Microscopes and magnification.

Question 1

Preparation of onion cells.

Answer 1

1) Cut onion and remove a leaf.
2) Insert forceps below epidermis on adaxial surface (upper on onion curving upwards).
3) Maintain tension on sheet that lifts off, cut with scissors and place on microscope slide.
4) Use scissors to cut piece of roughly 0.5 cm^2.
5) Put 2 drops of methylene blue on specimen and cover with cover slip.

Question 2

Process of viewing in the microscope.

Answer 2

1) Lower stage as far as possible.
2) Place the slide on the stage.
3) Use 10x objective and raise stage slowly until image in focus.
4) Move slide slightly so is in centre of the field of view.
5) Adjust light intensity with the sub-stage iris diaphragm.
6) Move the x40 objective into position and refocus with the fine focus control.
7) Readjust light intensity.
8) Repeatedly rotate fine focus control in both directions in order to view whole depth of specimen, while examining with x40 objective.

Question 3

Things to remember with drawings.

Answer 3

• Use sharp pencil.
• Use single, bold strokes.
• Do not shade in, only use outlines.
• At least half a page.
• Horizontal/parallel labels.
• Label the magnification.
• No arrows on lines.
• Use ruler.
• Line should end inside structure, referred to, not just touching the edge.
• Labels should not obscure drawing and end far from drawing.

Question 4

Magnification calculation.

Answer 4

Magnification= Image size/ Actual size.
Total magnification= eyepiece lens mag x objective lens mag.

Question 5

Units order.

Answer 5

Km, m, mm, micrometers(u), nm, pm. (difference of 1000 between each unit)(do not use cm).

Question 6

Calibration of the microscope.

Answer 6

• Allows you to measure lengths of structures in the microscope.
  Need:
• Eyepiece graticule ( in eyepiece, does not get magnified, made of 100 sections, called eyepiece units, epu. The higher the power of the objective=the smaller the length each division of the graticule represents).
• Stage micrometer (on the stage, does get magnified, made of 100 stage micromneter units= 0.01mm)
  Method:
• Line up the 2 locations of the eyepiece graticule and the stage micrometer that line up well , making sure graduation lines are parallel.
• Find distance between 2 points in epu and stage micrometer units.
• Find how many mm in your smu (stage micrometer units) distance.
• Divide to find how many mm in 1 epu.
  5) Use eyepiece graticule scale to work out how big the cells are in microscope using how many mm 1 epu is.
• Can the calculate mag/ actual image size.
  PRACTICE CALCULATION QUESTIONS.

Question 7

Field of view definition.

Answer 7

Everything you can see in a microscope.