Living Organisms and Cell Structure
This page of the Free biology test revision guide introduces the fundamental concepts of living organisms and cellular structure. It provides a comprehensive overview of the characteristics that define life and the organizational hierarchy of biological systems.
Definition: An organism is any living thing that carries out life processes.
The guide emphasizes that all living organisms must perform seven key life processes, known by the acronym MRS GREN:
Vocabulary: MRS GREN stands for Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, and Nutrition.
Each of these processes is briefly explained, providing students with a clear understanding of what constitutes a living organism.
The page also introduces the concept of biological organization, presenting a hierarchical structure from the smallest unit cells to the largest organisms:
Highlight: The levels of organization in living things are: Cells → Tissues → Organs → Organ Systems → Organisms
Examples are provided for both plant and animal systems to illustrate this hierarchy:
Example: In plants, palisade cells form palisade tissue, which is part of the leaf anorgan in the photosynthetic system of lilies anorganism.
Example: In animals, muscle cells form cardiac tissue, which makes up the heart anorgan in the circulatory system of a koala anorganism.
This comprehensive overview helps students understand the fundamental building blocks of life and how they are organized into complex living systems, which is crucial for GCSE Biology revision.
