2.2 cell structure and microscopes

Question 1

role of the mitochondria?

Answer 1

site of aerobic respiration and energy production for the cell
found in high quantities in areas that need a lot of energy e.g. sperm, muscles

Question 2

role of centrioles

Answer 2

involved in cell division and separation of chromosomes

Question 3

role of plasma membrane?

Answer 3

a semi-permeable membrane that keeps integrity of the interior cell and regulates what substances go in/out of the cell

Question 4

role of lysosomes?

Answer 4

membrane-bound organelles that contain many strong hydrolytic enzymes that digest all kinds of substances including the cell itself

Question 5

role of ribosomes?

Answer 5

the site of protein synthesis

builds proteins/amino acids and are either free floating or attached to the RER

Question 6

role of the golgi apparatus

Answer 6

a group of fluid-filled flattened sacks that are responsible for processing/packaging proteins and lipids into vesicles ready to be transported to where they need to be (also make ribosomes and lysosomes)

Question 7

role of vesicles?

Answer 7

fluid filled sacks that transport substances and fuse to cell membranes to allow transportation of proteins/hormones in and out of the cell

Question 8

role of the smooth endoplasmic recticulem?

Answer 8

involved in the production of lipids and steroid hormones

Question 9

role of the rough endoplasmic recticulum?

Answer 9

connects to the nuclear envelope and is involved in the production of proteins
it contains ribosomes and processed proteins

Question 10

role of the nuclear pores?

Answer 10

pores in the nuclear membrane that regulate what goes in/out of the nucleus e.g. DNA mRNA

Question 11

role of the nuclear envolope?

Answer 11

the membrane that encloses the nucleus and protects it from damage

Question 12

role of the nucleolus?

Answer 12

a dense ball of genetic material

Question 13

role of the cell wall?

Answer 13

a rigid structure made of cellulose that supports plant cells and gives them strength

Question 14

role of a large vacuole?

Answer 14

large fluid filled sacs containing water or nutrients the cell might need; it also helps maintain turgor by pushing the contents of the cell against the cell wall to keep it rigid

Question 15

role of chloroplasts?

Answer 15

important plastids containing photosynthetic pigments (chlorophyll) that allow plants to get energy through photosynthesis

Question 16

role of the cytoskeleton?

Answer 16

a network of protein threads that:
supports organelles by holding them in place and makes sure they keep their shape
strengthens the whole cell and ensures it keeps its shape
can provide intracellular transport
can contract/cause movement within the cell

Question 17

role of microfilaments?

Answer 17

long, thin, solid fibres formed from the protein actin that’s involved in cell contraction and movement

Question 18

role of microtubules?

Answer 18

hollow tubes composed of the protein tubulin that form scaffold-like structures and give the cell shape
act as tracks for the movement of organelles
make up the spindle fibres and centrioles used in cell division

Question 19

role of intermediate fibres?

Answer 19

provides mechanical strength and helps maintain the cells integrity

Question 20

what’s a prokaryotic cell?

Answer 20

a small, simple cell (0.5-1.0 micrometres) that doesn’t have a nucleus or membrane bound organelles

Question 21

features of a prokaryotic cell

Answer 21

no membrane bound organelles
no nucleus
small ribosomes (18 micrometres)
cell wall made of peptidoglycan
circular DNA in the form of plasmids
ATP made in mesosomes

Question 22

what’s a eukaryotic cell?

Answer 22

a large sophisticated cell (10-100 micrometres) that can have specialised functions

Question 23

features of a eukaryotic cell

Answer 23

has a nucleus
has large ribosomes (22 micrometres)
linear DNA
has many membrane bound organelles
ATP made in the mitochondria
make up plants, animals and fungi
in plants cell walls are made of cellulose, in fungi they're made of chitin

Question 24

what’s endosymbiont theory?

Answer 24

the theory that eukaryotic cells have prokaryotic ancestors; a prokaryote “ate” a smaller prokaryote which then evolved to not be digested because both the host and symbiont benefitted

Question 25

evidence for endosymbiont theory

Answer 25

mitochondria and chloroplasts are a similar size to bacteria

Question 26

how do you calculate the actual size of an image?

Answer 26

actual size = image size/magnification

Question 27

definition of magnification?

Answer 27

the degree to which the size of an image is larger in relation to its actual size

Question 28

definition of resolution?

Answer 28

how clearly you can distinguish between 2 points/objects that are very close together

Question 29

how does a light microscope work?

Answer 29

light illuminates the specimen in order to see it more clearly

Question 30

whats the maximum resolution of a light microscope?

Answer 30

0.2 micrometres

Question 31

what's the maximum magnification of a light microscope?

Answer 31

x 1,500

Question 32

advantages of a light microscope?

Answer 32

it's cheap produces a coloured image can use a dead or live specimen

Question 33

disadvantages of a light microscope?

Answer 33

can't produce a very detailed image | produces a 2D image

Question 34

how does a transmission electron microscope work?

Answer 34

electrons are transmitted through the specimen to produce an image

Question 35

what's the maximum magnification of a TEM?

Answer 35

x 500 000

Question 36

what's the maximum resolution of a TEM?

Answer 36

0.0002 micrometres

Question 37

advantages of a TEM?

Answer 37

has very good magnification/resolution | doesn't produce a coloured image but "false" colour can be added after based on electrons absorbed

Question 38

disadvantages of a TEM?

Answer 38

expensive produces a 2D image only dead specimens can be used (in a vaccum)

Question 39

how does a scanning electron microscope work?

Answer 39

electrons are reflected off the specimen and collected to produce a 3D image

Question 40

what's the maximum magnification of a SEM?

Answer 40

x 100 000

Question 41

what's the maximum resolution of a SEM?

Answer 41

0.005 micrometres

Question 42

advantages of a SEM?

Answer 42

has good resolution/magnification | produces a 3D image

Question 43

disadvantages of a SEM?

Answer 43

expensive picture has no colour the specimen has to be dead (in a vacuum coated in metal e.g. gold)

Question 44

why do we stain specimens?

Answer 44

to allow you to clearly distinguish details more clearly | helps some parts of the specimen absorb more light/electrons than others so there's more contrast

Question 45

why do we coat specimens in a heavy metal solution before viewing it in an SEM?

Answer 45

because metal scatters electrons which creates contrast in the image

Question 46

how do you prepare a dry mount?

Answer 46

solid specimens are sectioned into thin slices to allow light through it so you can see it clearly under a microscope it's placed in the center of the slide and a cover slip is placed on top hair, pollen and dust can be viewed this way

Question 47

how do you prepare a wet mount?

Answer 47

tiny aquatic organisms can be viewed this way by being suspended in a liquid (water, immersion oil); pipette a small drop of water on the slide and place the specimen on top, then place a cover slip on top by carefully tilting it at an angle until it's covered

Question 48

how do you prepare a squash slide?

Answer 48

prepare a wet mount then use a lens tissue to gently press down the cover slip and squash the sample root tips can be viewed this way

Question 49

how do you prepare a smear slide?

Answer 49

use the edge of a slide to smear the sample to create a thin, even coating on another slide then place a cover slip on top blood cells can be viewed this way

Question 50

what's laser scanning confocal microscopy?

Answer 50

a technique used for obtaining high resolution images with the ability to observe at different depths

Question 51

why is it a laser scanning "confocal" microscope?

Answer 51

because the position of the two pinholes means the light waves from the laser follow the same path as the light waves radiated when the sample fluoresces meaning they have the same focal plane

Question 52

how to LSCM work?

Answer 52

laser beams are used to illuminate a specimen that's been treated with a fluorescent dye which causes fluorescence (the absorption and re-radiation of light) from these compounds this light is then filtered through a pinhole aperture (opening) onto a detector that's hooked up to a computer which generates an image

Question 53

why's it better to use a laser instead of light?

Answer 53

a much clearer image is produced because only light radiated very close to the focal plane is detected and out of focus light from other parts of the specimen that would have caused blurring is blocked by the pinhole

Question 54

advantages of LSCM?

Answer 54

it's non invasive and can be used to diagnose diseases of the eye and help in the development of new drugs the internal structures of transparent objects can be seen images obtained from optical sectioning can be reconstructed with a computer to produce a 3D image of complex objects