Science: Building Blocks of Life: Interphase, Prophase and Metaphase (For CBSE, ICSE, IAS, NET, NRA 2022)

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Interphase

This is similar to that of mitosis except for the fact that in meiosis, it is followed by two cell divisions.

Prophase 1

  • Chromosomes condense and attach to the nuclear envelope. Synapsis then takes place and tetrads are formed, each composed of four chromatids. Crossing over of genetic material may occur during the synapsis as the chromosomes thicken and detach from the nuclear envelope.
  • Like in mitosis, also move and migrate to the poles as the nuclear and nucleoli start breaking down.

Metaphase 1

In this phase, tetrads align at the metaphase plate and the centromeres of the homologous chromosomes become oriented towards either side of the cell poles.

Anaphase 1

The chromosomes start moving to the opposite poles of the cells. The microtubules and kinetochore fibers also interact and there is movement. Unlike in mitosis, homologous chromosomes move to the opposite poles, but sister chromatids remain together.

Telophase 1

  • The spindle fibers continue moving homologous chromosomes to the poles after which either pole has a haploid number of chromosomes. Cytokines also tend to occur spontaneously.
  • Two daughter cells are formed each containing a half number of chromosomes as the original parent cell.
Telophase Buliding Blocks

Tissues

A tissue can be defined as a group of cells similar in size, shape, performing the same function and having a common origin. Plants are able to produce new tissues throughout their life. Animals can replace only some tissues under certain conditions. Muscles of heart and nervous tissue can never be formed again if damaged.

Plant Tissues

Plant tissues are of two types:

  • Meristematic tissue
  • Permanent tissue

Meristematic Tissue

They are found at the growing points of a plant such as at the tips of the roots, stems and branches.

  • They are aggregate of living cells, compactly arranged without intercellular spaces,
  • They are thin-walled and may be rounded, oval, polygonal or rectangular in shape.
  • The cells are small and have a large nucleus
  • They are capable of dividing indefinitely and add new cells to the plant.
  • They are usually found in the apices (open ends) of root and shoot.
Meristematic Tissue

Permanent Tissues

It is made up of cells, which have lost their ability to multiply. The permanent tissues are of three types.

  • Protective tissue: This tissue is made of cells with thick walls and occurs on the surface of leaves, stem and roots.
  • Supporting tissue: It provides support to various parts of the plant. This tissue includes cells that fill up the interior of potatoes, which store food; found in the leaf stalks etc.
  • Conducting Tissue: It is also called the vascular tissue. It provides passage for the fluids to move up and down in the plant. It is of two types – xylem and phloem . Xylem is located.

Animal Tissues

Animal tissues are grouped under four main categories:

epithelial, connective, muscular and nervous tissues.

Epithelial Tissue: Thin protective layer (or Generally located on the outer surface of the body, on the surface of the internal organs and the lining of the body cavities. There are three distinct types of epithelial tissues namely Squamous, Cuboidal, Columnar Epithelium layers) of cells. Epithelial tissues are formed by cells that cover surfaces (e. g. skin) and line tubes and cavities (e. g. digestive organs, blood vessels, kidney tubules and airways) . Epithelial tissue usually consists of a single layer of cells, however in certain cases there may be more than one layer. All epithelial tissues are free surfaces attached to the underlying layers of a basement membrane.

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