Cells , and its Structure

 Cells:-

The cell is the fundamental unit of all living
organisms and is the simplest form of life that can exist as a self-sustaining unit. 

Cells are, therefore,the building blocks of the human body.
Cells in the body take many forms, the size and shape being largely dependent on their specialised function.

 For example, some cells help fight disease,
others transport oxygen or produce movement,
some manufacture proteins or chemicals, and others function to store nutrients.

Cell structure:-

 Outer part of the cell

Cell membrane:-

The cell membrane, or plasma membrane, is a fine membrane that encloses the cell and protects its contents.

This membrane is semipermeable, in that it

selectively controls the movement of molecules into and out of the cell.

 Oxygen, nutrients and hormones

are taken into the cell as needed and cellular waste, such as carbon dioxide, passes out through the membrane.

As well as governing the exchange of

nutrients and waste materials, its function is also to maintain the shape of the cell.

 Inner part of the cell

Nucleus:-

The nucleus is the largest organelle in the cytoplasm.

It acts as the control centre of the cell, regulating the cell’s functions and directing most metabolic activities. 

The nucleus governs the specialised work

performed by the cell and the cell’s own growth, repair and reproduction.

All cells have at least one nucleus at some time in their existence. 

The nucleus is significant in that it contains all the information required for the cell to function and it controls all cellular operations.

The information required by the cell is stored in DNA, the genetic material. The DNA is found in a molecule called chromatin that Nucleuscondenses

to form thread-like structures known as

chromosomes.

Chromosomes carry the genetic information in the form of genes. 

The nucleus of a human cell

contains 46 chromosomes, 23 of which are from the mother and 23 of which are from the father.

 Each chromosome can duplicate an exact copy of itself at each cell division, so that every new cell formed receives a full set of chromosomes.

Chromatin:-

Chromatin is the substance inside the nucleus that contains the DNA and some proteins.

Nucleolus:-

The nucleolus is a dense spherical structure inside the nucleus, which contains ribonucleic acid (RNA)

structures that form ribosomes.

Nuclear membrane:-

Surrounding the cell nucleus is a double-layered membrane called the nuclear membrane, or nuclear envelope. 

This membrane separates the nucleoplasm,

or fluid inside the nucleus, from the cytoplasm, or fluid outside the nucleus.

The function of the nuclear membrane is to regulate the materials that enter or exit the nucleus.

Nuclear pores are tiny passageways through thenuclear membrane. 

They have a sophisticated biological entry and exit control system, only permitting selected chemicals to move in and

out of the nucleus.

 Middle part of the cell

Cytoplasm:-

Cytoplasm is the gel-like substance which is enclosed by the cell membrane. 

The cytoplasm contains the nucleus and the organelles.

Cell metabolism predominantly takes place inside the cytoplasm. The cytoplasm, as part of its function, contains elements that aid metabolic operation and break down waste.

The centrosome is an area of clear cytoplasm found next to the nucleus. 

It contains the centrioles.

Centrioles:-

Contained within the centrosome are the small spherical structures called centrioles. These areassociated with cell division, or mitosis. 

During cell division, the centrioles divide and migrate to opposite sides of the nucleus to form the spindle poles.

Chromatids are pairs of identical replicated strands of a chromosome. 

They are joined at the centromere and separate during cell division.

Ribosomes:-

Ribosomes are tiny organelles made up of RNA and protein. They may be fixed to the walls of the endoplasmic reticulum (ER) or may float freely in the cytoplasm.

 Their function is to manufacture proteins

for use within the cell and also to produce other proteins that are exported outside the cell.

Endoplasmic reticulum :-
(smooth ER and rough ER)

The ER is a series of membrane tubes that are continuous with the cell membrane. 

It functions like an intracellular transport system, allowing movement of materials from one part of the cell to another.

It also links the cell membrane with the nuclear membrane and assists the movement of materials in and out of the cell.

The ER contains enzymes and helps in the synthesis of proteins, carbohydrates and lipids. 

It serves to store material and to transport substances inside the cell, as well as to detoxify harmful agents. 

Some of the ER appears smooth, while some appears rough due to the presence of ribosomes.

Mitochondria:-

Mitochondria (oval-shaped organelles) lie in varying numbers within the cytoplasm and are the site of the cell’s energy production.

Mitochondria supply the majority of a cell’s adenosine triphosphate (ATP),

a compound that stores the cell’s energy.

Enzymes are protein catalysts that speed up chemicalchange. 

Mitochondria contain large amounts of

enzymes which power the cell’s activities through cellular respiration.

Lysosome:-

Lysosomes resemble round sacs and contain powerful enzymes capable of digesting proteins. 

They are present in the cytoplasm and work to destroy partsof cells that are no longer functioning. 

This process is known as lysis.

Vacuole:-

Vacuoles are membrane-bound spaces within the cytoplasm that contain waste materials or secretions produced by the cytoplasm.

Vacuoles function as temporary storage, for transportation from one part of a cell to another, and for digestive purposes in some cells.

Golgi body/apparatus:-

The Golgi body resembles a collection of flattened sacs and is located within the cytoplasm, typically near the nucleus and attached to the ER.

 The Golgi apparatus stores the protein manufactured in the ER and later transports it out of the cell.