Cells, tissues, organs, and systems in biology
Cells
- The smallest functional units of life, cells come in two types: prokaryotic and eukaryotic.
- Prokaryotic cells, found in bacteria and archaea, are simple and small with no nucleus or membrane-bound organelles.
- Eukaryotic cells, found in plants, animals, fungi, and protists, are complex and larger with a distinct nucleus and membrane-bound organelles.
- Cell functions include energy production, waste disposal, response to environmental changes, and reproduction.
- Many cell structures or organelles contribute to these functions. Key examples are mitochondria (energy production), the nucleus (genetic control), and ribosomes (protein synthesis).
Tissues
- A tissue is a group of similar cells that work together to perform a common function.
- Four basic types of tissue exist in the human body: epithelial tissue (covers body surfaces and lines internal organs), connective tissue (supports other tissues and binds them together), muscle tissue (enables movement), nervous tissue (receives stimuli and sends the signal to the rest of the body).
Organs
- An organ consists of two or more types of tissues that work together to perform a particular function.
- Examples include the heart, liver, lungs, and kidney in the human body. The heart, for instance, is composed of multiple tissues, including cardiac muscle tissue, nervous tissue, and connective tissue.
- Each organ has a distinct structure that contributes to its specific function. For instance, the billions of tiny filtering units in kidneys help filter out waste products from the blood.
Systems
- A system is a group of organs that work together to achieve a major physiological function.
- Examples are the digestive system (processes food, absorbs nutrients, disposes of waste), the respiratory system (delivers oxygen to cells, removes carbon dioxide), and the nervous system (controls body activities, interprets information from the outside environment).
- Each system relies on the others to maintain the body's overall health and functionality. For example, the respiratory system provides oxygen for the cells that the circulatory system delivers around the body.