Bio questions from destroyer

[Bigbirdo]

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1. For choice A in question 179, don't capillaries offer the greatest resistance to blood flow in the circulation because they are the smallest? Why the book says it is the arterioles offer the greatest resistance?

2. Question 183. A woman who is seemingly normal marries a normal man. The woman's father is a hemophiliac. What is the probability that the couple's son will have hemophilia?
The answer is 50%. I highly doubt the answer is wrong. I use 1/2 (1/2 chance of getting a boy) multiply by 1/2 (Out of the two boys, 1 of them is hemophiliac), so I got 25%. Can someone clarify this question for me?

3. Question 338, Consider a sample of DNA that undergoes four rounds of replication. What percent of the double strand DNA produced contains part of the original-stranded DNA?
The answer is 12.5%, and it is the smallest number among the answers. However, I honestly think it is 6.25% because each round the percentage of parent DNA is reduced to half, so 4 rounds is (1/2)^4*100%=6.25% Can someone explain to me why it is 12.5%?

 

[ChrisM07]

First one:

The book is correct in that it says arterioles. This is because, when determining this, you need to look at the cross sectional area of each vessel. The capillary is only one cell thick and has a large cross sectional area. The larger the cross sectional area, the less resistance a fluid will encounter, and the easier it will flow. The arteriole on the other hand, is thick with muscle and has a small cross sectional area. Therefore, it will encounter the greatest amount of resistance in terms of fluid flow.

Imagine the same volume of fluid flowing through each. The fluid will have an easier time flowing through the capillary because it has more room to do so despite the fact that the arteriole is physically larger.

Check this out. The top one is an arteriole (lots of smooth muscle). The bottom one is a capillary (only one cell thick).



Second one:

I made the same mistake. They are asking about the SONS ONLY. This means that out of the two sons, one will have it. 50%.

 

[game33]

I'll try to explain this the best way I can....bare with. I have the 2013 version and my #179 has to do with chlorophylls. Anyways let me know what version you have. As for question #2...okay you gotta realize that the woman's father is going to pass her an X chromosome that would make her a carrier. Even though she is normal she is still a carrier so the woman would be X X^c and the man would be X Y and if you do a punnett square you would see that indeed 50% of the boys would have hemophilia.

As for number #3...I used to make the same mistake as you on this question but what I came to realize is that you have to start with a single strand than continue from there. So it would be 1-->2-->4-->8-->16 and it would be 2/16 reduced to 1/8 which would be 12.5%. I hope that helps. If you ever see when it says dipole or double stranded from the beginning than you would do exactly what you did. The wording for #338 is very confusing.

 

[dent777]

Second one:

You can assume that the woman still possesses the recessive allele therefore she is XX^ (carrier) and her husband is XY. The question asks you to consider only the sons, therefore you disregard daughters when you create a Punnett square. Sons' genotype can only be XY or X^Y(Hemophiliac). Therefore, 50% of their sons would be Hemophiliac.

 

[FeralisExtremum]

First one:

The book is correct in that it says arterioles. This is because, when determining this, you need to look at the cross sectional area of each vessel. The capillary is only one cell thick and has a large cross sectional area. The larger the cross sectional area, the less resistance a fluid will encounter, and the easier it will flow. The arteriole on the other hand, is thick with muscle and has a small cross sectional area. Therefore, it will encounter the greatest amount of resistance in terms of fluid flow.

Imagine the same volume of fluid flowing through each. The fluid will have an easier time flowing through the capillary because it has more room to do so despite the fact that the arteriole is physically larger.

Check this out. The top one is an arteriole (lots of smooth muscle). The bottom one is a capillary (only one cell thick).

This isn't quite true, at least how the images present it. Don't confuse vessel diameter with total cross sectional area. Capillaries do have small diameters than arterioles. The reason why arterioles have the greatest resistance to flow anyway is because they have a lower total cross-sectional area (meaning the cross-sectional area of ALL vessels added together) than capillaries. Diameter of the vessels in humans is the primary determining factor of resistance (which seems contradictory to arterioles having the highest resistance to flow). The change in diameter going from arteries to arterioles is pretty significant. The change in diameter from arterioles to capillaries is much less significant and the fact that the cross-sectional area of capillaries is so much higher essentially negates any resistance advantage from the smaller vessels.

 

[ChrisM07]

I posted the picture to just show the difference in cross sectional are of the lumen.

 

[FeralisExtremum]

That picture doesn't accurately depict the cross-sectional area of the lumen, because the lumen of a single arteriole is still substantially larger than the lumen of a capillary.