Cell structure

Question 1

Complete the table by giving the letter labelling the organelle that matches the function.

Answer 1

• L
• H
• N

Question 2

Use the scale bar in the diagram above to calcualte the magnification of the drawing.
Show your working.

Answer 2

• 1800 - 2200

Question 3

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

( Table shows different strains of bacteria ( A, B and C ), A and C produce a toxin and A and B have an enzyme that neutralises acid )
( A bar graph of A, B and C, A has the highest result and B has the lowest, the standard deviations of the graphs B and C cross each other in range )

Answer 3

• Dense cells
• Form a pellet when centrifuged
• Supernatant can be removed

Question 4

The scientists measured cell damage by measuring the activity of lysosomes.
Give one function of lysosomes.

Answer 4

• break down cells

Question 5

H. pylori cells produce an enzyme that neutralises acid.

Suggest one advantage to the H. pylori of producing this enzyme.

Answer 5

• to reduce them from being damaged

- by stomach acid

Question 6

What do these data suggest about the damage caused to human cells by the toxin
and by the enzyme that neutralises acid?
Explain your answer.

Answer 6

• More cells are damaged when toxin and enzyme is produced
• Some cells are damaged by B and C
• Standard deviation doesn’t overlap for A with B and C so difference is real

Question 7

The scientists carried out a further investigation.
They treated the liquid from strain A with a protein-digesting enzyme before adding it to a culture of human cells.
No cell damage was recorded.
Suggest why there was no damage to the cells.

Answer 7

• Neutralising enzyme is broken down
• No toxin is produced is produced
• So toxin is the protein

Question 8

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

Answer 8

• Cells are broken open and debris is removed
• Solution is cold / isotonic / buffered
• Second pellet is chloroplast

Question 9

The figure below shows a photograph of a chloroplast taken with an electron
microscope.

Name the parts of the chloroplast labelled A and B.

Answer 9

• A - Stoma

- B - Granum

Question 10

Calculate the length of the chloroplast shown in the figure above.

Answer 10

• ( Length of chloroplast / length of bar )

- 8.3 / 1.8 = 4.6 mircro metres ( ??? )

Question 11

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

Answer 11

• Ribosome

- Cell surface membrane

Question 12

Starch and cellulose are two important plant polysaccharides.

The following diagram shows part of a starch molecule and part of a cellulose molecule.

Explain the difference in the structure of the starch molecule and the cellulose molecule shown in the diagram above.

Answer 12

• Starch is composed of alpha glucose while cellulose is composed of beta glucose
• Position of hydrogen and hydroxyl groups on carbon atom 1 is inverted

Question 13

Starch molecules and cellulose molecules have different functions in plant cells.
Each molecule is adapted for its function.

Explain one way in which starch molecules are adapted for their function in plant
cells.

Answer 13

• Insoluble

- so doesn’t effect water potential

Question 14

Explain how cellulose molecules are adapted for their function in plant cells.

Answer 14

• Long and straight chains
• Become linked together by many hydrogen bonds to form fibrils
• Provide strength

Question 15

Silkworms secrete silk fibres, which are harvested and used to manufacture silk fabric.

Scientists have produced genetically modified (GM) silkworms that contain a gene from a spider.

The GM silkworms secrete fibres made of spider web protein (spider silk), which is
stronger than normal silk fibre protein.

The method the scientists used is shown in the figure below.

( Shows steps of how a gene from a spider is inserted into the silkworm )

Suggest why the plasmids were injected into the eggs of silkworms, rather than into
the silkworms.

Answer 15

• Gene gets into most cells of the silkworm

- So gets into cells that make silk

Question 16

Suggest why the scientists used a marker gene and why they used the EGFP gene.

Answer 16

• Not all eggs will successfully take up the plasmid

- Silkworms that have taken in the gene will glow

Question 17

The scientists ensured the spider gene was expressed only in cells within the silk
glands.

What would the scientists have inserted into the plasmid along with the spider gene
to ensure that the spider gene was only expressed in the silk glands of the
silkworms?

Answer 17

• Promoter gene

Question 18

Suggest two reasons why it was important that the spider gene was expressed only
in the silk glands of the silkworms.

Answer 18

• So that the protein can be harvested

- Fibres in other cells might cause harm

Question 19

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 19

• Add a drop of water into the glass slide
• Obtain a thin section of tissue and place it on the slide
• Stain with iodine in potassium iodide
• Lower cover slip using mounted needle

Question 20

The figure below shows a microscopic image of a plant cell.

Give the name and function of the structures labelled W and Z.

Answer 20

• W - Chloroplast
• Function - Photosynthesis
• Z - Nucleus
• Function - Contain genetic information

Question 21

A transmission electron microscope was used to produce the image in the figure
above.
Explain why.

Answer 21

• High resolution

- Can see internal structure of the organelles

Question 22

Calculate the magnification of the image shown in the figure in part (a).

Answer 22

• ( Length of bar in mm × 1000 )

- 14 x 1000 = 14 000

Question 23

Describe how phospholipids are arranged in a plasma membrane.

Answer 23

• Bilayer
• Hydrophobic tails inside
• Hydrophilic heads outside
  ( Max 2 )

Question 24

Cells that secrete enzymes contain a lot of rough endoplasmic reticulum (RER) and
a large Golgi apparatus.

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

Answer 24

• Contains ribosomes

- to make proteins

Question 25

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

Answer 25

• Modifies proteins
• Put into vesicles
  ( Max 1 )

Question 26

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

Answer 26

• Cell homogenisation to break open cells
• Filter to remove whole cells and debris
• Use isotonic solution to prevent damage to organelles
• Keep cold to reduce damage by enzymes ( buffered )
• Centrifuge to separate nuclei
• Re - spin supernatant at a higher speed to get mitochondria as a pellet
  ( Max 5 )

Question 27

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

Answer 27

• Electrons pass through the specimen
• Denser parts absorb more electrons
• So appear darker
• However it cannot look at living specimens
• Specimen must be thin

Question 28

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

Answer 28

• DNA is replicated
• Involving complementary base pairing
• Two identical chromatids are formed
• Each chromatid moved to opposite poles of the cell

Question 29

A student cut thin sections of tissue at different distances from the tip of a root.
She stained the sections and viewed them with an optical microscope.

For each section, the student counted the number of cells in mitosis and the total
number of cells in each field of view.
She then calculated a mitotic index for each
section using the equation:

Mitotic index = number of cells in mitosis / total number of cells

The student’s results are shown in the graph.

( A graph of mitotic index against distance from the tip of the root, has a decreasing gradient )

The student cut thin sections of tissue to view with an optical microscope.
Explain why it was important that the sections were thin.

Answer 29

• To allow more light through

- A single layer of cells can be viewed

Question 30

What does the graph show about the growth of roots?

Use the data to explain your answer.

Answer 30

• More mitosis near the tip

- Almost no mitosis after 1.6 mm from the tip

Question 31

Researchers investigated whether the blood supply to slow and fast muscle fibres in a muscle changes with age.
They used diaphragms taken from hamsters (Mesocricetus auratus).
The diaphragm is in constant use for breathing.
They took diaphragms from groups of young, adult and old hamsters.

They removed the diaphragm from each animal and took a sample of muscle tissue.
They examined it under an optical (light) microscope.
For each sample they selected several
fields of view at random.
In each field of view, they then counted the number of capillaries associated with each type of muscle fibre.

This allowed the researchers to calculate the mean number of capillaries for each type of
muscle fibre, for each age group.

The table below shows the researchers’ results which include standard deviation (SD).

( A table that shows young, adult and old hamsters, adult hamsters have the highest SD in slow fibres, then old, then young.
In fast fibres, old have the highest SD, then adult, then young )

Give four precautions that the researchers took to make their calculations of mean
number of capillaries per fibre reliable.

Answer 31

• Fields of view are randomly chosen
• Several fields of view
• All same species of hamster
• Same muscle used

Question 32

The researchers examined the muscle of an animal in the old age group.
They found one field of view containing only slow muscle fibres.
They counted 69 capillaries in this field of view.

Use a calculation to estimate how many slow muscle fibres were visible in this field of view.
Show your working.

Answer 32

• 15

Question 33

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 33

• Calculation used the mean number of capillaries

Question 34

A student read the report of the researchers’ investigation.
She thought that the investigation was unethical but that a conclusion could still be made.

Suggest why she thought the investigation was unethical.

Answer 34

• Hamsters were killed in order to obtain the diaphragm

Question 35

She concluded that age had a significant effect on the mean number of capillaries per fibre.

Evaluate this conclusion.

Answer 35

• There’s a large significant difference between young and adult hamsters
• There’s no significant difference between adult and old hamsters
• For slow and fast fibres
• There’s a significant difference between young and old for first fibres