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