Eukaryotic Cell

Eukaryotic cells are those cells, which are complex and larger than the prokaryotic cells. The term eukaryote is derived from the Greek word- “eukaryote” meaning true or good nuclei. This cell includes all life kingdoms except monera. Eukaryotic cells can be easily distinguished through a membrane-bound nucleus. The life, which is present and visible by our naked eye, is all made up of these cells. Eukaryotic cells are membrane-bound organelles, which have a multiple membrane-bound organelles to carry out specific cell tasks. They have different internal membranes, which are known as organelles. These organelles play a vital role in cell maintenance and other functions. These organelles generally consist of cell wall, plasma membrane, nucleus, mitochondria, chloroplasts (plastids), endoplasmic reticulum, ribosome, Golgi apparatus, lysosomes, vacuoles, cytoplasm and chromosomes.

Parts of Eukaryotic Cell and their Functions

Cell wall: It helps in protecting the plasma membrane and plays a vital role in supporting and protecting the cells. It is a thick outer layer made of tough cellulose. Cell walls are present in plant cells and are absent in animal cells.

Plasma membrane: The plasma membrane is present in animal cells, plant cells and even in eukaryotic cells. It is a double layered, thin barrier, surrounding the cell that controls the entry and exit of certain substances. It also refers to a thin, fluid entity that manages to be very flexible and it is stable. It is also called as cell membrane. It is the living ultra thin biological membrane ranging from 6 to 8nm and composed of a dynamic layer that chemically comprises a molecule of lipids and proteins that are arranged in a fluid mosaic pattern. It acts as a protective barrier. This membrane plays a vital role in:

It acts as a boundary and separates the internal and external organelles of a cell. 

• Transportation of materials.
• Cell to cell recognition.
• Enzymatic activity.
• Signal transduction.

Nucleus: It is present both in animal cell and in plant cells. It is large and present in the center of a cell. It contains DNA and stores all the necessary information, which is required to control all the activities within the cell. Hence it is also called as a brain of the cell.

Nuclear membrane: It is a double layered, which surrounds the nucleus and helps in the entry and exits of material into the nucleus. It also separates the nucleus from the other parts of the cell.

Nucleolus: It is present in nucleus of both plant cell and animal cell. It plays a vital role in the synthesis of RNA and in the formation of the ribosome.

Mitochondria: The organelles that convert energy into usable forms, which are used by the cell to perform their cellular functions. They are double membranes, semi-autonomous organelles. This organelle plays a vital role in generating and transforming the energy. Albert von Kolliker recognized the structure of the mitochondria in the year 1880. It is a powerhouse of the cell, which produces energy by breaking down fats and carbohydrates. Mitochondria play a vital role in:

• The most important function of the mitochondria is to produce energy. 
• It converts glucose to ATP.
• Helps in cellular respiration.
•  It synthesizes ATP from the breakdown of sugars, fats and other fuels in the presence of oxygen.
• It plays a vital role in oxidative phosphorylation.

Chloroplast: They are the sub cellular sites of photosynthesis. Chloroplasts were discovered early in the 17th century and were identified by a scientist named Antony van Leeuwenhoek and by another scientist named Nehemiah Grew. Chloroplasts are important because, if there were no chloroplasts, plants cannot produce oxygen, sugars and starches, which other animals use and eat. They also produce energy in the daylight.  They are present only in plant cells and are absent in animal cells. Chloroplasts are also found in chlorophyll bacteria, blue-green algae, etc. It is a site for photosynthesis.  

Endoplasmic reticulum: It helps in movement of materials around thecell. Its main functions are storage and secretion. It is of two types:-

Rough endoplasmic reticulum - it manufactures proteins.

Smooth endoplasmic reticulum - it contains an enzymes that helps to build molecules.

Ribosome: They are biological molecule, which are composed of proteins and RNA. It is complex and smallest organelle in the cell. It plays a vital role in synthesis millions of protein, which are required for cells to perform several activities. These organelles are present in all animal cells and absent in plant cells.

Golgi Bodies: They are sac like structures, which are specifically used for storing or preserving all the substances made by the cell. It helps in the movement or transportation of materials within the cell and in synthesis of plant cell wall; hence it is also called as the post office of the cell. It also plays a vital role in the modification, transportation and processing of macromolecules, which includes proteins and lipids. These organelles are present in all animal cells and absent in plant cells.

Lysosomes: They are spherical organelles, which contains enzymes that help in maintaining the physiologic turnover of cellular constituents. These organelles are present in all animal cells and absent in plant cells. They play a vital role in breaking the food materials and making it easier to digest. The size of these Lysosomes varies from 0.1 to 1.2 µm. It is also called as suicidal bags as it helps in cell renewal and break down old cell parts. Lysosomes play a vital role in:

• Removal of dead cells, hence they are named as a suicide bags.
• They protect the cell by ingestion of other dying cells or larger extracellular material like-foreign invading microbes.
• Lysosomes attacks the foreign or disease-causing agents such as bacteria, viruses, fungi, food and old organelles and break them into small pieces that can hopefully be used again.
• Lysosomes play a vital role in protecting the cell from being digested by surrounding the cell membrane. 

Vacuoles: They are vesicle that helps in the digestion. They are present both in plant cells and in animal cells. In plant cells it helps in maintaining its shape and it also stores water, food, enzymes, wastes, etc.

Cytoplasm: It refers to the jelly like material with organelles in it. It is present both in plant and in animal cells. They consist of inner region of the plasma membrane and also the outer region of DNA. The cytoplasm is made of components, which benefits the cell by keeping the organelles separate from each other. This helps to keep a cell in stable. Cytoplasm also contains some important organelles like endoplasmic reticulum, lysosomes, mitochondria and   Golgi apparatus. Along with these organelles, it also contains chloroplast in plant cells. Every organelle is bound by a fatty membrane, which have some specific functions. A cytoplasm plays a vital role in:

• Storage and manufacturing of energy.
• Maintains the cells shape and its consistency and provides suspension to the organelles.
• All types of cell functions like: cell expansion, growth and replication are carried out in the cytoplasm of a cell.
• All types of cellular activities take place in this cytoplasm.
• Cytoplasm also helps in the movement of different elements or molecules present within the cell.

Chromosomes: The term chromosome is derived from the Greek word–“Chroma” meaning colour and “Somes” meaning the body. Chromosomes are small, coloured thread like structures present in the nucleoplasm of living cells, which helps in the inheritance or transmission of characters in form of Genes from one generation to another generation.  It is made up of DNA and stored in the nucleus, which contains the instructions for traits and characteristics. A chromosome plays a vital role in:

• Self-duplication.
• They help in transmitting or transferring the characters from one generation to another generation (or) from parents to offspring.
• Controls the  biological processes in the body of an organism.
• They control cell metabolism by directing the formatting of necessary proteins.
• They help in cell differentiation during development.
• A chromosome also helps in determining a sex of an individual.

Centrosomes: They are the small hollow cylindrical shaped organelles, which are composed of nine bundles of micro tubules.  They play a vital role in cell division or in the cell cycle. Centrosomes are present only in animal cells and are absent in plant cells. Centrosomes are also called by centrioles.