Hierarchical Organisation in Multicellular Organisms
Multicellular organisms have a hierarchical organisation of cells, tissues, organs, and systems that work together to perform essential functions:
- Cells: The basic unit of life, cells are specialised to carry out specific functions. For example, muscle cells contract to enable movement, while nerve cells transmit electrical signals.
- Tissues: Groups of similar cells that work together to perform a particular function. For example, muscle tissue is made up of muscle cells that work together to produce movement, while nervous tissue consists of neurons that transmit signals.
- Organs: Structures made up of different tissues that work together to perform specific functions. For example, the heart is an organ composed of muscle tissue, connective tissue and nervous tissue, all of which work together to pump blood.
- Systems: Groups of organs that work together to perform complex functions necessary for the survival of the organism. For example, the digestive system is responsible for obtaining nutrients, the respiratory system for exchanging gases, and the excretory system for removing wastes.
The hierarchical organisation of cells, tissues, organs, and systems in multicellular organisms is essential for efficiently carrying out complex functions like obtaining nutrients, exchanging gases, and removing wastes. At the cellular level, specialised cells perform specific tasks that are crucial for the organism’s survival. These cells group together to form tissues, which work in unison to perform broader functions. These tissues combine to form organs, each designed for a particular function.
Obtaining nutrients
Cellular Level: Specialised cells in the digestive system, such as epithelial cells lining the intestines, are responsible for absorbing nutrients from digested food.
Tissue Level: These epithelial cells form the lining of the intestines, a tissue that increases surface area for maximum nutrient absorption.
Organ Level: The intestines, part of the digestive system, work with the stomach and other organs to break down food, absorb nutrients, and transfer them to the bloodstream. The circulatory system then distributes these nutrients to all cells in the body, ensuring that each cell receives the necessary energy and building blocks for growth and repair.
Exchanging gases
Cellular Level: In the respiratory system, alveolar cells in the lungs facilitate the exchange of oxygen and carbon dioxide between the air and the blood.
Tissue Level: These alveolar cells form the thin, permeable tissue of the alveoli, which are small air sacs in the lungs that allow for efficient gas exchange.
Organ Level: The lungs, as organs of the respiratory system, work with the circulatory system to bring oxygen into the body and expel carbon dioxide. Oxygenated blood is then transported to cells throughout the body, while carbon dioxide is carried back to the lungs for exhalation.
Removing wastes
Cellular Level: In the excretory system, kidney cells, specifically in the nephrons, filter waste products from the blood, including urea, excess salts, and water.
Tissue Level: These kidney cells form the tissue of the nephrons, which are the functional units of the kidneys responsible for filtering blood and forming urine.
Organ Level: The kidneys, as organs of the excretory system, work with the circulatory system to remove waste products from the blood and excrete them as urine. This urine is then stored in the bladder before being expelled from the body, ensuring that toxic substances do not accumulate and disrupt cellular function.