cell exam questions

Question 1

What is a tumour?

Answer 1

Abnormal cells/tissue;
Uncontrolled mitosis/cell division;

Question 2

Describe how you would determine a reliable mitotic index from tissue observed with an optical microscope.
Don’t include details of how you would prepare the tissue observed with an optical
microscope.

Answer 2

1. Count cells in mitosis in field of view;
2. Divide this by total number of cells in field of view;
3. Repeat many/at least 5 times

Question 3

Describe viral replication.

Answer 3

1. Attachment proteins attach to receptors;
2. (Viral) nucleic acid enters cell;
3. Nucleic acid replicated in cell
4. Cell produces (viral) protein/capsid/enzymes;
5. Virus assembled and released (from cell);

Question 4

A student prepared a stained squash of cells from the root tips of garlic to calculate a mitotic index.
2. placed the root tips into a Petri dish containing 5 cm3 of hydrochloric acid for 12 minutes
(a) Suggest why the student soaked the root tips in hydrochloric acid in step 2.

Answer 4

To break down links between cells/cell walls

Question 5

Pressing the coverslip downwards enabled the student to observe the stages of mitosis clearly. Explain why.

Answer 5

Allowing the stain to pass/diffuse into the cells
OR
Allowing the cells to be (more easily) squashed;

Question 6

Other students in the class followed the same method, but calculated different mitotic
indices.
Apart from student errors, suggest two explanations why.

Answer 6

(Garlic roots) are a different age
OR
(Garlic) grown in different conditions;

Question 7

Describe how HIV is replicated.

Answer 7

1. Attachment proteins attach to receptors on helper T cell/ lymphocyte;
2. Nucleic acid/RNA enters cell;
3. Reverse transcriptase converts RNA to DNA;
4. Viral protein/capsid/enzymes produced;
5. Virus (particles) assembled and released (from cell);

Question 8

(a) A student prepared a stained squash of cells from the tip of an onion root and observed it using an optical microscope. During the preparation of the slide, he:
Explain why the student:
1. used only the first 5 mm from the tip of an onion root.

Answer 8

Where dividing cells are found / mitosis occurs;

Question 9

2. pressed down firmly on the cover slip.

Answer 9

Single / thin layer of cells / spread out cells so light passes through (making cells /
nuclei visible);

Question 10

Tick (✓) the name given to the division of cytoplasm during the cell cycle.
A Binary fission
B Cytokinesis
C Phagocytosis
D Segregation

Answer 10

b

Question 11

Describe and explain what the student should have done when counting cells to make sure that the mitotic index he obtained for this root tip was accurate.

Answer 11

1. Examine large number of fields of view / many cells;
2. To ensure representative sample;
3. Repeat count;
4. To ensure figures are correct;
5. Method to deal with part cells shown at edge /count only whole cells;
6. To standardise counting;

Question 12

A scientist treated growing tips of onion roots with a chemical that stops roots growing.
After 24 hours, he prepared a stained squash of these root tips. Figure 2 is a drawing showing the chromosomes in a single cell observed in the squash of one of these root tips in anaphase. This cell was typical of other cells in anaphase in these root tips. Use all of this information to suggest how the chemical stops the growth of roots.

Answer 12

1. Stops anaphase / cell division / mitosis;
2. (By) stopping / disrupting / spindle fibres forming / attaching / pulling;
3. Preventing separation of (sister) chromatids;
4. (So) no new cells added (to root tip);

Question 13

A student investigated mitosis in the tissue from an onion root tip.(a) The student prepared a temporary mount of the onion tissue on a glass slide. She covered the tissue with a cover slip. She was then given the following instruction. “Push down hard on the cover slip, but do not push the cover slip sideways.” Explain why she was given this instruction.

Answer 13

1. Push hard – spread / squash tissue;
2. Not push sideways – avoid rolling cells together / breaking chromosomes

Question 14

The figure above is different from an image of this bacterium obtained using a transmission electron microscope. Describe and explain one difference between these images.
Description
Explanation

Answer 14

1. 3D with SEM, but 2D with TEM
   OR Only surface visible with SEM, but internal structures visible with TEM;
2. (Because) electrons deflected/bounce off (using SEM)
   Accept Resolution is lower (with SEM)

Question 15

The resolution of an image obtained using an electron microscope is higher than the
resolution of an image obtained using an optical microscope.
Explain why.

Answer 15

Shorter wavelength between electrons;

Question 16

A student determined the size of a cell structure from a photograph obtained using a
microscope. he used a ruler and a calculator and gave the answer in μm. Describe how the student determined the size of the structure.

Answer 16

1. Measure (length of structure) and divide by magnification;
   Accept correct equation making reference to a measurement
2. Correct conversion from measured length to μm, either
   × 10 000 from cm

Question 17

(e) Name two structures found in all bacteria that are not found in plant cells.

Answer 17

1. Circular DNA (molecule in cytoplasm);
2. Murein cell wall

Question 18

(f) Name two features of HIV particles that are not found in bacteria.
Do not include attachment protein in your answer.

Answer 18

1. Capsid;
2. Reverse transcriptase;
3. RNA genome;
4. Envelope;

Question 19

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

Answer 19

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

Question 20

Name an organelle found in both a chloroplast and a prokaryotic cell.

Answer 20

(d) (70S) Ribosome;

Question 21

A biologist separated cell components to investigate organelle activity. She prepared a suspension of the organelles in a solution that prevented damage to the organelles.
Describe three properties of this solution and explain how each property prevented
damage to the organelles.
Property 1 /2 /3
Explanation

Answer 21

1. (Ice) cold to prevent/reduce enzyme activity;
2. Buffered to prevent denaturing of enzyme/protein;
3. Same water potential/ Ψ to prevent lysis/bursting (of organelle);
   Accept: isotonic for same water potential.

Question 22

Some scientists support the theory that mitochondria are organelles that evolved from prokaryotic cells. Give one piece of evidence that supports the theory that mitochondria evolved from prokaryotic cells.

Answer 22

Circular DNA / smaller/70S ribosomes / no introns / no histones/proteins associated with DNA;

Question 23

A scientist examined the structure of mustard plant leaves. He viewed temporary mounts of leaf tissues with an optical microscope. The figure below shows a drawing of typical results.
(a) Describe how temporary mounts are made.

Answer 23

1. Thin slice/ section
2. Put on slide in water / solution / stain;
3. Add cover slip

Question 24

Describe and explain how cell fractionation and ultracentrifugation can be used to isolate mitochondria from a suspension of animal cells.

Answer 24

1. Cell homogenisation to break open cells
2. Filter to remove debris / whole cells;
3. Use isotonic solution to prevent damage to mitochondria / organelles;
4. Keep cold to prevent / reduce damage by enzymes / use buffer to prevent protein / enzyme denaturation;
5. Centrifuge (at lower speed) to separate nuclei / heavy organelles;
6. Re-spin (after nuclei / pellet removed) at higher speed to get mitochondria in pellet / at bottom.

Question 25

Advantage of mitochondria

Answer 25

Able to respire aerobically;
So make (more) ATP/ release (more) energy;

Question 26

Describe the molecular structure of glycogen.

Answer 26

polymer/polysaccharide; (made of) α-glucose;
joined by 1,4 links;
glycosidic;
(chain is) branched;
1,6 links where branches attach

Question 27

Name the type of chemical reaction that takes place during the formation of glycogen.

Answer 27

hydrolyse, filtrate / juice / bond / non-reducing sugar;
with acid, then neutralise / add alkali
boil / heat with Benedict’s + test filtrate / repeat original procedure;

Question 28

This procedure does not test for non-reducing sugars, such as sucrose.
How should the procedure be altered to determine the concentration of non-reducing
sugar in the fruit juice?

Question 29

State one way, visible in the diagram above, in which the structure of fructose is: similar to glucose; different from glucose.

Answer 29

• same number, carbon / oxygen / hydrogen (atoms) / OH (groups); A hexose same formula;
• 5-membered ring / glucose has 6-membered ring;

Question 30

A student was carrying out tests to determine which biological molecules were present in a food sample. Describe a test that the student could carry out to discover whether this sample contained a lipid.

Answer 30

add / mix with, alcohol / ethanol / propanone / (suitable) organic solvent; then, add to / add / mix with, water;

Question 31

State what would be seen if a lipid was present.

Answer 31

emulsion / milky colour / cloudy

Question 32

Describe how the structure of a phospholipid differs from that of a triglyceride.

Answer 32

phospholipids have
1 less fatty acid / 2 fatty acid not 3; A hydrocarbon 1 less ester bond / 2 ester bonds not 3;
phosphate;
hydrophilic / polar, end / head;

Question 33

Describe how you would test a liquid sample for the presence of lipid and how you
would recognise a positive result.

Answer 33

Mix / shake sample) with ethanol, then water;
Sequence is important
2. White / milky (emulsion);

Question 34

Some seeds contain lipids. Describe how you could use the emulsion test to show that a seed contains lipids.

Answer 34

1. Crush / grind;
2. With ethanol / alcohol;
3. Then add water / then add to water;
4. Forms emulsion / goes white / cloudy;

Question 35

Explain why triglycerides are not considered to be polymers.

Answer 35

not made of monomers / many repeating units;

Question 36

a) Name the two scientists who proposed models of the chemical structure of DNA

Answer 36

Watson and Crick

Question 37

A scientist replicated DNA in a test tube. To do this, he mixed an enzyme with identical single-stranded DNA fragments and a solution containing DNA nucleotides. Name the enzyme used in this DNA replication.

Answer 37

DNA polymerase;

Question 38

Use your knowledge of semi-conservative replication of DNA to suggest:
1. the role of the single-stranded DNA fragments ____________________________
2. the role of the DNA nucleotides.

Answer 38

2. Determines order of nucleotides/bases;
3. Forms complementary pairs / A – T, G - C

Question 39

Nucleic acids, such as DNA, are polymers, made up of many repeating monomer units. Name the monomer from which nucleic acids are made.

Answer 39

nucleotide