Cell Division, Biodiversity, and Supporting Tissues in Plants
Mitosis
Mitosis is the division of the nucleus. Before starting, the DNA is duplicated to have two identical copies of genetic information. Mitosis seeks to ensure each new nucleus receives a copy of this information.
Phases:
- Prophase: The DNA condenses and forms chromosomes. The cytoplasm is organized in a system of protein tubules, which are the spindle. At the end of prophase, the nuclear membrane disappears and the chromosomes are free in the cytoplasm. The nucleolus also disappears.
- Metaphase: Each chromosome is attached to spindle fibers by a narrow zone, present in each, called the centromere. The union occurs in the middle of the spindle, forming the so-called equatorial plate.
- Anaphase: The spindle fibers break at the equatorial plane, and each chromosome is split into two chromatids. Broken spindle fibers contract and pull the chromatids toward the poles.
- Telophase: When the migration of the chromatids finishes, the remains of spindle fibers disappear, and a nuclear membrane forms around each group of chromatids. Two daughter nuclei are formed that are identical, each of which contains a copy of the genetic information of the parent cell. DNA becomes less condensed (chromatin), and chromosomes disappear.
Meiosis
- Prophase I: This is a long and complex process. The chromatin condenses and becomes chromosomes. Each chromosome is composed of two sister chromatids. It then produces a longitudinal pairing of homologous chromosomes. These couples, with their four chromatids, form a structure called a bivalent. Currently, one of the most important phenomena of meiosis takes place: crossing-over. Thanks to this, the chromatids of homologous chromosomes exchange pieces of chromosomal material. This translates into greater genetic variation in offspring, as there is a transfer of genes between both chromosomes. The points where the trading takes place are called chiasmata.
- Metaphase I: Each bivalent is located in the equator of the spindle, together with filaments of the spindle by their centromeres.
- Anaphase I: Each of the homologous chromosomes, with their two chromatids, is headed for a different pole. Thus, maternal and paternal chromosomes at the poles are distributed, but in each pole, there will be only an allocation of n chromosomes with two chromatids each.
- Telophase I: The two daughter nuclei originate from the regeneration of two nuclear membranes. Chromosomes undergo decondensation and enter a state of rest or interphase, where there is no DNA duplication. The interphase has a very short period of duration, and even in some cases may not exist.
Plasmotomy or Cytokinesis
The cytoplasm divides, allocating the cellular organelles, and produces two daughter cells. In animal cells, cytokinesis occurs by strangulation of the membrane, usually in the middle of the cell. In plant cells, it is formed in the central condensation of vesicles detached from the Golgi apparatus, causing a partition to merge, and thus, two new cells. During the period between two cell divisions, called interphase, cells grow and produce the synthesis of proteins and other organic biomolecules, as well as duplication of genetic material.
Biodiversity
Biodiversity is the variety of living organisms. This definition includes three concepts:
- Genetic diversity among individuals of a species.
- Diversity of species, which includes both the richness of species and their abundance.
- Diversity of ecosystems found on Earth.
Benefits:
- Ecological: It allows for ecosystem stability and maintenance of natural processes.
- Economic: It provides many useful products for humans, such as food, raw materials, and medicines.
- Ethical: All species deserve to survive.
- Aesthetic: The diversity of life is one of the great beauties of nature.
Biodiversity Loss Factors:
Environmental overhunting, habitat destruction, pollution of ecosystems, and introduction of alien species.
Protection of Biodiversity:
General measures and specific measures.
Supporting Tissues
The primary function of supporting tissues is giving consistency and rigidity to the plant. There are two classes:
- Collenchyma: Supporting tissue of the growing organism. Their cells are alive. It is located beneath the epidermis of herbaceous stems.
- Sclerenchyma: Supporting tissues in adult organs. These are lignified dead cells. Such cells can be:
- Fibers: Elongated cells that occur scattered or in groups in the roots, stems, etc.
- Xylem fibers: These are arranged in long lines forming part of the conducting tissue.
- Sclereids or stone cells: Short and very lignified cells can appear scattered or forming the bones of the fruit.