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 get it together.
Growth and development: the difference between concepts
These two biological processes are closely interconnected. Plant growth and development are the changes that occur to them. What is their difference? Growth is the quantitative increase in the entire 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, there is a complication in the structure of organisms. In a multicellular organism, this occurs through differentiation, which manifests itself in an increase in the diversity of organelles.
Growth processes are closely interlinked. The fact is that some stages of plant development cycles and the processes of vital activity accompanying them can occur only at certain sizes of organs.
During sexual reproduction, a new organism develops from a zygote - a fertilized egg. This structure is not specialized. It divides many times with the formation of 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 location.
The concept of phytohormones
Plant growth and development are determined not only by the size of the body. These processes are regulated by special chemicals - phytohormones. Depending on the composition and structure, they can influence plants of a different nature. 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. Just some of them are more saturated with substances compared to others. So, a high concentration of cytokinins is observed in the roots and seeds, and gibberellins in the leaves. But the effect of hormones is the same for all parts of the organs. Synthesizing in one of them, they are transported to others.
Educational fabric
Growth, and therefore the development of plants, is ensured by the activity of educational tissue, or meristem. Its cells have a polygonal shape, a large nucleus, numerous pores in the membrane and ribosomes in the cytoplasm.
Depending on the origin, general and special educational tissues are distinguished. The first develop from a seed germ. Their cells constantly divide and give rise to apical or apical meristems. And already from it the epidermis, parenchyma and procambia develop.
In addition to apical, depending on the location of the meristem, there are lateral (lateral), marginal (marginal) and intercalary. The latter provide intercalary growth. In the division of cells of the intercalary educational tissue, an extension of the internodes of the stem and the development of leaf petioles occur.
Stages of Plant Development
Each plant organism, like all living things, is born, grows and dies. Such development is called individual. It distinguishes several phases:
- seed at rest;
- from seed germination to the onset of the first flowering;
- from the first to the last flowering;
- from the last flowering to dying.
In representatives of different systematic units, the duration of the stages of plant development differs significantly. For example, sequoia lives 3 thousand years, and milk vetch - 3 years.
The historical development of plants is associated with evolutionary processes taking place on the planet. The first plants to appear on Earth were algae. Over time, the climate has changed significantly. The result was a "exit" of plants to land. So the higher spore plants appeared - mosses, crowns, horsetails and ferns. From them came modern seed plants.
From seed to bloom
In perennial plants, growth occurs rhythmically. This is due to seasonal changes in nature. In winter or during drought, plants are at rest. This applies not only to deciduous species, but also to evergreens. The development of flowering plants begins with the germination of a seed, which can be at rest even for several years. Their development is associated with the onset of favorable conditions. For the seed to sprout, moisture, heat and air are needed. First, it absorbs water and swells. Then a root begins to appear, which fixes the future plant in the soil. Then the shoot sprouts. 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 heat. Winter species require freezing temperatures.
Life cycle
Spore plants are characterized by a repetition of developmental stages. Consider this process with the example of mosses. In the life cycle of the development of plants of this department, the gametophyte predominates - the sexual generation. It is represented by a green leafy plant that attaches to the substrate with the help of rhizoids. Over time, a sporophyte forms on the gametophyte. It consists of a box with spores on the leg. Such a structure is short-lived and exists only during the growing season. So they call the season, favorable for the growth and development of plants.
When spores mature, they spill out into the soil. Of these, the gametophyte develops again. Gametangia with germ cells are formed on it. Further, with the help of water, fertilization occurs, the result of which is a sporophyte. The development cycle repeats again.
So, growth and development are interconnected processes. They are characteristic of all living organisms. Growth refers to quantitative changes that are manifested in an increase in the size and volume of the plant as a whole and its individual parts. Development is called qualitative change. This property is manifested in the specialization and differentiation of cell structures.