The basic unit that constitutes a living organism and facilities 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 multi-cellular 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.
What is the Difference Between Cells and Tissue?
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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 tumors or cancer. Most anti-tumor 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. Thereby, normal cells are also attacked and destroyed by the immune system of mistaking it as a foreign body. The latest researches are looking into the genetic and environmental reasons behind defective apoptosis and autoimmune diseases.