Cells, Tissues and Organs

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All living things are made of cells.  Cells are small and can only be seen with microscopes. Light microscopes are used in school, but in industry they might use an electron microscope.

Most cells have certain structures in common:

  • A nucleus to control the cell's activities
  • Cytoplasm - this is where many chemical reactions take place
  • A cell membrane that controls the movement of substances into and out of the cell
  • Mitochondria where energy is released during aerobic respiration
  • Ribosomes where protein synthesis takes place.

Plant and algal cells have other features,too:

  • A rigid cell wall made of cellulose for support
  • Chloroplasts that contain chlorophyll.  The chloroplasts absorb light energy to make food - photosynthesis takes place here
  • A permanant vacuole that contains cell sap

Algae are simple aquatic organisms that have many features that are similar to plant cells.


Bacteria are very small and can only be seen with a powerful microscope.  They have a cell membrane and a cell wall which surround cytoplasm.  They do not have a nucleus so the genetic material is in the cytoplasm.  When bacteria multiply they form a colony.  Bacterial colonies can be seen with the naked eye.

Yeast is a single-celled organism.  Yeast cells have a nucleus, cytoplasm and a membrane surrounded by cell wall.


There are many types of plant and animal cell.  As an organism matures, each cell develops into a particular type.  The structure of a cell is linked to its function.  If a cell has many mitochondria then it needs a lot of energy, eg muscle/sperm cell.  If a cell has many ribosomes it is making a lot of protein, eg gland cells that produce enzymes…


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