From CO2 to biological molecules (carbon fixation into oils)
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Question
What is carbon fixation?
Answer
Taking **carbon dioxide (CO₂)** from the air and building its carbon into an **organic molecule** — in plants this happens during **photosynthesis**.
Question
Where does all the carbon in a plant originally come from?
Answer
From **carbon dioxide (CO₂)** in the **atmosphere**, fixed during photosynthesis.
Question
Which molecule does a plant build FIRST from fixed carbon?
Answer
**Glucose** — the hub molecule from which everything else is built.
Question
Why is glucose called a 'hub' molecule?
Answer
Because the plant **converts** it into all its other molecules: starch, cellulose, amino acids and lipids.
Question
List the main fates of the glucose a plant makes.
Answer
**Respiration** (energy), **starch** (storage), **cellulose** (cell walls), **amino acids / proteins**, and **lipids (oils)**.
Question
How does a plant turn glucose into an oil?
Answer
Glucose is converted into **glycerol** and **fatty acids**, which are then **joined** (by condensation) to form a **lipid (oil)**.
Question
What are the building blocks of a lipid (oil)?
Answer
**Glycerol** and **fatty acids**.
Question
Outline how a plant builds oils from atmospheric carbon.
Answer
CO₂ is **fixed** in photosynthesis → **glucose** is made → glucose → **glycerol + fatty acids** → these **join** into a **lipid (oil)**, stored in seeds.
Question
Which food molecule stores the most energy per gram?
Answer
**Lipids (oils)** — this is why seeds often store energy as oil rather than starch.
Question
Where are plant oils most often stored?
Answer
In **seeds**, where their packed energy fuels the growth of the next plant.
Question
Which extra element does a plant need to make proteins (but not oils)?
Answer
**Nitrogen (N)** — taken up from the soil, as well as the carbon from CO₂.
Question
Is starch or oil made directly from glucose by joining glucose units?
Answer
**Starch** — it is built by joining glucose molecules; oils need glucose to be converted to glycerol and fatty acids first.
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Full study notes for From CO2 to biological molecules (carbon fixation into oils)
Topic 3.3 hub
Photosynthesis
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