Cell structure and micrlscopy qp

Question 1

Explain why it is not possible to determine the identity of the structures
labelled X using an optical microscope

Question 2

Describe the role of one named organelle in digesting these bacteria

Answer 2

1. Lysosomes;
2. Fuse with vesicle;
3. (Releases) hydrolytic enzymes;

Question 3

Give two structures found in all prokaryotic cells and in all eukaryotic cells.

Answer 3

1. Cell(-surface) membrane;
2. Ribosomes;
3. Cytoplasm;
4. DNA;

Question 4

Scientists have found that the rate of plasmid replication is faster in cells
growing in a culture with a high concentration of amino acids than in a
culture with a lower concentration of amino acids.
Suggest one explanation for the faster rate of plasmid replic

Answer 4

1. (Amino acids used in) protein synthesis;
2. (So) more enzymes (for DNA/plasmid replication)
   OR
   (So) more DNA polymerase;

Question 5

Describe how a sample of chloroplasts could be isolated from leaves.

Answer 5

1. Break open cells/tissue and filter
2. In cold, same water potential/concentration, pH controlled solution
3. Centrifuge/spin and remove nuclei/cell debris;
4. (Centrifuge/spin) at high(er) speed, chloroplasts settle out;

Question 6

The figure below shows transmission electron micrographs of two cells, one
animal cell and one prokaryotic cell.
ANimal cell magnification is 30k and prok cell mag is 60 k
Contrast the structure of the two cells visible in the electron micrographs
shown in the figure above.

Answer 6

1. Magnification (figures) show A is bigger than B;
2. A has a nucleus whereas B has free DNA;
3. A has mitochondria whereas B does not;
4. A has Golgi body/endoplasmic reticulum whereas B does not;
5. A has no cell wall whereas B has a murein/glycoprotein cell wall;
6. A has no capsule whereas B has a capsule;
7. A has DNA is bound to histones/proteins whereas B has
   DNA not associated with histones/proteins
   OR
   A has linear DNA whereas B has circular DNA;
8. A has larger ribosomes;

Answer 7

1. DNA in nucleus is code (for protein);
2. Ribosomes/rough endoplasmic reticulum produce (protein);
3. Mitochondria produce ATP (for protein synthesis);
4. Golgi apparatus package/modify;
   OR
   Carbohydrate added/glycoprotein produced by Golgi apparatus;
5. Vesicles transport
   OR
   Rough endoplasmic reticulum transports;
6. (Vesicles) fuse with cell(-surface) membrane;

Question 8

Suggest why a nucleus is not visible in above image

Answer 8

A section/slice (so nucleus in another part of cell)
OR
(Nucleus) not stained;

Question 9

Give one advantage of viewing a biological specimen using a transmission
electron microscope compared with using a scanning electron microscope.

Answer 9

Higher resolution
OR
View internal structures;

Question 10

The detail shown in the diagram above would not be seen using an optical
microscope.
Explain why.

Answer 10

1. Light has long(er) wavelength;
2. (So) low(er) resolution;

Question 11

Figure 2 shows a photograph of part of a mitochondrion from a mouse liver
cell taken using a transmission electron microscope at × 62 800
magnification.
Figure 2
Produce a scientific drawing of the mitochondrion in Figure 2 in the box
below.
Label the following parts of the mitochondrion on your drawing.
* Matrix
* Crista (this is justr fir teh mark scheme)

Answer 11

1. No sketched / hanging / crossing lines / shading;
   Ignore stippling
2. Must look similar;
3. Matrix and crista correctly labelled;
4. Correct scale stated (x 62 800);
   Accept other suitable scale g

Question 12

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

Answer 12

1. TEM use electrons and optical use light;
2. TEM allows a greater resolution;
3. (So with TEM) smaller organelles / named cell structure can be
   observed
   OR
   greater detail in organelles / named cell structure can be
   observed;
4. TEM view only dead / dehydrated specimens and optical (can)
   view live specimens;
5. TEM does not show colour and optical (can);
6. TEM requires thinner specimens;
7. TEM requires a more complex/time consuming preparation;
8. TEM focuses using magnets and optical uses (glass) lenses;

Question 13

Explain why the biologist used a blender and then filtered the mixture

Answer 13

Break open cells / homogenise / produce homogenate;
2. Remove unbroken cells / larger debris;

Question 14

Before the cell was examined using the electron microscope, it was
stained. This stain caused parts of the structure of the cell-surface
membrane to appear as two dark lines.
Suggest an explanation for the appearance of the cell-surface membrane
as two dark lines.

Answer 14

1. Membrane has phospholipid bilayer;
2. Stain binds to phosphate / glycerol;
3. On inside and outside of membrane.

Question 15

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 15

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

Question 16

A transmission electron microscope was used to produce the image in the
figure above.
Explain why.

Answer 16

1. High resolution;
2. Can see internal structure of organelles.