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Plastid : Types, Structure and Functions

Plastids are the cytoplasmic organelles which are associated with the special metabolic process of the plant cells. It is the second largest organelle of the cell which is bounded by a double unit membrane and may be colored or colorless. Mayer and Schimper first used the term plastid. Plastids are found in plant cells and some algae. It is primarily responsible for the manufacture and storage of some vital chemical substances which are used by the autotrophic eukaryotic cells. Plastids contain photosynthetic pigments for the production of glucose as energy by the process of photosynthesis with the help of sunlight and CO2.

Types of Plastid

Plastid can be divided into following types such as:

A. Chromoplasts

  • (1) Chloroplast
  • (2) Phaeoplast
  • (3) Rhodoplast
  • (4) Blue-green Chromoplast:

B. Leucoplasts:

  •  (1) Amyloplast
  • (2) Elaioplast
  • (3) Proteinoplast
image of plastid types

Types of Plastid

A. Chromoplasts

Chromoplasts: Chromoplasts (Gr. Chroma, color) are the photosynthetically active colored plastids of the plant cells.  They produce pigments and store them which are mainly found in leaves, flowers, ripe fruits and even roots of the plants. The most common chromoplasts are as follows:

(1) Chloroplast

Chloroplast (Gr. Chloros, pale green) is found in green algae and higher plants. It is the chlorophyll-bearing plastid of the plant cells which take part in the photosynthesis. It contains the pigments like chlorophyll a, chlorophyll b, DNA and RNA.

Plant cells contain many chloroplasts which are evenly distributed throughout the cytoplasm. Generally, they are found concentrated near the cell wall or the nucleus. In higher plants, chloroplasts are generally spherical or disc-shaped. The chloroplasts of some algae are in the form of stellate plates or spiral bands. The size of the chloroplasts varies from 4µm-6µm in diameter with 1 µm-3 µm in thickness.  The number of chloroplasts varies from cell to  cell. Chlamydomonas (algae) often contains a single huge chloroplast while in higher plants there are usually 30-40 chloroplasts per cell. Generally, chloroplast develops from proplastids. Proplast is a small double membrane-bound structure seen in meristematic cells. In the presence of sunlight, proplasts develop into normal chloroplasts.

image of development of chloroplast

Stages of development of chloroplast

Structure of Chloroplasts

The chloroplasts contain the following structures:

(1) Unit membrane: Each chloroplast is bounded by two unit membranes namely outer and inner membrane. Each membrane is trilaminar with 50-60 Å thickness and made up of lipoprotein. Between the two membranes, space is present which is known as periplastidal space which is 100 to 300 Å in diameter.

(2) Stroma: It is a transparent, clear and homogeneous colloidal gel-like fluid present within the inner membrane. It is also known as  matrix which contains the following substances:

  • 50% of the chloroplast proteins;
  • Fat globules;
  • Starch grains;
  • Osmiophilic granules;
  • Pyrinoids;
  • Enzymes;
  • Vitamin E and K;
  • 70s Ribosomes;
  • DNA;
  • RNA;
  • Different types of ions;

(3) Thylakoids: The inner membranous structures of the chloroplasts are organized into flattened sacs, known as thylakoids. They are embedded in the aqueous matrix. In the higher plants, the thylakoids are arranged in stacks, like a pile of coins. Each thylakoid is 100-300 Å wide. The thylakoids make the site for the light-dependent reactions of photosynthesis. The inner chamber of thylakoids contains the following components:

  • Photosynthetic pigments (Chlorophyll a and b, yellow to red carotenoids),
  • Lipid;
  • Enzymes;

(4) Grana: The stalked thylakoids constitute the grana. Granum (singular) is the functional unit of the chloroplast. The size of the ganaum may range from 0.3-2.7 µm. The number of thylakoids in a granum may vary from 50 to 100. Each chloroplast usually contains 40-60 grana in their matrix.

(5) Stroma Lamallae: The grana are interconnected by a network of tubules, known as stroma lamellae or intergranal frets.

(6) Quantosomes: The thylakoid is composed of smaller spherical bodies called quantosomes. Each quantosome consists of about 250-300 molecules of chlorophyll and few carotenoid particles which are capable of carrying on Hill reactions of photosynthesis.

image of structure of chloroplast

Structure of Chloroplast

Functions of Chloroplast

The chloroplast performs the following important functions:

  • Chloroplast receives light energy and converts it into biological energy;
  • They produce NADPH2 and ATP (Adenosine Tri-Phosphate) by the process of photo-phosphorylation;
  • They help to make food (carbohydrates) by the photosynthesis process. In this case, glucose is produced using sunlight, CO2, and H2O;
  • DNA and RNA of chloroplast synthesize of protein with the help of enzymes;
  • They fight against diseases as part of the immune system of the cell;
  • They store energy for the cell;
  • They make amino acids for the cell;

(2) Phaeoplast: It is brown colored plastid which contains the pigment fucoxanthin. Fucoxanthin is a carotenoid pigment which absorbs light and transfers the energy to chlorophyll a. These types of pigments are found in diatoms, brown algae, and dinoflagellates, etc.

(3) Rhodoplast: It is red colored plastid which contains the pigment phycoerythrin and they are found in red algae.

4. Blue-green Chromoplast: This type of chromoplast contains following pigments like phycocyanin, phycoerythrin, chlorophyll a and carotenoids. They are found in the blue-green algae.

B. Leucoplasts

This type of plastid does not have any pigments. They store food materials like carbohydrates, lipid, and protein. They are found in the sex cells and in the region of the plant that does not receive light. They may be rod-like or spherical in shape and are of many types:

(1) Amyloplast: It is double-enveloped organelle which can perform various biological pathways. It synthesizes and stores starch through polymerization of glucose in the endosperm, tubers, and cotyledons. Sometimes amyloplast can turn into the chloroplast.

(2) Elaioplast: This is one type of non-pigmented leucoplast which stores the lipid, oils, and they occur in seeds.

(3) Proteinoplast: It is identified in the year of 1960. It is also known as proteoplasts, aleuronaplasts, and aleuroplasts. This type of plastid stores protein. They are found in seeds of many plants peanuts, pulses, nuts, etc.

Plastid At  a Glance

Plastid types

Pigment types

Where found

Role

A. Chromoplast:

(1) Chloroplast

Chlorophyll a and b

Higher green plants and green algae

Photosynthesis

(2) Phaeoplast

Fucoxanthin

Brown algae, Diatoms, Dinoflagellates

Absorbs light and transfer energy

(3) Rhodoplast

Phycoerythrin

Red algae

Absorbs light and transfer energy

(4) Blue green chromoplast

Phycocyanin, phycoerythrin, chlorophyll a and carotenoids

Blue green algae

Photosynthesis

B. Leucoplast

 (1) Amyloplast

 -

Food storage cell

 Starch synthesis and store it

(2) Elaioplast

-

Some monocots and dicots seeds

Store oils and lipid

(3) Proteinoplast

-

Paenuts, pulses, nuts etc.

Stores protein

You may also read: ​Lysosome and its functions

Endoplasmic Reticulum : Types, Structure and Functions

All living organisms are composed of cells and cell products. Each eukaryotic cell contains several cytoplasmic organelles. Among the organelles, endoplasmic reticulum performs as intracellular transport system for various substances and also helps to exchange the materials between nucleus and cytoplasm.  Prokaryotic cells and RBC (red blood cell) do not have any endoplasmic reticulum.

Endoplasmic reticulum is the interconnected system of membrane-bounded tubules and vesicles which form irregular reticulum or network in the cytoplasmic matrix. All nucleated animal and plant cells contain endoplasmic reticulum. This membranous system extends throughout the cytoplasm from nuclear membrane to plasma membrane. According to some scientists, endoplasmic reticulum is originated by the invagination  of nuclear membrane but some suggested that they grow through the expansion of the pre-existing membrane.

In the light magnifying microscope, it would appear that a net in the cytoplasm consequently named as endoplasmic reticulum. The name endoplasmic reticulum was authored in 1953 by Keith R. Porter yet it had first seen by Porter, Claude and Fulum in 1945 after observing it under electron microscope of liver cells.

Physical Structure of Endoplasmic Reticulum

Morphologically, endoplasmic reticulum may happen in the three structures:

  • Lamellar structure or cisternae
  • Vesicular structures or vesicles and
  • Tubular structures or tubules.

Cisternae: They are long, flattened, unbranched membrane-bound tubule with a diameter of 40-50 µm. They arranged parallel to each other to form lamellae. They are coated with ribosome.

Vesicles: They are oval or rounded membrane-bound isolated vacuolar structure with a diameter of 25-500 µm.

Tubules: They are long and branched structures with a diameter of 40-90 µm which form the reticular system in the cytoplasm along with cisternae and vesicles. Like the unit membrane, it is made up of lipo-protein.

Types of Endoplasmic Reticulum

There are two types of Endoplasmic reticulum such as Rough Endoplasmic Reticulum (RER) and Smooth Endoplasmic Reticulum (SER).  Rough endoplasmic reticulum is also known as granular endoplasmic reticulum because it is attached with ribosomes while smooth endoplasmic reticulum is also known as agranular endoplasmic reticulum because they do not have attached ribosome with them.

image of Rough and smooth ER

Rough and Smooth Endoplasmic Reticulum

Chemical Composition of Endoplasmic Reticulum

Chemically, it is made up of the following components:

  • Protein (60-70%)
  • Lipid(30-40%) and
  • Enzymes (more than 15%)

Functions of Endoplasmic Reticulum

Endoplasmic Reticulum (ER) performs the following functions:

  • It forms the skeletal frame work of the cell.
  • It gives support to the cytoplasmic matrix.
  • Rough endoplasmic reticulum synthesizes protein while the smooth endoplasmic reticulum synthesizes lipid, glycogen, cholesterol etc.
  • Smoot endoplasmic reticulum also protects the cell from the effects of various substances by its detoxification properties.
  • Membrane of endoplasmic reticulum takes part to conduct intracellular impulse as seen in the muscles.
  • The endoplasmic reticulcum of certain cell such as testis or corpus luteum are concerned with the synthesis of respective steroid hormones.
  • Endoplasmic reticulum of parietal cells of stomach helps to secrete hydrochloride acid.
  • It acts as a circulatory system of the cell for transporting materials very quickly.
  • It helps to form various vacuoles.
  • It provides larger surface area which is useful for rapid synthesis of biochemicals.
  • Endoplasmic reticulum of one cell makes communicate wit endoplasmic reticulum of adjacent cells.
    It provides the mechanical support to the cells.
  • It provides sites to cytochromes to carry out the specific reactions.
  • It transmits information from outside to inside of the cells.
  • It also transmits information between different organelles of the same cells.
  • They help to form the new nuclear membrane after each nuclear division.
  • They produce some hormones such as progesterone, testosterone, etc
  • They help to transport of carbohydrates and proteins to another cell organelles such as plasma membrane, lysosomes, Golgi apparatus, etc.

Golgi Body : Structure and Functions

Golgi body is a flattened, membrane-bounded, parallely arranged sacs and other vesicles usually located near the nucleus in the cytoplasmic matrix of almost all eukaryotic cells. It is also known as Golgy complex, Golgi apparatus, Golgiosome, Lipochondria and in the plant cell, it is also called Dictyosome. Camillo Golgi first observed it in the nerve cell of barn owl in 1898.

Occurrence: They are generally present in the cytoplasm near the nucleus but in the glandular cells, they are located between the nucleus and apex of the cell.

Structure of the Golgi body: Its shape varies from cell to cell. It is large in nerve cell and small in muscle cells. The nerve cell, liver cell and most of the plant cells contain multiple Golgi bodies. The Golgi body forms from plasma membrane, nuclear envelop and endoplasmic reticulum. Generally, Golgi body consists of three membranous components such as:

  • Cisternae
  • Small tubules and vesicles
  • Large vacuoles
Image of Eukaryotic cell

Eukaryotic cell Showing Golgi Body

Cisternae: They are parallely arranged sacs like structure which are covered by smoothed-surfaced single membrane and piled one upon the other to form stacks. The number of sacs in the stack ranges from 3-20 in number which depends on the cell type. They are usually equally spaced in the stack.

Small vesicles: The vesicles are small droplet-like sacs and originate from the cisternae by building or “pinching off” process.

Large vacuoles: They are clear and large sac-like structures. They contain electron-dense materials.

Golgi body

Golgi body showing secretory vesicles

Functions of Golgi body

  • It plays an important role to form the cell wall at the end of the mitosis cell division.
  • They help to form new plasma membrane.
  • They form primary lysosomes.
  • They take part in the protein secretion.
  • Golgi body takes part in the formation of acrosome of the sperm.
  • It is responsible for neurosecretion.
  • They play an important role in the transport of lipids throughout the cells.
  • It releases the protein molecule out of the cell.
Please Watch the Video About Golgi Body.......

Mitochondria : Definition, Structure and Functions

Definition

The word mitochondria come from two Greek words, mito meaning thread and chondrion meaning granule. It has double membrane enclosed rounded or rod-like or filamentous bodies which generate chemical energy in the form of ATP. It is scattered throughout the cytoplasm in most of the cells.

History of Mitochondria

Scientist Kolliker (1850) first observed mitochondria in the striated muscle. Flemming (1882) named it as fila. Rechard Altmann (1897) referred to the mitochondria as Bioplasts. Carl Benda (1897) first called these organelles as mitochondria.

Distribution and occurrence 

It is not found in the prokaryotic cell and matured circulated RBC. Generally they are evenly distributed in the cytoplasm. It is also found in the base of the proximal convoluted tubules of nephron. The number of mitochondria present in the cell depends on its activities. Plant cell contains less number of mitochondria than animal cell. A normal liver cell may contain 1000-1600 mitochondria while some oocytes may contain more than 300000 mitochondria. On the other hand, Microasterias algae contain only one mitochondrion

Structure of Mitochondria

Mitochondria have generally spherical or rod-shaped or filamentous structures. It is about 3.0-7.0 µm in length and 0.2-2.0 µm in diameter. It usually consists of two unit membranes, two chambers, mitochondrial matrix and mitochondrial particles. Every mitochondria is bounded by the double membranes, the outer membrane and inner membrane. Each membrane is made up of lipo-protein and it is about 60 Angstrom thick. The outer membrane is smoothed and covers the mitochondria but the inner membrane remains folded inward at various points to form a number of incomplete partitions which are known as the cristae or mitochondrialis cristae. The two membranes remain 60-80 Angstroms apart from each other. The space between the two membranes is filled up with fluid.

Diagrammatically structure of mitochondria

Diagrammatically Structure of Mitochondrion

Chambers: It has two chambers, outer and inner chambers. The outer chamber is the space between the outer and inner membranes which is filled with watery fluid. The inner chamber is covered by the inner membrane. The inner chamber contains mitochondrial matrix.

Mitochondrial matrix: The inner chamber is filled with a relatively dense proteinaceous material usually called mitochondrial matrix. This matrix contains dense granules, ribosomes and mitochondrial DNA. The enzyme of the Krebs cycle is located in the matrix.

Mitochondrial particles: The cristae that project into the matrix are usually incomplete septa or ridge. The cristae are covered by mushroom-like particles of 85 Angstrom. These particles are known as F1-Particles or Fernandez-Moran subunits or elementary particles. Each particle consists of three parts; head, stem or stalk and base. The particles are spaced about 100 Angstrom interval on the cristae.

Detail structure of cristae

Detail Structure of Cristae

Functions of Mitochondria

  • It acts as a power house- Different enzymes present in the mitochondria help in oxidative phosphorylation and is thus site for formation of adenosine triphosphate (ATP). ATP is high energy-rich substrates which supply 95% energy to the cell.
  • Cell Respiration- Mitochondria are the respiratory organelles of the cell. Cell respiration includes glycolysis, oxidation of pyruvic acid, Krebs cycle and oxidative phosphorylation.
  • Oxidation of fat- Fatty acids of fats are oxidized at their β-position in the mitochondria.
  • Syntheses of lipid- A set of enzymes that control synthesis of phospholipids are present in the mitochondria. These enzymes help in the formation of the phospholipids.
  • Syntheses of protein- The mitochondrial matrix contain DNA which helps to synthesize RNA. This RNA and ribosome help for the formation of protein.
  • Mitochondria help to maintain proper concentration of calcium ions in the cell.
  • It helps to build certain parts of blood and hormones such as testosterone and estrogen.
Please Watch Video About Mitochondria...............

Cell Structure and Function

The cell is the structural and functional unit of life, which is also known as "building blocks of life." The science which deals with the study of cells is called Cytology or cell biology. Robert Hooke first discovered the cells in 1665. Matthias Jakob Schleiden and Theodor Schwann first developed a cell theory in 1839. Based on cell theory, all organisms are made from one or more cells. The word "cell" is derived from Latin words, cella, which means "small room."

The cell contains cytoplasm with proteins and nucleic acids, which is bounded by a membrane. Under a microscope, most plant and animal cells are visible, and their dimensions range from 1-100 µm.  The number of cells varies from species to species. The human contains about 4×1013 cells. The smallest known cell is a tiny single-celled bacterium, known as Mycoplasma, which is 0.2 μm in diameter.

Definition of cell

There are various definitions of the cell which are given below:

  • The structural and functional unit of living body is known as cell.
  • The protoplasm surrounded by the membrane is known as cell.
  • The smallest organized unit of the living body which is independent and self-reproducing under favorable condition, is known as cell (De Robertis and De Robertis, 1981).  
  • It is a unit of biological activity delimited by a semi-permeable membrane and capable of self reproduction in a medium free of other living system (Loewy and Sikevitz, 1969).
  • The cell is the basic unit in which matter energy are acquired, converted, stored, utilized and also in which biological information is stored, manipulated and expressed (Swanson and Webster, 1978).

Number of Cell

The number of cell varies in the living organisms. The unicellular organisms like bacteria, amoeba, diatoms, Euglena etc contain single cell in their body but most of the plants and animals are multi-cellular organisms which contain many cell in their body. The number of the cell is never fixed for any multi-cellular organism.

Shape of the Cell

The shape of the cells is highly variable. Generally, the animal cell is spherical in shape, but it may be elongated, cylindrical, oval, rounded, triangular, cuboidal, polygonal or irregular in different plants and animals. The shape of the cell remains correlated with its functions. The external and internal environment of the organism may also cause shape variations in the cell due to internal or mechanical stress or pressure and surface tension. The shape of the cell may vary from organ to organ, plant to plant and animal to animal.

Size of the Cell

The size of the cells varies from cell to cell. Most of the eukaryotic cells are microscopic in size but they are bigger than the bacteria. Generally, size of the cell varies from 1-175000 µm. Among the living organisms, the smallest cell is mycoplasma bacteria which are 0.1-0.25 µm in diameter while the biggest cell is ostrich egg (170 ×135 mm). The longest cell is the neuron cell which is about a meter or more in length.

Types of Cell

Generally, the cell is of two types: 

  • Prokaryotic Cell
  • Eukaryotic Cell
image of Eukaryotic and Prokaryotic Cell

Eukaryotic cell (left) and Prokaryotic cell (right)

Prokaryotic Cell

This type cell is lack of nuclear envelop and well defined cytoplasmic organelles such as endoplasmic reticulum(ER), Golgi body, Mitochondria, centriole etc. Example of eukaryotic cells: Bacteria, blue green algae etc.

Most Important Characteristics  of Prokaryotic Cell

  • The prokaryotic cells are unicellular and filamentous like form which is not exceeding 10 µm in diameter.
  • They have a more or less rigid cell wall and a jelly like mucilaginous capsule or sheath outside the plasma membrane.
  • This cell does not contain nucleus due to absence of nuclear envelop.
  • This type of cell also contain single naked chromosome with naked DNA.
  • The cytoplasm of the prokaryotic cell does not contain well defined cell organelles such as endoplasmic reticulum(ER), Golgi body, mitochondria, centriole, vacuoles, lysosome, chloroplast etc.
  • Most of the prokaryotic cells have motile organs such as cilia and flagella.
  • They multiply by binary fusion.

Eukaryotic Cell

The eukaryotic cell has the nucleus with a definite nuclear membrane. This type of cell also contains cytoplasmic organelles like endoplasmic reticulum, Golgi bodies, mitochondria, lysosomes, etc.

Characteristic Features of Eukaryotic Cell

The eukaryotic cell is the true cell which has the following characteristic features:

  • It is generally large in size, but only few cells being under 10 µm in diameter.
  • The cell is bounded by the plasma membrane in the animal cell but in the plant cell, it is bounded by the cell wall which is made up of cellulose.
  • This type of cell contains true nucleus which bears nucleoplasm, nucleolus, RNA, DNA, chromosomes and nuclear membrane.
  • The eukaryotic cell also contains cytoplasmic organelles like endoplasmic reticulum, Golgi bodies, mitochondria, lysosomes, etc.

Cell Structure and Their Functions

The eukaryotic cells have different shapes, sizes and physiology but all the cells are typically composed of:

image of plant cell

Structure of a Typical Plant Cell 

Cell-covering

Cell-covering has two parts such as plasma membrane and cell wall. Most of the cells are enclosed by a thin porous semi permeable membrane which is known as plasma membrane. The plasma membrane may be modified to form villi, cilia, flagella, cavities, and other special structures. The cell wall is present only in the plant cell. It is present outside of the cell membrane which is a thick semirigid, laminated, non-living cellulose covering.

image of Animal Cell

Structure of Animal Cell

Functions of Cell Covering

Plasma membrane is a permeable membrane by which extracellular substances entered into the cell while the cell wall provides protection and support to the plasma membrane and cytoplasm.

Cytoplasm

The substance which occurs between the plasma membrane and nuclear membrane is called cytoplasm. It is made up of the matrix and the organelles. Matrix is an amorphous, translucent, homologous colloidal liquid which is known as hyaloplasm or cytoplasmic matrix.

Functions of Cytoplasm

Cytoplasmic matrix contains glycolytic enzymes and structural materials such as sugars, amino acids, water, vitamins, nucleotides etc. They carry out the instructions sent from the nucleus. They also provide sites for cellular activities.

Cytoplasmic Organelles

The organelles are the membrane-bound living structures of a cell which are situated within the cytoplasm. Generally, they perform various important biosynthetic and metabolic activities such as transportation, support, storage, reproduction, respiration etc. The eukaryotic cell contains the following organelles:

Golgi Body

It is very important organelle of the cell and is covered by a single smooth membrane of lipoprotein. It consists of cisternae, vesicles and vacuoles.

Functions of Golgi Body

It plays an important role for the transportation of materials within the cell. It forms secretary vesicles and lysosomes. They also form cell wall of the plat cell and plasma membrane.

Endoplasmic Reticulum (ER)

They are inter-connectin tubules and vesicles which are bounded by a single unit membrane. The membranes may be rough and smooth due to presence or absence of ribosomes.

Functions of Endoplasmic Reticulum

They maintain intracellular circulatory system. They act as synthetic and storage organs. They provide mechanical support to the cell by making cytoplasmic frame work.

Lysosomes

It is found only in the animal cell and it is a tiny spheroid particles which consist of hydrolytic enzyme. They are enclosed within the single lipoprotein membrane.

Functions of Lysosomes

They mainly take part in the intracellular digestion of food materials within the cell by the process of pinocytosis and phagocytosis.

Ribosomes

They are minute spherical non-membranous structures which consist of RNA and protein.  They have two structural unequal sized subunits. The smaller subunit is called 40s subunit and a large subunit is called 60s subunit. They are located freely in the cytoplasm or remain attached to the surface of endoplasmic reticulum, nucleus etc.

Functions of Ribosomes

They provide sites for protein synthesis.   

Mitochondria

It is filamentous or granular hollow type structure which is bounded by a double lipoprotein membrane. The inner granulated membrane is convoluted to form cristae and divides the mitochondria into two chambers, the outer chamber and matrix filled inner chambers.  

Functions of Mitochondria

They are called power house of the body because they produce energy as ATP through Kreb`s cycle, electron transport chain, bet-oxidation of fatty acids etc.

Chloroplasts

It is a disc shaped chlorophyll containing organelle which is bounded by double membrane. It is only present in the plant cell. Within the inner membrane, stroma or matrix is present. Stroma contains small cylindrical structures called grana. Granum is a flattened vesicles which contains small structures or quantosomes.

Functions of Chloroplasts

They act as a storage for starch, pigments for photosynthesis. They help in the biosynthesis of food stuffs by the process of photosysnthesis.

Centrosomes

It is present only animal cell. It contains dense cytoplasm  which is placed near the nucleus of the cell.

Functions of Centrosomes

It forms the spindle during the cell division and help in the movement of chromosomes.

Nucleus

Nucleus is the brain of the cell which is generally rounded in shape and is placed at the center of the cell. The typical nucleus consists of the following components:

Nuclear membrane: It is also known as nuclear envelope. It is a bilayer membrane which is made of lipids and  the genetic material in eukaryotic cells. It encloses the nucleus where nucleo-cytoplasmic interchange takes place.

Nucleoplasm: It is clear like water substance which is present in the space between the nuclear membrane and nucleolus. It contains ribose sugar, phosphorus, protein, nuclic acid and nucleotides.

Nucleolus: It is a dense spherical body covered by single membrane which is present in the nucleoplasm. It mainly consists of nucleoprotein.

Chromosomes: In the nucleoplasm, a thread tike elongated structure is present which is known as chromosome. They appear only during the cell division.  

image of nucleus

Nucleus and its parts

Functions of Nucleus

  • They act as a brain for the cell. 
  • They synthesize RNA, ribosome and ribosomal protein.
  • Nuclear membrane makes partitions between nucleus and cytoplasm. 
  • They regulate the cellular process and bear the hereditary instructions.