Explain Atom Rearrangement in Synthesis

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Biology › Explain Atom Rearrangement in Synthesis

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1

A student claims: “When a plant makes new molecules like proteins and DNA, it creates new atoms inside its cells.” Which response best corrects the student using atom tracking ideas?

The student is incorrect because atoms are conserved; plants rearrange atoms from molecules like glucose and add needed atoms (such as N and P) from environmental nutrients to build macromolecules.

The student is incorrect because plants can only make carbohydrates; proteins and DNA must be taken in from the air as complete molecules.

The student is correct because growth requires creating new atoms; conservation of matter does not apply to living things.

The student is correct because sunlight is converted directly into carbon, nitrogen, and phosphorus atoms during synthesis.

Explanation

This question tests your understanding of how atoms from simple environmental molecules (CO2, H2O, soil nutrients) are rearranged through photosynthesis and synthesis reactions to build all the complex macromolecules in living organisms. Biological synthesis follows the law of conservation of matter—atoms are neither created nor destroyed, only REARRANGED from simpler molecules into more complex ones: the carbon atoms in all biological macromolecules (carbohydrates, proteins, lipids, nucleic acids) originally came from atmospheric CO2 that was fixed into glucose during photosynthesis, then those glucose carbon atoms are broken apart and rearranged (sometimes combined with additional atoms) to build different molecules. The student's claim is wrong because living things cannot create new atoms; instead, plants incorporate atoms from the environment (like C from CO2 into glucose) and rearrange them, adding elements like N and P from soil to synthesize proteins and DNA. Choice B correctly explains atom rearrangement by recognizing atoms from environmental sources (CO2, H2O, soil) are reorganized through synthesis, with conservation maintained. Choice A fails because it incorrectly states conservation doesn't apply to life; the law holds for all matter, including biological systems. Tracing atoms through synthesis—the element source map: (1) CARBON (C): from atmospheric CO2 → fixed into glucose during photosynthesis → glucose carbons rearranged into ALL organic molecules (carbohydrates, proteins, lipids, nucleic acids). Every carbon in your body was once atmospheric CO2! (2) HYDROGEN (H) and OXYGEN (O): from H2O absorbed by roots → incorporated into glucose → redistributed into all macromolecules. (3) NITROGEN (N): from soil (plants absorb nitrate or ammonium from soil, which came from nitrogen-fixing bacteria or fertilizers) → combined with C, H, O from glucose to make amino acids → amino acids link into proteins. Also used in nucleotide bases. Can't make proteins without nitrogen from environment! (4) PHOSPHORUS (P): from soil (plants absorb phosphate) → incorporated into nucleotides → nucleotides link into DNA/RNA. Also in ATP, phospholipids. (5) SULFUR (S): from soil (sulfate) → incorporated into some amino acids (cysteine, methionine) → proteins. Every element in biological molecules came from environment originally! The 'no atoms created' principle: if you account for every atom in reactants and products, they match perfectly (just in different arrangements). Excellent correction—atom tracking debunks myths like this!

2

A plant is grown in a sealed container with light, water, and air that contains CO2, but the soil lacks usable nitrogen compounds. The plant can still make glucose, but it grows poorly and makes very little protein. Which explanation best uses atom sources to explain why protein production is limited?

Protein production is limited because the plant must create nitrogen atoms from sunlight, and the container blocks sunlight.

Protein production is limited because nitrogen atoms needed for amino acids must be taken from soil nutrients; without a nitrogen source, the plant cannot add N to carbon skeletons made from glucose.

Protein production is limited because glucose atoms cannot be rearranged into other molecules; glucose can only be used for energy.

Protein production is limited because carbon atoms can only come from soil, and the sealed container prevents carbon from entering.

Explanation

This question tests your understanding of how atoms from simple environmental molecules (CO2, H2O, soil nutrients) are rearranged through photosynthesis and synthesis reactions to build all the complex macromolecules in living organisms. Biological synthesis follows the law of conservation of matter—atoms are neither created nor destroyed, only REARRANGED from simpler molecules into more complex ones: the carbon atoms in all biological macromolecules (carbohydrates, proteins, lipids, nucleic acids) originally came from atmospheric CO2 that was fixed into glucose during photosynthesis, then those glucose carbon atoms are broken apart and rearranged (sometimes combined with additional atoms) to build different molecules. The experimental setup provides C, H, and O (from CO2 and H2O) allowing glucose production, but lacks nitrogen compounds in the soil—without a nitrogen source, the plant cannot synthesize amino acids (which require nitrogen for their amino groups -NH2) and therefore cannot build proteins, even though it has plenty of carbon skeletons from glucose. Choice B correctly explains that protein production is limited because nitrogen atoms needed for amino acids must come from soil nutrients (like nitrates or ammonium), and without this nitrogen source, the plant cannot add N to carbon skeletons to form amino acids and proteins. Choice A incorrectly claims carbon comes from soil (it comes from CO2), Choice C wrongly states glucose cannot be rearranged (it can and must be), and Choice D incorrectly suggests plants create nitrogen from sunlight (atoms cannot be created from energy). This experiment demonstrates the limiting nutrient concept: even with abundant carbon from photosynthesis, protein synthesis is impossible without environmental nitrogen—you can't make amino acids without the "amino" (nitrogen-containing) part!

3

A plant makes glucose during photosynthesis by taking carbon from atmospheric CO2 and hydrogen/oxygen from H2O. Later, the plant builds proteins in its leaves. Which statement best traces where the atoms in the protein come from and what happens to them during synthesis?

Protein atoms are created by the plant as it grows; glucose only provides energy, not atoms.

Carbon, hydrogen, and oxygen atoms from glucose are rearranged into new molecules, and nitrogen atoms from soil nutrients are added to form amino acids that are linked into proteins.

Carbon atoms in proteins come mainly from soil minerals, while nitrogen atoms come from CO2 in the air.

Glucose turns into protein without rearranging atoms; the atoms keep the same arrangement but are renamed as protein.

Explanation

This question tests your understanding of how atoms from simple environmental molecules (CO2, H2O, soil nutrients) are rearranged through photosynthesis and synthesis reactions to build all the complex macromolecules in living organisms. Biological synthesis follows the law of conservation of matter—atoms are neither created nor destroyed, only REARRANGED from simpler molecules into more complex ones: the carbon atoms in all biological macromolecules (carbohydrates, proteins, lipids, nucleic acids) originally came from atmospheric CO2 that was fixed into glucose during photosynthesis, then those glucose carbon atoms are broken apart and rearranged (sometimes combined with additional atoms) to build different molecules. For example, to build PROTEINS, plants take carbon, hydrogen, and oxygen atoms from glucose and COMBINE them with nitrogen atoms absorbed from soil (as nitrate NO3⁻ or ammonium NH4⁺) to synthesize amino acids (which contain C, H, O, and N), then link those amino acids into protein polymers. In this case, the plant uses C, H, and O atoms from glucose produced in photosynthesis, rearranges them into carbon skeletons for amino acids, and adds nitrogen from soil nutrients to complete the amino acids, which are then polymerized into proteins—tracing the atom flow from environmental sources through rearrangement pathways. Choice C correctly explains atom rearrangement by recognizing atoms from environmental sources (CO2, H2O, soil) are reorganized through synthesis, with conservation maintained. Choice A fails because it suggests atoms are created by the plant, which violates conservation of matter; instead, all atoms come from the environment and are only rearranged. Tracing atoms through synthesis—the element source map: (1) CARBON (C): from atmospheric CO2 → fixed into glucose during photosynthesis → glucose carbons rearranged into ALL organic molecules (carbohydrates, proteins, lipids, nucleic acids). Every carbon in your body was once atmospheric CO2! (2) HYDROGEN (H) and OXYGEN (O): from H2O absorbed by roots → incorporated into glucose → redistributed into all macromolecules. (3) NITROGEN (N): from soil (plants absorb nitrate or ammonium from soil, which came from nitrogen-fixing bacteria or fertilizers) → combined with C, H, O from glucose to make amino acids → amino acids link into proteins. Also used in nucleotide bases. Can't make proteins without nitrogen from environment! (4) PHOSPHORUS (P): from soil (plants absorb phosphate) → incorporated into nucleotides → nucleotides link into DNA/RNA. Also in ATP, phospholipids. (5) SULFUR (S): from soil (sulfate) → incorporated into some amino acids (cysteine, methionine) → proteins. Every element in biological molecules came from environment originally! The "no atoms created" principle: if you account for every atom in reactants and products, they match perfectly (just in different arrangements). Example: glucose C6H12O6 (6 carbon, 12 hydrogen, 6 oxygen atoms) → if ALL glucose atoms go into starch (C6H10O5)n, the "missing" hydrogen and oxygen atoms were removed as water during dehydration synthesis (for every glucose added to starch, one H2O removed = 2H and 1O per linkage). Atom accounting: 6C from glucose go into starch (conservation). The 12H and 6O from glucose → some stay in starch (10H, 5O per glucose unit in chain), some leave as water (2H, 1O per linkage). Total atoms conserved: 6C + 12H + 6O in glucose = 6C + 10H + 5O in starch unit + 2H + 1O in water. Perfect accounting! This bookkeeping confirms conservation and rearrangement, not creation!

4

A plant makes glucose during photosynthesis by taking in CO2 from the air and H2O from the soil. Later, the plant builds proteins in its cells. Which statement best traces where the atoms in the plant’s proteins come from and what happens to them during synthesis?

Carbon atoms in proteins come mainly from minerals in the soil, while nitrogen atoms come from glucose made in photosynthesis.

Carbon, hydrogen, and oxygen atoms from glucose are rearranged into new molecules, and nitrogen atoms from soil nutrients are added to build amino acids that are linked into proteins.

Protein atoms are created during synthesis as the plant grows, so they do not need to come from earlier molecules like glucose.

Glucose atoms are destroyed and turned into energy, and that energy is converted into new carbon and nitrogen atoms to make proteins.

Explanation

This question tests your understanding of how atoms from simple environmental molecules (CO2, H2O, soil nutrients) are rearranged through photosynthesis and synthesis reactions to build all the complex macromolecules in living organisms. Biological synthesis follows the law of conservation of matter—atoms are neither created nor destroyed, only REARRANGED from simpler molecules into more complex ones: the carbon atoms in all biological macromolecules (carbohydrates, proteins, lipids, nucleic acids) originally came from atmospheric CO2 that was fixed into glucose during photosynthesis, then those glucose carbon atoms are broken apart and rearranged (sometimes combined with additional atoms) to build different molecules. For example, to build PROTEINS, plants take carbon, hydrogen, and oxygen atoms from glucose and COMBINE them with nitrogen atoms absorbed from soil (as nitrate NO3⁻ or ammonium NH4⁺) to synthesize amino acids (which contain C, H, O, and N), then link those amino acids into protein polymers. Choice C correctly explains atom rearrangement by recognizing atoms from environmental sources (CO2, H2O, soil) are reorganized through synthesis, with conservation maintained. Choice A fails because it claims atoms are created, which violates conservation of matter; atoms must come from existing molecules like glucose and soil nutrients. Tracing atoms through synthesis—the element source map: (1) CARBON (C): from atmospheric CO2 → fixed into glucose during photosynthesis → glucose carbons rearranged into ALL organic molecules (carbohydrates, proteins, lipids, nucleic acids). Every carbon in your body was once atmospheric CO2! (2) HYDROGEN (H) and OXYGEN (O): from H2O absorbed by roots → incorporated into glucose → redistributed into all macromolecules. (3) NITROGEN (N): from soil (plants absorb nitrate or ammonium from soil, which came from nitrogen-fixing bacteria or fertilizers) → combined with C, H, O from glucose to make amino acids → amino acids link into proteins. Also used in nucleotide bases. Can't make proteins without nitrogen from environment! The 'no atoms created' principle: if you account for every atom in reactants and products, they match perfectly (just in different arrangements). Keep practicing atom tracking—it's key to understanding how life builds complexity from simple inputs!

5

A teacher draws this element flow idea on the board: CO2 (air) → glucose → macromolecules. The teacher adds: “For proteins, we also need nitrogen from soil nutrients.” Which statement best matches this atom-tracking model?

Carbon atoms flow from CO2 into glucose and can be rearranged into many macromolecules; nitrogen atoms must be added from soil nutrients to make amino acids and proteins.

Carbon atoms in macromolecules come mainly from soil minerals, while CO2 provides only oxygen atoms.

Macromolecules form when plants turn energy from sunlight directly into new atoms, so tracking atoms from CO2 is unnecessary.

All atoms in proteins come from glucose, because glucose already contains C, H, O, and N.

Explanation

This question tests your understanding of how atoms from simple environmental molecules (CO2, H2O, soil nutrients) are rearranged through photosynthesis and synthesis reactions to build all the complex macromolecules in living organisms. Biological synthesis follows the law of conservation of matter—atoms are neither created nor destroyed, only REARRANGED from simpler molecules into more complex ones: the carbon atoms in all biological macromolecules (carbohydrates, proteins, lipids, nucleic acids) originally came from atmospheric CO2 that was fixed into glucose during photosynthesis, then those glucose carbon atoms are broken apart and rearranged (sometimes combined with additional atoms) to build different molecules. The teacher's model shows carbon flowing from CO2 to glucose to various macromolecules, with nitrogen added from soil for proteins, highlighting that while glucose provides C, H, O, additional elements like N are incorporated from the environment during synthesis. Choice B correctly explains atom rearrangement by recognizing atoms from environmental sources (CO2, H2O, soil) are reorganized through synthesis, with conservation maintained. Choice A fails because glucose lacks nitrogen (it's C6H12O6); N must be added from soil to form amino acids. Tracing atoms through synthesis—the element source map: (1) CARBON (C): from atmospheric CO2 → fixed into glucose during photosynthesis → glucose carbons rearranged into ALL organic molecules (carbohydrates, proteins, lipids, nucleic acids). Every carbon in your body was once atmospheric CO2! (2) HYDROGEN (H) and OXYGEN (O): from H2O absorbed by roots → incorporated into glucose → redistributed into all macromolecules. (3) NITROGEN (N): from soil (plants absorb nitrate or ammonium from soil, which came from nitrogen-fixing bacteria or fertilizers) → combined with C, H, O from glucose to make amino acids → amino acids link into proteins. Also used in nucleotide bases. Can't make proteins without nitrogen from environment! The 'no atoms created' principle: if you account for every atom in reactants and products, they match perfectly (just in different arrangements). You're connecting the dots beautifully—models like this make biology come alive!

6

A student says, “When a plant makes a protein, it turns glucose into protein.” Which correction best reflects atom rearrangement and element sources?

Plants make proteins by creating new nitrogen and carbon atoms from sunlight.

Proteins are made only from CO2; glucose is not involved in providing atoms.

Glucose molecules become proteins without changing; proteins are just stored glucose.

Glucose provides carbon skeletons that are rearranged into amino acids, and nitrogen atoms from soil nutrients are added; amino acids are then linked to form proteins.

Explanation

This question tests your understanding of how atoms from simple environmental molecules (CO2, H2O, soil nutrients) are rearranged through photosynthesis and synthesis reactions to build all the complex macromolecules in living organisms. Biological synthesis follows the law of conservation of matter—atoms are neither created nor destroyed, only REARRANGED from simpler molecules into more complex ones: the carbon atoms in all biological macromolecules (carbohydrates, proteins, lipids, nucleic acids) originally came from atmospheric CO2 that was fixed into glucose during photosynthesis, then those glucose carbon atoms are broken apart and rearranged (sometimes combined with additional atoms) to build different molecules. For example, to build PROTEINS, plants take carbon, hydrogen, and oxygen atoms from glucose and COMBINE them with nitrogen atoms absorbed from soil (as nitrate NO3⁻ or ammonium NH4⁺) to synthesize amino acids (which contain C, H, O, and N), then link those amino acids into protein polymers. The student's statement is partially correct in that glucose provides atoms for proteins, but it needs correction to emphasize that carbon skeletons from glucose are rearranged and combined with nitrogen from soil to form amino acids, which are then linked—it's not a direct transformation without changes. Choice B correctly explains atom rearrangement by recognizing atoms from environmental sources (CO2, H2O, soil) are reorganized through synthesis, with conservation maintained. Choice C fails because it suggests creating new atoms from sunlight, but sunlight provides energy for reactions, not atoms; all atoms come from environmental molecules. Tracing atoms through synthesis—the element source map: (1) CARBON (C): from atmospheric CO2 → fixed into glucose during photosynthesis → glucose carbons rearranged into ALL organic molecules (carbohydrates, proteins, lipids, nucleic acids). Every carbon in your body was once atmospheric CO2! (2) HYDROGEN (H) and OXYGEN (O): from H2O absorbed by roots → incorporated into glucose → redistributed into all macromolecules. (3) NITROGEN (N): from soil (plants absorb nitrate or ammonium from soil, which came from nitrogen-fixing bacteria or fertilizers) → combined with C, H, O from glucose to make amino acids → amino acids link into proteins. Also used in nucleotide bases. Can't make proteins without nitrogen from environment! (4) PHOSPHORUS (P): from soil (plants absorb phosphate) → incorporated into nucleotides → nucleotides link into DNA/RNA. Also in ATP, phospholipids. (5) SULFUR (S): from soil (sulfate) → incorporated into some amino acids (cysteine, methionine) → proteins. Every element in biological molecules came from environment originally! The "no atoms created" principle: if you account for every atom in reactants and products, they match perfectly (just in different arrangements). Example: glucose C6H12O6 (6 carbon, 12 hydrogen, 6 oxygen atoms) → if ALL glucose atoms go into starch (C6H10O5)n, the "missing" hydrogen and oxygen atoms were removed as water during dehydration synthesis (for every glucose added to starch, one H2O removed = 2H and 1O per linkage). Atom accounting: 6C from glucose go into starch (conservation). The 12H and 6O from glucose → some stay in starch (10H, 5O per glucose unit in chain), some leave as water (2H, 1O per linkage). Total atoms conserved: 6C + 12H + 6O in glucose = 6C + 10H + 5O in starch unit + 2H + 1O in water. Perfect accounting! This bookkeeping confirms conservation and rearrangement, not creation!

7

A student claims: “All of the atoms in a plant’s macromolecules (carbohydrates, proteins, lipids, nucleic acids) come from photosynthesis.” Which choice best evaluates this claim using element tracking?

The claim is correct because proteins and nucleic acids are made only of C, H, and O atoms.

The claim is incorrect because plants do not use CO2 to make glucose; they obtain glucose directly from the soil.

The claim is correct because photosynthesis produces all elements (including N and P) that plants need.

The claim is incorrect because photosynthesis provides C, H, and O (in sugars), but plants must obtain other elements like N (for proteins and nucleic acids) and P (for nucleic acids) from environmental nutrients, often in soil.

Explanation

This question tests your understanding of how atoms from simple environmental molecules (CO2, H2O, soil nutrients) are rearranged through photosynthesis and synthesis reactions to build all the complex macromolecules in living organisms. Biological synthesis follows the law of conservation of matter—atoms are neither created nor destroyed, only REARRANGED from simpler molecules into more complex ones: the carbon atoms in all biological macromolecules (carbohydrates, proteins, lipids, nucleic acids) originally came from atmospheric CO2 that was fixed into glucose during photosynthesis, then those glucose carbon atoms are broken apart and rearranged (sometimes combined with additional atoms) to build different molecules. While photosynthesis provides C, H, and O atoms (in glucose and other sugars), it cannot provide all elements needed for all macromolecules—proteins require nitrogen (N) for amino groups, nucleic acids require both nitrogen (N) for bases and phosphorus (P) for the backbone, and some proteins require sulfur (S) for certain amino acids, all of which must come from environmental nutrients, typically absorbed from soil. Choice B correctly evaluates the claim as incorrect because while photosynthesis provides C, H, and O through sugar production, plants must obtain other essential elements like N and P from environmental nutrients (usually soil) to build proteins and nucleic acids. Choice A incorrectly validates the claim (photosynthesis doesn't produce N or P), Choice C wrongly states proteins and nucleic acids contain only C, H, and O (they also need N, and nucleic acids need P), and Choice D incorrectly claims plants don't use CO2 for glucose (that's exactly what photosynthesis does). The complete element inventory shows: photosynthesis provides C, H, O (via glucose), but soil nutrients must provide N, P, S, and other elements—a plant in pure water with only CO2 and light could make sugars but not proteins or DNA!

8

A student tracks 60 carbon atoms that were originally in atmospheric CO2. After photosynthesis, those carbon atoms are now in glucose molecules in a plant. The plant later uses those glucose molecules to build starch and lipids. Which statement best describes what happens to the 60 carbon atoms during synthesis?

The carbon atoms leave the plant and are replaced by new carbon atoms made during synthesis.

Some carbon atoms are destroyed and turned into energy as starch and lipids are made.

The carbon atoms change into nitrogen atoms so the plant can make a wider variety of molecules.

The carbon atoms are conserved and rearranged into new molecules; the same carbon atoms can end up in starch and in lipid molecules (in different bonds/arrangements).

Explanation

This question tests your understanding of how atoms from simple environmental molecules (CO2, H2O, soil nutrients) are rearranged through photosynthesis and synthesis reactions to build all the complex macromolecules in living organisms. Biological synthesis follows the law of conservation of matter—atoms are neither created nor destroyed, only REARRANGED from simpler molecules into more complex ones: the carbon atoms in all biological macromolecules (carbohydrates, proteins, lipids, nucleic acids) originally came from atmospheric CO2 that was fixed into glucose during photosynthesis, then those glucose carbon atoms are broken apart and rearranged (sometimes combined with additional atoms) to build different molecules. The 60 carbon atoms that started in atmospheric CO2 and became part of glucose molecules can be tracked as they're redistributed: some carbon atoms might be linked together with dehydration synthesis to form starch (a glucose polymer), while others might be broken down and reassembled into fatty acid chains for lipids—but all 60 carbon atoms are conserved and simply rearranged into new molecular configurations. Choice B correctly explains atom rearrangement by recognizing the same 60 carbon atoms are conserved and can end up in different molecules (starch and lipids) through bond rearrangement. Choice A incorrectly claims atoms are destroyed for energy (atoms provide structure, not energy—energy comes from breaking bonds), Choice C impossibly suggests carbon changes into nitrogen (elements cannot transform), and Choice D incorrectly claims atoms leave and are replaced (violating conservation). The tracking strategy shows perfect atom accounting: 60 C atoms in CO2 → 60 C atoms in glucose → some become part of starch chains, others become part of lipid molecules, but the total remains 60 C atoms, just redistributed into different molecular homes!

9

A student tracks six carbon atoms that were once in atmospheric CO2. After photosynthesis, those carbon atoms are found in one glucose molecule (C6H12O6) in a leaf cell. Later, the plant makes starch for storage. What happens to those six carbon atoms when starch is made?

They are converted into energy, so the carbon atoms no longer exist as matter in the plant.

They are destroyed and replaced by new carbon atoms created during starch synthesis.

They are rearranged into a starch polymer by linking glucose units together; no carbon atoms are created or destroyed.

They stay together as the same glucose molecule and do not become part of starch.

Explanation

This question tests your understanding of how atoms from simple environmental molecules (CO2, H2O, soil nutrients) are rearranged through photosynthesis and synthesis reactions to build all the complex macromolecules in living organisms. Biological synthesis follows the law of conservation of matter—atoms are neither created nor destroyed, only REARRANGED from simpler molecules into more complex ones: the carbon atoms in all biological macromolecules (carbohydrates, proteins, lipids, nucleic acids) originally came from atmospheric CO2 that was fixed into glucose during photosynthesis, then those glucose carbon atoms are broken apart and rearranged (sometimes combined with additional atoms) to build different molecules. When glucose molecules are linked together to form starch, the six carbon atoms from each glucose unit remain intact and become part of the starch polymer—they are simply rearranged from individual glucose molecules into a long chain structure through dehydration synthesis, where glucose units connect by removing water molecules (H2O). Choice C correctly explains atom rearrangement by recognizing that the six carbon atoms are conserved and reorganized into the starch polymer structure, with no atoms created or destroyed. Choice A violates conservation of matter by suggesting atoms can be destroyed and created; choice B incorrectly implies glucose molecules remain separate rather than linking; choice D wrongly claims matter can be converted to energy and cease to exist as atoms. The tracking strategy here is straightforward: if you start with 6 carbon atoms in CO2, they become 6 carbon atoms in glucose, which become 6 carbon atoms incorporated into the starch chain—perfect conservation! This demonstrates how photosynthesis captures atmospheric carbon and plants then rearrange these captured carbon atoms into various storage and structural molecules.

10

A plant cell uses glucose (C6H12O6) to help build a nucleic acid (such as DNA). Besides the C, H, and O atoms that can come from glucose, which additional element(s) must be obtained from the environment to build nucleic acids?

Only carbon (C), because nucleic acids are made entirely of carbon chains.

Helium (He) and neon (Ne), absorbed from the air and added to glucose.

Nitrogen (N) and phosphorus (P), typically obtained as soil nutrients and incorporated into nucleotides.

Nitrogen (N) directly from the air as N2 gas, without any processing, because plants can use N2 immediately.

Explanation

This question tests your understanding of how atoms from simple environmental molecules (CO2, H2O, soil nutrients) are rearranged through photosynthesis and synthesis reactions to build all the complex macromolecules in living organisms. Biological synthesis follows the law of conservation of matter—atoms are neither created nor destroyed, only REARRANGED from simpler molecules into more complex ones: the carbon atoms in all biological macromolecules (carbohydrates, proteins, lipids, nucleic acids) originally came from atmospheric CO2 that was fixed into glucose during photosynthesis, then those glucose carbon atoms are broken apart and rearranged (sometimes combined with additional atoms) to build different molecules. To build NUCLEIC ACIDS (DNA and RNA), plants must combine the C, H, and O atoms from glucose with both NITROGEN and PHOSPHORUS atoms—nitrogen for the nitrogenous bases (adenine, guanine, cytosine, thymine/uracil) and phosphorus for the sugar-phosphate backbone that links nucleotides together. Choice B correctly identifies that nitrogen and phosphorus must be obtained from soil nutrients (as nitrate/ammonium and phosphate respectively) and incorporated into nucleotides to build nucleic acids. Choice A incorrectly claims nucleic acids contain only carbon; choice C absurdly suggests noble gases (helium and neon) which are chemically inert and not used in biological molecules; choice D wrongly states plants can use atmospheric N2 directly, when actually plants require nitrogen-fixing bacteria or soil nutrients to access usable nitrogen. The element tracking for nucleic acids: C from CO2 → glucose → ribose/deoxyribose sugars; N from soil → nitrogenous bases; P from soil → phosphate groups linking nucleotides. This shows how building complex molecules requires gathering specific elements from different environmental sources!

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