Cell Structure

Question 1

Outline a method a student could use to prepare a temporary mount of tissue for a light microscope.

Answer 1

. obtain a thin section of tissue

. place tissue in a drop of water

. stain tissue on a slide to make structures visible

. add coverslip using a mounted needle at 45
degrees to avoid trapping air bubbles.

Question 2

describe how light microscopes work (6 marks)

Answer 2

1. clip slide on stage
2. use lowest powered objective lens
3. use coarse adjustment knob to bring stage up
4. look down eyepiece and continue using the coarse adj. knob until its focused
5. use fine adjustment knob to focus till you get a clear image

Question 3

what are the limitations of using a light microscope?

Answer 3

. low resolution: resolution of 200 nm

. low magnification: magnification of x1500

Question 4

describe how a TEM works?

Answer 4

1. pass a beam of electrons through a thin slice of specimen
2. more dense structures appear darker since they absorb more electrons
3. focus image onto photographic plate

Question 5

describe how a SEM works?

Answer 5

1.focus on a beam of electrons onto a specimen’s surface using electromagnetic lenses

2. reflected electrons hit a collecting device and are amplified to produce an image on a photographic memory

Question 6

how does staining samples work for electron microscopes

Answer 6

objects are dipped in a solution of heavy metals like lead

metal ions scatter creating contrast so some parts appear darker than others

Question 7

define magnification and resolution

Answer 7

magnification: ability to make the image of a specimen larger than the specimen actually is

resolution: a measure of how detailed and clear an image is.

Question 8

why do samples need to stained for light microscopes?

Answer 8

.coloured dye binds to structures

. facilitates absorption and produces an image

Question 9

state the magnification and resolution of an optical microscope

Answer 9

M: x2000

R: 200 nm

Question 10

state the magnification and resolution of a TEM

Answer 10

M: x500 000

R: 0.5 nm

Question 11

state the magnification and resolution of a SEM

Answer 11

M: x500 000

R: 3-10 nm

Question 12

explain how to use an eyepiece graticule and stage micrometer

Answer 12

1. place micrometer on stage to calibrate eyepiece graticule
2. line up scales on graticule and micrometer.

3.Count how many graticule divisions are in 100 um on micrometer

3. length of 1 eyepiece division = 100 um / number of divisions
4. use calibrated values to calculate actual length of structures.

Question 13

describe the structure of the nucleus

Answer 13

contains DNA coiled around chromatin into chromosomes

nuclear envelope

nuclear pores

nucleolus

Question 14

describe the function of the nucleus

Answer 14

controls cells activities

pores allow substances to enter and exit the nucleus

nucleolus makes ribosomes

Question 15

describe the structure and function of the ER

Answer 15

made of cisternae

1. RER: covered with ribosomes, for protein synthesis and transport
2. SER: lipid synthesis

Question 16

describe the structure and function of the golgi apparatus

Answer 16

stack of membrane bound, flattened sacs and

makes vesicles, lysosomes and glycoproteins

processes and packages proteins and lipids

Question 17

describe the structure and function of ribosomes

Answer 17

formed of protein and rRNA and NOT membrane bound

Question 18

what is the function of the ribosomes

Answer 18

large subunit joins with AA

small subunit joins with mRNA binding site

protein synthesis

Question 19

describe the structure of the mitochondrion

Answer 19

double membrane

folded inner membrane forms cristae

fluid matrix

Question 20

describe the structure of the chloroplast

Answer 20

double membrane

thylakoids

lamellae

stroma

Question 21

state the function of mitochondria and chloroplasts

Answer 21

M: site of aerobic respiration to produce ATP

C: site of photosynthesis which can happen in grana or stroma

Question 22

describe the structure and function of lysosomes

Answer 22

single membrane

contains hydrolytic enzymes (lysozymes)

digests contents of phagosome

exocytosis of digestive enzymes

Question 23

describe the structure and function of a plant cell wall

Answer 23

made of cellulose

supports plant cells

Question 24

what are bacterial and fungal cell walls made of

Answer 24

peptidoglycan

chitin

Question 25

describe the structure and function of centrioles

Answer 25

hollow cylinders made of microtubules found in animal and SOME plant cells

seperates chromosomes

Question 26

describe the structure and function of the flagella

Answer 26

hollow helical tube made of flagellin

9+2 formation of microtubules

microtubules contract to make it move

Question 27

describe the structure and function of cilia

Answer 27

hair-like structures found on cell surface membrane of animal cells

9+2 formation of microtubules

microtubules contract to make it move

Question 28

which organelles are involved in the production and secretion of proteins?

Answer 28

nucleus - DNA
ribosomes
ER
GA

Question 29

why is the cytoskeleton important

Answer 29

mechanical strength
maintains shape - support and stability
movement of chromosomes
movement of cilia and flagella

Question 30

how are prokaryotic and eukaryotic cells similar

Answer 30

both have:
cell membrane
cytoplasm
ribosomes

Question 31

how are prokaryotic and eukaryotic cells different

Answer 31

P:
unicellular
no membrane bound organelles / nucleus
circular DNA
small ribosomes
binary fission
peptidoglycan

E:
multicellular
organelles and nucleus
linear chromosomes
larger ribosomes
sexual reproduction
cellulose cell wall

Question 32

what is cisternae

Answer 32

systems of membranes filled with fluid

Question 33

what is stroma

Answer 33

thick fluid found in chloroplasts

Question 34

what are lamellae

Answer 34

thin flat pieces of the thylakoid membrane and join grana

Question 35

what are grana

Answer 35

stacks of thylakoids (discs)