A 2.2 CELL STRUCTURE (WHOLE TOPIC), A 2.2 CELL STRUCTURE (WHOLE TOPIC)

• what are cells?

  basic structural unit of all living organisms
• who came up with the term 'cells'


  scientist named Robert Hooke
• what are the three main ideas of cell theory

  1. All organisms are composed of one or more cells2. The cell is the basic functional unit 3. All cells come from pre-existing cells
• What do all cells have

  surrounded by cell membranecontain genetic materialhave chemical reactions occuring within cell which are catalysed by enzymes
• how do optical light microscopes work?

  light directed through the thin layer of biological material (on glass slide) and is focused through several lenses so image is visible
• Magnification calculation

  Image size/actual size
• 1m

  1000mm
• 1mm


  1000um
• 1um

  1000nm
• what are microscopes used for

  used to analyse cell components and observe organelles
• What is magnification?

  tells you how many times bigger the image produced by microscope is than the real object
• what is resolution


  ability to distinguish between objects that are close together (focus)
• what are the 2 types of microscopes

  optical and electron
• what is an optical microscope


  uses light to form an image
• what is a limitation of optical microscopes

  optical microscopes have a maximum resolution of 0.2 micrometres thus cant be used to observe smaller organisms such as ribosomes, endoplasmic reticulum or lysosomes
• what is the maximum useful magnification of optical microscopes

  x 1500
• what are electron microscopes

  use electrons to form an image thus increasing the resolution of image compared to optical microscopes
• what is the maximum resolution of electron microscopes?


  0.2 nanometres (1000 x greater than optical microscopes)
• what can electron microscopes be used for

  used to observe small organelles such as ribosomes, endoplasmic reticulum and lysosomes
• what is the maximum magnification of electron microscopes

  x 1500000
• what are the 2 types of electron microscopes

  transmission electron microscopes and scanning electron microscopes
• What are TEMs

  use electromagnets to focus a beam of electrons to be transmitted through the specimen
• how does the specimen appear when using a TEMs

  denser parts appear darker as more electrons are absorbed
• TEMs advantages

  high-resolution images allowing internal structures to be seen within cells
• TEMs disadvantages

  As there is a vacuum inside a TEM, all the water must be removed from the specimen and so living cells cannot be observed, meaning that specimens must be dead. Optical microscopes can be used to observe live specimens
• how is the image produced by a TEM different from an optical microscope

  dont produce a colour image like optical microscopes
• what are SEMs

  scan a beam of electrons across the specimen which bounces off the specimen surface and electrons are detected forming an image
• what is a major benefit of SEMs

  can produce a 3D image allowing the external surface of the specimen to be observed
• SEMs disadvantages

  low resolution images, no colour and cant be used to observe live specimens
• what 3 things are always present in a cell?

  DNA, cytoplasm, plasma membrane
• what does the presence of DNA mean

  means a new cell can be formed from an old cell, as genetic material is able to be stored and transferred
• what does DNA control

  production of enzymes and other vital proteins within the cell; contain all information needed for cells to carry out all its functions
• where is cytoplasm found

  within the boundary of the cell
• what is cytoplasm composed of

  mainly of water with dissolved substances; also has enzymes which catalyse the chemical reactions
• what is cytoplasm fluid known as

  cytosol
• What occurs in the cytoplasm?

  chemical reactions
• what is the plasma membrane

  outer boundary of the cell and controls what enters and leaves the cell
• how many layers does the plasma membrane have

  2 layers - called bilayer
• what does the bilayer consist of

  lipids (vary depending on the type of organism) which control the permeability of the membrane
• what is the function of the plasma membrane


  responsible for controlling interactions of cell interior with cell exterior