Exam specific answers

Question 1

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

Answer 1

lysosomes
fuse with the vesicle
they release hydrolytic enzymes

Question 2

outline the role of organelles in the production, transport and release of proteins from eukaryotic cells? (5)

Answer 2

DNA in nucleus codes for proteins
ribosomes produce proteins
mitochondria produce ATP for protein synthesis
Golgi apparatus package and modify proteins
RER transports proteins

Question 3

name two structures found in all bacteria that are not found in plant cells? (2)

Answer 3

plasmids, 70S ribosomes, murein cell wall

Question 4

why is it important that a thin section of tissue is cut for light microscopy? (2)

Answer 4

so the light rays can penetrate through the tissue to prevent overlapping of organelles

Question 5

describe two ways in which molecules of cellulose are similar to molecules of starch? (2)

Answer 5

they are both polymers
they are both made of monomers
both molecules can be broken down by a hydrolysis reaction
both contain glycosidic bonds

Question 6

contrast the way optical microscopes and transmission electron microscopes work and contrast their limitations? (6)

Answer 6

TEM uses electrons and optical use light
TEM allows greater resolution
with TEM smaller organelles can be observed
TEM only views dead specimens and optical can view live specimens
TEM doesn’t show colour but optical can
TEM requires thinner specimens
TEM requires more complex preparation
TEM focuses using magnets and optical uses lenses

Question 7

explain how to prepare a specimen for viewing with an optical microscope? (4)

Answer 7

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

Question 8

explain why the solution used in homogenisation must be cold, isotonic and buffered? (3)

Answer 8

cold - slow enzyme activity to prevent digestion of organelles
isotonic - prevent osmosis so organelles don’t shrink
buffer - maintain pH so enzymes aren’t denatured

Question 9

give two ways in which the hydrolysis of ATP is used in cells? (2)

Answer 9

1. to provide energy for other reactions
2. to add phosphate to other substances and change their shape

Question 10

how would you create a serial dilution of concentration 0.15mol/dm3 and volume 30cm3? (2)

Answer 10

add 4.5cm3 of sucrose solution to 25.5cm3 of distilled water
(think of it like ratio 0.15:0.85, then find 15% of 30 to get volume of sucrose solution)

Question 11

describe and explain 2 aseptic techniques that would be used when transferring bacteria from a broth culture to an agar plate. (4)

Answer 11

1. open the lid of the Petri dish as little as possible to stop unwanted bacteria from contaminating the dish
2. wear gloves to prevent contamination from bacteria on hands

Question 12

what is a tumour? (2)

Answer 12

a mass of cells which occurs due to cells undergoing uncontrolled division by mitosis

Question 13

describe how you would determine a reliable mitotic index from tissue observed with an optical microscope? (3)

Answer 13

count the total number of cells in the field of view
count the number of cells in the field of view undergoing mitosis and divide this number by the total number of cells
repeat many times (at least 5)

Question 14

what is the advantage of the cells lining the human intestine completing the cell cycle in a short time? (1)

Answer 14

allows the cells to be replaced quickly

Question 15

describe how substances move across cell-surface membranes by facilitated diffusion. (3)

Answer 15

substances bind to a carrier protein
the carrier protein is specific to the substance
the substance moves down the concentration gradient