Methods Of Studying Cells

Question 1

what are cells?

Answer 1

• the cell is the basic unit of life

- however some cells are not visible to the naked eye and can only be seen under a microscope

Question 2

what is magnification?

Answer 2

-the magnification of an object is how many times bigger the image is when compared to the object

Question 3

what is resolution?

Answer 3

-the resolving power of a microscope is the minimum distance apart that two objects can be in order for them to appear as separate items

Question 4

what is cell fractionation?

Answer 4

• in order to study the structure and function of the various organelles that make up cells you must obtain large numbers of isolated organelles
• so cell fractionation involved cellar being broken up and different organelles being separated out

Question 5

How is cell fractionation carried out?

Answer 5

• the tissue is placed in a cold, buffered solution of the same water potential as the tissue
• homogenisation then ultracentrifugation is carried out

Question 6

what is homogenation?

Answer 6

• cells are broken up by a homogeniser (blender) which releases the organelles from the cell
• the resultant fluid is known as homogenate is then filtered to remove any complete cells and large pieces of debris

Question 7

what is ultracentrifugation?

Answer 7

-the process by which the fragments in the filtered homogenate are separated in a machine called a centrifuge which spins tubes of homogenate at very high speeds in order to create a centrifugal force

Question 8

what is the process of ultracentrifugation in animal cells?

Answer 8

• the tube of filtrate is placed in the centrifuge and spun at a low speed
• the heaviest organelles like the nuclei are forced to the bottom of the tube where they for a pellet
• the supernatant is removed leaving the pellet
• the supernatant is transferred to another tube and spun at a greater speed
• the next heaviest organelle like mitochondria form a pellet
• this is repeated at a faster speed each time

Question 9

what have techniques like cell fractionation enabled?

Answer 9

• advances in biological knowledge

- they allowed a detailed study of the structure and function of organelles by showing what isolated compounds do

Question 10

How do microscopes work?

Answer 10

• a simple convex glass lens can act as a magnifying glass

- such lenses work more efficiently if they are used in pairs in a compound light microscope

Question 11

What is a limitation of the compound light microscope and how is it overcome?

Answer 11

• the long wavelength of light rays means that a light microscope can only distinguish between two objects of they are 0.2um or further apart
• this can be overcome by using beams of electrons rather than beams of light
• the shorter wavelength and the beam of electrons in the electron microscope can distinguish between two objects only 0.1nm apart

Question 12

What is the object?

Answer 12

-the material that’s put under the microscope

Question 13

What is the image?

Answer 13

-the appearance of the object when viewed under the microscope

Question 14

What do you need to remember when calculating magnification?

Answer 14

-you have to ensure that the units of length are the same for both the object and image

Question 15

What are microscopes?

Answer 15

-instruments that produce a magnified image of an object

Question 16

What does resolution power depend on?

Answer 16

-whatever the type of microscope used the resolving power depends on the wavelength or form of radiation used

Question 16

Which type of wavelength us used in a light microscope?

Answer 16

-0.2um which means any two objects which are 0.2um or more will be seen separately but any other objects seen as 0.2um will appear as a single item

Question 16

What happens to the image when the resolution increases?

Answer 16

-there is a greater clarity and the image produced is clearer and more precise

Question 16

What happens when you increase magnification?

Answer 16

-the size of the image increases but the resolution does not always increase as every microscope has a limit of resolution so increasing the magnification up to this point will appear in more detail however past this point increasing the magnification will cause the image to appear larger but more blurred

Question 17

Why does cell fractionation require a cold solution?

Answer 17

-to reduce enzyme activity that might break down the organelle

Question 18

Why does cell fractionation require a buffered solution?

Answer 18

-it stops the pH from fluctuating as any change in pH could alter the structure of the organelles or affecting the functioning of enzymes

Question 19

Why does cell fractionation require a solution with the same water potential as the tissue?

Answer 19

-to prevent organelles bursting or shrinking as a result of osmotic gain or loss of water

Question 20

What is the supernatant?

Answer 20

-the fluid at the top of the tube