[Biology Class Notes] on Cells Pdf

A cell is defined as the very smallest structural and functional unit and a building block of any living organism. It is always considered as membrane-bound and is made up of cytoplasm, genetic material, and other cell organelles or components of the cell. All cells are made from the same major classes of organic molecules such as nucleic acids, proteins, carbohydrates, and lipids.

A collection of cells that have the same stimulating and life giving functions is called a tissue. When tissues are conjoined to perform their functions, organs are developed and from those organs, bodily functions are developed. Therefore, it can be said that the human body will fail to perform its basic bodily functions if there were no tissues. On the other hand, if there were no cells, there would be no tissues either. So the entire process of cell development and tissue development is interrelated. 

Types of Cell

Cells that are exceptionally designed are fundamentally a part of multicellular organisms. For instance, a plant has a multiple variety of cells like root cells, stem cells and leaf cells. On the other hand, a human being has a wide variant of cells that are responsible  for keeping the heart, nerves and skin together. When it comes to human beings, even the functions of those cells are multifarious as each of those cells is designed to perform different specialized functions. 

Cell Structure

Talking about cells like prokaryotic and eukaryotic cells, they share some significant similarities in terms of structure. One dominant structural resemblance between them is the presence of plasma membranes in both of them. Plasma membrane is responsible for transferring substances in both of the cells both from inside and outside the cell. Moreover, the interior structure of both the cells is termed as cytoplasm. The presence of ribosomes that specializes in protein coalescence is another structural similarity between prokaryotic and eukaryotic cells.

Cell Theory

As far as cell theory goes, it is a universally accepted fact that “living organisms are made up of cells.” Moreover, cell theory has also established that “all cells come from pre-existing cells” and “cells are the structural unit of all living organisms.” Cells are also known as the “basic unit of reproduction.”

Discovery of Cell

The discovery of cell was made by Robert Hooke in 1665 when various microscopic advancements were taking place. He came to discover cells when he was observing some slices of bottle cork under microscope. He gave the name of his discovery “cells” which means “a small room” in Latina. However, Hooke didn’t realize at that time that the things that he was observing were, in fact, alive. It was the observation of Anton van Leewenhoek which proved that cells were living organisms as his observation told that cells were motile objects. 

Characteristics of Cells

The interior structure of a cell is made up of organelles. Of all those organelles, the most vital one is the mitochondria as it is responsible for transporting energy to the cell. Moreover, the endoplasmic reticulum works as an active transporting system for the cell which is a product of the cell’s tubular network. 

Besides that, the role of being the packaging system of the cell is fulfilled by the golgi apparatus. Lysosomes fulfill the function of being digestive enzymes and ribosomes synthesize protein for the cells. Another important characteristic of the cell is that the organelles are protected by a jelly-like substance called the cytoplasm. 

Cell Organelles and Their Functions

Organelles are seen as the multiple subunits of the cell. Each cell organelle has a separate function to perform and each of them is endowed with a special characteristic that helps them fulfill their respective functions.

1. Plasma Membrane: The function of plasma membrane is to protect the cell by acting as a protective layer. Besides that, the role of the plasma membrane is also to monitor the movement of the substances that come in and out of the cell.

2. Ribosomes: By using RNA and amino acids, ribosomes supply protein for the cells by utilizing the information supplied by the RNA.

3. Mitochondria: Also known as the powerhouse and one of the largest organelles of the cell, mitochondria functions as an active respiratory agent for the cell.

4. Vacuoles: The chief role of vacuoles is to relieve the cell from any kind of toxicity by getting rid of all the waste products. Vacuoles are also involved in the task of maintaining the pH balance of the cell.

5. Cytoskeleton: The main function of cytoskeleton is to maintain the shape of the cells as well as their elasticity. Moreover, they are also involved in the task of supporting cell contents and anchoring the nucleus.

6. Plastids: Plastids are of various kinds and each of them is endowed with a different function. The functions of each individual plastid are mentioned below:

• Chloroplasts: Chloroplasts are responsible for producing food as they are the main site for the process of photosynthesis.

• Chromoplasts: Chromoplasts safeguard chlorophyll in plants as well as collect light energy. They are also responsible for producing and storing pigments that protect chlorophyll in plants and absorb light energy.

• Gerontoplasts: These are responsible for protecting the necessary nutrients after a cell expires.

• Leucoplasts: Their main function is to act as storage agents for lipids, proteins and starch.

7. Endoplasmic Reticulum: Endoplasmic reticulum is again divided into two types: 

The function of smooth endoplasmic reticulum is to produce enzymes in the liver, transport vesicles, synthesize hormones in the brain cell and contract muscle cells. On the other hand, the role of rough endoplasmic reticulum is to supply the required proteins in the smooth endoplasmic reticulum as well as to produce insulin and antibodies.

8. Golgi Apparatus: The main responsibility of Golgi apparatus is to manufacture and transport and store products from the endoplasmic reticulum.

 Conclusion

• Cells are the fundamental unit of human life.

• The discovery of cells was made by Robert Hooke.

• Cells are composed of different organelles that are meant to perform different functions.

• A cell is structured by cytoplasm, plasma membrane and ribosomes.