Know About Cell and Tissue
The basic unit that constitutes a living organism and facilitates life functions is called a cell. All living organisms comprise cells, and millions of microorganisms like bacteria are nothing but a cell capable of fully functioning on its own. Further, for complex multicellular organisms like plants and animals, these cells are organized into tissues, organs, and organ systems. Cells are categorized as eukaryotic cells and prokaryotic (primitive) cells based on the presence or absence of the nucleus and other membrane-bound organelles.
Tissues are formed by cells of similar functions being grouped together. The tissues further develop into organs with specific functions. Tissues are hence similar to cells but more organized and specialized to perform a particular function. In plants, there are broadly two types of tissues- meristematic tissues that contain actively dividing cells, and permanent tissues that are differentiated to do specific functions.
In animals, the tissues are divided into specialized categories as follows.
Epithelial Tissues - They form the outer surfaces, membranes, and linings of organs and organ systems.
Muscle Tissues - They form the skeletal muscles, voluntary muscles, involuntary muscles, and cardiac muscles. They account for movement inside and outside the body.
Connective tissues constitute blood, bone, ligaments, tendons, and adipose tissues, connecting between other tissues.
Nervous tissues are the tissues in the brain, spinal cord, and peripheral nervous system that transmit neural messages for control and coordination.
One can differentiate between cell and tissue as follows.
Interesting Facts:
The ovum or the mature egg released by a female human's ovaries is the largest cell in the body. Its diameter is 120µm. On the contrary, the smallest cell in humans is the head of a spermatozoon, which is 5µm.
About 95% of the cells inside a human body are bacteria, and most of these bacteria live in the digestive tract. Human skin also hosts billions of bacteria. There are more bacterial cells in the human body compared to human cells. These bacteria are all not bad for us either. Unlike disease-causing bacteria, many bacteria within the human body are useful and are called 'probiotics.' These bacteria protect the body from infections and provide several essential nutrients for the healthy functioning of our system.
Cells suicide when they become infected! Whenever a cell is damaged or infected, the lysosomes within a cell break. The potent digestive enzymes destroy the whole cell. This is why lysosomes are called ‘suicidal bags’ of the cell. This process of self-destruction by cells is called autophagy. Apoptosis is a similar process for programmed cell death. These self-destruction processes are natural, beneficial, and keep the body's functioning and mitosis regulated. Whenever our body cannot self-destruct unnecessary cells, it can lead to conditions like tumours or cancer. Most antitumor drugs work by inducing apoptosis among cells to tackle cancerous cells.
Conversely, when there is a defect in these self-destruction systems, situations like autoimmune diseases occur. Therefore, normal cells are also attacked and destroyed by the immune system, mistaking it as a foreign body. The latest researches are looking into the genetic and environmental reasons behind defective apoptosis and autoimmune diseases.
Is There a Distinction between a Cell and a Tissue?
Cells and tissues make up a live organism. Both are structurally present in all living organisms and are equally important. Cells are an essential component of tissues; without them, there would be no problems, and cells compose the many types of tissues in all multicellular animals. Every live organism has at least one cell. Let's look at the distinction between a cell and a tissue.
Cells Vs Tissues
Cell
The cell is the smallest structural and functional unit of life.There is no living species on the planet Earth that does not have a cell. As a result, it is regarded as a basic unit of life. Every bodily function is carried out by these tiny cells.
Robert Hooke, an English physicist, invented the term cell for the first time in 1665. Some living organisms are unicellular, consisting of only one cell that can execute all life tasks. Amoeba, algae, bacteria, fungi, and Protista are examples of unicellular creatures. Multicellular organisms are made up of various types of cells with varied activities. Multicellular organisms include plants, animals, humans, and birds.
Tissue
Tissues are collections of related cells that collaborate to fulfill a certain task. They resemble cells in terms of structure and function. The word tissue comes from a Latin phrase that means "to weave."
Tissues are split into two categories in the plant kingdom: Meristematic tissue and Permanent tissue.
Tissues are classified into four categories in the animal kingdom:
Blood, bone, tendon, adipose tissue, and ligament are all examples of connective tissue.
Muscle Tissue includes skeletal muscle, cardiac muscle, and smooth muscle, among others.
Nervous Tissue includes the brain, spinal cord, and peripheral nervous system, among others.
Epithelial Tissue includes the surface of the skin, the reproductive tract, the airways, and the inner lining of the digestive tract.
FAQs on Difference Between Cell and Tissue
1. What is the main difference between a cell and a tissue?
The main difference lies in their level of organization and function. A cell is the smallest, fundamental structural and functional unit of life, capable of independent existence. In contrast, a tissue is a group of structurally similar cells that work together to perform a specific, collective function. Essentially, cells are the individual building blocks, while tissues are the structures built from those blocks.
2. How are cells and tissues related in the structural hierarchy of an organism?
Cells and tissues represent two consecutive levels in the biological hierarchy. The relationship is progressive:
- Cells are the foundational level.
- Similar cells group together to form tissues.
- Different tissues combine to form an organ (like the heart or stomach).
- Organs work together in an organ system (like the digestive system).
- All organ systems make up the complete organism.
3. Can you provide some examples of cells and the specific tissues they form?
Certainly. Here are a few examples of how specialized cells form distinct tissues:
- Muscle cells (myocytes) are long and contractile. They group together to form muscle tissue, which is responsible for movement.
- Nerve cells (neurons) have long axons to transmit signals. They form nervous tissue, which controls and coordinates body functions.
- Red blood cells, white blood cells, and platelets are different cell types within blood, which is considered a type of fluid connective tissue.
- Epithelial cells are tightly packed to form epithelial tissue, which covers body surfaces and lines internal organs, acting as a protective barrier.
4. Why can't a single cell perform all the complex functions of a human body?
A single cell, like an amoeba, can perform all life functions, but only for a simple, unicellular organism. In a large, complex organism like a human, a single cell faces limitations in efficiency and capability. The principle of division of labour is crucial. By grouping into tissues, specialized cells can perform one function with maximum efficiency. For instance, a nerve cell is optimized for transmitting signals, while a muscle cell is optimized for contraction. This specialization allows the entire organism to perform a vast range of complex activities simultaneously, which would be impossible for a single, unspecialized cell.
5. How do different tissues develop from the same initial set of cells in an embryo?
This process is called cell differentiation. Although most cells in an organism contain the same genetic information (DNA), they become specialized by expressing different sets of genes. In an early embryo, embryonic stem cells are pluripotent, meaning they can become any cell type. As the embryo develops, chemical signals trigger specific genes to be 'turned on' or 'turned off'. This selective gene expression causes cells to develop unique structures and functions, leading to the formation of diverse tissues like muscle, nerve, and skin tissue from a common origin.
6. Do all cells and tissues in the human body have the same lifespan?
No, their lifespans vary dramatically based on their function and the amount of wear and tear they endure. For example:
- Cells lining the stomach are replaced every few days due to exposure to harsh acids.
- Skin cells have a lifespan of about 2 to 4 weeks.
- Red blood cells circulate for about 120 days.
- In contrast, some of the most critical cells, like most neurons in the brain and cells in the heart's muscle tissue, are meant to last a lifetime and have very limited ability to regenerate.
7. What is the difference between a 'cell type' and a 'tissue type'?
A 'cell type' refers to a specific kind of individual cell defined by its unique structure and function, such as a neuron, a myocyte (muscle cell), or an osteocyte (bone cell). A 'tissue type' refers to one of the four primary categories of tissue in the body: epithelial, connective, muscular, and nervous. A tissue type is a broader classification and is often composed of multiple cell types working together. For instance, connective tissue (a tissue type) can contain fibroblasts, macrophages, and fat cells (all different cell types).
