(P1) Topic 2- Cell structure and Division, cell membranes, cells and immune system

Question 1

1)what is cell fractionation?
2)Describe step 1 of cell fractionation?
3)what are the Step 1 conditions? (3)

Answer 1

1) process in which cells are broken up and the different organelles are separated out. To study the structure and function.
2) The tissue is placed in a cold, buffered solution with the same water potential (water concentration) as the cells.
3) -> cold to reduce enzyme activity
-> buffered to Stop protein denaturation by maintaining a constant pH (some proteins in the cell make the structures without it would fall apart)
-> same water potential (//concentration) as the cell to prevent cell lysis (bursting) (osmosis)

Question 2

1)Describe Step 2 homogenation?
2)Describe step 2 homogeniser?
3)Describe step 2 homogenate?
4)what then happens in step 2 to the homogenate?

Answer 2

1)Homogenation- (ACTION process) process of breaking up cells
2)Homogeniser- blender used to break up the cells
3)Homogenate- (ATE liquid) liquid is produced
4)homogenate is then filtered to remove unbroken cells and larger debris

Question 3

1)what is ultracentrifugation and how does it work?
2)Describe step 4 steps in ultracentrifugation (cell fractionation)?
3)what is supernatant?
4)what is iodine used for in a plant cell?

Answer 3

1)fragments in the filtered homogenate are separated in a centrifuge. spins tubes of homogenate at very high speed in order to create a centrifugal force.

2)
1. Spin the liquid at a slow speed
2. denser organelles (nuclei) are forced to the bottom of the tube and form a pellet.
3. Remove the supernatant (the liquid). (Leaving the sediment of the nuclei)
4. Repeat steps 1-4 at increasingly faster speeds to remove increasingly lighter organelles.

3)
->supernatant is transferred to another tube and spun in the centrifuge at a faster speed than before.

4)
-iodine in potassium iodide solution to identify starch grains in plant cells.

Question 4

1)Plant cells largest to smallest (weight) organelles and what is broken up?
2)What are speeds of centrifugation for nuclei, mitochondria, lysosomes?

Answer 4

1) Plant cells largest to smallest organelles:
Vacuole, nucleus, chloroplast, mitochondria, ribosomes
->cell wall, cell membrane are broken up
->cytoplasm is in the supernatant
2)

Question 5

1)definition of resolution?
2)what does resolution depend on?
3)which one provides better resolution: long or short wave lengths?

Answer 5

1)Resolution= minimum distance two objects need to be apart for them to appear as two separate objects.
2)dependent on wavelength, form radiation
3)

Question 6

Resolution needed to view organelles:
1)mitochondria?
2)cell membrane?
3)nucleus?
4)virus particles?

Answer 6

1)Mitochondrion (500nm)
2)Cell membrane (10nm)
3)Nucleus (600nm)
4)Virus particle (100nm)

Question 7

1) 1m to mm?
2) 1,000mm to um?
3) 1,000,000 um to nm?

Answer 7

Question 8

Light, Transmission electrons, scanning electrons:

Answer 8

Question 9

1)Advantage of electron microscopes? (2)
2)How do transmission electron microscope produce an image? (2)
3)Photomicrograph?

Answer 9

1)Advantages of electron microscopes:
. electron beam has a very short wavelength it has a high resolving power.
• As electrons are negatively charged beam can be focused using electromagnets
2) Transmission electron microscope:
-absorb the electrons appear dark
-pass through appear bright
3) Photomicrograph- image produced on screen from microscope is photographed

Question 10

1)why is the resolving power not always achieved with TEM? (2)
2)What are the main limitation of TEM and SEM? (4)

Answer 10

1)
• difficulties preparing the specimen limit the resolution that can be achieved
• a higher energy electron beam is required and this may destroy the specimen. (penetrating it from below. )

2)
• The whole system must be in a vacuum and therefore living specimens cannot be observed.
• A complex ‘staining’ process is required and even then the image is not in colour.
• The specimen must be extremely thin. (TEM only)
• image may contain artefacts.

Question 11

1)what are artefacts?
2)why must TEM specimens be thin?
3)how can you create a 3-D image using TEM?

Answer 11

1) Artefacts are things that result from the way the specimen is prepared.
2) electrons to penetrate. flat, 2-D image.
3) series of sections through a specimen. build up a 3-D image photomicrographs produced. Slow and complicated

Question 12

1)How does SEM use electrons?
2)How is an image from specimens?

Answer 12

1)
.beam of electrons on to the surface of the specimen from above not below
.beam is then passed back and forth across a portion of the specimen in a regular pattern.
.electrons are scattered by the specimen and the pattern of this scattering depends on the contours of the specimen surface
2)
->3-D image by computer analysis of the pattern of scattered electrons and secondary electrons produced.

Question 13

1)what does magnification do?
2)what increasing the magnification do?

Answer 13

1) Increasing the magnification increases the size of an image, not increase the resolution.
2)
magnification will increase detail but beyond resolution increasing the magnification won’t increase detail it will be larger and blurred.

Question 14

What is the magnification equation?

Answer 14

Question 15

1)explain the process of finding the actual length?

Answer 15

1)
1. Use the formula triangle to identify the equation you need.
2. Measure the correct part of your diagram (in mm) to find the size of the image.
3. Read the question and find the units used to give the size of the object (usually μm but
sometime nm). Convert your measurement from step 2. into these units.
4. Put the numbers into the equation and use your calculator to find the answer.
5. Round to the same number of significant figures as in your original measurements.

Question 16

1)mean length?
2)unit of magnification?
3)what is a scale bar?
4)How do you use scale bar?

Answer 16

1)Mean length= multiple organelles measure and take a mean
2) X
3)Scale bar= shows the distance represented by the length of the bar
4)Calculate length of scale bar and then the actual length scale bar (image/real) make sure same units

Question 17

1)magnification?
2)calculating the magnification?

Answer 17

1) magnification of an object is how many times bigger the image when compared to the object.
2) calculating the magnification units of length are the same for both the object and the image.

Question 18

1)Why is the condition cold need for cell fractation?
2)why is the condition of same water potential needed?

Answer 18

1)Slows / stops enzyme activity to prevent digestion of organelles
2)Same water potential - Prevents osmosis so no lysis / shrinkage of organelles

Question 19

1)The second centrifuge tube was spun at a higher speed to obtain the sample of organelles labelled C in the diagram
Suggest why?
2) Explain why the homogenate was filtered before spinning at low speed in the centrifuge?

Answer 19

1) organelle C less dense than nucleus / organelle in first pellet.
2) removes debris / intact cells / sand; which would contaminate sediment A / interfere with the results;

Question 20

1)Explain why the organelles in sediment C could be seen with a transmission electron microscope but not with an optical microscope?
2) Give one advantage of using a TEM rather than a SEM?
3) Give one advantage of using a SEM rather than a TEM?

Answer 20

1)write about only the TEM because it comes before OP is just context
2) Higher resolution / higher (maximum) magnification / higher detail and internal details / structures within (cells) to be seen / cross section to be taken;
3) Thin sections do not need to be prepared / shows surface of specimen / can have 3-D images;

Question 21

1)Explain why the solution the biologist used was ice-cold, buffered and the same water potential as the liver tissue (step 1)?
2) Explain why the biologist used a blender and then filtered the mixture (steps 2 and 3).

Answer 21

1) Ice-cold - stops enzyme activity to prevent digestion of organelles
2. Buffered - Maintains pH so that enzymes / proteins are not denatured
3. Same water potential - Prevents osmosis so no lysis
2)
Break open cells / homogenise / produce homogenate;
Remove unbroken cells / larger debris;

Question 22

1)Explain why the homogenate was filtered before spinning at low speed in the centrifuge?
2) Explain why the organelles in sediment C could be seen with a transmission electron microscope but not with an optical microscope?
3) Give one advantage of using a TEM rather than a SEM?
4) Give one advantage of using a SEM rather than a TEM?

Answer 22

1) removes debris / intact cells / sand;
which would contaminate sediment A / interfere with the results
2) an electron microscope has a higher resolution;
electrons with shorter wavelength;
3) Higher resolution / higher (maximum) magnification / higher detail (of
image);
4) Thin sections do not need to be prepared / shows surface of specimen /
can have 3-D images;

Question 23

1)A transmission electron microscope was used to produce the image in the figure above. Explain why?
2) Explain why it is not possible to determine the identity of the structures labelled X using an optical microscope?

Answer 23

1) High resolution! Can see internal structure of organelles
2) Resolution (too) low, Because wavelength of light is (too) long;

Question 24

1)Name the the 4 steps to finding the distance of one eyepiece graticule division?

Answer 24

1. Place a stage micrometer slide on the stage of the microscope. Note that the smallest division on the stage micrometer equals 100 μm.
2. Using the low-power objective, focus the microscope on the stage micrometer. Rotate the eyepiece and move the slide so that the scales of the eyepiece graticule and the stage micrometer are on top of each other.
3. Line up the lines on the eyepecie graticule and stage micrometer so that two pairs of lines are directly on top of each other. The further apart the lines are the more precise your measurements will be.
4. Repeat for the medium- and high-power objectives. calibrated the eyepiece graticule, use it to measure cells.

->stage micrometer distance chose rights hand side the other one must always be on the right hand side

Question 25

1)Name the eye piece graticule scale, stage micrometer scale?

Answer 25

Question 26

1)6 rules for drawing cells?
2)correct ways to daraw cells? (3)
3)How to draw scale bars? (4)

Answer 26

1)
o Sharp pencil used to draw single lines that meet exactly without gaps or crossing over Outline only (no colouring or shading)
o Correct shape and relative size of structure
o Ruler used to draw label lines (no arrow heads)
o Label lines do not cross over
o Title
o Magnification of microscope OR ruled line labelled with measurement

2)Correct type of drawing:
o Cell drawing – only 1-3 cells drawn
o Tissue map – no individual cells shown, only lines separating the different tissues
o Body plan – a representation of the main body parts seen

How to draw a scale bar?
1-measure cell using graticule
2-measure image size
3-draw the image size on a line
4- multiply the graticule measurement by the divisions by the graticule due magnification write this on the line

Question 27

1)How to measure cells? (3)
2)what to include when drawing cells? (4)
3)Calculating the real length using a microscope?

Answer 27

1)
1-measure it using eyepiece graticule
2-multiply the number by eyepiece graticule division due magnification
3-length of cell in um
2)
Magnification, labels, name, scale bar
3) eye piece graticule length cell x multiplier eyepiece graticule division= real length

Question 28

Contrast how an optical microscope and a transmission electron microscope work and contrast the limitations of their use when studying cells?

Answer 28

-TEM use electrons and optical use light;
-TEM allows a greater resolution;
-(So with TEM) smaller organelles / named cell structure can be observed
-TEM view only dead / dehydrated specimens and optical (can) view live specimens:
-TEM does not show colour and optical (can);
-TEM requires thinner specimens:
-TEM requires a more complex/time consuming preparation;
-TEM focuses using magnets and optical uses (glass) lenses:

Question 29

Describe how you could make a temporary mount of a piece of plant tissue to observe the position of starch grains in the cells when using an optical (light) microscope?

Answer 29

1.Add drop of water to (glass) slide:
2.Obtain thin section (of plant tissue) and place on slide / float on drop of water;
Stain with / add iodine in potassium iodide.
3. Allow any appropriate method that avoids trapping air bubbles
4. Lower cover slip using mounted needle.

Question 30

Calculate the length of the chloroplast shown in the figure above?

Answer 30