Absorption of specific wavelengths of light by photosynthetic pigments
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Question
Why do leaves look green?
Answer
**Chlorophyll reflects green light** (while absorbing blue and red). The reflected green is what we see.
Question
Which colours of light does chlorophyll absorb most strongly?
Answer
**Blue** (~450 nm) and **red** (~660 nm).
Question
Which colour does chlorophyll absorb least?
Answer
**Green** (~550 nm) — it is mostly reflected.
Question
Define a pigment.
Answer
A **coloured molecule** that absorbs some wavelengths of light and reflects others; the colour you see is the light it does **not** absorb.
Question
What is an absorption spectrum?
Answer
A graph of **how much light a pigment absorbs** at each wavelength (chlorophyll peaks in blue and red, dips in green).
Question
What is an action spectrum?
Answer
A graph of the **rate of photosynthesis** at each wavelength of light.
Question
Why do the absorption and action spectra have the same shape?
Answer
Because **only absorbed light can power photosynthesis** — the wavelengths absorbed are the wavelengths that drive it.
Question
What are accessory pigments?
Answer
Extra pigments (e.g. **carotenoids**) that absorb wavelengths **chlorophyll misses** and pass the energy on to chlorophyll.
Question
Why are accessory pigments useful?
Answer
They **widen the range of wavelengths** captured, so the plant loses less of the available light energy.
Question
The colour you see from a pigment is...
Answer
The light the pigment **does NOT absorb** (the reflected light), not the light it absorbs.
Question
What does chromatography of a leaf extract show?
Answer
That a leaf contains **more than one pigment** — they separate into different **colours** (different Rf values).
Question
Roughly what wavelength range is visible light?
Answer
About **400 nm (blue/violet)** to **700 nm (red)**, with green near **550 nm**.
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Topic 3.3 hub
Photosynthesis
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