Cells - revision notes. All living things are made up of cells which have an outer boundary, nucleus, cytoplasm and organelles.

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Cell Theory

  1. All living things are made up of cells
  2. Cells are the smallest unit of life
  3. All cells arise from pre-existing cells

1. All living things are made up of cells which have an outer boundary, nucleus, cytoplasm and organelles. However there are many exceptions to this rule.    

Eg: Muscle cells are multi nucleated, fungi have no cell membrane or cell wall, viruses behave like non-living entities, RBC’s have no nucleus

2. Cells are the smallest unit of life that can show all the characteristics of a living organism. Its functions are carried out by organelles. Eg: mitochondria and chloroplasts are autonomous organelles and have their own DNA

3. All cells arise from pre-existing cells by the process of cell division. In primitive organisms like amoebas, it occurs by binary fission while in higher organisms, it occurs by mitosis. The first cell however was formed by spontaneous generation. This bio-molecule should have been self-replicating like macromonial RNA


They carry out all the functions with the help of a single cell. The main functions of such cells are:

  1. Response to change in environment
  2. Homeostasis: maintenance and regulation of the internal environment
  3. Metabolism: respiration, synthesis of ATP
  4. Growth: increase in cell size and volume
  5. Reproduction: asexual methods
  6. Nutrition: synthesis of organic molecules, absorption of organic matter


  1. Differentiation/Specialization- It is the process by which cells within a multi-cellular organism specialize in their functions. It takes place due to the switching off of genes in particular groups of cells. As a result, cells modify themselves to have specific shapes, functions and adaptations. It helps in making the multi-cellular organism more efficient when competing for a specific resource. Eg: transport in plants can take place from one cell to another by diffusion. However this process becomes more efficient when there is a specialized group of cells like xylem and phloem
  2. Emergent Properties- It is the occurrence of unexpected characteristics pr properties in a complex system. These properties are from all the components present in a particular system
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They are undifferentiated cells which retain the capacity to divide and they have the ability to differentiate along different pathways. Under the right conditions, they can be modified to express particular genes and to differentiate into a particular type of cell stem cells are two types:

  1. Embryonal Cells – They are obtained from an undifferentiated embryo and have the capacity to differentiate into any kind of cell. They can be cultured easily. However the chances of rejection are high especially if it is from a donor
  2. Adult Cells – They differentiate cell ...

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