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2 Feb 2019

The question is pretty simple: what is happening molecularlywhen hair turns grey or white? I would imagine that it is due tothe lack of a particular compound. I'm also interested in why somepeople's onset of grey hair happens much later than others.

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Nelly StrackeLv2

5 Feb 2019

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I'm sure many of you have experienced this - you scratch yourback or brush your hand over your arm and find a ridiculously longthin white hair, sometimes as long as 3 or 4 inches. I know a fewpeople who get these quite frequently, and anecdotal evidence seemsto suggest they almost grow almost overnight. A quick Google searchfor "single long white hair" throws up plenty of references tothem, and various beauty advice, but I'd like to know the biologybehind them.

What triggers abnormal body hair growth?
What causes these hairs to grow so much longer than other"normal" body hairs in physical proximity?
Why are they so thin and white compared to other bodyhair?

My primary hypothesis is that the hair cell grows rapidly in anuncontrolled manner, similar to how cancer might, and that theunusual appearance is due to the cells being starved of nutrients.I may be completely wrong, though.

I'm mainly interested in humans here, but if more in-depthresearch is available on animals that'd be interesting too.

An organism that is cephalized is probably ___________________.

		bilaterally symmetrical
		is segmented
		is diploblastic
		has a coelom

1 points

QUESTION 33

Cotton-topped tamarins are small primates with tufts of long white hair on their heads. While studying these creatures, you notice that males with longer hair get more opportunities to mate and father more offspring. To test the hypothesis that having longer hair is adaptive in these males, you should _____.

		test whether other traits in these males are also adaptive
		look for evidence of hair in ancestors of tamarins
		determine if hair length is heritable
		test whether males with shaved heads are still able to mate

1 points

QUESTION 34

Which of these is not an animal?

		ctenophore
		poiferan
		choanoflagellate
		cnidaria

1 points

QUESTION 35

What would be the best anatomical feature to look for to distinguish a gastropod from a chiton?

		presence of muscular foot
		presence of a radula
		production of eggs
		number of shell plates

1 points

QUESTION 36

If radial cleavae occurs during development, the animal will be a protostome.

True

False

1 points

QUESTION 37

The "heart" of arthopods is located ______________.

		ventrally
		centrally
		dorsally
		sagitally

1 points

QUESTION 38

Which structure do bivalves use for feeding?

		radula
		ctenidia (gills)
		beak
		foot

1 points

QUESTION 39

Claytonia virginica is a woodland spring herb with flowers that vary from white to pale pink to bright pink. Slugs prefer to eat pink-flowering over white-flowering plants (due to chemical differences between the two), and plants experiencing severe herbivory are more likely to die. The bees that pollinate this plant also prefer pink to white flowers, so that Claytonia
with pink flowers have greater relative fruit set than Claytonia with white flowers. A researcher observes that the percentage of different flower colors remains stable in the study population from year to year. Given no other information, if the researcher removes all slugs from the study population, what do you expect to happen to the distribution of flower colors in the population over time? 22.2

		The percentage of pink flowers should increase over time.
		The percentage of white flowers should increase over time.
		The distribution of flower colors should not change.
		The distribution of flower colors should randomly fluctuate over time.

1 points

QUESTION 40

The water vascular system of echinoderms _____________.

		functions as a circulatory system that distributes nutrients to body cells
		function in locomotion and feeding
		is bilateral in organization, even though the adult animal is not blaterally symmetrical
		is analogous to the gastrovascular cavity of flatworms

1 points

QUESTION 41

In Phylum Mollusca, the fluid of the open circulatory system is called hemolymph.

True

False

1 points

QUESTION 42

You find what you believe is a new species of animal. Which of the following characteristics would enable you to argue that it is more closely related to a flatworm than it is to a roundworm?

		It is a suspension feeder. It is a suspension feeder.
		It has no coelom.
		It is shaped like a worm.
		It has a mouth and an anus.

1 points

QUESTION 43

You observe that a mystery organism in a pond never comes up to the pond's surface. If you are able to catch one of these organisms, bring it to the lab and dissect it, you should find ______________.

		gills
		spiracle
		trachea
		book lungs

1 points

The Hermann Grid creates the illusion of grey areas at each ofthe intersections of the white bars. If you stare at any oneintersection, the illusion is not as strong (and may disappearaltogether). However, the illusion persists at the intersectionsthat you are not directly looking at. This illusion has beenexplained as being due at least in part to the receptive fieldproperties of your retinal ganglion cells (which are similar inmost vertebrates, including toads). Explain how such properties maygive rise to this illusion most strongly in our peripheral vision,and why the illusion is not as strong for the intersection that youstare at directly. You may draw a picture or pictures toillustrate, but you must also explain in words.

I can't paste the grid for some reason, but if you're familiarwith it, please help !