Maize

Answer choices

1. A

   Correct71% picked this

   The greater productivity of maize, as compared with many other crops, is due to its C-4 photosynthetic process, in which the reactions that build

   Why this is right

   The main clause is "the greater productivity of maize is due to its C-4 photosynthetic process". That seems on point. It's about our central topic and it's giving us the main payoff idea of the Answer a Question framework. Do the rest of the details check out? In C-4 photosynthesis, is it true that the reactions that build sugars are protected from the effects of excess oxygen. We were hoping it would say "rubisco is prevented from competitively binding with oxygen". Well, in the 2nd paragraph we're told that "an enzyme, rubisco, assists in the sugar-forming chemical reaction", so it looks like "the reactions that build sugars" is just a buzzphrase for "rubisco". Can we live with "the effects of excess oxygen" as a match for "oxygen binds competitively with rubisco"? The end of the 2nd paragraph says, "when the concentration of oxygen relative to carbon dioxide in a leaf rises to a certain level ... oxygen begins to bind competitively to the enzyme, thus interfering with the photosynthetic reaction". If oxygen concentration rising to a certain level is what's causing the problem then I guess we can accept "the effects of excess oxygen" as a buzzphrase for this idea.

   Skill tested: Main Point · how this choice captures the passage's function is the move to repeat next time.

   71%
2. B

   Wrong Emphasis Wrong Causal Relationship10% picked this

   Because of their ability to produce greater quantities and higher qualities of nutrients, those plants, including maize, that use a C-4 photosynthetic process have

   The main clause here is "Those plants that use a C-4 photosynthetic process have helped to shape the development of many human cultures". That seems off for two reasons: 1) it doesn't mention maize 2) the main point was about how these C-4 plants have such impressive productivity, not about how much they've shaped the development of many cultures. This is basically First Sentence Bait. It's emphasizing an idea from the very first sentence because students are often hoping the first or last sentence of the passage is the main point. This also misconstrues the causal relationship between C-4 and cultures who have cultivated it. These plants aren't special because of "higher quality and quantity of nutrients". They're special because of their sheer productivity. They just grow more and more easily than other plants, because they have a more efficient photosynthetic process that doesn't get derailed by oxygen.

   10%
3. C

   Wrong Causal Relationship Wrong Emphasis2% picked this

   C-4 photosynthesis, which occurs in maize, involves a complex sequence of chemical reactions that makes more efficient use of available atmospheric hydrogen than

   This answer's central topic is C-4 photosynthesis, which is not a total dealbreaker but not centering maize the way we expected. This says the magic sauce of C-4 is that the plant makes more efficient use of atmospheric hydrogen (rather than it prevents rubisco from competitively binding with oxygen). It doesn't seem like atmospheric hydrogen is used at all in photosynthesis. Plants get hydrogen from breaking about liquid water into hydrogen and oxygen. And then plants use atmospheric CO2.

   2%
4. D

   Wrong Causal Relationship3% picked this

   The presence of the enzyme rubisco is a key factor in the ability of C-4 plants, including maize, to circumvent the negative effects of

   Like (B) and (C), this makes maize an aside rather than putting it in the main clause. And like (B) and (C), it misidentifies what makes C-4 plants so awesome. They're awesome because rubisco is sequestered in airtight pockets. This answer is saying they're special because rubisco is present. Rubisco is present in all photosynthetic plants (or at least the vast majority). Its presence isn't the key factor that allows C-4 to thrive more than other plants. Its isolated presence within the airtight bundle sheath cells is the key factor. This answer is also a little weird for insinuating that the obstacle normal plants face is "the negative effects of gases such as oxygen". There wasn't a plurality of gases messing things up, of which oxygen is just one example. It was oxygen alone that was messing things up.

   3%
5. E

   Too Strong: prevent gases from leaves14% picked this

   Some of the world’s most productive crop plants, including maize, have evolved complex, effective mechanisms to prevent atmospheric gases that could bind competitively to

   This is pretty close. Again, maize is not center stage, which doesn't feel quite right, but it's still in there. The problem here is that C-4 plants do not prevent atmospheric gases from entering the plants leaves. They just prevent atmospheric gases from entering the bundle sheath cells, which are the protected cave that rubisco lives in. We know from the 2nd paragraph that "During photosynthesis, carbon dioxide that the plant takes in from the atmosphere is used to build sugars within the plant". All plants are taking in the atmospheric gas of CO2 into their leaves. What makes C-4 special is that these atmospheric gases are excluded from the cells containing rubisco, but they're not excluded from entering the plants' leaves entirely.

   14%