• THE CELL.

Cell is the smallest microscopic structural and functional unit of the human body. The cells in it are important for the function of every organ in the body. Every organ can perform normal function only with the function of this cell. There are many different types of cells in the body. Here we study about the basic cell of the body and its structure.

The components in Selma are as follows.

Cell membrane

Nucleus

Cytoplasm

Protoplasm

Mitochondria

Golgi apperatus

Ribosomes

Endoplasmic Reticulum (Smooth Endoplasmic Reticulum and Rough Endoplasmic Reticulum)

• Write the structure and functions of cell.

Cell is the basic functional and structural unit of human body. It is the main working tax unit.

A cell is known as a mass of protoplasm. Inside the cell are organelles that are covered by a plasma membrane.

A zygote is formed by the fusion of ovum and sperm in the human body. The growth and cell division of this zygote leads to the formation of the human body.

The fluid part inside the cell is known as cytoplasm. It contains many organelles.

The structure of a cell is as follows.

Plasma membrane.

The membrane surrounding the cell is called the plasma membrane. This membrane has selective permeability (movement of only selected substances). Due to which some substance can come inside the cell and some substance can go out of the cell. Thus the cell maintains the structure of its cytoplasm through this membrane.

The plasma membrane is a double layer membrane composed of phospholipids. It works to provide protection to the organelles of the cell and to maintain the shape of the cell.

the nucleus. (Nucleus)

Nucleus is located in the center of the cell. It contains a liquid called protoplasm. The nucleus is surrounded by the nuclear membrane. This membrane also has selective permeability.Nucleus membrane partially separates cytoplasm and protoplasm. Nucleus controls all the activities inside the cell and only with its help the cell can stay alive.

Inside the nucleus there are proteins like tension which are called Chromatin. This chromatin turns into chromosomes during cell division and performs the function of cell division.

These chromosomes inside the nucleus are responsible for the inherited traits of an individual. Chromosomes are found in 23 pairs in the cells of the human body. 22 pairs of these chromosomes are called ordinary chromosomes while 1 pair is called sex chromosomes.

Mitochondria. (Mitochondria)

Mitochondria is a rod shape structure. Which is located in the cytoplasm inside the cell. There is a double membrane around it, the structure of the membrane is similar to the plasma membrane. The outer layer of this membrane is a smooth layer and the inner layer has many folds. This series of folds is called cristae.

Within these cristae are enzymes that release ATP.This is why mitochondria are called the power house of the cell.

ribosomes. (Ribosome)

They are tiny granules in the cytoplasm. They are made up of proteins and RNA. It carries out the function of protein synthesis from amino acids. Some ribosomes lie free in the cytoplasm and some are attached to the surface of the endoplasmic reticulum.

endoplasmic reticulum. (Endoplasmic Reticulum)

It is a series of interconnecting membrane or channel like structures. which connects one structure of cytoplasm with another structure.There are two types of it.

1. Smooth endoplasmic reticulum..

Its surface is smooth. It functions in steroid hormone and lipid synthesis. It also helps to detoxify certain drugs.

2. Rough endoplasmic reticulum..

Its surface is rough. Ribosomes are located on its surface.These ribosomes perform the function of protein synthesis.

Endoplasmic reticulum also helps transport substances from one place to another in the cytoplasm of the cell.

Golgi apparatus. (Golgi Apparatus)

The Golgi apparatus is a bag-like structure with four to eight folds. These folds overlap each other. The end portion of this structure forms a pouch-like structure called a cisterna. Proteins synthesized by ribosomes are collected and stored in the form of secretory vesicles at the ends of these cisternae. When needed, these secretory vesicles release proteins into the cytoplasm. The Golgi apparatus is a structure located near the nucleus.

lysosomes. (Lysosome)

Lysosomes are a type of secretory vesicles that are secreted through the membrane of the Golgi apparatus. These lysosomes contain the content of certain enzymes that break down certain large molecules in the cytoplasm of the cell. It works to protect cells from foreign material and microorganisms. These lysosomes also work to remove the waste material accumulated inside the cell.

There is also a sun-shaped centrosome in the cytoplasm of the cell, which plays an important role in cell division.

Apart from this, the cyto plasm of the cell also contains a network of microfilaments and microtubules which work to maintain the shape of the cell and to protect and support the structure of the cell.

• Functions of the Cell. (Functions of the Cell)

A cell has the property of movement with the help of which the cell can move from one place to another. This function of the cell is called motile function or mobility.

The cell uses oxygen and performs cellular activity, finally the carbon dioxide accumulated in the cell goes out of the cell, thus the cell performs the function of respiration as it performs gas exchange.

The cell obtains nutrient material from the blood and performs cell activity i.e. cell nutritional function.

The waste product deposited inside the cell exits the cell through the plasma membrane thereby performing the cell excretory function.

The cell transports the nutrient materials within itself from one cell to another and from one place within the cell to another place, thus the cell also performs the function of circulation and transportation.

A cell performs the function of reproduction as it has the property of multiplying and dividing.

Due to the enzymes inside the cell, it acts to destroy micro-organisms and pathogens, thus it performs the action of phagocytosis.

Cells have the ability to receive nerve impulses and pass them on, thus performing functions of irritability and conductivity. This cell function is mainly found in nerve cells.

• cell division. (Cell Division)

Cell division means increase in number of cells. A zygote is formed mainly by the joining of ovum and sperm inside the human body. This zygote undergoes cell division and increases in number.

Cells divide and form tissue, different tissues join and form an organ, such organs combine to form a system, many such systems function in the human body and the human body is managed.

Cell division is necessary for the normal functioning of the human body. This cell division occurs mainly in two ways.

1. Mitosis. (Mitosis)

Mitosis Cell division is mainly found in all parts of the body. Which is very necessary for the growth of the body.

In mitosis cell division, two identical daughter cells are formed from one parent cell. This divided cell has the same number of chromosomes and the same number of chromosomes as the parent cell.Mitosis The process of cell division is divided into phases as follows.

Prophase.. (Prophase)

Mitosis is the first phase of cell division in which the parent cell matures for cell division. First the membrane surrounding its nucleus is destroyed and the chromatin in the nucleus is converted into chromosomes. During this time the centrosome in the cytoplasm is pulled towards the north and south poles.

Metaphase. (Metaphase)

Mitosis is the second stage of cell division. In which the centrosome is pulled more towards both the north and south poles and the chromosomes are arranged in a row between the centrosomes i.e. arranged in a rod shape.

anaphase. (Anaphase)

Mitosis is the third phase of cell division.In which centrosome filaments are pulled more towards each other, the chromosomes arranged in the rod shape in the middle divide equally towards the north and south poles and the filaments break from the middle. Hence identical chromosomes are sold with both centrosomes. Cell length also increases.

telophase. (Telophase)

Mitosis is the last stage of cell division. In which the nucleus membrane is formed towards both North and South poles. Chromosomes are arranged inside the nucleus membrane. Cytoplasm remains the same on both sides, from which all the organelles of the cell begin to form. Due to excessive stretching of the cell along its length, it breaks in the middle and two daughter cells are formed from one parent cell.

46 chromosomes are formed in both these daughter cells. Cytoplasm and all organelles are formed.

Thus, at the end of mitosis cell division, one parent cell produces two identical daughter cells. This is how cell multiplication and cell division takes place.

2. Meiosis Cell Division. (Meiosis cell division)

Meiosis cell division occurs only in the division of sex cells.

In which the fusion of male germ cell sperm and female germ cell ovum produces a new cell called zygote.This zygote contains 23 chromosomes from both male and female. Cell division of this zygote determines the sex of the child going forward. If X chromosome is received from both male and female, female child is born and if x and y chromosome are received from both male and female, male child is born.

Thus Meosis cell division determines the sex of the child which occurs only in sex cell division.

• Mutation.

When there is a change in the genetic structure of any cell, it is called a mutation.There are many reasons for this alteration.

Mutation mainly causes changes in the structure of micro-organisms and causes disease progression and pathological changes in the body.

ex. Pathogens of covid diseases often mutate and spread diseases.