What Is Cell? Definition, Types, Structure, Characteristics

Introduction to Cell 

 

Cell in biology, it is the basic structural and functional unit of all living organisms.

The cell is the smallest and fundamental unit of life and building block of the life of all living things.

The study of cells is called cytology or cellular biology or cell biology. A cell can replicate itself independently and produce the construction of an identical or similar copy of itself. So that’s why reason is called building blocks of life.

Each cell consists of a fluid called the cytoplasm, which is enclosed by a plasma membrane or cell membrane.

Know here what is the function of cell organelles is?

 

Discovery of Cells

 

The cell was first discovered in 1665 by British scientist Robert Hooke, which can be found to be described in his book Micrographia.

Robert Hooke made a drawing structure of cork that was published in the book Micrographia.

In 1665, Hooke had improved the design of the existing compound microscope. While examining a thin slice of cork through a self-designed compound microscope, he observed that the cork consisted of numerous tiny compartments structures that resembled look like “honeycomb”. The very tiny box (minuscule boxes) is referred to as cells.

 

Later Dutch scientist Anton Van Leeuwenhoek, observed cells under another microscope with higher magnification. He observed and detected other hidden, minuscule organisms; bacteria and protozoa, and makes the first observations of bacteria and protozoa. 

In 1883, Robert Brown, a Scottish botanist was the first to describe observations of nuclei, which he observed in plant cells.

Robert Brown provided the very first insights into the cell structure; he was able to detect and describe the nucleus present in the cells of orchids.

 

Types of Cell

 

All organisms are consisting of cells.

 

1. Based on the number of cells distribution, an organism is classified into two categories-

 

a. Unicellular organism 

Made up of single cells only.

 For example; bacteria

 b. Multicellular organism

Made up of more than one cell.

For example; molds, plants, and animals.

 

2. Based on the cellular organization, cells are divided into two categories-

 

a. Prokaryotic cells (without nucleus)

Prokaryotes include bacteria and archaea.

Get here details on prokaryotic cell structure and function.

 

b. Eukaryotic cells (eu- true, karyotes- nucleus)

Eukaryotic include Plants, animals, protists, fungi, slime molds, protozoa, and algae are all eukaryotic.

 

Understand the structures of eukaryotic cells and types of eukaryotic cells?

 

Prokaryotes are single-celled organisms and, Eukaryotes are can be either single-celled or multicellular organisms.

 

Find here difference between prokaryotic cell and eukaryotic cell.

 

1. Prokaryotic cells (Without Nucleus)

 

Prokaryotic cells are single-celled microorganisms, Prokaryotes include Bacteria and Archaea and some unicellular protozoans.

The photosynthetic prokaryotes include; cyanobacteria (blue-green algae) that perform photosynthesis.

 

Prokaryotes are bounded in a cell membrane. The cell membrane is the outer covering of cells that allows them to create a specific environment within the cytoplasm. Cytosol allows biochemical reactions to take place.

A prokaryote reproduces asexually through binary fission, in this process simply splits duplicated DNA into separate cells.

 

 

Characteristics of Prokaryotic Cells

 

Key points are- 

 

1. It is the simplest form of cell

2. Typical prokaryotic cells range from 0.1 to 5.0 micrometers (μm) in diameter.

3. They have lacked a membrane-bound nuclear means a membrane-bound well-defined nucleus is absent.

4. It lacks Mitochondria, Golgi bodies, chloroplast, lysosomes, and other organelles.

6. They consist of genetic material chromosome single and circular, double-helical DNA, densely coiled.

7. Ribosome is present of 70s type. 

8. They divide asexually by binary fission

 

Prokaryotic Cell Diagram

 

 

Prokaryotic Cell Structure

 

Prokaryotic cell structure consists of -

 

1. Capsule

2. Cell wall

3. Cell membrane/ plasma membrane

4. Cytoplasm

5. Nucleoid

6. Ribosomes

7. Plasmid

8. Flagellum

9. Pili

10. Mesosome

11. Inclusion body

 

2. Eukaryotic cells (eu- true, karyotes- nucleus)

 

1. Eukaryotic cells have a true nucleus means the cell's DNA is surrounded by a membrane.

2. A eukaryotic cell contains membrane-bound organelles such as a nucleus, mitochondria, and endoplasmic reticulum, Golgi apparatus; and chloroplasts can be found in plants and algae. 

3. Eukaryotic cell size ranges from 10-100 µm in diameter.

4. Eukaryotic cells divide using the processes of mitosis and meiosis; reproduce sexually or asexually through mitosis.

5. Eukaryotes may be either unicellular or multicellular. For example, most protists are single-celled eukaryotes.

 

Types of Eukaryotes

 

There are four types of eukaryotes-

 

1. Animals

2. Plants

3. Fungi, and

4. Protists (such as protozoa, algae, slime molds)

 

Check out here difference between animal cell and plant cell.

 

Characteristics of Eukaryotic Cell

 

Key points are- 

 

1. Size of eukaryotic cells is larger than prokaryotic cells, size ranges from 10-100 µm in diameter.

2. Eukaryotic cells have a well-defined nucleus and membrane-bound organelles

3. Genetic material of eukaryotic cells is DNA. Eukaryotic cells typically have multiple linear chromosomes.

4. Eukaryotic cells have a cytoskeleton structure.

5. Plastids or chloroplast, are double-membrane structures and are found only in plant cells.

 

Note - Yes, prokaryotes have plastids. Plastids or chloroplasts are present in one kind of bacteria; cyanobacteria (earlier called blue-green alga).

 

Eukaryotic Diagram

 

 

 

Eukaryotic Cell Structure

 

Eukaryotic cell structure consists of-

 

1. The Nucleus and Its Structures

2. Cell membrane/ Plasma membrane/ Cytoplasmic membrane

3. Cell wall- found in plant cells

4. Golgi Apparatus

5. Ribosomes

6. Mitochondria

8. Cytoskeletal structures

9. Lysosomes

10.  Endoplasmic reticulum (ER)

a. Smooth endoplasmic reticulum

b. Rough endoplasmic reticulum

 

11. Vacuole

12. Peroxisome

13. Centrosome

14. Plastids - double-membraned structures, found only in plant cells.

 

Plant Cells

 

The cell wall is composed of cellulose, which provides support to the plant. A plant cell has a larger vacuole in the cytoplasm, that maintains the turgor pressure of the cell and provides the shape and structure of the cell.

 

Plant Cell Structure

Plant Cell organelles

 

The organelles found only in plant cells include-

1. Chloroplast

2. Cell wall

3. Plastids

4. Large central vacuole

5. Nucleus

6. Ribosome

7. Smooth Endoplasmic reticulum

8. Golgi Apparatus

9. Mitochondria

10. Cell membrane

11. Cytoskeleton

 

 

 

Animal Cells

 

Animal cells do not have cell walls, they have a cell membrane. It allows the cell to acquire different shapes and aids the process of phagocytosis and pinocytosis. That’s why animals have varied shapes.

 

Major cell organelles and cellular structures include-

 

1. Nucleus

2. Ribosome

3. Endoplasmic reticulum

4. Golgi apparatus

 5. Cytoskeleton

6. Mitochondria

7. Lysosome

8. Centriole

9. Vesicles

 10. Vacuoles