light microscopes -
cells range in size

• animal cells - between 0.01mm - 0.05mm
• plant cells - between 0.01mm and 0.10mm
  the human eye can see object as small as 0.05mm so a microscope is designed to see a cell in depth
  microscopes magnify the image of a biological specimen so that it appears larger
  school labs use compound microscopes
  
  

calculating magnification of a microscope -
the compound microscope uses two lenses to magnify the specimen -

• the eyepiece
• an objective lens
  there is a choice of objective lenses to use
  magnification can be varied according to the size of the specimen and the level of detail required
  equation -
  magnification of the microscope = magnification of eyepiece × magnification of objective
  magnification of an eyepiece is ×10 and the objective is ×4, the magnification of the microscope is 10 x 4 = 40
  

cell size -
small stuff - some sub-cellular structures, for instance ribosomes, or organisms such as viruses, it’s best to use a smaller unit – the nanometre, symbol nm
average - best unit to measure most cells is the micrometre, symbol μm

millimetre (mm) - 1/1000 metre
micrometer (μm) - 1/1000 millimetre
nanometre (nm) - 1/1000 micrometre

standard form -
millimetre (mm) - 1 × 10^-3 m
micrometre (μm) - 1 x 10^-6 m
nanometre (nm) - 1 x 10 ^-9 m

preparing biological samples for experimentation -
cheek cell test -

• put a small drop of water in the microscope slide
• gently swab the inside of your cheek with a clean cotton bud
• gently rub the cotton bud in the drop of water and will be able to see the cells with naked eye
  
  

onion skin cell -

• put a small drop of water in the microscope slide
• peel some onion skin from inside one of the leaves in an onion bulb
• use forceps to transfer it to the drop of water- make sure the onion skin is flat and there is not trapped air bubbles- stain cells with iodine
  
  

square or circle of thin glass called a coverslip is placed over the specimen - protects the microscope and makes sure the slide doesn’t dry out
mounted needle can be used to hold the specimen in place as the coverslip is lowered- important that no air bubbles are trapped underneath

risks -

• illumination may be too bright (hard on the eyes)
• care while using microscope stains
• care when handling coverslips, microscope slides and mounted needles

electron microscope-
use a beam of electrons instead of light rays
there are two types of electron microscope -

• scanning electron microscope (SEM) has a large field of view so can be used to examine the surface structure of specimens- SEMs are often used at lower magnifications
• transmission electron microscope (TEM) is used to examine thin slices or sections of cells or tissues

sperm cell -

• head of the sperm contains the DNA of fertilisation
• acrosome on the head contains enzymes so the sperm can penetrate the egg
• middle piece is packed with mitrochondria to release energy needed to swim and fertilise the egg
• tail enables the sperm to swim
  

nerve cell -

• extended so that nerves can run to and from different parts of the body to the central nervous system
• cell has extensions and branches so that it can communicate with other nerve cells, muscles and glands
• nerve cell covered in a fatty sheath to insulate nerve cells and speed up nerve impulses
  

muscles cells -

• contain filaments of protein that slide over each other, causing muscle contractions
• arrangement of filaments causes banded appearance of cardiac muscle and skeletal muscle
• contains many well developed mitochondria to provide beefy for muscle contractions
• in skeletal muscle, cells murge so that the muscle fibres contract in unison