Magnification and Practical 1. Onion cells

Magnification

the number of times bigger the image is than the actual

resolution

the ability to distinguish between two points

visible organelles in plants (for light microscope)

cel wall, nucleus, vacuole and cytoplasm

visible organelles in humans (for light microscope)

cell membrane, nucleus, cytoplasm

Place where we place our slides

the stage

Lens used to locate cells

Lowest power objective lens / 4x lens as it gies us a larger field of view to find the cells before magnifying further

Process used to focus on cells part 1

• turn on microscope and change brightness of light, ensuring it passes through your specimen

process used to focus on cells part 2

• have the 4x objective lens in place

process used to focus on cells part 3

Lower stage as far as possible and then slowly bring it upwards using the large focus wheel

process used to focus on cells part 4

• when you can see the cells, bring into sharp focus using the smaller focus wheel

overall magnification

eye piece magnification x objective magnification

Hazards for the onion practical

• sharps - scalpels

• chemical stain age/irritant - iodine solution

• electricity - microscope

• biological - onion

Risk and precaution for sharps

• cuts due to using scalpels while cutting onion

• direct cutting away from body, safe and sensible work place at all times

Risk and precaution for chemical stainage/irritant

• eye damage, skin irritation or staining of clothes due to spills or splashes while dyeing onion cells

• wear goggles, gloves and wipe s[ills up immediately

Risk and precaution for electricity

• electrocution ‘due to’ iodine/water spills ‘while’ using electric microscope and preparing samples

• have dry hands/work area, wipe up spills immiedietly

Risk and precaution for biological

• potential allergen that could trigger a response due to contact with onion while preparing slides

• student should void contact with food item if allergic

converting mm to uM (micrometers)

multiply by 1000

calibration

determines true length of an eyepiece graticule division (in uM) for a specific objective lens by aligning the eyepiece scale against a stage micrometer of known length

Magnification =

Image size (mm) / actual size (um)