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2.5 Summary

2.5 Summary (ESG5D)

The discovery of cells:

  • All living organisms are made of cells.
  • Cells are very small therefore magnifying instruments such as lenses and microscopes are used to view them.
  • By using a light microscope the simple features of cells can be studied. The light microscope uses a beam of light focused by various glass lenses.
  • Electron microscopes have higher power of magnification than the ordinary light microscope, therefore allowing us to see very small structures inside the cells. These microscopes use a beam of electrons focused by electromagnets to magnify objects instead of light rays and lenses.
  • Robert Hooke (1665) used a light microscope to examine non-living cork cells.
  • Antonie van Leeuwenhoek was the first person to observe living cells using a microscope.
  • The development of cell theory was from the study of microscopic cells.

Cell structure and function

  • All cells have the same basic structure. They are all surrounded by a cell membrane and contain cytoplasm and organelles.
  • Cells have different sizes, shapes and structures in order to carry out specialised functions.
  • The cell membrane is made of phospholipids and proteins and controls substances which move in and out of the cell.
  • The structure of the cell membrane is referred to as the Fluid Mosaic Model.
  • The nucleus is made up of a nuclear membrane with nucleopores, chromatin material and the nucleolus inside the nucleoplasm.
  • Mitochondria release chemical potential energy (ATP) for the cell during cellular respiration.
  • Ribosomes are important for protein production.
  • Cytoplasm is used for storage and circulation of various materials.
  • Endoplasmic reticulum transports substances from one part of the cell to another.
  • The Golgi body modifies, secretes, packages and distributes various organic molecules (proteins and lipids) around the cell.
  • Vacuoles are used for storage. In plant cells these are large, whilst in animal cells, if present, are very small.
  • Lysosomes are mainly found in animal cells.
  • Centrioles are only found in animal cells.
  • The cell wall is found only in plant cells and is made up of cellulose. The cell wall gives the plants shape, support and protection.
  • Plastids are found only in plant cells. There are three types of plastids:
    • chloroplasts contain chlorophyll and their function is the production of food by photosynthesis
    • chromoplasts give colour to fruits and flowers
    • leucoplasts are white and are used mainly for starch storage