Cell Structure

• What is the animal cell range in size?

  between 0.01mm - 0.05mm
• What is the range of size does plant cells have?

  between 0.01mm - 0.10mm
• equation for microscope?

  magnification of the microscope = magnification of eyepiece x magnification of objective.
• Calculating the magnification of an image?

  magnification = sign of image/ real size of object
• What is the smallest cell?

  naked eye is about 0.05mm
• What is cells measured in?

  Micrometers
• What is the aims of the preparing biological samples

  to examine a range of cells and other structures with a microscope to understand their basic structure.
• Cheek Cells - Preparing Biological samples

  put a small drop of water on microscope slide.

  gently swab the your mouth with a clean cotton bud.

  gently rub cotton bud in the water.
• Onion epidermal cells - Preparing Biological samples.

  put a small drop of water on microscope slide.

  peel some onion skin from inside one of the leaves.

  use forceps to transfer it to water. Make sure the onion skin is flat, and there are no trapped air bubbles.

  stain cells with iodine
• Risk for preparing biological samples.

  care must be taken when looking down the microscope if the illumination is too bright.

  care when using microscope stains.

  care when handling coverslips, microscope slides and mounted needles.
• Rotate

  rotate the objective lenses so that the low power, e.g. x 10, is in line with the stage.
• Focus

  turn the coarse focus so that the stage is as close to the objective lens as possible. You should not look through the microscope to do this.
• Place the slide

  on the stage. line it up so that the specimen is in the centre of the stage where the light passes through it.
• Focus

  focus the slide towards you by turning the coarse focus adjustment.
• Record an image

  draw a low power image of what you see. Then rotate the objectives so that the high power objective i.e. x 40, is in line with the stage.
• Re-focus

  bring the slide back into focus using the fine focus adjustment. if you don not succeed go back to low power and re-focus they try again.
• How have light microscopes developed?

  1590s - Dutch spectacle makers Janssen made the first compound microscope.
• How was the light microscope developed?

  1650 - British scientist, Robert Hooke 1650 observed and drew cells using a compound microscope.
• What is a compound microscope?

  uses two lenses, the objective lens and the eyepiece. The very short focal length objective lens produces a greatly-magnified image, then the short focal length eyepiece magnifies this further.
• how did microscopes develop in the late 1600s?

  Dutch scientists Antonie van Leeuwenhoek constructed a microscope with a single spherical lens. It magnified up to x 275.
• how did the microscope develop by the 1800s.

  the optical quality of lenses increased and the microscopes are similar to the ones we use today.
• What has the TEM revealed?

  revealed structures in cells that are not visible with the light microscope.
• What is TEM stand for?

  Transmission electron microscope.
• What is the resolution of light microscopes?

  resolution of light microscope is around 200nm. This means that it cannot distinguish two points closer than 200nm.
• What is the magnification on electron microscopes?

  maximum magnification of around x 1,000,000 but images can be enlarged beyond that photographically. The limit of resolution of transmission electron microscope is now less than 1nm.
• Cytoplasm

  a jelly-like material that contains dissolves nutrients and salts and structure called organelles. It is where many of the chemical reactions happen.
• Nucleus

  contains genetic material, including DNA, which controls the cell's activities.
• Cell membrane

  it's structure is permeable to some substances but not to others. it therefore controls the movement of substances in and out of the cell.
• mitochondria

  organelles that contain the enzymes for respiration, and where most energy is released in respiration.
• ribosomes

  tiny structure where protein synthesis occurs.
• chloroplast

  organelles that contains the green pigment, chlorophyll, which absorbs light energy for photosynthesis. contains the enzymes needed for photosynthesis.
• cell wall

  made from cellulose fibres and strengthens the cell and supports the plant.
• permanent vacuole

  filled with cell sap to help keep the cell turgid
• methods - measuring cell size.

  place a stage micrometer on the stage of the microscope.

  line up one of the divisions on the eyepiece graticule with a fixed point on the stage micrometer.

  count the number of divisions on the eyepiece graticule that correspond with a set measurement on the stage micrometer.

  calculate the distance in micrometers of one division on the eyepiece graticule.