Cytoplasm and Nucleus – Overview, Structure, Functions, Examples

The cell is the basic structural and functional unit of living organisms. In biology, the cell has the same central position as that of an atom in the physical sciences. The bodies of living organisms are made up of microscopic units called cells. Cells have evolved a variety of different lifestyles. Many organisms, such as bacteria(both archaebacteria and eubacteria), protozoa(e.g., amoeba), and yeasts consist of single cells (called unicellular organisms) that have the ability to perform a function like self-replication. More complex organisms, called multicellular organisms,  those consists of collections of cells that perform particular functions.

Term cell was discovered by Robert Hook in his book ‘MICROGRAPHIA’. The size of the cell is  10^-16 micrometers. The shape of the cell may be polygonal, disc-like amoeboid,thread-like, cuboid or irregular, oval, hexagonal, circular, branched, elongated, etc. The cells are too small to be seen with naked eyes. so, it is studied with the help of microscopes.

Structure of Cell

Though the shape and size of a cell vary,  all cells have the following three major functional regions:

1. The cell membrane or plasma membrane, and cell wall
2. The nucleus
3. The cytoplasm

Nucleus

The nucleus is a large, centrally located spherical cellular component. It represents the whole eukaryotic complex that contains genetic information. It is bounded by two nuclear membranes, both forming a nuclear envelope. A nuclear envelope encloses the space between two nuclear membranes and is connected to the system of membranes called ER( endoplasmic reticulum).

The nuclear envelope separates the nucleus from the cytoplasm. The nuclear envelope contains many pores( the nuclear pores) and encloses the liquid ground substance, the nucleoplasm.

Nucleopores allow the materials to transfer between the nucleoplasm and the cytoplasm. Two types of nuclear structures are embedded within nucleoplasm – the nucleolus and chromatin material. The nucleolus may be one or more in number and is not limited by any membrane. It is rich in protein and RNA(ribonucleic acid) molecules and acts as the site for ribosome formation. the nucleolus is known as the factory of ribosomes. ribosomes are known as the factory of protein synthesis in the cytoplasm.

The chromatin material is a thin,thread-like mass of chromosome material and consists of the genetic substance DNA (deoxyribonucleic acid) and proteins(i.e., histones). the nucleosome is a part of DNA that is coiled around a core of proteins.

Function of Nucleus

• The nucleus is known as the controller of a cell and its metabolic activities. If the nucleus is removed from a cell, the protoplasm will dry up and dies ultimately.
• The nucleus is responsible for the cell cycle, it regulates it.
• The nucleus plays an important role in transmitting the hereditary traits from parent to offspring.
• The nucleus controls the protein and enzyme synthesis.
• The nucleus is the storehouse of DNA, RNA, and ribosomes.

Cytoplasm

The cytoplasm is the part of the cell which comes between the cell membrane and nuclear envelope. The inner granular mass of the cytoplasm is called endoplasm, while the outer, clearer layer is called ectoplasm. The cytoplasm consists of gel-like fluid or thick solution inside the cell which contains a variety of cell organelles. It is mainly composed of salts, water, and proteins. moreover, it is the medium for chemical reaction and thus, is an essential component of the cell.

Cell organelles such as ER( endoplasmic reticulum), ribosomes, Golgi apparatus(Golgi body or Golgi complex), Lysosomes, Mitochondria, plastids, chloroplasts, vacuoles, peroxisomes, and centrosomes are embedded in the cytoplasm and perform different functions in the cell.

The largest cell organelle is Ribosome while the largest cell structure is Nucleus. Furthermore, the Largest cellular organelle in plants is Plastids and in animals is Mitochondria.

Function of Cytoplasm

• Living cytoplasm is always at the site of movement.
• The cytoplasm is the site of many metabolic reactions to take place such as glycolysis.
• The synthesis of fatty acids, nucleotides, and some amino acids also takes place in the cytosol.
• Cytosol(cytoplasm) acts as the storehouse of vital chemicals such as amino acids, glucose, vitamins, ions, etc.
• Cytoplasm enables other organelles to perform their functions in the cell of organisms.

Conceptual Question

Question 1: Who discovered the cells and how?

Answer:

Robert Hooke 1665 discovered the cells. he examined a thin slice of cork under a self-designed microscope and observed that the cork resembled the structure of a honey comb. Later on, it consists of many tiny compartments. Hooke called them cellular, now termed cells.

Question 2:  Why is a plasma membrane called a selectively permeable membrane?

Answer:

The plasma membrane is called the selectively permeable membrane because it allows only selected molecules to move into the cell.

Question 3: Write the names of cell organelles that are embedded in the cytoplasm? 

Answer:

The endoplasmic reticulum, ribosomes, mitochondria, vacuoles, lysosomes, centrosomes, chloroplast, etc. are the cell organelles present in the cytoplasm.

Question 4: Write the function of the nucleus?

Answer:

It is the controller of the cell and its metabolic activities. It controls the protein and enzyme synthesis and is responsible for cell cycle.

Question 5: Why is a cell called the structural and functional unit of life?

Answer:

All living organisms are made up of cells. Thus, the cell is the functional unit of life. each living cell has the power to perform certain basic functions.cell organelles together constitute the basic unit of structure and function called the cell.

Question 6: Which molecules are present in chromatin?

Answer: 

DNA, histone proteins, and acid proteins are present in chromatin.