With the collaboration of the students of 2º Bachibac
Wearing striped clothing could help protect holidaymakers
from mosquito bites, scientists have found after solving the mystery of why
zebras are black and white.
It is a question which has plagued biologists for centuries
but now a team from the University of California, Davis, believe zebras’
unusual monochrome markings evolved in order to repel biting insects, such as
horseflies and tsetse flies, which tend to avoid striped surfaces. And the
findings could help humans cut their risk of being bitten by donning stripy
T-shirts, although scientists cautioned that the type of striped surface and
material used may alter its effectiveness.
“A T-shirt may help somewhat but it might not be the whole
story. Certainly if you are going to buy a T-shirt make sure the stripes are
thin,” Tim Caro, lead author and UC Davis professor of wildlife biology said.
“Don’t buy a striped jumper too quickly. Black and white striped surfaces reflect
different sorts of visible light but they also reflect different sorts of
polarised light which we can’t see but flies can. “The extent of polarised
light reflected also depends on the nature of the surface – think of gloss and
matte paint – and hairs probably reflect polarised light in different ways. “So
it may be that the different hairs of the zebra’s pelt are important in
preventing flies from landing on them.”
Varying explanations for zebra stripes, which have been
proposed since Alfred Russel Wallace and Charles Darwin debated the problem 120
years ago, have included a form of camouflage, assisting escape from predators
by visually confusing them, heat management or some kind of social function.
The study, published in the journal Nature Communications,
mapped the geographic spread of seven different species of zebras, horses and
asses and their subspecies and recorded the thickness, location and intensity
of their stripes on several parts of the body. It compared the animals’
geographic reach with other variables such as woodland habitats, the range of
predators, temperatures and the numbers of ectoparasites such as tsetse flies.
After examining where the striped animals and variables overlapped the
scientists ruled out all but one of the existing explanations, that of avoiding
blood sucking flies.
"No one knew why zebras have such striking
colouration," Prof Caro said. "But solving evolutionary conundrums
increases our knowledge of the natural world and may spark greater commitment
to conserving it." According to Prof Caro it is not yet known why biting
flies avoid striped surfaces. He said: “Some ideas include lateral inhibition
but these are not researched as yet.”
Question 1: [2 POINTS] Indicate whether the following statements are TRUE or
FALSE and write down the sentences or part of the text that justifies
your answer. No points will be given if the evidence is not correct.
a) It has never been an interesting question why zebras
are white and black.
b) Wearing a striped T-shirt prevents you from being
bitten by insects.
c) The explanation for zebra stripes had been proposed a
long time ago.
d) One reason about zebra stripes could be a way to
control their temperature.
e) The study has shown that it is probably that the aim
of stripes is to avoid flies.
f) According to Prof Caro, solving evolution mysteries is
pointless.
g) We know for sure why biting flies avoid striped
surfaces.
Question 2: [2 POINTS] Choose and answer only TWO of the following questions in your own words according to the text.
a)
According to Davis, why do zebras have stripes?
b)
Why aren’t zebras bitten by insects?
c)
What can flies see in black and white striped
surfaces but humans cannot?
d)
Which comparations were done among the different
species of zebras, horses and asses?
e)
Why do zebras have such striking colouration?
Question 3: [1,5 POINTS] Find words or phrases in the text that correspond to the words and definitions given. You only need to have five correct answers to get 1,5 points.
a)
Disturb (paragraph 2)
b)
Hold back (paragraph 2)
c)
Modify (paragraph 2)
d)
Complete (paragraph 3)
e)
Sweater, pullover (paragraph 3)
f)
Issue (paragraph 4)
g)
Help (paragraph 4)
h)
Mystery (paragraph 6)
i)
Dedication (paragraph 6)
Question 4: [1,5 ] Choose the correct option – a, b, c or d – for each
question and COPY both the letter and the sentence that follows onto
your answer sheet.
- Biting flies avoid …
- any stripy T-shirts.
- zebras’ pelt
- white and black surfaces
- thin stripes
- Black and white striped surfaces
reflect …
- all sorts of light
- different sorts of visible and
polarized light
- visible light that we cannot see but
flies can.
- only polarized light.
- The explanation given for the stripes
of zebras after the study published in the journal Nature Communications
is that …
- it is a kind of social function.
- it is a form of repelling flies.
- it protects them from predators.
- it doesn’t give any clear explanation
Written production (3 points)
Write a short
essay (120 – 150 words) on the following topic. Essays up to 200 words will not
be penalized.
“Zoos should be banned since animals should live in the wild”. Do you agree with this statement?
Key
Question
1: [2 POINTS] Indicate whether the following statements are TRUE or
FALSE and write down the sentences or part of the text that justifies
your answer. No points will be given if the evidence is not correct.
a)
It has
never been an interesting question why zebras are white and black.
(p 2) False It is a question which has plagued
biologists for centuries
b)
Wearing a
striped T-shirt prevents you from being bitten by insects.
(p 3) False A T-shirt may help somewhat but it
might not be the whole story
c)
The
explanation for zebra stripes had been proposed a long time ago.
(p 4) True explanations for zebra stripes,
which have been proposed since Alfred Russel Wallace and Charles Darwin debated
the problem 120 years ago.
d)
One reason
about zebra stripes could be a way to control their temperature.
(p 4) True have included a form of camouflage,
assisting escape from predators by visually confusing them, heat management
e)
The study
has shown that it is probably that the aim of stripes is to avoid flies.
(p5) True the scientists ruled out all but
one of the existing explanations, that of avoiding blood sucking flies.
f)
According
to Prof Caro, solving evolution mysteries is pointless.
(p 6) False But solving evolutionary conundrums
increases our knowledge of the natural world and may spark greater commitment
to conserving it.
g)
We know for
sure why biting flies avoid striped surfaces.
(p 6) False it is
not yet known why biting flies avoid striped surfaces
Question 2: [2 POINTS] Choose and answer only TWO of the following questions in your own words according to the text.
a) According
to Davis, why do zebras have stripes?
(p2)They have
them because they are an evolution change which allows zebras to repel insects
that always try to avoid striped surfaces.
b) Why
aren’t zebras bitten by insects?
(p3) Insects
tend to avoid striped surfaces; however, black and white surfaces reflect
different sorts of polarised light which can only be seen by them, so it may be
that the different hairs of zebra’s pelt are important in preventing flies from
landing on them.
c) What
can flies see in black and white striped surfaces but humans cannot?
(p3) different sorts of polarised light
d) Which
comparations were done among the different species of zebras, horses and asses?
(p5)The study
compares the natural place of the animals with factors like the kind of
habitat, other dangerous species, the temperature and parasites such as tsetse
flies.
e) Why
do zebras have such striking colouration?
(p 6) It isn’t
known yet,
Question
3: [1,5 POINTS] Find words or phrases in the text that correspond to
the words and definitions given. You only need to have five correct answers to
get 1,5 points.
a)
Disturb (paragraph 2) plagued
b) Hold
back (paragraph 2) repel
c) Modify
(paragraph 2) alter
d) Complete
(paragraph 3) whole
e) Sweater,
pullover (paragraph 3) jumper
f) Issue
(paragraph 4) problem
g) Help
(paragraph 4) assisting
h) Mystery
(paragraph 6) conundrum
i) Dedication
(paragraph 6) commitment
Question
4: [1,5 ] Choose the correct option – a, b, c or d – for each
question and COPY both the letter and the sentence that follows onto
your answer sheet.
- any stripy T-shirts.
- zebras’ pelt
- white and black surfaces
- thin stripes
- Black and white striped surfaces reflect …
- all sorts of light
- different sorts of visible and polarized light
- visible light that we cannot see but flies can.
- only polarized light.
- The explanation given for the stripes of zebras
after the study published in the journal Nature Communications is that …
- it is a kind of social function.
- it is a form of repelling flies.
- it protects them from predators.
- it doesn’t give any cleat explanation
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