SUMMARY QUESTIONS - Cell structure

Question 1

Distinguish between magnification and resolution

Answer 1

• Magnification is how many times bigger the image is compared to the real object
• Resolution is the minimum distance apart that 2 objects can be in order for them to appear as separate items

Question 2

An organelle that is 5 micrometers in diameter appears under a microscope to have a diameter of 1mm. Calculate how many times an organelle has been magnified

Answer 2

200 times

Question 3

A cell organelle called a ribosome is typically 25 nm in diameter. Calculate its diameter when viewed under an electron microscope that magnifies it 400 000 times

Answer 3

10 mm

Question 4

At a magnification of x12 000 a structure appears to be 6mm long. Determine its actual length

Answer 4

500nm (0.5 micrometers)

Question 5

Chloroplasts have a greater mass than mitochondria but a smaller mass than nuclei. Starting with a sample of plant cells, describe briefly how you would obtain a sample rich in chloroplasts

Answer 5

• Keep the plants in a cold, buffered solution with the same water potential as the cells
• Break up the cell using a mortar and pestle/homogeniser
• Filter the homogenise to remove cell debris
• Centrifuge the homogenate at 1000 times gravity and remove supernatant liquid (leaving nuclei behind in the sediment)
• Then centrifuge the supernatant liquid at 2000-3000 times gravity
• The sediment produced will be rich in chloroplasts

Question 6

Explain how the electron microscope is able to resolve objects better than a light microscope

Answer 6

• EM uses beam of electrons that has a much smaller wavelength than light

Question 7

Explain why specimens have to be kept in a near-vacuum in order to be viewed effectively using an electron microscope

Answer 7

Electrons are absorbed by the molecules in air and, if present, this would prevent the electrons reaching the specimen

Question 8

In practice, the theoretical resolving power of an electron microscope can’t always be achieved. Why not?

Answer 8

• The preparation of the specimens may not be good enough
• A higher energy electron beam is required and this may destroy the specimen

Question 9

In a photomicrograph, an organelle measures 25mm when its actual size is 5 micrometers. Calc the magnification of this photmicrograph

Answer 9

The organelle measures 25mm (=25 000 micrometers) long and represents 5 micrometers.
Magnification is therefore 25 000 divided by 5
Magnification = 5000 times

Question 10

Finnish the Gap:
To measure the size of the object under a ____ microscope you can use an ___ graticule and a _____ micrometer

Answer 10

Light
Eyepiece
Stage

Question 11

Finish the Gap:
Before you can use the graticule to measure the size of objects it must first be ____.

Answer 11

Calibrated

Question 12

Finish the sentence:
A photograph of a cell under an electron microscope is magnified 5000 x. On the photograph the nucleus measures 100mm in diameter. The actual size of the nucleus is therefore ___ micrometers

Answer 12

20

Question 13

State in which process ribosomes are important

Answer 13

Protein synthesis

Question 14

List 3 carbohydrates that are absorbed by an epithelial cell of the small intestine

Answer 14

Glucose, fructose, galactose

Question 15

State the organelle that is being referred to in each of the following descriptions:
A: possesses structures called cristae
B: contains chromatin
C: It synthesises glycoproteins
D: It digests worn out organelles

Answer 15

A: mitochondrion
B: nucleus
C: Golgi apparatus
D: lysosome

Question 16

The following list gives a type of cell and a brief description of its role. Suggest 2 organelles that might be numerous and/or well developed in each of the cells
A: A sperm cell swims a considerable distance carrying the male chromosome
B: One type of white blood cell engulfs and digests foreign material
C: Liver cells manufacture proteins and lipids at a rapid rate

Answer 16

A: Mitochondria, nucleus
B: Golgi apparatus, lysosomes
C: Rough ER, ribosomes, mitochondria, smooth ER

Question 17

Explain what is meant by a tissue

Answer 17

Collection of similar cells working together to perform a specific function

Question 18

Explain why an artery is described as an organ whereas a blood capillary isn’t

Answer 18

• Artery is made up of more than one tissue (epithelial, muscular, connective)
• whereas a blood capillary is made up of only 1 (epithelial)

Question 19

State whether each of the following is a tissue or an organ
A: Heart
B: xylem
C: lungs
D: epithelium

Answer 19

A: O
B: T
C: O
D: T

Question 20

This table lists some of the features of cells. For each letter in the box, write down if it is present, absent, or sometimes (occurs in some cells and not others)

Answer 20

A = absent
B = present
C = present
D = sometimes
E = sometimes
F = sometimes
G = present
H = present
I = sometimes
J = absent
K = present
L = present
M = absent
N = absent

Question 21

If a bacterium is 6 micrometers long and a virus is 150 nano meters long, calculate how many times larger the bacterium is than the virus

Answer 21

• 6 micrometers = 6000 nanometers
• 6000nm divided by 150nm = 40 times

Question 22

Suggest an advantage and a disadvantage of having offspring that are genetically identical to thrift parents

Answer 22

• ADV: genetic make-up of parent has enabled it to survive and reproduce, if offspring has same make-up, they’re also likely to survive and reproduce
  -DADV: genetic variety is limited, if environmental conditions change —> species may not have individuals with necessary genes to survive in new conditions —> fails to adapt and becomes extinct

Question 23

Fill in the gaps:
The period when a cell isn’t dividing is called (A). The stage of mitosis when the chromosomes are first visible as distinct structures is called (B). During this stage thin threads develop that span the cell from end to end and together form a structure called the (C). Towards the end of this stage, the (D) breaks down and the (E) disappears. The stage when the chromosomes arrange themselves across the centre of the cell is called (F). During the stage called (G) the chromatids move to opposite ends of the cell.

Answer 23

A = interphase
B = prophase
C = spindle
D = nuclear envelope
E = nucleolus
F = metaphase
G = anaphase

Question 24

State the names of the 5 stages represented by the letters A-E in the following picture. In each case give a reason for choosing your answer

Answer 24

A = telophase: chromosomes in two sets, one at each pole
B = prophase: chromosomes visible but randomly arranged
C = interphase: no chromosomes visible
D = metaphase: chromosomes lined up at the equator
E = anaphase: chromatids in two sets, each drawn towards pole

Question 25

List the 3 main stages of the cell cycle

Answer 25

• interphase
• nuclear division
• cell division

Question 26

Using the graph, state at what time(s), or during which period each of the following occur
A: cell division
B: replication of DNA

Answer 26

A = 12 hours and 24 hours
B = 6-9 hours and 18-21 hours

Question 27

It would be possible to kill more cancer cells if the same dose of the drug was given more frequently or the frequency was kept the same but a larger dose of the drug was used each time. Suggest why:
A - the drug wasn’t given more frequently
B - the does of the drug wan’t increased

Answer 27

A: if frequency increased the healthy body cells wouldn’t have time to increase their numbers to near normal again between treatments their numbers would decline rapidly after a few treatments and possibly kill the patient
B: the increased dose would kill even more healthy cells each time and again their numbers would decline rapidly after a few treatments and possibly kill the patient