The basic structural unit of body tissues. There are around 10 billion cells in the human body and they are structurally and functionally linked to carry out the body’s many complex activities.
A mass of protoplasm containing a nucleus or nuclear material; the structural unit of all animals and plants. Cells and cell products form all the body tissues; their structures are correlated with the functions of the organs of which these tissues are a part. Cells arise only from pre-existing cells, through cell division. Growth and development result from the increase in numbers of cells and their differentiation into different types of tissues. Specialized germ cells, the spermatozoa and ova, contain the genes to be passed to offspring.
The smallest independently functioning unit in the structure of an organism.
Basic units of all living things from bacteria to plants to animals, including human beings.
A solitary unit of a battery that converts chemical energy into electrical energy.
The fundamental building block of all living organisms is the cell. The human body consists of billions of cells, which are intricately interconnected both structurally and functionally to carry out the intricate processes essential for sustaining life. While there may be variations in size and function, most cells share a similar basic structure.
Every cell is a minute, microscopic entity encapsulating a fluid called cytoplasm. It is enveloped by a membrane that governs the movement of vital substances such as oxygen and nutrients into the cell, while allowing the elimination of waste materials like carbon dioxide and the secretion of manufactured substances such as hormones. Certain cells, like those found in the lining of the small intestine, possess microvilli—projections that augment the surface area of the cells, facilitating efficient absorption.
With the exception of red blood cells, all cells possess a nucleus, which serves as the command center for major cellular activities by controlling the production of proteins in terms of quantity and type. Within the nucleus, chromosomes are present, composed of the nucleic acid DNA. This DNA carries the instructions for protein synthesis, which are transported into the cytoplasm by a specific type of RNA, another nucleic acid. The decoding of these instructions takes place in ribosomes, which are tiny particles. Additionally, the nucleus contains a spherical structure known as the nucleolus, which contributes to the production of ribosomes.
Within the cytoplasm, numerous small structures called organelles are present, each with specific roles. Mitochondria play a vital role in generating energy by breaking down sugars and fatty acids. To safeguard the cytoplasm from potentially harmful substances, lysosomes and peroxisomes contain such materials. The endoplasmic reticulum, a network of membranes, facilitates the transportation of materials throughout the cell. Furthermore, the Golgi complex, composed of flattened sacs, receives and processes proteins received from the endoplasmic reticulum.
Vesicles, which are small sac-like structures, facilitate the secretion of enzymes and hormones at the cell surface. Vacuoles, created by the cytoplasm, serve as storage spaces for waste products and other materials. The cytoplasm is composed of a network of fine tubes called microtubules and filaments called microfilaments, collectively known as the cytoskeleton. This cytoskeleton provides the cell with a defined shape and structure.