Diatoms are single-celled photosynthetic microalgae. How do diatoms obtain energy to carry out cellular work?

Question

BlackTom AI · Accepted Answer

Photosynthetically produced carbohydrates are catabolized by the cell to make ATP for cellular work.

1) Relevant knowledge points and concepts
- Diatoms are primarily photoautotrophs: chloroplasts capture light energy and fix CO2 into carbohydrates (photosynthesis: light reactions + Calvin cycle).
- Cells obtain usable chemical energy by breaking down carbohydrates via cellular respiration (glycolysis, pyruvate oxidation, Krebs cycle, and oxidative phosphorylation) in the cytosol and mitochondria to synthesize ATP.
- ATP generated in mitochondria is the immediate energy currency for most cellular processes; ATP produced in chloroplasts is largely used locally for the Calvin cycle and is not extensively exported.

2) Step-by-step reasoning process
- Light reactions in the chloroplast generate ATP and NADPH, and the Calvin cycle uses those to build triose phosphates → glucose and other carbohydrates.
- These carbohydrate products (sugars) are exported to the cytosol and/or sent to mitochondria.
- Glycolysis in the cytosol converts glucose to pyruvate, producing a small amount of ATP and NADH.
- Pyruvate enters mitochondria, is converted to acetyl-CoA, enters the citric acid cycle producing NADH and FADH2.
- NADH/FADH2 donate electrons to the mitochondrial electron transport chain, creating a proton gradient that drives ATP synthase to produce the bulk of ATP.
- The ATP produced fuels cellular work (transport, biosynthesis, motility, etc.).

3) Intermediate steps (biochemical sequence)
- Photosynthesis → glucose/triose phosphates.
- Glycolysis: glucose → 2 pyruvate + net 2 ATP + 2 NADH.
- Pyruvate → acetyl-CoA → Krebs cycle: produces NADH/FADH2.
- Oxidative phosphorylation: NADH/FADH2 → electron transport → ~30–34 ATP per glucose (varies).

4) Why the correct answer is correct
- Option b states they use carbohydrates made in chloroplasts to make ATP, which matches the above biochemical pathway: photosynthesized sugars are substrates for cellular respiration to produce ATP.

5) Why other options are incorrect
- a: Inorganic nutrients (nitrate, phosphate, iron) are essential for growth and enzyme cofactors but are not direct energy substrates to synthesize ATP.
- c: ATP generated in chloroplasts is mostly consumed within the chloroplast; cells do not rely on large-scale direct transport of ATP from chloroplasts to power cytosolic processes.
- d: Using external organic molecules describes heterotrophy; while some diatoms can be mixotrophic, the defining primary mechanism is photosynthesis-derived carbohydrates, so d is not the best general answer.

6) Conclusion
This explanation confirms answer b: They use carbohydrates made in the chloroplasts to make ATP.

Diatoms are single-celled photosynthetic microalgae. How do diatoms obtain energy to carry out cellular work?单项选择题

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