Cell: Definition, Structure and Functions

A cell is defined as the smallest, basic unit of life that is responsible for all of life’s processes.

Cells are all living beings’ structural, functional, and biological units. A cell can replicate itself independently. Hence, they are known as the building blocks of life. In every cell, you’ll find a liquid known as cytoplasm, surrounded by a membrane. You’ll discover various biomolecules within the cytoplasm, such as proteins, nucleic acids, and lipids—cell organelles, which are cellular structures, also float within the cytoplasm.

Who discovered cells?

Robert Hooke discovered the cell in 1665. Robert Hooke observed a piece of bottle cork under a compound microscope and noticed minuscule structures that reminded him of small rooms. Consequently, he named these “Rooms” cells. However, his compound microscope had limited magnification, and hence, he could not see any details in the structure. Owing to this limitation, Hooke concluded that these were non-living entities.

Later, Anton Van Leeuwenhoek observed cells under another compound microscope with higher magnification. This time, he had noted that the cells exhibited some form of movement (motility). As a result, Leeuwenhoek concluded that these microscopic entities were “live.” Eventually, after a host of other observations, these entities were named animalcules.

In 1883, Robert Brown, a Scottish botanist, provided the very first insights into the cell structure. He was able to describe the nucleus present in the cells of orchids.

Parts of the cell

1. Cell Membrane

The cell membrane, the outer layer of the cell, consists of lipids and phospholipids and actively performs several critical roles.

The cell membrane serves various crucial functions, including:

1. Firstly, it shapes and sizes the cell.

2. Moreover, it actively regulates selective permeability, controlling what substances can enter or exit the cell.

3. Additionally, it acts as a barrier, effectively preventing the entry of unwanted materials into the cell.

4. Furthermore, it actively forms a physical boundary between the cell’s interior and its external environment.

5. It also actively facilitates the establishment of distinct internal and external environments within the cell.

6. In addition, it actively maintains the cell’s ionic concentration and osmotic pressure.

7. Besides, it actively establishes connections with neighboring cells, contributing to tissue formation.

8. Lastly, it actively provides protection to the cell.

2. Endoplasmic Reticulum

The endoplasmic reticulum (ER) performs several vital functions:

• It synthesizes lipids, such as phospholipids and cholesterol.
• It participates in carbohydrate metabolism.

The Endoplasmic Reticulum comes in two varieties:

• Smooth ER: This type stores and releases calcium ions, especially crucial for the nervous and muscular systems. It is also responsible for producing and releasing steroid hormones.
• Rough Endoplasmic Reticulum: This type features ribosomes, where protein synthesis takes place.

3. Ribosome

Ribosomes have a primary function, which is protein synthesis, a process referred to as translation. Here are some key characteristics and details:

1. Ribosomes are synthesized in the nucleus.
2. These organelles consist of dense, spherical granular particles that move freely in the cell’s matrix.
3. Ribosomes are present in both the cytoplasm and the nucleus.
4. They are composed of a combination of numerous proteins and RNA (ribonucleic acid).
5. Ribosomes also play a role in the synthesis of lysosomes.

4. Golgi apparatus / Golgi complex

Eukaryotic cells typically have this organelle, which falls within a size range of 0.5 to 1.0 micrometers. Here’s an explanation of its functions:

• It actively generates energy by processing vital nutrients, resulting in the formation of charged molecules.
• These charged molecules then actively combine with oxygen to create ATP molecules, a process widely recognized as oxidative phosphorylation.
• In the scientific community, they commonly refer to it as the cell’s powerhouse.

5. Mitochondria

Eukaryotic cells contain a membrane-bound structure.

This structure ranges in size from 0.5 to 1.0 micrometers.

It actively generates energy by processing simple nutritional molecules, leading to the production of charged molecules. These charged molecules then combine with oxygen to produce ATP molecules, a process known as oxidative phosphorylation.

This structure is also known as the cell’s powerhouse.

6. lysosome

• Small bodies in the cytoplasm actively house potent digestive enzymes, enhancing the breakdown of cellular components.
• They are present in both plant and animal cells.
• Lysosomes actively manage waste removal in animal cells, contribute to overall health, and aid in the body’s defense against disease.
• They also play an active role in repairing the cell membrane.
• In addition, they are commonly referred to as the cell’s “suicidal bag.”

7. Nucleus

• The most important structure in the cell is the nucleus, often referred to as the control center because it houses chromosomes, which are thread-like units of heredity passed from parents to offspring.
• A double-layered nuclear membrane encases it.
• The fluid medium within the nucleus, known as nucleoplasm, actively contains a colloid suspension of proteins, nucleic acids, DNA, and RNA.
• Inside the nucleus, there is a smaller, globular, spherical particle referred to as the nucleolus, composed of DNA, RNA, and proteins. This structure is where ribosomal synthesis occurs.

Functions of a cell encompass a wide range of vital processes, including:

• Providing support and structure to the body of an organism.
• Acquiring nutrition.
• Facilitating the exchange of materials with the environment, such as taking in oxygen and expelling carbon dioxide.
• Reproduction of the cell itself.
• Detecting and responding to various signals and stimuli.