Midterm 1 question

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Midterm 1 question

Post  funcrazgrl on Sun Mar 16, 2008 8:17 am

5: To collect maple sugar, one inserts a tube into the trunk until the end reaches the phloem. If instead a tube were inserted with the end reaching the xylem, the result would be
a) water and minerals flowing steadily out only if it had rained recently.
b) water and minerals flowing steadily out only if the sun were shining.
c) water and minerals flowing steadily out unless the air was extremely humid.
d) water and minerals flowing out only until xylem pressure was relieved.
e) no flow of water or minerals.

Why is the answer e)? is it because in xylem, the water is flowing upwards? Also, isn't the minerals dissolved in the water, or is there completely no minerals in the water that's going up in the xylem?

18: All of the following are true about the nitrogen in human bodies except:
a) it is all derived from atmospheric nitrogen.
b) it was all processed at some point in the absence of oxygen.
c) it was all processed at some point by nitrogen fixing bacteria.
d) it was all processed at some point by nitrifying bacteria.
e) it was all present at some point as ammonia.

Can't the answer also be a) because you can use material from the ground itself like organic material and use ammonifying bacteria to convert it to NH4+?

37: Which of the following undergoes hydrolysis in the alimentary canal?
a) amino acid
b) fatty acid
c) nucleic acid
d) glycerol
e) monosaccharide

Why is the answer c)?

34: In plant tropisms
a) an imbalance in ethylene concentration causes curvature.
b) roots or shoots always grow toward the stimulus.
c) responses occur at sites distinct from where stimuli are received.
d) either the root or the shoot responds, but never both.
e) changes occur in the zone of cell division of the apical meristem.

why would the answer be c)? doesn't the resoponses occur at the same place the stimuli are received. For instance, when there's light shining at the plant, the plant will move towards the light, where it is being stimulated. Why can't it be d)? For phototropism, only the shoot is curving, or for gravitation, only the roots are growing more downwards or is it not this answer because there is negative and postive tropism?

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Re: Midterm 1 question

Post  TA Sean on Sun Mar 16, 2008 6:58 pm

I'd get these answered at the rev session. Since everyone has finals to type out explanatory responses just takes a lot of time.

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Re: Midterm 1 question

Post  axie on Tue Mar 18, 2008 3:57 am

I dont know if those questions were gone over in rev session because i wasn't there for the last hour. But I would also like to know the reasons behind those answers. I know everyone has finals including the TA's but it'll be much appreciated >_<
.
-thanks

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Re: Midterm 1 question

Post  TA Allison on Tue Mar 18, 2008 4:33 am

For #5, phloem has pressure that has built up inside (remember Pressure-Flow Mechanism?) so when you puncture it, the pressure causes the syrup to come flowing out. Xylem, on the other hand, does not have the pressure that phloem has. Water molecules, if you recall, are strung together due to hydrogen bonding and the chain moves unidirectionally up the tree as evaporation occurs. So due to H-bonding and the fact that there's no pressure that's built up in the xylem, no water would flow out. (There are some minerals that have dissolved in the water too.)

18: Before it can be used by humans, it must be converted into a usable substance. And the starting material, the nitrogen, is taken from the atmosphere. then the bacteria in anaerobic nodules of plants can "fix" atmospheric Nitrogen and supply it as ammonium, which is form readily used by plants. so this process starts because nitrogen from the air.

37: amino acid, fatty acid, glycerol, and monosaccharides are the smallest you can get to after digestion. Amino acids are the end-product of polypeptide/protein breakdown, fatty acids and glycerol are the end-products for fat breakdown, and monosaccharides are the end-product of starch/polysaccharide breakdown. Nucleic acids are the only ones on the list that haven't been broken down into it's smaller parts of nitrogenous bases, sugars, and phosphates. (If you look on page 859, the table gives a good review of the steps of digestion and the enzymes involved.)

34: if you recall the different experiments that professor wasserman talked about in the first lecture, the basic conclusion was that the signal was received at the tip and was transduced throughout the plant. the coleoptile is bending, but it isn't just the tip, where the stimulus was received, that is bending. Remember how the "dark side" has the highest concentration of auxin? This is because it traveled down that side of the plant.
You wrote: "Why can't it be d)? For phototropism, only the shoot is curving, or for gravitation, only the roots are growing more downwards or is it not this answer because there is negative and postive tropism?" Let's think about this. Why can't both the roots and shoots respond in some way? If you have a coleoptile, and there's light shining on it from the side, the auxin moves to the dark side of the coleoptile, travels down the dark side and causes cells to elongate on the dark side, thus causing curvature. At the same time, gravity is also working on the plant, causing the roots to go downward due to positive gravitropism. So both roots and shoots are responding to some kind of tropism. If you were only talking about phototropism, shoots have (+) phototropism, while roots have (-) phototropism.

I hope this helps! let us know if you're still confused.

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Re: Midterm 1 question

Post  akiang on Tue Mar 18, 2008 7:55 am

what's the difference between nitrifying bacteria and nitrogen fixing bacteria?

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Re: Midterm 1 question

Post  ylk001 on Tue Mar 18, 2008 9:04 am

nitrifying bacteria converts ammonium into nitrate (NH4+ -> NO3-) whereas nitrogen-fixing bacteria converts N2 from the atmosphere to ammonia (NH3). Refer to the figure 37.9

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