Structural and Functional Units of a Living Cell in Cytology
The cell is the fundamental unit of life for all the living beings and the study of the structure and function of cell studies under the field of biology in which is called as cytology or cell biology. The cells make the tissues, and the tissue makes the organs, and then different organs make an organism. By understanding the functional processes going on in a cell, we can easily get a detailed understanding of the tissue and organs as well. There is some organism which has only one cell, and these are called as unicellular organisms. There are some who do not have any cell, and they are called as a cellular organisms. Majority of the life on earth have organisms comprise a vast number of cells.
Cytology gives us an insight into the structure of a cell and the functions of various components of it. It also deals with the chemical processes going on inside the cell which keep it alive. The terms which you need to know to understand the concepts of cell biology are as following:
As it is said earlier, the cells are the building blocks of all living organisms. By structure, the cells are classified into two categories which are prokaryotic cells and eukaryotic cells. The presence of absence of organelles is the defining difference between these two. Other distinguishing factors among them are their size, the way of their reproduction, and the number of cells etc.
In eukaryotic cells, animal cells, plant cells protozoan cells, fungi are included and the one thing shared between all of them is they all have a nucleus which is enclosed by a nuclear membrane. But when we speak about the prokaryotic cells, they do not have an enclosed nucleus in them, and the example of prokaryotic organisms are bacteria and archaea. The size of eukaryotic cells is much bigger than the prokaryotic ones. In fact, the prokaryotic organisms are the smallest living form of life on earth.
An organelle is defined as the subunit of the cell. There are numerous organelles in a single cell and all of them a specific function. The function of each organelle is vital for the sustenance and life of a cell. Every organelle has a lipid bilayer around them which separate them from other organelles inside the cell. The organelles are part of a cell similarly as organs are to a body.
- Cytosol or Cytoskeleton
When all the organelles and plasma membrane is removed from a eukaryotic cell then only a thick aqueous gel leaves behind, this aqueous gel is known as the cytosol. There are many large and small molecules which compose cytosol. This is also known as the cytoskeleton because it forms a criss-cross structure to give a structure to the cells. This cytoskeleton is helpful in many functions such as the strengthening of the cells, cell division and the muscle contractions. This is the site where all the chemical reactions happen inside the cell, which is critical for the cells to live and function well.
Cytoplasm is the fluid inside the cell where all the organelles and cell parts lie. Cytoplasm is made up of water and salt mostly. Cytoplasm is also known as protoplasm, and the nucleus is not included in it. Protoplasm comprises of all the cell organelles and the cytosol as well but excluding the nucleus. In case of prokaryotes where is no nuclear membrane for the nucleus and it lies in the cytoplasm only. But in case of eukaryotic cells, the nucleus has its protoplasm which is known as nucleoplasm.
A well-defined nucleus is present in only eukaryotic cells. It is the organelle which contains the genetic material of the cell which is organized in the form of long and linear molecules of DNA along with complex proteins called as his tones which form the chromosomes. In the cells of all eukaryotic organisms, the nucleus is surrounded by a nuclear membrane which is also known as the nuclear envelope. The DNA which is present inside the nucleus is responsible for encoding of the genetic information of that particular organism.
Mitochondria are also known as the powerhouse of the cell because it has the function of generating chemical energy for the cell. The food molecules are oxidized, and then the energy is produced by the mitochondria. The mitochondrionis also found in all eukaryotic cells, and each of them is surrounded by tow membranes. One is an inner membrane, and the other is an outer membrane.
Chloroplasts are what differentiate plant cells from the animal cells. Chloroplasts are only present in the plant cells, and they are also found in some eukaryotic organism also such as some forms of algae. The chloroplasts are green organelles and are the site where the process of photosynthesis takes place. The green pigment present in the chloroplasts is known as chlorophyll, and this pigment only helps for tapping the sunlight in the form of energy. Chloroplasts have their DNA, and they can divide as well.
The irregularly shaped organelle of the cells which have an only single membrane around them is called as lysosomes. This part of cell helps in the in the intracellular digestion. Lysosomes assist in releasing the nutrients after breaking down the ingested food molecules. It also breaks down the unwanted particles and then they are excreted by the cells.
Chromosomes are those cellular organelles which have all the cell information. They are made up of DNA segments which helps the cell to reproduce, survive and grow. The DNA segments have some specific patterns which are called as genes. The chromosomes are found in the nucleus which is protected with the nuclear envelope in eukaryotes.
- Plasma Membrane
There is a membrane which encloses a cell is called plasma membrane. This is a semi permeable membrane which is usually 5nm thick. The main purse and function of a cell membrane are to separate the cellular components from the outer environment. The plasma membrane is a biological membrane, and it protects the integrity of the single cell by regulating the entry and exit of all the molecules from it.