Growth and development are one of the main properties of living organisms, including plants. For each systematic group, these processes have their own characteristics. From our article you will learn about the types of growth and development cycles of plants. What do these concepts mean? Let's figure it out together.
Growth and development: the difference between concepts
These two biological processes are closely related. The growth and development of plants are the changes that occur to them. What is their difference? Growth is the quantitative increase in the whole living organism or its individual parts. This process takes place throughout life. This type of growth is called unlimited. Plant development is a qualitative change. Over time, the complexity of the structure of organisms occurs. In a multicellular organism, this occurs through differentiation, which manifests itself in an increase in the diversity of organelles.
Growth processes are closely interrelated. The fact is that some stages of the cycles of plant development and the accompanying life processes can only occurwith certain organ sizes.
During sexual reproduction, a new organism develops from a zygote - a fertilized egg. This structure is not specialized. It divides repeatedly to form new cells called blastomeres. Initially, they have the same structure. But when the number of blastomeres reaches 32, their structure begins to change depending on the location.
The concept of phytohormones
Growth and development of plants are determined not only by the size of the organism. These processes are regulated by special chemicals - phytohormones. Depending on the composition and structure, they can have a different effect on plants. For example, abscisins contribute to the onset of leaf fall, auxins stimulate the growth of the root system. Under the influence of cytokinins, cells begin to divide, and the appearance of flowers is associated with the release of gibberellins.
Plants do not have special organs that secrete phytohormones. It's just that some of them are more saturated with substances compared to others. Thus, a high concentration of cytokinins is observed in roots and seeds, and gibberellins in leaves. But the influence of hormones is the same for all parts of the organs. Being synthesized in one of them, they are transported to others.
Educational fabric
Growth, and hence the development of plants, is provided by the activity of the educational tissue, or meristem. Its cells have a polygonal shape, a large nucleus, numerous pores in the membrane and ribosomes incytoplasm.
Depending on the origin, there are general and special educational fabrics. The first develop from the germ of the seed. Their cells are constantly dividing and give rise to apical or apical meristems. And already from it the epidermis, parenchyma and procambium develop.
In addition to the apical, depending on the location of the meristem, there are lateral (lateral), marginal (marginal) and intercalary. The latter provide intercalary growth. When the cells of the intercalary educational tissue divide, the internodes of the stem are elongated and the petioles of the leaves develop.
Stages of plant development
Every plant organism, like all living things, is born, grows and dies. This development is called individual. It distinguishes several phases:
- seed at rest;
- from seed germination to first flowering;
- from first to last bloom;
- from last bloom to death.
In representatives of different systematic units, the duration of the stages of plant development is significantly different. For example, sequoia lives 3 thousand years, and milk vetch - 3 years.
The historical development of plants is connected with the evolutionary processes taking place on the planet. The first plants that appeared on Earth were algae. Over time, the climate has changed significantly. The result of this was the "exit" of plants to land. So higher spore plants appeared -mosses, club mosses, horsetails and ferns. They gave rise to modern seed plants.
From seed to bloom
Perennial plants grow rhythmically. This is due to seasonal changes in nature. In winter or during drought, the plants are dormant. This applies not only to deciduous species, but also to evergreens. The development of flowering plants begins with the germination of the seed, which can be dormant even for several years. Their development is associated with the onset of favorable conditions. Seeds need moisture, heat, and air to germinate. First, it absorbs water and swells. Next, a root begins to appear, which fixes the future plant in the soil. Then the shoot grows. The required amount of heat and moisture depends on the type of plant. For example, carrot seeds germinate at 5 degrees, and cucumbers and tomatoes - at 15 degrees. Winter species require sub-zero temperatures.
Life cycle
Spore plants are characterized by the repetition of stages of development. Consider this process on the example of mosses. In the life cycle of plant development in this department, the gametophyte - the sexual generation - predominates. It is represented by a green leafy plant, which is attached to the substrate with the help of rhizoids. Over time, a sporophyte develops on the gametophyte. It consists of a box with spores on a stem. Such a structure is short-lived and exists only during the growing season. This is the name of the season favorable for the growth and development of plants.
When disputesripe, they spill out into the soil. They develop into a gametophyte. On it, gametangia with germ cells are formed. Further, with the help of water, fertilization occurs, the result of which is a sporophyte. The cycle of development is repeated again.
So, growth and development are interrelated processes. They are characteristic of all living organisms. Growth is called quantitative changes, which are manifested in an increase in the size and volume of the plant as a whole and its individual parts. Development refers to qualitative changes. This property is manifested in the specialization and differentiation of cellular structures.
