1. Cell Biology (microscopy & required practical 1 - light microscope)

Question 1

What is required practical 1?

Answer 1

How to use a light microscope to view onion cells

Question 2

What are the equipment needed for the practical?

Answer 2

• light microscope
• onion
• tweezers
• iodine solution
• cover slip
• water

Question 3

What are the steps for the practical? (6 steps)

Answer 3

1. Clean up the slide by adding a drop of water
2. Cut an onion and separate it out into layers. Use tweezers to peel some epidermal tissue from the bottom of one of the layers
3. Place tissue onto the slide making sure its flat
4. Add a few drops of iodine
5. Take a cover slip and carefully place over tissue, trying not to get any air bubbles
6. Clip the slide onto the stage of the light microscope

Question 4

Why do we use iodine (a stain)?

Answer 4

Iodine stains the cell, so highlights objects in a cell by adding colour

Question 5

Why do we use a thin layer of tissue?

Answer 5

So more light can travel through so we can see the specimen

Question 6

Why should you avoid the tissue rolling up?

Answer 6

So you can avoid viewing multiple layers of the cell at the same time

Question 7

What is magnification?

Answer 7

Magnification is how much bigger you have an object (scale factor)

Question 8

What is the equation for magnification?

Answer 8

Image size / Actual size

Question 9

What is resolution?

Answer 9

The ability to distinguish between two points that are close together

Question 10

What are the two types of microscopes that are used to view cells?

Answer 10

Light and Electron microscopes

Question 11

What do light and electron microscopes use to form an image?

Answer 11

• Light microscopes use glass + light
• Electron microscopes use electrons + magnetic lenses

Question 12

What are the differences between light and electron microscopes?
(5)

Answer 12

• Light microscopes produce 2D images whereas electron microscopes produce 3D
• Light microscopes have low resolution whereas electron have high resolution.
• In light microscopes you can see the main structures (nucleus, etc) of a cell, whereas in electron you can see the sub cellular structures (mitochondria,etc)
• Light microscopes produce colour images whereas electron produce black and white images.
• Light microscopes have a lower magnification then electron microscopes, which have a high magnification.

Question 13

What do microscopes allow us to do?

Answer 13

To see things that otherwise wouldn’t be able to see with just the naked eye

Question 14

How has electron microscopy increased the understanding of subcellular structures?

Answer 14

• An electron microscope has much higher magnification and resolving power than a light microscope
• This means that it can be used to study cells in much finer detail
• This has enabled biologists to see and understand many more sub-cellular structures

Question 15

Do light microscopes produce coloured images?

Answer 15

Yes

Question 16

Do electron microscopes produce coloured images?

Answer 16

No

Question 17

What is the maximum magnification of a light and electron microscope?

Answer 17

Light: Around x2000
Electron: Around x 1,000,000

Question 18

How do you convert from millimetres to micrometres?

Answer 18

x1000

Question 19

How do you convert from micrometres to nanometres?

Answer 19

x1000

Question 20

How do you convert from nanometres to micrometres?

Answer 20

divide by 1000

Question 21

How do you convert from micrometres to millimetres?

Answer 21

divide by 1000

Question 22

What are the steps for observing a specimen using a light microscope?

Answer 22

1. Start by clipping the slide you’ve prepared onto the stage
2. Select the lowest powered objective lens
3. Use the coarse adjustment knob to move the stage up to just below the objective lens
4. Look down at the eyepiece. Use the coarse focussing knob to move the stage downwards until the image is roughly in focus
5. Adjust the focus with the fine adjustment knob, until you get a clear image of what’s on the slide
6. If you need to see the slide with greater magnification, swap to a higher powered objective lens

Question 23

What should you do when drawing your specimen (onion cells)

Answer 23

• draw in pencil with clear unbroken lines
• no colour or shading
• subcellular structures should be drawn in proportion to one another
• add title+ labels
• add magnification of drawing

Question 24

How do you calculate the magnification of a drawing?

Answer 24

length of drawing of cell / real length of cell