3.2.1 - CELL STRUCTURE + MICROSCOPY

Question 1

explain why it is not possible to determine the identity of structure X using an optical microscope (2)

Answer 1

1. the resolution is too low
2. because the wavelength of light is too long

Question 2

U. marinum cells ingest bacteria and digest them in the cytoplasm.

describe the role of one named organelle in digesting these bacteria (3)

Answer 2

1. lysosomes
2. fuse with the phagosome (vesicle)
3. releases lysozymes (hydrolytic enzymes)

Question 3

describe how a sample of chloroplasts could be isolated from leaves (4)

Answer 3

1. homogenise (break open the cells) and then filter to remove insoluble tissue and debris
2. in cold, isotonic, buffered solution
3. centrifuge to remove nuclei
4. centrifuge at a higher speed, chloroplasts will then pellet

Question 3

suggest why a nucleus is not visible in the above image (1)

Answer 3

any one:

1. only a section of the cell, nucleus may be in another part of the cell
2. nucleus is not stained

Question 3

give two structures found in all prokaryotic and eukaryotic cells (2)

Answer 3

any two:

1. cell membrane
2. ribosomes
3. cytoplasm
4. DNA

Question 4

give one feature of the chloroplast that allows protein to be synthesised inside the chloroplast and describe one difference between this feature in the chloroplast and similar features in the rest of the cell (2)

Answer 4

answer 1:
1. DNA
2. it is not associated with histones but nuclear DNA is/it is circular but nuclear DNA is linear/it is shorter than nuclear DNA

answer 2:
1. ribosomes
2. are smaller than ribosomes in the chloroplast - 70S ribosomes in chloroplast, 80S chloroplasts in cytoplasm

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 replication in cells growing in a culture with a high amino acid concentration (2)

Answer 4

answer 1:
1. amino acids are used in protein synthesis
2. so more enzymes (DNA polymerase) for DNA (plasmid) replication

answer 2:
1. amino acids are used in respiration
2. so more ATP for DNA (plasmid) replication

Question 4

eukaryotic cells produce and release proteins.

outline the role of organelles in the production, transport and release of proteins from eukaryotic cells.

do not include details of transcription and translation in your answer. (4)

Answer 4

1. DNA in the nucleus is the code for protein
2. ribosomes produce protein
3. mitochondria produce ATP for protein synthesis
4. Golgi body package and modify/carbohydrate added (glycoprotein produced) by Golgi
5. vesicles transport
6. vesicles fuse with cell surface membrane

Question 5

give one advantage of viewing a biological specimen using a transmission electron microscope compared to a scanning electron microscope (1)

Answer 5

1. higher resolution
   OR
2. view internal structures

Question 6

name an organelle found both in a chloroplast and a prokaryotic cell (1)

Answer 6

70S ribosome

Question 7

a biologist separated cell components to investigate organelle activity. she prepared a suspension of the organelles in a solution. this solution prevented damage to the organelles.

describe three properties of this solution and explain how each property prevented damage to the organelles (3)

Answer 7

1. cold to reduce enzyme activity
2. buffered to prevent denaturing of enzymes
3. isotonic to prevent organelles bursting

Question 8

contrast how an optical microscope and a transmission electron microscope work and contrast the limitations of their use when studying cells (6)

Answer 8

1. TEM uses electrons and optical uses light
2. TEM allows greater resolution
3. so with TEM smaller organelles (ribosomes) can be observed
4. TEM can only view dead specimens, optical can view live specimen
5. TEM does not show colour, optical can
6. TEM requires thinner specimens
7. TEM requires a more complex preparation
8. TEM focuses using magnets and optical uses glass lenses

Question 9

name two structures present in plant cells but not in animal cells (2)

Answer 9

any two:

1. chloroplasts
2. cell wall
3. cell vacuole
4. starch grains

Question 10

the cell-surface membrane can be seen with a TEM but not an optical microscope. explain why (1)

Answer 10

1. electron microscope has higher resolution than optical

Question 11

no organelles are visible in the cytoplasm of a red blood cell. suggest why (1)

Answer 11

1. the cytoplasm is filled with haemoglobin

Question 12

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 (3)

Answer 12

1. membrane has phospholipid bilayer
2. stain binds to the phosphate/glycerol (phosphate head)
3. on the inside and outside of the membrane

Question 13

name two structures in a eukaryotic cell that cannot be identified using an optical microscope (1)

Answer 13

any two:

1. mitochondria
2. ribosome
3. endoplasmic reticulum
4. lysosome
5. cell-surface membrane

Question 14

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 microscope (4)

Answer 14

1. add drop of water to the glass slide
2. obtain a thin section of the plant tissue and place it on the slide
3. add potassium iodide
4. lower cover slip using mounted needle

Question 15

scientists measured cell damage by measuring the activity of lysosomes. give one function of lysosomes (1)

Answer 15

break down cells/toxins

Question 16

H. pylori cells produce an enzyme that neutralises acid. suggest one advantage to the H. pylori of producing this enzyme (2)

Answer 16

1. to stop them being killed
2. by stomach acid

Question 17

cells that secrete enzymes contain a lot of rough endoplasmic reticulum and a large Golgi apparatus.

describe how the RER is involved in the production of enzymes (2)

Answer 17

1. RER (has) contains ribosomes
2. ribosomes make proteins
3. enzyme is a protein

Question 18

describe and explain how cell fractionation and ultracentrifugation can be used to isolate mitochondria from a suspension of animal cells (5)

Answer 18

any five from:

1. cell homogenisation to break open cells
2. filter to remove large debris and insoluble tissue
3. use isotonic solution to prevent damage to organelles
4. use cold solution to prevent enzyme activity
5. use buffer solution to prevent enzyme denaturing
6. centrifuge at lower speed to separate
7. re-spin at higher speed to get mitochondria to pellet to the bottom

Question 19

describe the principles and the limitations of using a TEM to investigate cell structure (5)

Answer 19

principles:
1. electrons pass through thin specimen
2. denser parts absorb more electrons
3. so denser parts appear darker
4. electrons have a short wavelength so they give a high resolution

limitations:
1. cannot look at living material
2. specimen must be very thing
3. there may be artefacts present
4. there is a long, complex staining process (preparation time)
5. the image produced is in 2D not 3D

Question 20

a student cut thin sections of tissue to view with an optical microscope. explain why it was important that the sections were thin. (2)

Answer 20

1. to allow more light to through
2. so that a few layers of cells can be viewed

Question 21

the student cut thin sections of tissue to view with an optical microscope. explain why it was important that the sections were thin (2)

Answer 21

1. to allow more light through
2. a single layer of cells to be viewed