cells exam questions

Question 2

Describe and explain how centrifuging the culture allowed the scientists to obtain a
cell-free liquid.

Answer 2

• heavy/dense cells
• form a pellet at bottom of tube when centrifuged
• supernatant liquid can be removed

Question 3

Describe how you could use cell fractionation to isolate chloroplasts from leaf tissue

Answer 3

Homogenise to break open cells and remove debris;
.Solution is cold / isotonic / buffered;
Second pellet is chloroplast.

Question 4

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 4

Add drop of water to (glass) slide;
Obtain thin section (of plant tissue) and place on slide / float on drop of
water;
Stain with / add iodine in potassium iodide.
Lower cover slip using mounted needle.

Question 5

Describe how phospholipids are arranged in a plasma membrane.

Answer 5

• hydrophilic heads point outwards ( in contact with the aq solution)
• hydrophobic tails point inwards towards the centre of the membrane

Question 6

Describe how the RER is involved in the production of enzymes.

Answer 6

• contains ribosomes on the surface
• ribosomes are the site of protein synthesis

Question 7

Describe how the Golgi apparatus is involved in the secretion of enzymes

Answer 7

• packages proteins into vesicles which are then transported to cell surface

Question 8

What are some things to note about the fluid mosaic model of cell membrane

Answer 8

-contains a phospholipid bilayer
- contains channel and carrier proteins
- has proteins embedded in it
- cholesterol is present
- glycolipids and glycoproteins present

Question 9

Name and describe five ways substances can move across the
cell-surface membrane into a cell

Answer 9

(Simple) diffusion of small/non-polar molecules down a
concentration gradient;

Facilitated diffusion down a concentration gradient via
protein carrier/channel

Osmosis of water down a water potential gradient;

Active transport against a concentration gradient via
protein carrier using ATP

co-transport of 2 different substances using a carrier protein;

Question 10

Describe and explain two features you would expect to find in a cell
specialised for absorption.

Answer 10

Folded membrane/microvilli so large surface area (for absorption);

thin walls ( one cell thick) for short diffusion pathway for substances being absorbed

Question 11

The movement of substances across cell membranes is affected by
membrane structure. Describe how.

Answer 11

Phospholipid (bilayer) allows movement/diffusion of nonpolar/lipid-soluble substances

Carrier proteins allow active transport;

channel proteins allow for facilitated diffusion

membrane surface area determines how much diffusion takes place

number of protein channels/ carrier proteins determines how much diffusion

Question 12

Q6.
A student investigated the effect of surface area on osmosis in cubes of potato.
* He cut two cubes of potato tissue, each with sides of 35 mm in length.
* He put one cube into a concentrated sucrose solution.
* He cut the other cube into eight equal-sized smaller cubes and put them
into a sucrose solution of the same concentration as the solution used for
the large cube.
* He recorded the masses of the cubes at intervals.

Describe the method the student would have used to obtain the results in
the graph. Start after all of the cubes of potato have been cut. Also
consider variables he should have controlled.

Answer 12

Method of controlling temperature;
Accept ‘at room temperature’ for method

Method of drying cubes before measuring ie dry with a paper towel

Measure mass of cubes at stated time intervals ie every 20 minutes

Question 13

Describe how HIV replicated

Answer 13

attachment proteins attach to receptors on helper T cell/lymphocyte;
Nucleic acid/RNA enters cell;
Reverse transcriptase converts RNA to DNA;
Viral protein/capsid/enzymes produced;

Question 14

Describe how a phagocyte destroys a pathogen present in the blood.

Answer 14

• engulfs the pathogen
• forms vesicle and fuses with lysosome
• lysozymes released to hydrolysed pathogen

Question 15

Explain how HIV affects the production of antibodies when AIDS develops
in a person

Answer 15

Less/no antibody produced;
(Because HIV) destroys helper T cells;
so no/ less B cells undergo mitosis/differentiate/form plasma cells;

Question 16

Give two types of cell, other than pathogens, that can stimulate an immune response

Answer 16

(Cells from) other organisms/transplants

cancer cells

Question 17

Suggest and explain two further investigations that should be done before
this ADC ( antibody monoclonal) is tested on human breast cancer patients.
( after being tested on mice)

Answer 17

Tested on other mammals to check for safety/side effects;

Tested on (healthy) humans to check for safety/side effects;

Investigate different concentrations of ADC to find suitable/safe
dosage

( 2 max)

Question 18

Describe the principles and the limitations of using a transmission electron
microscope to investigate cell structur

Answer 18

Principles:
Electrons pass through / enter (thin) specimen;
Denser parts absorb more electrons;
(So) denser parts appear darker;
Electrons have short wavelength so give high resolution

( max three points)

Weaknesses:
Cannot look at living material / Must be in a vacuum;
Specimen must be (very) thin
Artefacts present
Complex staining method

( max three points)

Question 19

The events that take place during interphase and mitosis lead to the production of two
genetically identical cells. Explain how.

Answer 19

DNA replicated;
(Involving) specific / accurate / complementary base-pairing;
(Ref to) two identical / sister chromatids;
Each chromatid / moves / is separated to (opposite) poles / ends of cell.

Question 20

The actual number of slow muscle fibres in the field of view was not the same
as the number you calculated in question (i).
Give one reason why.

Answer 20

mean number of capillaries used in calculation

Question 21

Give two ways in which pathogens can cause disease

Answer 21

• kill cells/tissues
• release toxins

Question 22

Putting bee honey on a cut kills bacteria. Honey contains a high concentration of
sugar.
Use your knowledge of water potential to suggest how putting honey on a cut kills
bacteria

Answer 22

Water potential in (bacterial) cells higher (than in honey)
Water leaves bacteria / cells by osmosis;
(Loss of water) stops (metabolic) reactions.

Question 23

Between 1980 and 1990, there were three peaks in the number of reported cases of
whooping cough. After 1981, the number of cases of whooping cough in each peak
decreased.
Use the information from the graph to suggest why.

Answer 23

Vaccination rate increases;
Fewer people to spread the disease

Question 24

The percentage of the population vaccinated does not need to be 100% to be
effective in preventing the spread of whooping cough.
Suggest why

Answer 24

• more people are immune
• so unvaccinated people are less likely to infect the population and also less likely to be infected because the disease won’t spread

Question 25

LDL enters the liver cells (lines 3−4).
Using your knowledge of the structure of the cell-surface membrane, suggest how
LDL enters the cell.

Answer 25

Lipid soluble / hydrophobic
2. Enters through (phospholipid) bilayer

OR

3. (Protein part of) LDL attaches to receptor on carrier/ channel protein
4. Goes through carrier / channel protein ( either FD or active transport)

Question 26

A mutation of a tumour suppressor gene can result in the formation of a tumour.
Explain how

Answer 26

(Tumour suppressor) gene inactivated / not able to control / slow down
cell division;

Rate of cell division too fast / out of control

Question 27

Some cancer cells have a receptor protein in their cell-surface membrane that binds
to a hormone called growth factor. This stimulates the cancer cells to divide.
Scientists have produced a monoclonal antibody that stops this stimulation.
Use your knowledge of monoclonal antibodies to suggest how this antibody stops
the growth of a tumour.

Answer 27

Antibody has specific tertiary structure / binding site / variable region;
Complementary (shape / fit) to receptor protein, so will bind to it
Prevents GF binding (to receptor protein).

Question 28

HSV infects nerve cells in the face (line 1). Explain why it infects only nerve cells

Answer 28

Outside of virus has antigens / proteins;
With complementary shape to receptor / protein in membrane of
nerve cells;
3. (Receptor / protein) found only on membrane of nerve cells.

Question 29

Suggest one advantage of programmed cell death (line 4)

Answer 29

Prevents replication of virus