year 12 additional questions (cell structure)

King Edward VI Camp Hill School For Girls 1

1. Answers should be written in continuous prose. Credit will be given for biological accuracy, the organisation and presentation of the information and the way in which the answer is expressed.

The following extract has been taken from a dictionary of biological terms.

cell membrane: a membrane found either on the outside of a cell or within it. Cell membranes are extremely thin. They are only about 7 nm thick and so cannot be seen with a light microscope. A transmission electron microscope however shows a cell membrane consists of three lines forming a sandwich. The two outer lines are dark in colour while there is a lighter one in between. As it is impossible, even with an electron microscope, to see how the actual molecules are arranged in a cell membrane, it is necessary to produce a model to explain the membrane’s properties. The most accurate model of membrane structure that has been developed is the fluid mosaic model and this can be used to describe most of the properties of a cell membrane. Cell membranes play a very important part in the biology of cells and they are particularly important in regulating the movement of substances into and out of cells.

Source: W.J.E. INDGE, The Complete A-Z Biology Handbook (Hodder & Stoughton) 1997

(a) (i) Describe the structure of a cell membrane.

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(ii) Describe two ways in which the appearance of a plant cell wall would differ from a cell membrane when viewed with an electron microscope.

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(b) Describe the part played by cell surface membranes in regulating the movement of substances into and out of cells.

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(c) Describe how the distribution of cell membranes in a prokaryotic cell such as a bacterium differs from that in a cell from a plant leaf.

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(QWC 3) (Total 20 marks)

2. (a) An electron microscope has a much greater resolving power than an optical microscope.

(i) Explain the meaning of the term resolving power.

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(ii) Explain the reason for this difference in resolving power.

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The diagram represents the structure of an animal cell as it would appear when seen with an electron microscope.

(b) Name one structure:

(i) that is present in this cell but would not be in a bacterial cell;

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(ii) that is not present in this cell but may be present in a bacterial cell.

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(c) Describe one function of the organelle labelled X.

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(Total 5 marks)


3. The diagram shows a mitochondrion.

DNA loop

X

Ribosomes

(a) (i) Name the part labelled X.

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(ii) A human liver cell contains several hundred mitochondria. A cell from a plant root has only a small number. Suggest an explanation for this difference.

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(iii) Mitochondria contain some DNA and ribosomes. Suggest the function of these.

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(b) Mitochondria may be separated from homogenised sells by differential centrifugation. During this process the cells must be kept in an isotonic solution. Explain why.

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(c) Ribosomes in bacterial cells differ from those in the cytoplasm of eukaryotic cells. When centrifuged at high speed, the eukaryotic cell ribosomes sediment more rapidly than bacterial ribosomes. Explain what this tells you about the difference between bacterial and eukaryotic ribosomes

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(Total 8 marks)

4. The diagram shows a bacterium.


(a) Give the function of

(i) organelle X;

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(ii) organelle Y.

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S (b) (i) Give two ways in which the structure of this bacterium is similar to the structure of a cell lining the human small intestine.

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(ii) Give two ways in which the structure of this bacterium differs from the structure of a cell lining the human small intestine.

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(Total 6 marks)


5. (a) Small samples of plant tissue were placed in a cold, isotonic solution and then treated to break open the cells to release the organelles. The different organelles were then separated. Describe a technique that could be used to

(i) break open the cells;

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(ii) separate the organelles.

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(b) One group of organelles was placed in a hypotonic solution. The diagram shows one of these organelles seen under an electron microscope before and after it was placed in the hypotonic solution.

(i) Name the organelle.

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(ii) Describe and explain the effect on the organelle of placing it in the hypotonic solution.

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(Total 7 marks)

6. Cell organelles can be separated by centrifuging a cell extract in a sucrose density gradient. The organelles settle at the level in the sucrose solution which has the same density as their own.

Some animal cells were broken open and the cell extract centrifuged in a sucrose density gradient. Three distinct fractions were obtained, A, B and C, as shown in the diagram.

A

B

C

Increasingdensity ofsucrosesolution


One fraction contained nuclei, one contained ribosomes and a third contained mitochondria.

Complete the table by identifying the organelle in each fraction and describing one function of each organelle.

Fraction Organelle Function

A

B

C

(Total 4 marks)


7. The diagram shows part of an animal cell as seen through an electron microscope.

X

A

B

Y

C

(a) Name organelles A, B and C.

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B ....................................................................

C .................................................................... (3)


(b) Describe the function of organelle X.

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(c) The actual diameter of organelle Y is 0.5 pm.µm.

Calculate the magnification of the diagram. Show your working.

Magnification ..................................... (2)

(Total 7 marks)

8. (a) The table shows some features of cells. Complete the table with ticks to show those features which are present in an epithelial cell from the small intestine and those features which may be present in a prokaryotic cell.

Feature Epithelial cell from small intestine

Prokaryotic cell

Golgi apparatus

Mitochondrion

Nuclear envelope

Plasmid

Ribosome

(2)


(b) (i) Explain why it is possible to see the detailed structure of a prokaryotic cell with an electron microscope but not with a light microscope.

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(ii) Care must be taken in interpreting electron micrographs. Some features visible in an electron micrograph may not be present in the living cell. Explain why.

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(Total 5 marks)

9. The drawing shows some bacterial cells.

Cell A

Capsule


(a) This drawing has been magnified 6000 times Calculate the actual length, in micrometres, of cell A. Show your working.

Answer ............................ µm (2)

(b) Each of these bacterial cells is surrounded by a capsule. The main chemical constituent of this capsule is a nitrogenous polysaccharide. List the elements present in this compound.

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(c) Give one way in which:

(i) the genetic material in this bacterial cell would differ from that in an animal cell;

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(ii) the distribution of membranes in this bacterial cell would differ from the distribution of membranes in a plant cell.

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(Total 5 marks)


10. The diagram shows a bacterium.

A

B

C

D

E

F


Identify the structures labelled A to F and give one function of each.

A ................................................................................................................................

Function. ....................................................................................................................

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B ................................................................................................................................

Function. ....................................................................................................................

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C ................................................................................................................................

Function. ....................................................................................................................

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D ................................................................................................................................

Function. ....................................................................................................................

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E .................................................................................................................................

Function. ....................................................................................................................

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F .................................................................................................................................

Function. ....................................................................................................................

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11. Read the following passage.

In a human, there are over 200 different types of cell clearly distinguishable from each other. What is more, many of these types include a number of different varieties. White blood cells, for example, include lymphocytes and granulocytes.

Although different animal cells have many features in common, each type has adaptations. 5 associated with its function in the organism. As an example, most cells contain the same

organelles, but the number may differ from one type of cell to another. Muscle cells contain many mitochondria, while enzyme-secreting cells from salivary glands have particularly large amounts of rough endoplasmic reticulum.

The number of a particular kind of organelle may change during the life of the cell. An 10 example of this change is provided by cells in the tail of a tadpole. As a tadpole matures into a

frog, its tail is gradually absorbed until it disappears completely. Absorption is associated with an increase in the number of lysosomes in the cells of the tail.

Use information from the passage and your own knowledge to answer the following questions.

(a) Explain the link between.

(i) mitochondria and muscle cells (lines 6 - 7);

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(ii) rough endoplasmic reticulum and enzyme-secreting cells from salivary glands (lines 7 - 8).

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(b) Use information in the passage to explain how a tadpole’s tail is absorbed as a tadpole changes into a frog.

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(c) Starting with some lettuce leaves, describe how you would obtain a sample of undamaged chloroplasts. Use your knowledge of cell fractionation and ultracentrifugation to answer this question.

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(Total 13 marks)


12. The drawing shows part of an animal cell.

(a) Name feature X.

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(b) Describe the function of organelle Y.

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(c) Describe one way in which the function of organelle Z is related to the function of organelle Y.

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(d) Calculate the actual length of the mitochondrion in micrometres. Show your working.

Answer .............................. µm (2)

(Total 5 marks)

13. (a) An extract of mitochondria was made by centrifuging a liver preparation that had been ground up in a blender (homogeniser).

Suggest and explain precautions that could have been taken to:

(i) prevent damage by enzymes released in the processing;

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(ii) prevent osmotic damage to the mitochondria.

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(b) If the cell preparation had been contaminated with bacteria, why might it have been difficult to separate the mitochondria from the bacteria?

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(Total 5 marks)

14. (a) The drawing was made from an electron micrograph. It shows some microvilli on an epithelial cell from the small intestine.

X

Y

(i) A transmission electron microscope uses a beam electrons. Explain how a beam of electrons allows the microvilli to be seen in detail.

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(ii) Explain why the microvilli labeled X and Y differ in appearance.

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(b) Different cells contain different numbers of mitochondria. Suggest the advantage of large numbers of mitochondria in

(i) a cell from a plant root which absorbs mineral ions from the soil;

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(ii) a muscle cell.

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(Total 6 marks)


15. The diagram shows part of a cell that secretes enzymes.

(a) Give one piece of evidence, visible in the diagram, which shows that this cell is a eukaryotic cell.

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(b) Some cells similar to that shown in the diagram were grown in a culture. Radioactive amino acids were added to the solution in which they were being grown. The radioactivity acts as a label on the amino acid so that it can be detected wherever it is. This radioactive label allows amino acids to be followed through the cell. At various times, samples of the cells were taken and the amount of radioactivity in different organelles was measured. The results are shown in the table.

Time after radioactiveamino acids were

added to the solution/minutes

Golgi apparatus Rough endoplasmaticreticulum

Vesicles

Amount of radioactivity present/arbitrary units

1

20

40

60

90

120

21

42

86

76

50

38

120

68

39

28

27

26

6

6

8

15

28

56

(i) What happens to the amino acids in the rough endoplasmic reticulum?

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(ii) Use the information in the table to draw arrows on the diagram showing the path of radioactivity through and out of the cell at X.

(3)

(iii) Name the process which is occurring at point X on the diagram.

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(Total 7 marks)


16. The drawing has been made from a photograph. It shows an organelle.

(a) Optical microscopes, transmission electron microscopes and scanning electron microscopes may be used to investigate the structure of cells

(i) What type of microscope was used in taking the photograph from which this drawing was made

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(ii) Give one piece of evidence for your answer.

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(b) Explain why a cell involved in active transport would contain a large number of these organelles.

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(c) The scale bar on this drawing represents a length of 1 µm. Calculate the magnification of the drawing. Show your working.

Magnification = ...................................... (2)

(Total 6 marks)

year 12 additional questions (cell structure)

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