Unicellular and Multicellular Organisms – Lesson Summary

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Learning Objective

In this lesson we will compare unicellular and multicellular organisms and look at different types of animal and plant cells.

Learning Outcomes

By the end of this lesson you will be able to:

  • Classify animals, plants, fungi, protists and bacteria as unicellular or multicellular organisms.
  • Compare the roles of cells in unicellular and multicellular organisms.
  • Give examples of specialised cells in animals and plants and describe how their structure relates to their function.

 
unicellular and multicellular organisms contents

(Image: Frank Fox, Wikimedia Commons)

Lesson Topics

1 | Unicellular Organisms

2 | Multicellular Organisms

3 | Tissues, Organs and Organ Systems

4 | Specialised Cells in Animals

5 | Specialised Cells in Plants

6 | Summary

Lesson Summary

  • Unicellular organisms are organisms that consist of a single cell.
  • They include all bacteria (prokaryotes) and most protists (eukaryotes).
  • Multicellular organisms are organisms that consist of many cells.
  • They include all animals, all plants and most fungi, all of which are eukaryotes.
  • The cells of unicellular organisms carry out all the functions of a living organism.
  • The cells of multicellular organisms have specialised functions.
  • They aggregate into tissues, which form organs, which are part of organ systems that which perform specific bodily functions.
  • Examples of cell types in animals include:
  • Muscle cells – found in skeletal muscles, smooth muscles and cardiac muscles.
  • Nerve cells – found in the brain, spinal cord and nerves.
  • Red blood cells – transport oxygen and carbon dioxide through the bloodstream.
  • White blood cells – found in the bloodstream and in lymph tissue where they form part of the body’s immune system.
  • Fat cells (adipose cells) – include brown fat cells and white fat cells which are found under the skin and between organs.
  • Egg cells and sperm cells – the female and male reproductive cells.
  • Examples of cell types in plants include:
  • Palisade cells – photosynthetic cells mostly found near the upper surface of leaves.
  • Guard cells – pairs of cells found on the surfaces of leaves, which create openings called stomates for the movement of gases in and out of the leaf.
  • Xylem cells and phloem cells – conducting cells that form vascular bundles for the transport of substances around a plant.
  • Root hair cells – cells on the surfaces of roots that contain tiny hair-like projections that increase the absorption of water and minerals.
  • Epidermal cells – cells that form a protective layer called the epidermis on the outer surfaces of a plant.

 
 
stem cross-section

(Image: RolfDieterMueller, Wikimedia Commons)

(Header image: Nephron, Wikimedia Commons)