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1500 questions
22
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3 answers
Why is a mosquito feeding on human blood not a parasite?
I recently read in my Ecology course notes that a mosquito feeding on human blood is not considered as a parasite. However, since it sucks blood from the human body, shouldn't it be regarded as a parasite, just like lice and ticks?
user31223
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Cells of umbilical cord - mom's or son's?
Let's say we have a mother giving a birth to a son. In a very clear manner the cells of these two individuals are very different, of course. Yet there is an umbilical cord connecting them. Then there should be a clearly defined "border" somewhere on…
maxint
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22
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1 answer
Can a human be made with ovum but without sperm?
This article says that scientists were successful in making a mouse using only a sperm and no egg (ovum). The article also states that this procedure could be applicable to humans.
However, I want to know why didn't they try with only an ovum?
Can a…
Mesentery
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5 answers
How did the cardiovascular system evolve?
How has evolution created our blood, lungs and the heart?
We can't exist without blood, which transports the oxygen to all areas of our body. However, the blood needs a lung, which gives it the oxygen to transport. The blood also needs something…
asparagus
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22
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3 answers
Why are vaccines for polio taken orally while vaccines for TB need to be injected?
My thoughts are that maybe the TB antigens necessary to produce an immune response are proteins; therefore they can be digested in the stomach and small intestine. But I may be wrong though. I am confused why I can't say the same for polio vaccine.
James
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22
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1 answer
Why does regular exercise increase brain volume?
It has been shown in several studies that regular aerobic exercise increases brain volume in aging humans. The changes were observed in hippocampus and were correlated with dramatic reduction of age-related dementia. Interestingly, the intensity of…
Aleksandra Zalcman
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22
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4 answers
Height and natural selection in humans?
I watched the documentary "Evolve" recently and in the segment on "size" Scott V. Edwards, Harvard evolutionary biologist mentioned the idea that humans might evolve to be 7' tall in 'hundreds of years'. (I think this may have been taken out of…
futurebird
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22
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1 answer
Why can't I read everything in my field of view?
When I look at a piece of text, I can see all the text on the paper, no matter where I look, because my field of view covers it all. However, if I stare at a specific word, I cannot read the text a few lines above the position I am staring at, even…
986
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22
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2 answers
Why is 70% ethanol preferred for aseptic techniques?
Are other concentrations (say 80%) less effective,or is this just for convenient manufacturing? Is the concentration chosen only because it is less volatile than 100 percent ethanol and hence safer?
CubeMaker
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22
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2 answers
If dinosaurs could have feathers, would they still be reptiles?
I just finished watching a video where it was mentioned that nowadays birds are dinosaurs and non-avians dinosaurs could have feathers.
I confirmed this from wikipedia:
Birds are highly advanced theropod dinosaurs, characterised
by feathers, a…
Armfoot
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22
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2 answers
Is there an advantage to linear chromosomes?
The DNA copying enzymes have a hard time working to the end of a chromosome. For circular chromosomes this is not a problem, since there is not a sharp 'end'. However, for a linear chromosome, without extra mechanisms in place, a bit of DNA is lost…
Artem Kaznatcheev
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22
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2 answers
Evolutionarily, why do male rats and horses lack nipples?
Developmentally male rats don't have nipples because (reddit)
Testosterone release in the fetal male rat happens before the stage of mammogenesis where the teat is formed whereas other species halt that same process after the teat is…
mic
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1 answer
Are lymphocyte sizes clustered in two groups?
Tortora writes in Principles of Anatomy and Physiology:
Lymphocytes may be as small as 6–9 μm in diameter or as large as 10–14 μm in diameter.
Those ranges are quite close to each others. Should the above be taken to mean that lymphocytes sizes…
user24
22
votes
3 answers
Why does hair turn grey or white, and why does it happen later for some?
The question is pretty simple: what is happening molecularly when hair turns grey or white? I would imagine that it is due to the lack of a particular compound. I'm also interested in why some people's onset of grey hair happens much later than…
LanceLafontaine
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22
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9 answers
Why didn't the polar bear change its color from white to black during evolution to absorb heat?
Polar bears are white in color and white color is not a good absorbant of heat. Why then didn't they evolve a black color to absorb more heat?
bhanu
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