Q.36 Filamentous photosynthetic algae were placed on a microscopic slide and
illuminated with light of different colors as illustrated.
The bacteria that are known to migrate towards the region of high 𝑂ଶ were also
added uniformly on the slide. Which one of the following options illustrates the
distribution of bacteria along the length of the microscopic slide after
illumination?

Filamentous phototrophic bacteria on an algal filament show distribution patterns based on oxygen production from photosynthesis under different colored lights. The correct option is (C), where bacteria distribute uniformly along the microscope slide length.​

Question Analysis

This CSIR NET-style question tests Engelmann’s classic 1882 experiment on photosynthesis action spectrum using filamentous algae and aerobic bacteria. The setup involves illuminating an algal filament on a slide with blue, green, or red light; bacteria cluster near oxygen-rich zones from effective photosynthesis. Graphs (A–D) depict bacterial density: Gaussian peaks indicate clustering, while uniform distribution shows even spread.​

Option Breakdown

• Option (A): Bacteria cluster at both slide ends under blue, green, red lights. Incorrect—reveals uneven distribution from wavelength-specific oxygen gradients, unlike prism-separated light in Engelmann’s setup.​

• Option (B): Uniform toward one slide end. Incorrect—suggests biased illumination or chemotaxis to one side, not matching broad uniform exposure.​

• Option (C): Uniform along entire slide length. Correct—white or unseparated light (implied by “filamentous phototrophic algae”) delivers all wavelengths evenly, producing consistent oxygen without peaks in blue/red zones.​

• Option (D): Clusters at both ends. Incorrect—mirrors spectral separation (blue/red peaks), but question specifies single-color or uniform illumination without prism.​

Engelmann Experiment Principle

Engelmann exposed algal filaments to prism-split light; bacteria accumulated in blue (~450 nm) and red (~650–700 nm) regions due to chlorophyll absorption maxima driving high O₂ evolution. Green light (~550 nm) caused least clustering as chlorophyll reflects it. Phototrophic bacteria here act as O₂ indicators, relevant for CSIR NET photosynthesis topics.​

Introduction Snippet for Article: In the filamentous phototrophic bacteria distribution microscope slide illumination experiment, bacteria show uniform spread along the algal filament under broad light, unlike spectral clustering. Ideal for CSIR NET Life Sciences prep—master photosynthesis action spectrum today.​