Pollutants and the environment Bill Indge. Pollutants and the environment Liver cell Cytoplasm Nucleus Vitellogenin (VTG) production in the liver Oestrogen

Pollutants and the environment

Bill Indge


Liver cell

Cytoplasm

Nucleus

Vitellogenin (VTG) production in the liver

Oestrogen receptor

Gene coding for VTG

Ribosome



Oestrogen receptor

Gene coding for VTG

Ribosome

Oestrogenenters the

nucleus and binds with the oestrogen

receptor



Gene coding for VTG

The activated receptor now attaches to the target gene

The DNA is transcribed and VTG mRNA is produced



Gene coding for VTG

The VTG mRNA migrates to the ribosomes in the cytoplasm



Gene coding for VTG

VTG is synthesised and secreted from the liver


The title of the original paper on which this exercise is based is:

Fathead minnow and bluegill sunfish life-stage responses to 17 β-estradiol exposure in outdoor mesocosmsSarah M. Elliott, Richard L. Kiesling, Zachary G. Jorgenson, Daniel C. Rearick, Heiko L. Schoenfuss, Kim T. Fredricks and Mark P. Gaikowsk

A laboratory-based investigation


In a laboratory-based investigation, sexually mature fathead minnows were randomly divided into two groups — an experimental group and a control group.

• A solution of synthetic oestrogen was added to the tank containing the experimental group of fish. The resulting concentration of oestrogen reflected environmental concentrations.

• A control solution was added to the tank containing the control group.

1 Explain why it was important that the fish were randomly dividedinto the two groups. (2 marks)

1 The idea of preventing conscious choice; This might influence results; [2]


2 A control solution was added to the tank containing the controlgroup of fish. What would you expect to be in this control solution?Explain your answer. (2 marks)

Think carefully about the nature of the control that is appropriate in this investigation. With the information provided, ‘nothing’ would be an inappropriate response. ‘Water’ might be a standard answer but it makes assumptions about the composition of the synthetic oestrogen solution.





2 Everything that was added to the fish in the experimental tank other than the synthetic oestrogen;

This ensures that any difference would result from the oestrogen/ would not be the result of other substances in the solution; [2]




2 A control solution was added to the tank containing the controlgroup of fish. What would you expect to be in this control solution?Explain your answer. (2 marks)


Treated with synthetic oestrogen Control

Body condition factor

total mass/g × 100 000total length3

1.07 1.10*

Gonadosomatic index

testis mass/g × 100body mass/g

0.802 0.761

Hepatosomatic index

liver mass/g × 100body mass/g

1.55 1.35*

Secondary sexual characters index 2 3*

Some differences between fathead minnows treated with synthetic oestrogens and controls

* Significantly different, p<0.01



Hepatosomatic indexliver mass/g × 100body mass/g

1.55 1.35*

3 One of the control fish had a hepatosomatic index of 1.35. The bodymass of this fish was 2.73 g. Calculate the mass of its liver. Show your working. (2 marks)

Remember• If you don’t attempt the question, you cannot gain credit.• Show your working: you can gain marks even if the answer is wrong.• Use some common sense…the liver won’t weigh more than the fish!



3 2 marks for correct answer of 0.04 g;

1 mark for incorrect answer but clearly showing that the calculation is based on the formula: hepatosomatic index = liver mass × 100;

body mass

3 One of the control fish had a hepatosomatic index of 1.35. The body mass of this fish was 2.73 g. Calculate the mass of its liver. Show your working. (2 marks)



1.55 1.35*




Gonadosomatic indextestis mass/g × 100body mass/g

0.802 0.761

4 The testis mass is given as an index. Explain why it was given as an index, not the actual mass. (2 marks)

4 Allows results to be compared/standardised/body size to be taken into consideration;

Because testis mass will vary with body mass/larger fish will have larger testes; [2]


5 The scientists who carried out this investigation reported that large protein-containing vesicles had accumulated in the cytoplasm of the liver cells in a significant number of the experimental group of fish.

(a) Explain how the data in the table support this observation.(2 marks)

5(a) The experimental/oestrogen-treated group have a (significantly) higher hepatosomatic index;

(Larger liver) caused by the protein-containing vesicles; [2]



1.55 1.35*



5(b) Use your knowledge of the way in which oestrogen affects vitellogenin production to explain the presence of the protein-containing vesicles in the liver cells of the experimental group of fish.

(3 marks)

5(b) Binds with oestrogen receptors present in liver cells;

Stimulates transcription of VTG mRNA;

VTG protein synthesised;

VTG accumulates in vesicles in liver cells; [3 max]



1.55 1.35*





Body condition factor

total mass/g × 100 000total length3

1.07 1.10*

Gonadosomatic index

testis mass/g × 100body mass/g

0.802 0.761

Hepatosomatic index

liver mass/g × 100body mass/g

1.55 1.35*

Secondary sexual characters index 2 3*

6 Using only data from the table, explain why synthetic oestrogens may affect the reproductive success of male fathead minnows. (4 marks)



Body condition factortotal mass/g × 100 000total length3

1.07 1.10*


Mating success is likely to depend on body condition/Males with poorer body condition likely to have lower mating success;




Gonadosomatic indextestis mass/g × 100body mass/g

0.802 0.761

The difference in gonadosomatic index is not significant/The oestrogen-treated fish have significantly lower body condition and secondary sexual characters index;






1.55 1.35*

Larger liver in oestrogen-treated males likely to be linked to high vitellogenin production;





Secondary sexual characters index

2 3*

Secondary sexual character important in courtship/defence of territory;




The title of the original paper on which this exercise is based is:

Collapse of a fish population after exposure to a synthetic estrogenKaren A. Kidd, Paul J. Blanchfield, Kenneth H. Mills, Vince P. Palace, Robert E. Evans, James M. Lazorchak and Robert W. Flick

A field-based investigation


The protocol

Control lake (B) Experimental lake (A)

2 years prior to starting treatment

3 years of treatment

No synthetic oestrogen added

Regular addition of synthetic oestrogen

2 years after treatment stopped

Measurements collected from fathead minnows from both lakes of•concentration of the egg protein vitellogenin (VTG)•concentration of vitellogenin mRNA•numbers and lengths of fish


3

2

1

0

600040002000

The concentration of VTG in whole-body homogenate samples of male fathead minnows captured during the spring of each of the years shown

Lake B Lake A

Year


3

2

1

0

600040002000

Lake B Lake A

1 Explain the advantage of the break in the y-axis on this graph. (1 mark)

2 Explain what is meant by a whole-body homogenate. (2 marks)

1 Allows a wide range of values/high and low values to be plotted/read accurately; [1]

2 In homogenate the cells have been mechanically disrupted; In this case the whole fish/all tissues homogenised; [2]


3

2

1

0

600040002000

Lake B Lake A

3 Explain the difference in the results for lakes A and B. (3 marks)

3 Lake B and lake A in 2000 and 2001 show natural variation/small differences may not be significant; Synthetic oestrogen added to lake A in 2002; Stimulates secretion of VTG by liver; Carried by blood to all organs (so homogenate concentration increases); [max 3]


Year

Mean population index


1999 490.3 180.0

2000 19.1 50.3

2001 56.1 117.7

2002 9.6 0.7

2003 20.6 2.6

2004 51.9 0.1

2005 355.9 0.1

Addition of synthetic oestrogen

Numbers of fish given as a population index


Year

Mean population index


1999 490.3 180.0

2000 19.1 50.3

2001 56.1 117.7

2002 9.6 0.7

2003 20.6 2.6

2004 51.9 0.1

2005 355.9 0.1

4 Explain why the figures were given as the population index and not as the total population.(1 mark)

5 Describe the results shown in the table. (3 marks)

4 Difficulty of obtaining an accurate/reliable count; [1]

5 Variable population in lake B, and in lake A before treatment; In 2002/year after treatment large drop in population of lake A; Population in lake A after treatment stays low/does not recover; [3]


Fork length

Total length

Measuring fathead minnows

6 Fork length gives a more reliable measurement of the length of the fish than total length. Suggest why. (1 mark)

6 The ends of the tail may be worn/two lobes of tail fin may be different lengths; [1]


Fork length Fork length

Lake B Lake A

Histogram showing lengths of fish

2000

2002

2004


Fork length

Lake B Lake A

2000

2002

2004


7(a) Few fathead minnows live beyond 2 years. In any given year there are young fish that hatched that year and mature fish that hatched in the previous year. Explain how thehistograms support this information. (1 mark)


Fork length

Lake B Lake A


7(a) The histogram is bimodal/contains two peaks, suggesting two classes of fish. [1]

2000

2002

2004


Fork length

Lake A7(b) Use the data from the table to explain the results for 2002 in lake A. (3 marks)

7(b) The table shows the large decrease in population the year after the addition of synthetic oestrogen;

Histogram shows no young fish hatch in 2002;

Small number in histogram the result of few fish hatching in 2001; [3]

2000

2002

2004


Collapse of a fish population after exposure to a synthetic estrogenKaren A. Kidd, Paul J. Blanchfield, Kenneth H. Mills, Vince P. Palace, Robert E. Evans, James M. Lazorchak and Robert W. Flick

But also…

• Feminising males means extinction• Fish devastated by sex-changing chemicals in municipal

wastewater• Because of oestrogen, Canadian fish are too ‘confused’ to

mate• Birth control for fish

Documents

Pollutants and the environment Bill Indge. Pollutants and the environment Liver cell Cytoplasm Nucleus Vitellogenin (VTG) production in the liver Oestrogen