Photosynthetic pigments: absorption by chlorophyll in eukaryotes and cyanobacteria Chlorophyll molecules used by eukaryotic phototrophs and by cyanobacteria absorb radiant energy most strongly in which portion(s) of the visible spectrum?

Introduction / Context:
Understanding the absorption spectrum of chlorophyll explains why plants look green and how photosynthetic organisms harvest light. Chlorophyll a (and accessory chlorophylls) in algae, plants, and cyanobacteria have characteristic peaks that determine light-use efficiency in photosynthesis.

Given Data / Assumptions:

• Organisms considered: eukaryotic phototrophs (plants/algae) and cyanobacteria.
• Main pigment: chlorophylls (especially chlorophyll a).
• We are focusing on the visible spectrum region where absorption is strongest.

Concept / Approach:

Chlorophyll strongly absorbs blue/violet (short wavelengths) and red (long wavelengths) light, while reflecting/transmitting green light, which is why many phototrophs appear green. Accessory pigments broaden capture, but the primary strong absorption bands remain in the blue and red regions for chlorophyll a-containing organisms, including cyanobacteria.

Step-by-Step Solution:

Verification / Alternative check:

Standard spectra show strong Soret band in blue and Qy band in red for chlorophyll a; cyanobacteria also contain phycobiliproteins that capture additional wavelengths but do not change the core chlorophyll peaks.

Why Other Options Are Wrong:

• Red only: Ignores strong blue absorption.
• Green: Chlorophyll reflects green; absorption is minimal.
• Green and ultraviolet: Not aligned with chlorophyll’s main peaks.
• Yellow only: Not a primary chlorophyll absorption maximum.

Common Pitfalls:

• Assuming the color seen equals the absorption peak; it is the opposite.

Final Answer:

red and blue