegetative reproduction

Unlike what we just studied, the asexual reproduction of plants, also known as vegetative reproduction, does not involve the production and germination of a seed.

Instead, many plants develop special structures that help them multiply in a short time and without the need for two different parents; the result of this multiplication is a group of genetically identical individuals, often called clones.

Thanks to sexual reproduction, a plant that is adapted to a relatively stable environment can multiply rapidly, very "sure" that its "offspring" will also be successful in the same place.

Consider, for example, a plant that grew from a seed and now reproduces by asexual reproduction.

- This can develop horizontal “stems” known as stolons, for example, which, moving away from the plant, can develop their own roots and establish themselves as a new individual.

- It may also be the case that one of its leaves touches the ground and roots develop at the contact site, which may later make a new individual independent.

- Suppose, furthermore, that a horticulturist cuts or extracts a portion of the plant, say a fragment of the stem, and plants it in a different pot. This fragment can develop roots and become a new plant.

References

1. Bales, K. (2020). ThoughtCo. Retrieved April 26, 2020, from thoughtco.com
2. Nabors, MW (2004). Introduction to botany (No. 580 N117i). Pearson,.
3. Raven, PH, Evert, RF, & Eichhon, S. (2014). Vegetal biology.
4. Solomon, EP, Berg, LR, & Martin, DW (2011). Biology (9th edn). Brooks / Cole, Cengage Learning: USA.
5. Walbot, V., & Evans, MM (2003). Unique features of the plant life cycle and their consequences. Nature Reviews Genetics, 4 (5), 369-379.