save my exams microscope cell studies

Question 1

magnification

Answer 1

tells you how many times bigger the image produced by the microscope is than the real-life object you are viewing

Question 2

resolution

Answer 2

ability to distinguish between objects that are close together

Question 3

two main microscope

Answer 3

Optical microscopes (sometimes known as light microscopes)
Electron microscopes

Question 4

opitcal microscope

Answer 4

use light to form an image
limits the resolution
wavelength of visible light is between 500-650 nanometres (nm), so an optical microscope cannot be used to distinguish between objects closer than half of this value
cannot be used to observe smaller organelles such as ribosomes, the endoplasmic reticulum or lysosomes
The maximum useful magnification of optical microscopes is about ×1500

Question 5

trasnmission electron microscope

Answer 5

use electromagnets to focus a beam of electrons
This beam of electrons is transmitted through the specimen
Denser parts of the specimen absorb more electrons
This makes these denser parts appear darker on the final image produced

Question 6

advantage of tem

Answer 6

high-resolution images
his allows the internal structures within cells (or even within organelles) to be seen

Question 7

disadv of tem

Answer 7

very thin specimens or thin sections
cannot be used to observe live specimens (as there is a vacuum inside a TEM, all the water must be removed from the specimen and so living cells cannot be observed, meaning that specimens must be dead,

Question 8

adv sem

Answer 8

They can be used on thick or 3-D specimens
They allow the external, 3-D structure of specimens to be observed

Question 9

disadv sem

Answer 9

They give lower resolution images
cannot be used to observe live specimens
do not produce a colour image

Question 10

electron microscope

Answer 10

electrons to form an image
greatly increases the resolution
can be used to observe small organelles such as ribosomes, the endoplasmic reticulum or lysosome
×1,500,000

Question 11

how to draw

Answer 11

title
magnification recorded
sharp HB pencil
clear, single lines
No shading
proper proportions
Label lines
ruler

Question 12

electron vs light

Answer 12

large-cant be moved
vaccum neded
complicated sample prep
higher mad loweer res
dead specimens vs lving and dead

Question 12

using iodine to detect starch

Answer 12

These starch grains are commonly found in:
the stroma of chloroplasts
storage organs such as potato tubers
the seeds of cereals and legumes
light microscope but they first require staining in order to be seen easily
Iodine - stain starch grains
adding a drop of potassium iodide onto the specimen
iodine in potassium iodide solution has a light orange-brown colour but turns blue-black in the presence of starch

Question 13

three stages of fractionation

Answer 13

Homogenisation
Filtration
Ultracentrifugation

Question 14

cell fractionatiin

Answer 14

The process of separating cell organelles from each other is known as cell fractionation

Question 15

homogenisation

Answer 15

breaking up of cell
Ice-cold to reduce the activity of enzymes that break down organelles
Isotonic (it must have the same water potential as the cells being broken up) to prevent water from moving into the organelles via osmosis, which would cause them to expand and eventually damage them
Buffered (have a buffer solution added) to prevent organelle proteins, including enzymes, from becoming denatured
The tissue-containing solution is then homogenised using a homogeniser
This is a blender-like machine

Question 16

filteration

Answer 16

homogenate
filtered through a gauze
separate out any large cell debris or tissue debris that were not broken up
The organelles are all much smaller than the debris and are not filtered out (they pass through the gauze)
This leaves a solution (known as the filtrate) that contains a mixture of organelles

Question 17

ultracentrafugation

Answer 17

filtrate is placed into a tube and the tube is placed in a centrifuge
A centrifuge is a machine that separates materials by spinning
The filtrate is first spun at a low speed
This causes the largest, heaviest organelles (such as the nuclei) to settle at the bottom of the tube, where they form a thick sediment known as a pellet
The rest of the organelles stay suspended in the solution above the pellet
This solution is known as the supernatant
The supernatant is drained off and placed into another tube, which is spun at a higher speed
Once again, this causes the heavier organelles (such as the mitochondria) to settle at the bottom of the tube, forming a new pellet and leaving a new supernatant
The new supernatant is drained off and placed into another tube, which is spun at an even higher speed
This process is repeated at increasing speeds

Question 18

order of organelle mass

Answer 18

Nuclei
Chloroplasts (if carrying out cell fractionation of plant tissue)
Mitochondria
Lysosomes
Endoplasmic reticulum
Ribosomes