Cell Biology

Introduction

All living organisms possess cells. It is most important structurally, biologically, and functionally. Cells are either unicellular or multicellular. By division, cells increase in number and form all the structures in the body. There are three essential parts that are present in a cell, namely, plasma membrane, cytoplasm, and nucleus. The cell is surrounded by a thin selective membrane which is known as a plasma membrane. The cytoplasm is a semiliquid substance where cell organelles are present. It is located between the plasma membrane and the nucleus. The cell was discovered by Robert Hook in 1665, In this tutorial, we will learn about the cell in depth.

Cell as a Unit of Life

Cell is most important structurally, biologically, and functionally. Cells are able to do all the biochemical processes that are required for the body. Whether it's a unicellular or a multicellular organism all the functions are done by cells. All the living species that are present in our ecosystem need to respire, consume and digest food in order to get energy.

In the meantime, metabolic waste that is produced in the body should be removed. As it's harmful to the body. Cells are also able to do all the metabolic functions of the body. Hence the cell is considered a unit of life.

Cell Theory

Cell theory was proposed by Schwann, Schleiden, and Rudolph Virchow. The theory states that

• All living organisms possess cells. The cells are either unicellular or multicellular.

• The basic unit of life is the cell.

• The cell always emerges from the pre-existing cells.

The modern theory of cells states that

• The flow of energy occurs within the cells.

• The genetic material DNA which carries the hereditary information is passed from one cell to another.

• The basic chemical composition of all living cells is similar.

Cell Structure

The structure of the cell is described below:

Cell Membrane

• It is the outermost layer of the cell.

• The cell is surrounded by a thin selective membrane which is known as a plasma membrane or cell membrane.

• Because of selective permeability in nature, it modulates the entry of certain ions and molecules into the cell.

• The cell membrane is present in both plant and animal cells.

• It gives protection to the cell.

• It perpetuates the shape of the animal cell.

Cell Wall

• Cell wall is present only in plant cells.

• The cell wall surrounds the cell membrane and is a non-living protective layer.

• Cell membrane mainly constitutes cellulose and is freely permeable.

• The main function of the cell wall is to give protection, inflexibility, and shape to the cell.

Cytoplasm

• The cytoplasm is a semiliquid substance where cell organelles are present.

• It is located between the plasma membrane and the nucleus.

• The cytoplasm is the site for most of the chemical reactions.

• The cell organelles like vacuoles, endoplasmic reticulum, mitochondria, and ribosomes are located in the cytoplasm.

Nucleus

• The nucleus is a spherical organelle that is located toward the center of the cytoplasm.

• It is present in eukaryotic cells containing genetic material (DNA) and takes part in cell division.

• The content of the nucleus is surrounded by a double-layer membrane which is known as a nuclear membrane.

• Nucleoids are unevenly shaped and contain genetic material in prokaryotic cells.

Cell Organelles

Nucleolus

• It is present within the nucleus.

• It is a dense membrane-less structure. It mainly consists of protein and RNA.

• The nucleus synthesizes ribosomes.

Nuclear membrane

• The content of the nucleus is surrounded by a double-layered membrane which is known as a nuclear membrane.

• Its main function is to protect the nucleus.

Chromosome

• The nucleus contains chromosomes which is the genetic material.

• Chromosomes consist of deoxyribonucleic acid. The DNA contains genetic information and instructs the cells accordingly.

• Chromosomes consisting proteins and DNA or RNA are termed as chromatin, which is further subdivided into euchromatin and heterochromatin.

Endoplasmic Reticulum

• It plays a crucial role in the transportation of substances.

• Apart from this, it helps in carbohydrate metabolism, lipid synthesis, and protein synthesis.

• The endoplasmic reticulum is further subdivided into smooth and rough endoplasmic reticulum.

Golgi Bodies

• It helps in the process of packaging protein and lipid molecules.

Ribosomes

• The ribosome is the site for protein synthesis.

Mitochondria

• It generates adenosine triphosphate (ATP), the cell's main energy source.

• Mitochondria are commonly called the powerhouse of the cell.

Lysosome

• Lysosomes are an important membrane-bound cell organelle that is present in the eukaryotic cells of animals.

• It contains digestive enzymes that help break down proteins, nucleic acids, carbohydrates, and lipids.

• The lysosome is also known as the suicide bag of the cell.

Chloroplast

• It is present only in plant cells.

• Chloroplast contains chlorophyll.

Vacuoles

• It is the site for storing food, waste materials, and water.

Images Coming soon

Difference between Plant Cells and Animal Cells

Plant cell	Animal cell
Larger in size	Smaller in the size
Cell wall is present	Absent of cell wall
Plastid is present	Plastid is absent
Prominent, fewer vacuoles are present	Vacuoles are small in size that is mainly associated with secretion and excretion
Centromere is present.	Centromere is absent.

Importance of Cell Biology with Application

Cell biology is the branch of Biology that studies the cell. The study of cells includes cell anatomy, cell division, cellular respiration as well as the death of cells. Cell biologists study the cell in detail to know how it works in normal conditions as well as in anomalies in the cells. By examining the cell, scientists are able to discover new drugs and vaccines that are more effective for certain diseases. Cell biology is closely correlated to molecular biology, genetics, and biochemistry. Biochemistry is applied mainly in medicine, agriculture, and nutrition.

Conclusion

All living organisms possess cells. It is most important structurally, biologically, and functionally. Cells are either unicellular or multicellular. By division, they increase in number and form all the structures in the body. There are three essential parts that are present in a cell namely plasma membrane, cytoplasm, and nucleus.

FAQs

Q1. Why lysosome is known as a suicide bag?

Ans: Lysosome cell organelles contain enzymes that help in digestion. The digestive enzyme starts eating its own cell in case lysosomes burst open. So lysosomes are considered suicide bags.

Q2. What do you mean by euchromatin and heterochromatin?

Ans: Euchromatin is a delicate and less condensed organization of chromatin. In transcribing cells euchromatin is found in large numbers. Heterochromatin is a highly condensed organization of chromatin. It is transcriptionally inactive. Heterochromatin is present adjacent to the nuclear membrane.

Q3. What is a ribosome?

Ans: A ribosome is present inside the cell. It is made up of RNA and protein. The ribosome is the site for protein synthesis. Protein is required by many cells for the activities like different chemical processes and damage repair of the cell.

Q4. What is a lipid?

Ans: Lipids are hydrocarbon molecules. Lipids form the building framework of the structure and function of cells of living organisms.

Q5. What are prokaryotic cells?

Ans: Prokaryotic cells are single-celled organisms. True nucleus and membrane-bound cell organelles are absent in prokaryotic cells. Example: bacteria.