GCSE Biology - Levels of Organisation - Cells, Tissues, Organs and Organ Systems (2026/27 exams)

Summary

Key Points

• —Multicellular organisms, such as humans, are organized in a hierarchy, starting from subcellular structures and culminating in the complete organism. 0:28
• —The lowest level of organization begins with organelles, which are subcellular structures like the nucleus, ribosomes, and mitochondria, each performing a specific role within a cell. 0:36
• —Multiple organelles combine to form a cell, which are specialized units like epithelial, muscle, or glandular cells, varying in shape, size, and organelle composition. 0:42
• —Tissues are formed by groups of similar specialized cells working together to carry out a particular function, such as epithelial tissue covering body surfaces or muscle tissue enabling movement. 1:26
• —Organs represent the next level, defined as a group of different tissues that collaborate to perform a specific function, like the stomach which combines various tissues to kill microorganisms and break down proteins. 2:27
• —An organ system consists of multiple organs working in concert to carry out a major bodily function, such as the digestive system comprising the stomach, pancreas, and liver to process food and absorb nutrients. 2:51
• —The highest level of organization is the complete organism, which is formed by the coordinated function of multiple organ systems. 3:10
• —While the video provides specific examples for each level, there are numerous types of organs and approximately 12 different organ systems, including the immune, nervous, and respiratory systems, in a complex organism. 3:36