Cell Structure + Microscopy

Question 1

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

Answer 1

Resolution (too) low;

Because 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.

Answer 2

Lysosomes;

Fuse with vesicle;

(Releases) hydrolytic enzyme

Question 3

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

Answer 3

Cell(-surface) membrane;

Ribosomes;

Cytoplasm

Question 4

All prokaryotic cells contain a circular DNA molecule and some prokaryotic cells
contain plasmids.

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.

Answer 4

Amino acids used in) protein synthesis;

(So) more enzymes (for DNA/plasmid replication)
OR
(So) more DNA polymerase;

(Amino acids used in) respiration;

(So) more energy/ATP (for DNA/plasmid replication);

Question 5

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

(Cell Centrifugation process)

Answer 5

Break open cells/tissue and filter
OR
Grind/blend cells/tissue/leaves and filter;

In cold, same water potential/concentration, pH controlled solution;

Centrifuge/spin and remove nuclei/cell debris;

(Centrifuge/spin) at high(er) speed, chloroplasts settle out;

Question 6

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.

Answer 6

DNA;
Is not associated with protein/histones but nuclear DNA is

OR

Is circular but nuclear DNA is linear

OR

Is shorter than nuclear DNA;

Ribosomes;
Are smaller than cytoplasmic ribosomes;

Question 7

Eukaryotic cells produce and release proteins.

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

Answer 7

DNA in nucleus is code (for protein);

Ribosomes/rough endoplasmic reticulum produce (protein);

Mitochondria produce ATP (for protein synthesis);

Golgi apparatus package/modify;
OR
Carbohydrate added/glycoprotein produced by Golgi apparatus;

Vesicles transport
OR
Rough endoplasmic reticulum transports;

(Vesicles) fuse with cell(-surface) membrane;

Question 8

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

Answer 8

Higher resolution
OR
View internal structures;

Question 9

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

Answer 9

(70S) Ribosome

Question 10

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.

Answer 10

(Ice) cold to prevent/reduce enzyme activity;

Buffered to prevent denaturing of enzyme/protein;

Same water potential/ Ψ to prevent lysis/bursting (of organelle);

Question 11

Name the process by which prokaryotic cells divide.

Answer 11

Binary fission;

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

TEM use electrons and optical use light;

TEM allows a greater resolution;

(So with TEM) smaller organelles / named cell structure can be
observed
OR
greater detail in organelles / named cell structure can be
observed;

TEM view only dead / dehydrated specimens and optical (can)
view live specimens;

TEM does not show colour and optical (can);

TEM requires thinner specimens;

TEM requires a more complex/time consuming preparation;

TEM focuses using magnets and optical uses (glass) lenses;

Question 13

Explain why the solution the biologist used was ice-cold, buffered and the
same water potential as the liver tissue

Answer 13

Ice-cold – Slows / stops enzyme activity to prevent digestion of organelles / mitochondria;

Buffered – Maintains pH so that enzymes / proteins are not denatured;

Same water potential – Prevents osmosis so no lysis / shrinkage of
organelles / mitochondria

Question 14

Explain why the biologist used a blender and then filtered the mixture
(steps 2 and 3).

Answer 14

Break open cells / homogenise / produce homogenate;

Remove unbroken cells / larger debris;

Question 15

Give two ways in which the nucleotides in DNA are different from the
nucleotides in RNA.

Answer 15

DNA contains thymine and RNA contains uracil;

DNA contains deoxyribose and RNA contains ribose.

Question 16

Name two structures in a eukaryotic cell that cannot be identified using an
optical microscope.

Answer 16

Mitochondrion / ribosome / endoplasmic reticulum / lysosome / cell
surface membrane.

Question 17

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 17

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.