Cell: An Introduction
Do you know the egg of an ostrich is an example of the largest cell? And the cells which are present in our body are so small that can't be seen by the naked eye. What is the meaning of a cell? How these microscopic cells comprise our whole body. Do you know the types of cells and their functions? Do you know the different components of cells? Do you know the difference between plant cells and animal cells? Do you know bacterial cells are prokaryotic cells whereas human cells are eukaryotic cells? What is the difference between eukaryotic and prokaryotic cells? You will get answers of all these questions after reading this article. Human body cell structure is also explained below.
Cell Definition
The cell is the smallest functional and structural unit of all living organisms. All organisms are made of cells, a group of cells makes tissues, and a group of tissues makes organs.
What are the Types of Cells?
There are mainly two types of cells based on structure.
Eukaryotic cell
Prokaryotic Cells
These cells are found in lower or primitive organisms. These cells do not have a nucleus and the genetic material of these cells is suspended freely in the cytoplasm in a region called the nucleoid. These types of cells reproduce by asexual methods. The cell size is generally 0.1-0.5 micrometres. The hereditary material may be either DNA or RNA.
Eukaryotic Cells
These types of cells have true nuclei, and their size is between 10 and 100 micrometres. These cells can reproduce by both asexual and sexual methods. Eukaryotic cells involve animal cells, plant cells, fungi, and protists.
Structure of a Cell
The basic structure of a cell contains cell membranes, nuclei, cytoplasm, and various cell organelles.
All cell organelles are present in the cytoplasm of a cell.
Cytoplasm semifluid substance present between cell membrane and nucleus.
Different Parts of Cell and Functions
The following different parts of the cell and human cell function are explained below:
Nucleus - It is the main cell organelle and is also known as the master of the cell. It contains genetic material. The nuclear membrane is the outermost layer of the nucleus. Nuclear pores are present on the nuclear membrane to allow the movement of particles and molecules inside and outside of the cell.
Endoplasmic reticulum - Endoplasmic reticulum is also known as the palate particle in the name of discovery. It consists of membranes present inside the membrane.
It is of two types: Rough endoplasmic reticulum and smooth endoplasmic reticulum.
Rough endoplasmic reticulum - These are rough in appearance due to the presence of ribosomes on the surface of the endoplasmic reticulum. Rough endoplasmic reticulum synthesises protein and smooth endoplasmic reticulum is known as smooth because of an absence of ribosomes, which synthesise lipids, steroids, and other substances.
Mitochondria - These are sausage-shaped structures present in the cytoplasm. And synthesis of ATP molecules. It is also known as the powerhouse of the cell. It is a double membrane structure, an inner and outer membrane. Cristae are the fold of the inner membrane to increase the surface area. Matrix is the space present inside the inner membrane of mitochondria containing various types of enzymes and RNA.
Golgi Apparatus - These are the flattened and stacked pieces called cisternae and perform the functions of modifying, and packaging. It has two faces cis and trans. Various cisternae are held together by a matrix.
Lysosomes - These are membrane-bound organelles that contain a variety of enzymes that break biological polymers.
Human Cell Functions
The basic functions of the cell are given below:
Provide structural support.
Allow movement of substances inside and outside the cell.
Helps in reproduction through the process of meiosis and mitosis.
Cells contain mitochondria which help in energy production.
Help in the growth of organisms.
Cells of the Human Body
There are various types of cells in the human body depending on the structure and function they perform. Some examples of cells are provided below:
Blood Cells - There are different types of blood cells such as lymphocytes, leukocytes, and thrombocytes. Blood cells are produced from bone marrow.
Fat Cells - These cells contain or store fat droplets in the form of triglycerides. These are also known as adipocytes.
Nerve Cells - These cells comprise the whole nervous system. These are the basic units of the nervous system. Helps in the transmission of signals to and from the central nervous system. Contain a nucleus, cytoplasm, and some cell organelles.
Endothelial Cells - These cells form the innermost lining of the blood vessels. These cells make the new blood vessels.
Important Questions
1. Who discovered the cell?
Ans: The first dead cell was discovered by Robert Hooke in 1665 in the cork of bark. And first, the live cell was discovered by Leeuwenhoek.
2. What is the function cell?
Ans: The different functions of the cell are to provide structural support, convert food into energy, and also provide energy to various cells of the body. Cells also perform specialised functions for body cells.
3. What are cells made of?
Ans: Cells are made of various components: organic molecules, inorganic molecules, and water.
Interesting Facts
The ovum is the largest cell of the female human body.
A mature red blood cell does not have any nucleus.
The size of the longest neuron may be about 1m.
Plant cell does not rupture when placed over water.
Whenever there is damage to any organ of a pregnant woman, the foetus will send stem cells to regenerate the damaged organ.
Key Features
In this article, we studied cells, their types, and different examples of cells.
The cell is the structural and functional unit of living organisms.
There are mainly two types of cells: eukaryotic and prokaryotic.
Prokaryotes are the primitive type of cells whereas eukaryotes are the modern type of cells.
Important components of the cell are the plasma membrane, lysosomes, endoplasmic reticulum, mitochondria, etc.
The nucleus is known as the master of the cell.
Practice Questions
1. What is a cell mother?
2. Where do cells come from?
3. How many cells are in the human body?
4. Which organ is known as the mother of all cells?
5. Explain the human body cell structure.
6. What are different cell parts and functions?
FAQs on Parts of the Cell
1. What are the primary parts of a cell and what are their functions?
A typical eukaryotic cell contains several specialised parts called organelles. The main parts and their functions are:
- Nucleus: Controls all cell activities and contains the genetic material (DNA).
- Cell Membrane: A semi-permeable barrier that controls which substances enter and leave the cell.
- Cytoplasm: The jelly-like substance that fills the cell and holds organelles in place.
- Mitochondria: The site of cellular respiration, generating most of the cell's supply of ATP (energy).
- Ribosomes: Responsible for synthesising proteins.
- Endoplasmic Reticulum (ER): Involved in protein and lipid synthesis and transport.
- Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.
- Lysosomes: Contain digestive enzymes to break down waste materials and cellular debris.
2. What are the key differences between a plant cell and an animal cell?
Plant and animal cells have several distinct differences based on their functions. Plant cells possess a rigid cell wall made of cellulose outside the cell membrane, providing structural support, which animal cells lack. They also contain chloroplasts, the site of photosynthesis. Furthermore, plant cells typically have a large central vacuole that maintains turgor pressure, whereas animal cells may have several small, temporary vacuoles.
3. What is the main difference between prokaryotic and eukaryotic cells?
The primary difference lies in their structure and complexity. Eukaryotic cells (found in plants, animals, fungi) have a true, membrane-bound nucleus that houses their genetic material. They also contain various other membrane-bound organelles like mitochondria and the Golgi apparatus. In contrast, prokaryotic cells (like bacteria) lack a nucleus; their genetic material floats freely in the cytoplasm in a region called the nucleoid. They also do not have membrane-bound organelles.
4. What is the function of the cell membrane and why is it described as selectively permeable?
The cell membrane, also known as the plasma membrane, acts as a protective barrier enclosing the cell's cytoplasm. Its primary function is to regulate the movement of substances into and out of the cell. It is described as selectively permeable because it allows certain molecules, like water and oxygen, to pass through freely, while actively blocking or transporting other substances like ions and larger molecules. This control is crucial for maintaining the cell's internal environment.
5. Why is the mitochondrion often called the 'powerhouse of the cell'?
The mitochondrion earns this title because it is the primary site of cellular respiration in eukaryotes. During this process, it converts chemical energy from food molecules, like glucose, into adenosine triphosphate (ATP). ATP is the main energy currency that powers nearly all metabolic activities and functions of the cell, from muscle contraction to DNA replication.
6. How do the nucleus and ribosomes work together to build proteins?
This process is central to cell function. The nucleus holds the cell's master blueprint, the DNA. It transcribes a specific gene from the DNA into a messenger RNA (mRNA) molecule. This mRNA then travels out of the nucleus into the cytoplasm and attaches to a ribosome. The ribosome reads the instructions on the mRNA and assembles amino acids in the correct sequence to create a specific protein.
7. What would happen to a cell if its lysosomes were to stop functioning?
If a cell's lysosomes, its 'recycling centre', were to stop working, the consequences would be severe. Lysosomes contain powerful digestive enzymes that break down waste products, damaged organelles, and foreign invaders. Without functional lysosomes, these waste materials would accumulate within the cell, leading to cellular damage, toxicity, and disrupting normal metabolic processes, which could ultimately cause the cell to die.
8. How does the structure of the plant cell wall relate to its primary function?
The structure of the plant cell wall is perfectly suited for its function of providing support and protection. It is primarily made of cellulose, a strong polysaccharide that forms rigid fibres. This rigidity prevents the cell from bursting when it absorbs a lot of water (maintaining turgor pressure) and provides the structural strength that allows plants to stand upright and withstand environmental stresses like wind and gravity.
9. Why is cell theory considered a fundamental principle of biology?
Cell theory is fundamental because it provides a unifying framework for understanding all living organisms. It states that all living things are composed of cells, that the cell is the basic unit of life, and that all new cells arise from pre-existing cells. This principle connects diverse fields like genetics, medicine, and evolution by establishing a common structural and functional basis for all forms of life, from single-celled bacteria to complex multicellular animals.
