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IB Biology HL 1.3.6 Absorption and Action Spectra

Practise analysing absorption and action spectra at HL depth, linking pigment wavelengths to photosynthetic rate and using algal light data to justify ecological conclusions.

Syllabus
First assessment 2025
Course
Biology HL
Level
HL

Exam points

  • Analyse absorption and action spectra to link pigment wavelengths with photosynthetic rate.
  • Construct and interpret labelled action-spectrum graphs with wavelength peaks and troughs.
  • Use algal light data to justify pigment use and habitat depth from action spectra.

C1.3.6—Absorption vs. action spectra question 1

[Maximum number: 3]

In water, shorter wavelengths of light such as blue and green penetrate deepest, and longer wavelengths of light penetrate less far. Red light does not reach depths of more than 50 m . Marine algae live at various water depths. Certain species of algae contain the pigments that enable them to adapt to life at different depths.

The graphs show the absorption and action spectra for two species of algae: Ulva taeniata, which is green, and Porphyra nereocystis, which is red.

Figure for Question C1.3.6—Absorption vs. action spectra question 1 — IB Biology HL

Absorption / \%

Figure for Question C1.3.6—Absorption vs. action spectra question 1 — IB Biology HL
Figure for Question C1.3.6—Absorption vs. action spectra question 1 — IB Biology HL

Question (a)

(a)

In each species, identify the colour of light that is used mainly for photosynthesis.

Ulva taeniata:
Porphyra nereocystis:

[ 2 ]

Question (b)

(b)

Deduce, with a reason, which algae lives at a greater depth.

[ 1 ]
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