Download Chapter 3 Natural selection and evolution extra worksheet 1

Chapter 3 Natural selection
and evolution
EXTRA WORKSHEET 1:
SCIENCE UNDERSTANDING
Evolution of icefish
LOGICAL/MATHEMATICAL
Name: _____________________ Class: _________ Date: __________
Fish of the Family Channichthyidae, found in the waters around Antarctica,
are very unusual. They have evolved in extremely cold water, and are
commonly called ‘icefish’ (Figure 1). There are 25 species of icefish.
Scientists have been interested in these fish since they were first discovered,
because of their amazing ability to avoid freezing to death in extremely cold
waters.
Research has shown that icefish’s body contains special ‘antifreeze’
chemicals called glycoproteins, which seemed to work by preventing ice
crystals growing. The antifreeze chemical coats ice crystals so water cannot
come into contact with the surface and add to the crystal. These chemicals
are so effective that they are being researched for possible applications
where freezing needs to be prevented. Possible applications include
increasing the ability of crop plants to withstand frost, lengthening the shelf life
of frozen foods and potential applications in surgery, storing organs for
transplant and treating hypothermia.
Figure 1
Ocellated icefish, Chionodraco rastrospinosus.
Icefish blood
Another amazing fact about icefish in this family is that they have almost no
red blood cells. Red blood cells contain a chemical called haemoglobin, which
Copyright © Pearson Australia 2012 (a division of Pearson Australia Group Pty Ltd)
ISBN 978 1 4425 2366 1
Page 1
bonds to oxygen and transports it in the blood of all other vertebrates. But
these fish contain no haemoglobin and their blood is almost transparent. So
scientists wondered how oxygen was carried in the blood of these fish, and
how their blood can carry enough oxygen to the cells to maintain respiration.
Research discovered that:
•
the antifreeze production and the haemoglobin loss were both shown
to be specific genetic mutations
•
icefish have large hearts that pump out a high volume of blood each
beat
•
icefish have a very high volume of blood in their body
•
very cold water holds a lot more oxygen than warm water.
Evolution and icefish
These icefish seemed to present an evolutionary puzzle. Scientists wondered
why fish without red blood cells were not removed by natural selection.
The conclusion of scientists studying these fish is that they evolved in the
following way:
•
A mutation in an ancestral species allowed formation of the antifreeze
chemicals.
•
A much later second mutation occurred which caused a loss of
haemoglobin. This would normally be fatal in any vertebrate organism.
•
The ancestors of the icefish were present in Antarctica as the climate
began cooling.
•
The loss of haemoglobin was not fatal as colder water could carry
more oxygen and the antifreeze helped them cope with the cold water.
•
There would not be much competition from other fish since those fish
lacked the antifreeze chemicals and most seem to have been unable
to survive the cold.
Copyright © Pearson Australia 2012 (a division of Pearson Australia Group Pty Ltd)
ISBN 978 1 4425 2366 1
Page 2
Questions
1
Identify the adaptation of icefish that enables them to maintain liquid
water in their bodies despite the extreme cold.
___________________________________________________________
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2
Describe three adaptations of the icefish that enabled them to survive
without haemoglobin.
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3
Explain how natural selection could have acted on all the Antarctic fish
and selected in favour of the icefish.
___________________________________________________________
___________________________________________________________
___________________________________________________________
4
Justify the view that the antifreeze mutation came before the
haemoglobin mutation.
___________________________________________________________
___________________________________________________________
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5
Propose whether the adaptations in the circulatory system of the icefish
came before or after the loss of haemoglobin.
___________________________________________________________
___________________________________________________________
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Copyright © Pearson Australia 2012 (a division of Pearson Australia Group Pty Ltd)
ISBN 978 1 4425 2366 1
Page 3