Biology » Introducing the Cell » Cell Organelles


Cell Organelles

We will now look at the key organelles that make up the cell. It is important to bear in mind that structure and function are closely related in all living systems. When studying each organelle, ensure that you observe the specific structures (from micrographs) that allow the organelle to perform its specific function.


The cytoplasm is the material within a living cell, excluding the cell nucleus. Components of a typical animal cell: 1. Nucleolus; 2. Nucleus; 3. Ribosome (little dots); 4. Vesicle; 5. Rough endoplasmic reticulum; 6. Golgi apparatus (or “Golgi body”); 7. Cytoskeleton; 8. Smooth endoplasmic reticulum; 9. Mitochondrion; 10. Vacuole; 11. Cytosol (fluid that contains organelles, comprising the cytoplasm); 12. Lysosome; 13. Centrosome; 14. Cell membrane. Image credit: “Kelvinsong”, via Wikimedia Commons (public domain)


The cytoplasm is the jelly-like substance that fills the cell. It consists of up to 90% water. It also contains dissolved nutrients and waste products. Its main function is to hold together the organelles which make up the cytoplasm. It also nourishes the cell by supplying it with salts and sugars and provides a medium for metabolic reactions to occur.


You may have encountered the terms cytoplasm, nucleoplasm and protoplasm earlier in your biology classes. Cytoplasm is the part of the cell that is within the cell membrane and excludes the nucleus. Nucleoplasm is the substance of the cell nucleus, i.e. everything within the nucleus that is not part of the nucleolus. Protoplasm is the colourless material comprising the living part of a cell, including the cytoplasm, nucleus and other organelles.

All the contents of prokaryotic cells are contained within the cytoplasm. In eukaryotic cells, all the organelles are contained within the cytoplasm except the nucleolus which is contained within the nucleus.

Functions of the Cytoplasm

  • The cytoplasm provides mechanical support to the cell by exerting pressure against the cell’s membrane which helps keep the shape of the cell. This pressure is known as turgor pressure.
  • It is the site of most cellular activities including metabolism, cell division and protein synthesis.
  • The cytoplasm contains ribosomes which assist in the synthesis of protein.
  • The cytoplasm acts a storage area for small carbohydrate, lipid and protein molecules.
  • The cytoplasm suspends and can transport organelles around the cell.

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