Every organism on the planet is made of cells. However, these cells are not all the same.

The common characteristics of human cells are:

  • A nucleus to store the genetic information.
  • A cell membrane to hold the cell together and to control what enters and leaves the cell.
  • A cytoplasm where chemical reactions take place.
  • Mitochondria, where aerobic respiration takes place.
  • Ribosomes, where proteins are made.


Plant cells have all of the characteristics of humans cells mentioned above, as well as 3 more. These are:

  • A cell wall to support and protect the cell.
  • A permanent vacuole which contains cell sap to maintain pressure within the cell, and is involved in the removal of unwanted chemicals.
  • Chloroplasts which contain chlorophyll for photosynthesis.
cell diagram, beginner biology

Bacterial cells don’t have a nucleus. Instead, their genetic information floats freely within the cell.

The characteristics that make red blood cells adapted to carry oxygen are:

  • They are packed with hemoglobin which absorbs oxygen.
  • They are concave to give the cells a greater surface area for absorbing oxygen.
  • They have no nucleus, so they can pack even more hemoglobin to absorb more oxygen.

The characteristics that make egg and sperm cells adapted for the roles are:

  • Egg cells have larger food reservoirs to feed the embryo.
  • Sperm cells have a long tail with many mitochondria, so it can swim towards the egg quickly.
  • Sperm cells have digestive enzymes on their tip, so they can digest through the egg’s cell membrane for fertilisation.

The ways these cells are able to work together to make the human body work is through organisation. When multiple specialised cells work together towards a specific function they form a tissue. When multiple tissues work together towards a specific function they form an organ. And when multiple organs work together they form an organ system.

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