Topic 2A - Year 1 - Cell Structure and Division - Analysis of Cell Components

Question 1

What is magnification?

Answer 1

Magnification is how much bigger the image is than the specimen.

Question 2

How do you calculate magnification?

Answer 2

You calculate magnification by dividing the size of the image you see by the size of the real object.

You need to make sure all distances are in the same unit in this calculation.

Question 3

To convert a millimetre (mm) to a micro metre (um) you times by which value?

Answer 3

x1000

Question 4

To convert micrometres (um) to nanometres (nm) you times by which value?

Answer 4

x1000

Question 5

What is Resolution?

Answer 5

Resolution is how detailed an image s . more specifically it is how well a microscope distinguishes between two pints which are close together on a specimen. If a microscope cant separate two objects then increasing magnification won’t help.

Question 6

What are the two types of microscope ?

Answer 6

Optical (light) microscopes

Electron microscope

Question 7

What does an optical microscope use to form an image?

Answer 7

An optical microscope uses light to form an image. Light has quite a long wavelength which means the resolution of a light microscope is smaller as its harder to distinguish between two points.

Question 8

Generally what is the highest magnification of an optical microscope?

Answer 8

x1500

Question 9

Generally what is the maximum resolution of an optical microscope?

Answer 9

0.2 um

Question 10

Due to a lack of resolution some organelles cant be seen by an optical microscope , name some of these organelles:

Answer 10

Ribosomes
The rough endoplasmic reticulum
The smooth endoplasmic reticulum
Lysosmes

Question 11

What does an electron microscope use to form an image?

Answer 11

An electron microscope uses electrons form an image. Electrons have tiny wavelengths so Gove the microscope high resolutions as its easy to distinguish between two points.

Question 12

Generally what is the greatest magnification of an electron microscope?

Answer 12

x1500 000

Question 13

Generally what is the maximum resolution of an electron microscope?

Answer 13

0.0002 um

Question 14

There are two types of electron microscope name these two types.

Answer 14

Transmissions electron microscope (TEM)

Scanning electron microscope (SEM)

Question 15

How does a transmissions electron microscope work?

Answer 15

TEMs use electromagnets to focus a beam of electrons , this beam of electrons is then transmitted through the specimen being viewed.

Denser parts of the specimen absorb more electrons so the image produced shows these parts in a darker colour.

Question 16

Why can you not look at living organisms in a transmissions electron microscope?

Answer 16

When using a TEM you must look at the specimen in a vacuum , also the specimen must be sliced very thinly.

Question 17

How does a scanning electron microscope work?

Answer 17

A SEM scans a beam of electrons across a specimen, it can in doing this produce a 3D image of the cell surface, this image is not viewed through a lens it is viewed on a computer screen

Question 18

How are some images from an electron microscope coloured?

Answer 18

Electron microscopes do not form coloured images their images are always black and white , she images may be coloured on a computer after the image has been produced by the electron microscope.

Question 19

What is the difference between the specimens that can be viewed under a TEM and a SEM?

Answer 19

A sample viewed under an SEM is usually thicker , a sample viewed under a TEM must be sliced extremely thin.

Question 20

What type of slide do you use to look at a sample under a optical microscope?

Answer 20

You use a temporary mount to view a sample under an optical microscope.

Question 21

How do you prepare a temporary mount?

Answer 21

Firstly you take a slide and pipets a small droplet of water onto it.
You then use tweezers to transfer a small (thinly sliced) piece of specimen onto the water droplet.
Next you add a drop of stain to highlight objects in the cell.
You then add a square cover slip very carefully gradually lowering it over the sample
Make a conscious effort not to trap and air bubbles between the slide and cover slip.

Question 22

Why are temporary mounts called temporary mounts?

Answer 22

Temporary mounts are called temporary mounts as they cannot be stored for very long.

Question 23

What is a microscope artefact?

Answer 23

A microscope artefact is something that is seen in the image that is not part of the cell or specimen you are looking at, they may include finger prints ,air bubbles or dust. Artefacts are normally accidentally created in the preparation of the slide.

Question 24

Are artefacts more common in electron microscopes or optical microscopes?

Answer 24

Artefacts are more common in electron microscopes as the slides take more preparation hence there is more opportunities for artefacts to be created.

Question 25

If you wanted too look at some cells under an electron microscope you would need to first separate them from the rest of the cell , by which process can you separate organelle from the rest of the cell?

Answer 25

Cell fractionation.

Question 26

What is homogenisation ?

Answer 26

Homogenisation is breaking up cells.

Question 27

Name 4 ways in which cells can be homogenised

Answer 27

• The cells can be broken up with high frequency sound waves
• A mild detergent can be used to make holes in the plasma membrane
• Cells could be forced through a small hole at hight pressure (for instance being sucked in and out of a syringe)
• Cells could be sheared apart between the thick walls of a glass vessel and tight fitting plunger.

Question 28

What is the product of homogenisation referred to as

Answer 28

The homogenate

Question 29

Why must the solution the homogenate is contained within be kept ice cold?

Answer 29

The homogenate should be kept in a solution that is ice cold to reduce enzyme activity as enzymes may break down the cells organelles.

Question 30

The solution the homogenate is contained within must also be isotonic why is this?

Answer 30

To have something that is isotonic to your solution means that it has the same concentration as your solution . It is important that the solution that the homogenate solution is put in is isotonic as if it was not the organelles could be burst , as water would flood in or out to even the water potential gradient by osmosis.

Question 31

The solution that the homogenate is contained in must also be buffered by a pH buffer , why is this ?

Answer 31

The pH should be buffered in the solution so that it does not interfere with the organelles if it fluctuates.

Question 32

What type of solution should a homogenate be placed in?

Answer 32

A cold isotonic buffered solution

Question 33

What happens in the filtration stage of cell fractionation ?

Answer 33

In the filtration stage of cell fractionation the homogenised cell solution is filtered through a cause to separate the large cell debris or tissue debris out from the organelles. The organelles are much smaller than the debris so pass through the gauze.

Question 34

Why is the homogenate solution filtered?

Answer 34

To separate the organelles which pass easily through the gauze out from the cell and tissue debris.

Question 35

Why do scientist homogenise the cells?

Answer 35

To break open the cell and release the organelles.

Question 36

After homogenisation and filtration what is the next step in cell fractionation?

Answer 36

Ultracentrifugation (separating out the organelles)

Question 37

After filtration in cell fractionation what remains?

Answer 37

After filtration a solution contains the organelles of a cell is left behind.

Question 38

What machine is used in cell fractionation?

Answer 38

A centrifuge

Question 39

What are the steps in ultracentrifugation?

Answer 39

The filtrate is poured into a test tube , this test tube is placed into a centrifuge and the centrifuge is spun. The heaviest organelles get flung to the bottom of the test tube and form a pellet which is a thick sediment. The organelles that don’t form part of the pellet remain suspended in the fluid are referred to as the supernatant.

The supernatant is then drained off into another test tube and put in the centrifuge. this time the centrifuge spins the organelles more quickly and the next heaviest organelles deposit as pellet at the bottom of the tube .

This process is continued at continually increasing speeds until all the organelles have been separated out.

Question 40

What is a the supernatant?

Answer 40

The supernatant is the solution of organelles that remains and is not sedimented as a pellet when spun in the centrifuge.

Question 41

which organelles deposit first when spun in a centrifuge?

Answer 41

The heaviest organelles form the first pellet . the organelles separate out heaviest first too lightest last.

Question 42

Which organelles may be found in the first pellet created in ultracentrifugation?

Answer 42

Cell debris

Nuclei

Question 43

Which organelles may be found in the second pellet created in ultracentrifugation?

Answer 43

Mitochondria

Chloroplasts

Question 44

Which organelles may be found in the third pellet created in ultracentrifugation?

Answer 44

Lysosomes

Ribosomes